2. Chapter 1 Introduction
1‐1
1. Introduction
This report describes the commissioning of the Pencil Beam (PB) photon dose
calculation algorithm implemented in a commercial advanced radiotherapy
treatment planning system (iPlan RT Dose 4.5.1; BrainLab AG; Germany).
The BrainLab PB dose algorithm is developed based on publications by
Mohan et al. 1-3 to calculate dose distribution in a heterogeneous-density
phantom or patient for arbitrarily shaped megavoltage (MV) photon beams.
The BrainLab iPlan RT Dose system uses advanced treatment planning
techniques in conjunction with the PB algorithm to perform highly conformal
3D dose distributions calculation for both cranial and extra-cranial targets.
Treatment planning techniques available in the iPlan Dose system include:
• Conformal Beams technique. It uses multiple static beams collimated with
multileaf collimators (MLC) to conform to beam’s eye views (BEV) of the
planning target volume (PTV) varying in configuration for different beam
angles or orientations.
• Conformal Arcs technique. It adjusts the field aperture with the MLC
according to the PTV shape varying over an arc radiation plane, delivered
through a gantry rotation at a given treatment couch angle. Multiple non-
coplanar arcs (between 4 and 10) are typically used in linac-based stereo-
tactic radiosurgery.4-5 Conformal Arcs have both static and dynamic field-
shaping options. With the Static Conformal Arcs option, a single, static
conformal field is used throughout an arc. This MLC-defined, conformal
field shape is taken by averaging the PTV shapes (plus user-specific
margins) varying in shape over gantry angles involved in the arc. With
the Dynamic Conformal Arcs option, radiation field configurations are
continually shaped with the MLC to adjust the varying PTV projections in
every 10°-interval during the gantry rotation.
• Intensity Modulated Radiation Therapy (IMRT) technique. It modulates
radiation intensities in several static, planar or non-coplanar MLC fields
to maximize dose coverage to PTV and minimize doses to surrounding
normal tissues and organs at risk. Intensity modulation is calculated with
inverse planning optimization and delivered in practice using MLC leaf
sequencing.
• HybridArcs technique. It is a combination of the dynamic conformal arcs
and IMRT techniques. Inverse-planned IMRT fields are added to dynamic
conformal arcs in order to improve 3D isodose distributions for either one
of the two techniques alone.
The iPlan PB algorithm is commissioned to perform accurate conformal 3D
dose distributions calculation for the new, state-of-the-art stereotactic radio-
therapy-dedicated linear accelerator system (TrueBeamTM STx; Varian; Palo
3. Chapter 1 Introduction
1‐2
Alto; USA) installed in the Nova Scotia Cancer Centre (NSCC). The Varian’s
TrueBeamTM system integrates real-time tracking and precise treatment
delivery to address complex clinical cases, such as lung, prostate, head and
neck, etc. With this integration, the latest advanced radiotherapy techniques,
e.g., stereotactic radiosurgery or radiotherapy (SRS/SRT), stereotactic body
radiotherapy (SBRT), volumetric modulated arc therapy (VMAT) or
RapidArc®, and image-guidance radio-therapy (IGRT) can be delivered in
high (spatial and dosimetric) precision for these complicated treatment sites.
The TrueBeam system incorporates an on-board imager (OBI) kilo-voltage
(kV) imaging system to enhance pre-treatment tumor targeting based on 2D
or 3D matching of the high-quality, setup kV-images (planar or cone-beam
CT) with reference (planning) images. The TrueBeam STx system installed in
our clinic is dedicated to stereotactic irradiation and uses high definition 120
MLC leaves (with the finest resolution of 2.5 mm at the isocenter) to perform
small-fields SRS or SBRT procedures in the brain, lung, and prostate cases.
The TrueBeam system is characterized by its versatile, flexible architecture
that allows interfaces with multiple technologies for imaging and tumor-
specific solutions. Our TrueBeam STx unit (from now on termed “TrueBeam
1”) is interfaced with a combined room-based kV-imaging and robotic patient
positioning couch system (ExacTrac®; BrainLab; Germany) to facilitate
precise patient set-up and accurate tumor targeting for inter-fractional and
also intra-fractional radiotherapy. The BrainLab ExacTrac® IGRT system
consists of a pair of room-mounted kV-imaging units to perform 3-D tumor
targeting during radiation delivery. Pairs of kV X-ray images are acquired to
instantly track the field-to-field tumor displacement or patient movement,
thus enabling real-time, intra-fractional motion management. In addition, an
ExacTrac® Robotic Patient Alignment system is mounted on top of the linac’s
couch support and fully integrated with the electro-mechanical interface of
the TrueBeam system to correct for residual positional errors after an initial
tattoo- or infrared-based patient setup. This advanced patient positioning
system provides two rotational motions (i.e., pitch and roll) in addition to the
existing 3D translations and couch rotation, allowing precise patient setup
with six degrees of freedom and thus higher level of setup accuracy. Figure
1.1 shows a picture of the TrueBeam 1 linac with the integrating ExacTrac
IGRT (imaging and patient-positioning) system.
For cranial SRS, the integration of the ExactTrac IGRT system with the
TrueBeam 1 linac offers highly accurate dose delivery on a frameless basis.
The use of stereoscopic kV-imaging with the ExacTrac system in conjunction
with a BrainLab cranial stereotactic immobilization system achieves sub-
millimetric precision required in a SRS procedure. The non-invasive
attachment of the immobilization system with the head improves patient’s
comfort during treatment.
4. Chapter 1 Introduction
1‐3
Figure 1.1 Picture of the TrueBeam STx linac installed in the Nova Scotia Cancer Centre (NSCC). The linac is equipped with the portal MV imager, kV
on-board imager (OBI) as well as ExacTrac imaging and automatic 6D-positioning system to perform multi-options IMRT/IGRT treatments.
5.
6. Chapter 2 Pencil beam algorithm
2‐1
2. Pencil beam algorithm
The pencil beam (PB) algorithm is a model-based dose calculation algorithm
developed in the BrainLab’s iPlan RT Dose treatment planning system.
Based on the knowledge of linac-specific energy spectra and measured beam
characteristic data of the unit, 3D dose distributions for irregularly shaped
photon beams in an arbitrary phantom or patient contour with tissue
heterogeneities are calculated. Dose calculations are, in principle, performed
using 2D convolution of relative primary photon fluence distributions with
pencil beam kernels. The convolution PB kernel essentially represents cross-
sectional dose distributions of a pencil beam (PB) as a function of depths in a
uniform-density medium.
In the PB algorithm, an incident irregular field is divided into many tiny
beam-lets called pencil beams. Dose distributions of each pencil beam, known
as kernels, are calculated with Monte Carlo (MC) simulation incorporating
photon energy spectra specific to a given treatment unit or linac. The MC-
calculated pencil beam kernels are modified with a source function correction
to account for the influence of the finite focal spot size, curvature of MLC
leaves, and linac head scatter on doses. Total 3D dose distributions for an
irregular field are calculated by convolution of corrected pencil beam kernels
with the primary fluence distribution, using the Fast Fourier Transformation
(FFT). The algorithm uses fast ray tracing and adaptive grid methods to
enhance dose calculation efficiency and accuracy. With these optimizations,
3D dose distributions for a single, irregularly shaped field can be effectively
calculated within milli-seconds. This section dedicates to explain several key
parameters constituting the PB dose formalism.
2.1 Pencil beam kernels
A pencil beam is defined as a narrow beam with an infinitesimal cross-
sectional field. Assume the pencil beam is mono-energetic with a photon
energy E . As the pencil beam impinges on a flat surface of a homogeneous
phantom, 3D dose distributions are generated in the medium of the phantom
(see Figure 2.1). Point P refers to a location where first collisions (or photon
interactions) of the pencil beam take place, at depth P
t below the phantom
surface. Collision density Pc,
ρ is defined as the number of the first (photon)
collisions per unit volume in a small volume surrounding point P and is
expressed by:
( ) ( ) ( ) ( )[ ]PPPPc,
tEEEtE ×−××Φ= μμρ exp, , (2.1)
where
7. Chapter 2 Pencil beam algorithm
2‐2
Figure 2.1 Definition of differential pencil beam (DPB).
( )EP
Φ is the fluence of the un-attenuated incident photons of energy E
at the point P of first (photon) collisions.
μ is the linear attenuation coefficient depending on photon energy.
A differential pencil beam (DPB) refers to a fraction of pencil beam photons
that have their first collisions in a small volume surrounding a given point P.
DPB kernel is a 3D dose distribution in a medium as a result of the DPB. It
depends on three parameters: (1) photon beam energy E ; (2) radial distance
PQ
r between point P of first collisions and the observation point Q; (3) polar
angle θ between the incident pencil beam and the ray line joining point P
and point Q.
DPB occurs at every depth P
t along the incident pencil beam direction in the
medium. As a result, the dose deposited at the observation point Q due to the
pencil beam is a line integral of kernels corresponding to the DPBs generated
along the pencil beam axis in the medium and is thus expressed by:
( ) ( ) ( )[ ] ( ) PPQDPBPP
dtErktEEEDQ
×××−××∫ Φ= ,,exp θμμ , (2.2)
8. Chapter 2 Pencil beam algorithm
2‐3
Equation (2.2) assumes mono-energetic pencil beam spectrum Φ . However,
the energy spectrum of a linac is a poly-energetic bremsstrahlung spectrum.
Thus, the total dose at the point Q for a realistic poly-energetic pencil beam
from the linac is an integration of the DPB doses over the multiple-energy
spectrum ( ) EE ddφ . It is known as the pencil beam kernel ( )dyxK ,, and is
given by:
( ) ( ) ( ) ( )[ ] ( ) EtErktEE
E
E
dyxK dd
d
d
DPB
×∫ ×××−××∫= ,,exp,, θμμ
φ
. (2.3)
Note that the DPB kernels ( )Erk ,,θDPB
were typically pre-calculated with MC
simulation in a range of photon energies E between 100 keV and 50 MeV to
account for the energy fluence distribution of a typical medical linac.
2.2 Primary fluence distribution
The pencil beam kernel K requires photon fluence distribution, as shown in
Equation (2.3). Primary photon fluence of a linac is typically calculated by
MC simulation which takes into account the geometry of a linac treatment
head as well as incident electron beam characteristics, such as electron beam
width and energy spread, etc. The primary photon fluence spectra are scored
in a plane perpendicular to the beam’s central axis at the isocenter level.
Photon fluence distribution for an arbitrarily shaped field is calculated by
convolving the scored primary fluence distribution with a “geometric kernel”
(see Figure 2.2) for the field. This kernel is a 2D matrix with pixel values
depending on the field coverage: Pixels located in fully exposed areas have a
kernel value of 1; pixels located in fully closed areas have a kernel value of 0;
pixels partially blocked by the field (i.e., on the field edge) have fractional
values varying between 0 and 1 depending on the extent of the field coverage.
The above photon fluence calculation for an irregular field neglects variation
in the fluence spectra relative to the radius from the beam central axis, that
is confirmed in previous studies including a MC study by Mohan et al.1 Due
to the conical shape of a flattening filter, the spectra soften as the off-axis
distance increases. To account for this off-axis beam softening effect, a radial
factor is used. The planar photon fluence distribution ( )dyx ,,Φ in air at a
level corresponding to an arbitrary depth d in a medium is thus given by:
( ) ( ) ( )drRFSyxdyx ,,,, 0
×Φ=Φ , (2.4)
where
9. Chapter 2 Pencil beam algorithm
2‐4
Figure 2.2 Geometry kernel for calculation of a photon fluence distribution for an irregular MLC-
shaped field. Blue outline refers to the boundary of the MLC field aperture. Kernel value is assigned
to 1 for pixels fully exposed in the open field and 0 for voxels fully blocked by the MLC leaves. For
voxels partially covered by the leaves, fractional values, proportional to the degree of the leave
coverage, are used: the more the leave coverage the smaller the fraction.
( )yx,0
Φ is the fluence distribution at the isocenter which accounts for
the field shaping effect of the MLC leaves (see Figure 2.2).
( )drRFS , is the radial factor correcting for the beam softening effect on
the photon fluence at a radial distance 22
yxr += from the
beam central axis at a level corresponding to the given depth d
in the medium.
The radial factors are dose functions that run across the beam central axis at
various depths in water. They correct the off-axis variation in the primary
photon fluence spectra. Radial factors are directly obtained from the off-axis
ratios along the radial distance from the beam central axis and are given by:
( ) ( )
( )
( )
( )fdD
fdyxD
fdD
fdrD
drRFS
,,0,0
,,,
,,0
,,
, == , (2.5)
where
10. Chapter 2 Pencil beam algorithm
2‐5
Figure 2.3 Geometry for (a) calibration of dose at a reference point Pcal for a reference field Aref and
(b) pencil beam modelled calculation of total dose at an arbitrary point Q for an irregular MLC-
shaped field in water.
( )fdrD ,, is the radially symmetric dose along the radius 22
yxr += from
the beam central axis at a depth d in the medium for a given
source-to-surface (SSD) distance f .
2.3 Total dose calculation formalism
Pencil beam kernels K and photon fluence spectra for an irregular field are
calculated by MC simulations. A 2D convolution of the MC pre-calculated
pencil beam kernels K and total photon fluence distribution Φ results in an
idealized dose distribution given by:
( ) ( ) yxdyyxxKdyxdyxIDD ′′−′−′⋅∫∫ ′′Φ= dd,,,,),,( . (2.6)
IDD is essentially a relative 3D dose distribution normalized to 1 at a point of
calibration Pcal in water for a given calibration geometry (see Figure 2.3a).
For an irregular field, the total dose ( )dyxD ,, at an arbitrary point Q in a
medium (see Figure 2.3b) is related to the kernel-based IDD and also basic
dosimetric parameters by the following equation:
11. Chapter 2 Pencil beam algorithm
2‐6
( ) ( ) ( )QQt
lyxIDD
df
df
AlTPRAASKdyxD ,,
~
,
~
,),,(
2
SADSAD
calcal
Qmlcjaw
MU ⋅⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
+
+
⋅⋅⋅⋅= & , (2.7)
where
MU is monitor unit applied to the linac;
K& is nominal linac output giving an absorbed dose per MU for a
reference field ref
A of 10×10 cm2 at the isocenter level with a
calibration SSD cal
f at a depth of calibration cal
d in water;
( )mlcjaw
AASt
~
, is the total scatter factor for the equivalent square area jaw
A of
the collimator jaw opening and the effective square area mlc
A
~
of
the MLC field aperture projected at the isocenter level with the
source-axis distance SAD of 100 cm for a standard linac;
( )Q
AlTPR Q
~
, is the tissue-phantom-ratio at the point of calculation Q in water
with the radiological pathlength Q
l of the ray line joining the
source with the point Q for an effective MLC-shaped field area
Q
A
~
projected at depth d ;
cal
f is the SSD for the geometry of output calibration;
f is the SSD for the geometry of dose calculation;
IDD is the idealized dose distribution at the radiological depth Q
l for
the off-axis distances ( )yx, of the point Q projected at the level of the iso-
center with ( )dfxx +⋅= SADSAD
and ( )dfyy +⋅= SADSAD
.
2.4 Other correction factors
Several corrections are used to account for deviations from the simplistic
geometries assumed in the above dose calculation formalism. These include:
(1) tissue inhomogeneity and surface curvature corrections; and (2) source
function and radiologic field corrections.
Calculations of DPB dose distributions assume an semi-infinite homogeneous
medium of unit density. In a non-uniform density phantom, inhomogeneities
are taken into account by primary fluence attenuation correction as well as
radiological pathlength correction.
12. Chapter 2 Pencil beam algorithm
2‐7
Figure 2.4 Difference between the radiologic and geometric MLC field. Radiologic field (in red) is
measured 50% isodose profile and the geometric field (in black) is MLC-defined field.
Primary fluence attenuation correction accounts for inhomogeneities in the
pencil beam path between the source and the point P of first collisions (see
Figure 2.1). The total linear attenuation coefficient μ used for a unit-density
medium is replaced with the effective linear attenuation coefficient eff
μ given
by the coefficients averaged over tissues of various densities in a non-uniform
density medium. Heterogeneities also occur between the scattering voxel and
computation point Q (see Figure 2.1). Radiological pathlength correction is
used to scale the physical distance PQ
r by the effective density accounting for
inhomogeneities traversed by the transport of scattered electrons.
Radiological pathlength correction also accounts for curved irregular surfaces
irradiated by photon fields. The PB algorithm uses ray-tracing along the ray
between the source and the observed calculation point Q (see Figure 2.3) to
calculate radiological pathlength l . The radiological pathlength is calculated
based on CT Hounsfield units representing relative electron densities. Thus,
a correct calibration of the CT simulator used for imaging of patients is
crucial to accurate radiologic pathlength calculation in the PB algorithm.
13. Chapter 2 Pencil beam algorithm
2‐8
Source function correction accounts for the influence of finite focal spot size,
head scatter, and other effects broadening the penumbra of the beam profile.
The function is modeled with a Gaussian distribution with a width σ and
amplitude A for a given depth d in water. It is incorporated in the PB dose
calculation by convolution with the pencil beam kernels ( )dyxK ,, . The width
and amplitude are acquired empirically by fitting calculated dose profiles
with measured ones. The pencil beam algorithm requires the widths and
amplitudes for two depths in water. Sigma and amplitude values for any
intermediate depths are linearly interpolated for dose profile calculations.
Radiological field correction accounts for small deviations of the radiological
field from the nominal MLC-defined field as a result of the MLC design (i.e.,
the round leaf-end and tongue-and-groove). This offset is defined as the static
(radiological) leaf shift sΔ and is given by:
( )mlc
sss −×=Δ %50
5.0 , (2.8)
where
%50
s is the width of a measured beam profile at the 50% isodose level;
mlc
s is the nominal MLC-defined field width.
2.5 Beam modeling data acquisition
Table 2.1 briefly summarizes general beam data required to model the pencil
beam algorithm for 3D in-phantom dose distribution calculations for static
conformal fields and dynamic conformal arcs techniques. General beam data
measurement geometries and dosimeters recommended for characterizing the
beam parameters are also described in the table.
The dosimetry data shown in Table 2.1 are essential to a comprehensive
pencil beam modeling. Accuracy of the dose calculation is directly dependent
on the accuracy and the range of the measured beam data. For detailed
information about the beam data measurement as well as review of the pencil
beam algorithm, readers are referred to the Brainlab's Physics Technical
Reference Guide.6
14. Chapter 2 Pencil beam algorithm
2‐9
Table 2.1 Beam data required for pencil beam modeling for 3D isodose distributions calculations with irregularly shaped linac-photon beams.
Beam data Measurement conditions Modelled
paramters
Dosimeters
Linac output SSD: 100 cm; Depth d : 10 cm; Jaws field:
(10×10) cm2; MLC field: (10×10) cm2.
K& Calibrated ion chamber.
MLC leakage SSD: 100 cm; Depth d : 10 cm; (Open jaws,
open MLCs): (10×10, 10×10) cm2; (Open
jaws, closed MLCs): (10×10, 0×0) cm2;
(Closed jaws, closed MLCs): (0×0, 0×0) cm2.
Background
leakages
Calibrated ion chamber.
PDD SSD: 100 cm; d range: (0-30) cm; MLC field
range: (5×5-300×220) mm2; Jaws field
range: (8×8-300×220) mm2.
TPR Medium-sized ion chamber for
large field PDDs; High-resolution
detectors for small fields PDDs.
Scatter factors SSD: 100 cm; Depth d : 10 cm; MLC field
range: (5×5-300×220) mm2; Jaws field
range: (8×8-300×220) mm2.
t
S Ion chamber in combination with a
high-resolution detector for small
fields.
Diagonal radial
dose profiles
SSD: 100 cm; Jaws field: (40×22) cm2; MLC
field: (40×22) cm2.
( )drRFS , Small-sized ion chamber or high-
resolution detector.
Transverse dose
profiles
SSD: 100 cm; Jaws field: (15×15) cm2; MLC
field: Brainlab-specified (see Physics
Guide pp.90)6.
Source function
and radiological
field corrections
High-resolution detector or films.
15.
16. Chapter 3 Square MLC fields dosimetry verification
3‐1
3. Dosimetry verification for MLC-defined square fields
At the NSCC, the nominal dose output of 100 cGy per 100 MU is specified in
an isocentric setup with a reference field size of (10×10) cm2 at a reference
depth of 5 cm in water for a reference SSD of 95 cm. The output calibration
geometry applies to linacs with megavoltage photon energies of 6 MV or
lower, including the TrueBeam 1 unit. As a fundamental check of the PB
model accuracy, a dose of 100 cGy was prescribed to a reference point in a
synthetic water phantom (ID: T41009) under the same output calibration
geometry. The number of monitor units (MU) for 6 MV and 6 MV flattening
filter free (FFF) modes were both calculated to be 99 MU, as shown in parts a
and b, respectively, of Figure 3.1. Recalculation using identical beam setup in
a CT-scanned unit-density IMRT phantom (ID: T41010) also results in the
same number of calculated MU’s. The 1% difference between the expected
(100 MU) and calculated (99 MU) values was observed in both phantom
calculations. These discrepancies, though non-negligible but acceptable, may
be attributed to uncertainties in the dose calculation.
3.1 Percent depth dose (PDD) distributions
Figures 3.2 and 3.3 compare PB-calculated and measured PDD distributions
for 6 MV and 6 MV FFF beams, respectively, for an SSD of 100 cm for various
MLC and jaw field settings, ranging from (5×5) mm2 to (220×220) mm2. Two
different detectors were used for PDD measurements, depending on the field
sizes. For small MLC-defined field areas from (5×5) mm2 to (20×20) mm2, a
small-field stereotactic diode (SFD; IBA; Germany) was used. For field areas
larger than (20×20) mm2, a 0.13-cc mini-ionization chamber (CC-13; IBA;
Germany) was used. PDD data were measured with these two detectors in a
3D water phantom (Blue Phantom2; IBA; Germany). Variable depth
resolution was used in the PDD measurements: 2-mm resolution for shallow
depths from 0 to 2.5 cm and 5-mm resolution for depths larger than 2.5 cm.
PDDs for MLC-defined square fields were calculated with the PB algorithm
in the iPlan RT Dose platform. 3D dose distributions including PDDs were
calculated in a synthetic 50-cc water phantom (ID: T41009) using adaptive
grid algorithm. Calculated PDD data were sampled with 1-mm resolution in
depth. To evaluate degrees of agreement between measured and calculated
PDDs, gamma values7 versus depths are plotted for each MLC field in
Figures 3.2 and 3.3 for 6 MV and 6 MV FFF beams, respectively. Gammas
are evaluated based on criteria of 2-% dose difference and 2-mm distance-to-
agreement (DTA). Results show that PDDs calculated by the PB algorithm
are in excellent agreement with the measured data with (2%,2-mm)-based
gamma values less than 1 for all fields and all depths, except those in the
build-up region.
18. Chapter 3 Square MLC fields dosimetry verification
3‐3
Figure 3.2(a) PB-calculated (in blue line) and measured (in red dots) PDD distributions for 6 MV photon beams for an SSD of 100 cm for various
(MLC, jaws) field sizes: (0.5×0.5, 0.8×0.8), (1.0×1.0, 1.2×1.2), (2.0×2.0, 2.2×2.2), (4.0×4.0, 4.2×4.2) cm2
. Gamma values (in magenta dashed line) based on
(2%, 2 mm) criteria are also plotted in the graph. PDDs were calculated with the PB algorithm of the iPlan RT dose platform in a unit-density phantom
(ID: T41009, Plan02). Measured PDDs were carried out in a water tank (Blue Phantom2
; IBA; Germany) with a SFD diode detector for small MLC-
defined fields smaller than (2×2) cm2
and a mini-ion chamber for large MLC-defined fields larger than (2×2) cm2
.
19. Chapter 3 Square MLC fields dosimetry verification
3‐4
Figure 3.2(b) PB-calculated (in blue line) and measured (in red dots) PDD distributions for 6 MV photon beams for an SSD of 100 cm for various
(MLC, jaws) field sizes: (6×6, 6×6), (10×10, 10×10), (22×22, 22×22) cm2
. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also
plotted in the graph. PDDs were calculated with the PB algorithm of the iPlan RT dose platform in a unit-density phantom (ID: T41009, Plan02).
Measured PDDs were carried out in a water tank (Blue Phantom2
; IBA; Germany) with a SFD diode detector for small MLC-defined fields smaller
than (2×2) cm2
and a mini-ion chamber for large MLC-defined fields larger than (2×2) cm2
.
20. Chapter 3 Square MLC fields dosimetry verification
3‐5
Figure 3.3(a) PB-calculated (in blue line) and measured (in red dots) PDD distributions for 6 MV FFF photon beams for an SSD of 100 cm for various
(MLC, jaws) field sizes: (0.5×0.5, 0.8×0.8), (1.0×1.0, 1.2×1.2), (2.0×2.0, 2.2×2.2), (4.0×4.0, 4.2×4.2) cm2
. Gamma values (in magenta dashed line) based on
(2%, 2 mm) criteria are also plotted in the graph. PDDs were calculated with the PB algorithm of the iPlan RT dose platform in a unit-density phantom
(ID: T41009, Plan03). Measured PDDs were carried out in a water tank (Blue Phantom2
; IBA; Germany) with a SFD diode detector for small MLC-
defined fields smaller than (2×2) cm2
and a mini-ion chamber for large MLC-defined fields larger than (2×2) cm2
.
21. Chapter 3 Square MLC fields dosimetry verification
3‐6
Figure 3.3(b) PB-calculated (in blue line) and measured (in red dots) PDD distributions for 6 MV FFF photon beams for an SSD of 100 cm for various
(MLC, jaws) field sizes: (6×6, 6×6), (10×10, 10×10), (22×22, 22×22) cm2
. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also
plotted in the graph. PDDs were calculated with the PB algorithm of the iPlan RT dose platform in a unit-density phantom (ID: T41009, Plan03).
Measured PDDs were carried out in a water tank (Blue Phantom2
; IBA; Germany) with a SFD diode detector for small MLC-defined fields smaller
than (2×2) cm2
and a mini-ion chamber for large MLC-defined fields larger than (2×2) cm2
.
22. Chapter 3 Square MLC fields dosimetry verification
3‐7
3.2 Lateral dose profile distributions
Figures 3.4 and 3.5 compare calculated and measured lateral dose profiles for
6 MV and 6 MV FFF beams, respectively, for an SSD of 100 cm for various
MLC-defined square field sizes, ranging from (5×5) mm2 to (220×220) mm2
and for various depths in water: 1.5 ( maxd ); 5; 10; and 20 cm. Measured and
also calculated profiles were acquired in two orthogonal axes: (1) the cross-
plane axis parallel to the MLC leaf direction (or the X-jaws direction) and (2)
the in-plane axis perpendicular to the MLC direction ( or the Y-jaws
direction). For accuracy, all beam profiles were measured in the scanning 3D
water tank (IBA Blue Phantom2) with the high-resolution SFD-diode.
Scanning step sizes of the tank are variable depending on the scanned profile
regions: step sizes of (2-5) mm were used for uniform-dose areas, while step
sizes of (0.5-1) mm were used for high-dose gradient regions, i.e., penumbras.
3D dose distributions including PDDs and beam profiles at various depths in
water (ID: T41009; Plan02 and Plan 03) for the MLC-defined square fields of
the 6 MV and 6 MV FFF photon beams were calculated with the PB model in
the iPlan RT Dose treatment planning system. Calculated dose profiles at
depths of 1.5 cm, 5 cm, 10 cm, and 20 cm for comparison with diode-measured
data were sampled with very high spatial resolution of 0.2 mm. This very fine
resolution facilitates precise gamma evaluation across profiles, in particular
to sharp-gradient penumbra region where a high spatial resolution and small
step size of the scanning diode detector were used.
For both 6 MV and 6 MV FFF photon beams of the TrueBeam 1 linac, diode-
measured beam profiles agree well with the PB-calculated profiles for all
MLC field areas ranging from small (5×5) mm2 to large (220×220) mm2, as
shown in Figures 3.4 and 3.5, respectively. Gamma values based on (2%, 2-
mm) criteria are generally less than 1 in the central uniform-dose region for
all dose profiles. Higher gamma values greater than 1 occur most frequently
in the sharp dose-gradient penumbra regions but also occasionally in the
transmission tails, especially for larger depths (e.g., 20 cm) in water and for
larger field sizes (e.g., 220×220 mm2). The higher γ discrepancies between
measured and calculated doses in the transmission region for the large field
may be attributed to the energy-dependent response of the diode as a result
of increased phantom scatter (of lower photon energies) for increased field
size. In general, discrepancies between measured and calculated dose profiles
increase as depth increases. Overall, agreements are good based on the mean
gamma values shown in the figures for each beam profile in comparison.
.
23. Chapter 3 Square MLC fields dosimetry verification
3‐8
Figure 3.4(a) PB-calculated (in blue line) and SFD-diode-measured (in red dots) cross-plane (leaf-parallel or X-jaws) dose profile distributions for 6 MV
photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (0.5×0.5, 0.8×0.8) cm2
at various depths in water: 1.5; 5; 10; 20
cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the
central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan02) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
24. Chapter 3 Square MLC fields dosimetry verification
3‐9
Figure 3.4(b) PB-calculated (in blue line) and SFD-diode-measured (in red dots) in-plane (leaf-perpendicular or Y-jaws) dose profile distributions for 6
MV photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (0.5×0.5, 0.8×0.8) cm2
at various depths in water: 1.5; 5; 10;
20 cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the
central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan02) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
25. Chapter 3 Square MLC fields dosimetry verification
3‐10
Figure 3.4(c) PB-calculated (in blue line) and SFD-diode-measured (in red dots) cross-plane (leaf-parallel or X-jaws) dose profile distributions for 6 MV
photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (1.0×1.0, 1.2×1.2) cm2
at various depths in water: 1.5; 5; 10; 20
cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the
central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan02) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
26. Chapter 3 Square MLC fields dosimetry verification
3‐11
Figure 3.4(d) PB-calculated (in blue line) and SFD-diode-measured (in red dots) in-plane (leaf-perpendicular or Y-jaws) dose profile distributions for 6
MV photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (1.0×1.0, 1.2×1.2) cm2
at various depths in water: 1.5; 5; 10;
20 cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the
central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan02) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
27. Chapter 3 Square MLC fields dosimetry verification
3‐12
Figure 3.4(e) PB-calculated (in blue line) and SFD-diode-measured (in red dots) cross-plane (leaf-parallel or X-jaws) dose profile distributions for 6 MV
photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (2.0×2.0, 2.2×2.2) cm2
at various depths in water: 1.5; 5; 10; 20
cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the
central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan02) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
28. Chapter 3 Square MLC fields dosimetry verification
3‐13
Figure 3.4(f) PB-calculated (in blue line) and SFD-diode-measured (in red dots) in-plane (leaf-perpendicular or Y-jaws) dose profile distributions for 6
MV photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (2.0×2.0, 2.2×2.2) cm2
at various depths in water: 1.5; 5; 10;
20 cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the
central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan02) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
29. Chapter 3 Square MLC fields dosimetry verification
3‐14
Figure 3.4(g) PB-calculated (in blue line) and SFD-diode-measured (in red dots) cross-plane (leaf-parallel or X-jaws) dose profile distributions for 6 MV
photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (4.0×4.0, 4.2×4.2) cm2
at various depths in water: 1.5; 5; 10; 20
cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the
central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan02) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
30. Chapter 3 Square MLC fields dosimetry verification
3‐15
Figure 3.4(h) PB-calculated (in blue line) and SFD-diode-measured (in red dots) in-plane (leaf-perpendicular or Y-jaws) dose profile distributions for 6
MV photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (4.0×4.0, 4.2×4.2) cm2
at various depths in water: 1.5; 5; 10;
20 cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the
central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan02) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
31. Chapter 3 Square MLC fields dosimetry verification
3‐16
Figure 3.4(i) PB-calculated (in blue line) and SFD-diode-measured (in red dots) cross-plane (leaf-parallel or X-jaws) dose profile distributions for 6 MV
photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (6×6, 6×6) cm2
at various depths in water: 1.5; 5; 10; 20 cm.
Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the central
axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan02) with high spatial resolution of 0.2 mm.
Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step size of 1
mm in high dose gradient (or penumbra) regions.
32. Chapter 3 Square MLC fields dosimetry verification
3‐17
Figure 3.4(j) PB-calculated (in blue line) and SFD-diode-measured (in red dots) in-plane (leaf-perpendicular or Y-jaws) dose profile distributions for 6
MV photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (6×6, 6×6) cm2
at various depths in water: 1.5; 5; 10; 20 cm.
Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the central
axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan02) with high spatial resolution of 0.2 mm.
Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step size of 1
mm in high dose gradient (or penumbra) regions.
33. Chapter 3 Square MLC fields dosimetry verification
3‐18
Figure 3.4(k) PB-calculated (in blue line) and SFD-diode-measured (in red dots) cross-plane (leaf-parallel or X-jaws) dose profile distributions for 6 MV
photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (10×10, 10×10) cm2
at various depths in water: 1.5; 5; 10; 20 cm.
Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the central
axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan02) with high spatial resolution of 0.2 mm.
Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step size of 1
mm in high dose gradient (or penumbra) regions.
34. Chapter 3 Square MLC fields dosimetry verification
3‐19
Figure 3.4(l) PB-calculated (in blue line) and SFD-diode-measured (in red dots) in-plane (leaf-perpendicular or Y-jaws) dose profile distributions for 6
MV photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (10×10, 10×10) cm2
at various depths in water: 1.5; 5; 10; 20
cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the
central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan02) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
35. Chapter 3 Square MLC fields dosimetry verification
3‐20
Figure 3.4(m) PB-calculated (in blue line) and SFD-diode-measured (in red dots) cross-plane (leaf-parallel or X-jaws) dose profile distributions for 6
MV photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (22×22, 22×22) cm2
at various depths in water: 1.5; 5; 10; 20
cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the
central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan02) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
36. Chapter 3 Square MLC fields dosimetry verification
3‐21
Figure 3.4(n) PB-calculated (in blue line) and SFD-diode-measured (in red dots) in-plane (leaf-perpendicular or Y-jaws) dose profile distributions for 6
MV photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (22×22, 22×22) cm2
at various depths in water: 1.5; 5; 10; 20
cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the
central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan02) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
37. Chapter 3 Square MLC fields dosimetry verification
3‐22
Figure 3.5(a) PB-calculated (in blue line) and SFD-diode-measured (in red dots) cross-plane (leaf-parallel or X-jaws) dose profile distributions for 6 MV
FFF photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (0.5×0.5, 0.8×0.8) cm2
at various depths in water: 1.5; 5; 10;
20 cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the
central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan03) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
38. Chapter 3 Square MLC fields dosimetry verification
3‐23
Figure 3.5(b) PB-calculated (in blue line) and SFD-diode-measured (in red dots) in-plane (leaf-perpendicular or Y-jaws) dose profile distributions for 6
MV FFF photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (0.5×0.5, 0.8×0.8) cm2
at various depths in water: 1.5; 5;
10; 20 cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at
the central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan03) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
39. Chapter 3 Square MLC fields dosimetry verification
3‐24
Figure 3.5(c) PB-calculated (in blue line) and SFD-diode-measured (in red dots) cross-plane (leaf-parallel or X-jaws) dose profile distributions for 6 MV
FFF photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (1.0×1.0, 1.2×1.2) cm2
at various depths in water: 1.5; 5; 10;
20 cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the
central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan03) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
40. Chapter 3 Square MLC fields dosimetry verification
3‐25
Figure 3.5(d) PB-calculated (in blue line) and SFD-diode-measured (in red dots) in-plane (leaf-perpendicular or Y-jaws) dose profile distributions for 6
MV FFF photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (1.0×1.0, 1.2×1.2) cm2
at various depths in water: 1.5; 5;
10; 20 cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at
the central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan03) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
41. Chapter 3 Square MLC fields dosimetry verification
3‐26
Figure 3.5(e) PB-calculated (in blue line) and SFD-diode-measured (in red dots) cross-plane (leaf-parallel or X-jaws) dose profile distributions for 6 MV
FFF photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (2.0×2.0, 2.2×2.2) cm2
at various depths in water: 1.5; 5; 10;
20 cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the
central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan03) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
42. Chapter 3 Square MLC fields dosimetry verification
3‐27
Figure 3.5(f) PB-calculated (in blue line) and SFD-diode-measured (in red dots) in-plane (leaf-perpendicular or Y-jaws) dose profile distributions for 6
MV FFF photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (2.0×2.0, 2.2×2.2) cm2
at various depths in water: 1.5; 5;
10; 20 cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at
the central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan03) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
43. Chapter 3 Square MLC fields dosimetry verification
3‐28
Figure 3.5(g) PB-calculated (in blue line) and SFD-diode-measured (in red dots) cross-plane (leaf-parallel or X-jaws) dose profile distributions for 6 MV
FFF photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (4.0×4.0, 4.2×4.2) cm2
at various depths in water: 1.5; 5; 10;
20 cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the
central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan03) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
44. Chapter 3 Square MLC fields dosimetry verification
3‐29
Figure 3.5(h) PB-calculated (in blue line) and SFD-diode-measured (in red dots) in-plane (leaf-perpendicular or Y-jaws) dose profile distributions for 6
MV FFF photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (4.0×4.0, 4.2×4.2) cm2
at various depths in water: 1.5; 5;
10; 20 cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at
the central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan03) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
45. Chapter 3 Square MLC fields dosimetry verification
3‐30
Figure 3.5(i) PB-calculated (in blue line) and SFD-diode-measured (in red dots) cross-plane (leaf-parallel or X-jaws) dose profile distributions for 6 MV
FFF photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (6×6, 6×6) cm2
at various depths in water: 1.5; 5; 10; 20 cm.
Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the central
axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan03) with high spatial resolution of 0.2 mm.
Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step size of 1
mm in high dose gradient (or penumbra) regions.
46. Chapter 3 Square MLC fields dosimetry verification
3‐31
Figure 3.5(j) PB-calculated (in blue line) and SFD-diode-measured (in red dots) in-plane (leaf-perpendicular or Y-jaws) dose profile distributions for 6
MV FFF photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (6×6, 6×6) cm2
at various depths in water: 1.5; 5; 10; 20
cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the
central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan03) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
47. Chapter 3 Square MLC fields dosimetry verification
3‐32
Figure 3.5(k) PB-calculated (in blue line) and SFD-diode-measured (in red dots) cross-plane (leaf-parallel or X-jaws) dose profile distributions for 6 MV
FFF photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (10×10, 10×10) cm2
at various depths in water: 1.5; 5; 10; 20
cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at the
central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan03) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
48. Chapter 3 Square MLC fields dosimetry verification
3‐33
Figure 3.5(l) PB-calculated (in blue line) and SFD-diode-measured (in red dots) in-plane (leaf-perpendicular or Y-jaws) dose profile distributions for 6
MV FFF photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (10×10, 10×10) cm2
at various depths in water: 1.5; 5;
10; 20 cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at
the central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan03) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
49. Chapter 3 Square MLC fields dosimetry verification
3‐34
Figure 3.5(m) PB-calculated (in blue line) and SFD-diode-measured (in red dots) cross-plane (leaf-parallel or X-jaws) dose profile distributions for 6
MV FFF photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (22×22, 22×22) cm2
at various depths in water: 1.5; 5;
10; 20 cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at
the central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan03) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
50. Chapter 3 Square MLC fields dosimetry verification
3‐35
Figure 3.5(n) PB-calculated (in blue line) and SFD-diode-measured (in red dots) in-plane (leaf-perpendicular or Y-jaws) dose profile distributions for 6
MV FFF photon beams of TrueBeam 1 unit for an SSD of 100 cm for (MLC, jaws) field sizes of (22×22, 22×22) cm2
at various depths in water: 1.5; 5;
10; 20 cm. Gamma values (in magenta dashed line) based on (2%, 2 mm) criteria are also plotted in the graph. All dose profiles were normalized to 1 at
the central axis point. Profiles were calculated with the PB algorithm in a unit-density phantom (ID: T41009, Plan03) with high spatial resolution of 0.2
mm. Profiles were measured with the SFD diode in the 3D water phantom with a large step size of (2-5) mm in uniform dose regions and a small step
size of 1 mm in high dose gradient (or penumbra) regions.
51.
52. Chapter 4 Irregular MLC fields dosimetry verification
4‐1
4. Dosimetric verification for irregular MLC-shaped fields
Dosimetry calculated with the iPlan pencil beam (PB) dose algorithm was
verified using a 2-D ion chambers array detector system (I’mRT MatriXX;
IBA; Germany). The I’mRT MatriXX detector is used in conjunction with the
plastic water phantom (MULTICube; IBA; Germany) for 2D dosimetric
verification with rotational therapy techniques, including IMRT, VMAT, as
well as conformal fields and arcs techniques used in the iPlan RT Dose
treatment planning system. Figure 4.1 shows the setup of the MultiCube-
MatriXX dosimetry system for dosimetry measurement in the TrueBeam 1
linac’s room.
The I’mRT MatriXX dosimeter measures 2D dose distributions for both jaw-
defined fields and MLC-defined (static or sliding) fields. Using a movie mode
with a time resolution down to 20 ms, 2D dose maps can be measured for
dynamic fields used in rotational therapy such as Dynamic conformal arcs or
VMAT.
Figure 4.1 Setup of the MatriXX ion-chambers array detector embedded in a plastic water phantom
(MULTICube; CIRS; USA) for dosimetric verification of MLC-defined complex fields. The solid
water layer overlying the MatriXX system is 11 cm thick, and the backscatter layer is 7.5 cm thick.
53. Chapter 4 Irregular MLC fields dosimetry verification
4‐2
4.1 Calibration of the MatriXX system
Accurate dosimetry with the MatriXX system requires output calibration in
the reference irradiation geometry. The ion chambers array underlying the
MatriXX measurement surface is set up at the isocenter level. The MatriXX
system is sandwiched inside the MULTICube plastic water phantom which
has 8-cm thick solid water underneath the MatriXX system and 11-cm thick
solid water layer on top of the MatriXX system. A (10×10) cm2 jaw-defined
field with retracted MLC leaves is used for the output calibration.
With this measurement setup, a reference dose for the given linac beam (i.e.,
the 6-MV or the 6-MV FFF beam) is entered in the dose analysis software
(OmniPro I’mRT; IBA; Germany) to calibrate the MatriXX system. As
recommended8, the reference dose value is best obtained from direct linac
calibration measurement. 9 Alternatively, it can also be referenced by dose
calculation in a treatment planning system which, however, incorporates
heterogeneity corrections for the materials in the MatriXX system.
In the commissioning process, reference doses were obtained from a simple
TPR ratio measured directly with the MatriXX system independent of
planned dose calculation. Assuming the linac output is accurately calibrated
and the effect of heterogeneity in the body of the MatriXX-MULTICube
system on the dose distribution is small, reference doses of 80.6 cGy and 78
cGy were measured for 6 MV and 6 MV FFF beam, respectively, and were
used subsequently for calibration of the detector. Figure 4.2 compares the
resulting measured dose distributions with the ones calculated with the PB
algorithm for the calibration (10×10 cm2) fields. Differences between the
MatriXX-measured and PB-calculated doses are less than 1% for both 6 MV
and 6 MV FFF fields. Table 4.1 summarizes the ratio of measured dose to PB-
calculated dose for consecutive calibrations of the MatriXX system used
during the commissiong measurements. Similar dose differences (of < 1%)
were found. These differences may be attributed to two possible reasons: (1)
small offset of the linac output; (2) the inhomogeneity effect corrected by the
PB dose calculation but not taken into account in measurements with the
MatriXX system.
54. Chapter 4 Irregular MLC fields dosimetry verification
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Figure 4.2(a) Comparison of MatriXX-measured dose plane (coronal) and PB-calculated dose plane
for a single jaw-defined (10×10) cm2
, 6-MVfield in a calibration setup of the MatriXX detector. Both
measured and calculated doses were normalized to 100% at the central axis point. Gamma results
were evaluated based on dose difference of 3% and distance-to-agreement (DTA) of 3 mm. Dose
difference between measurement and calculation at the normalization point is 0.5% for this
calibration setup.
55. Chapter 4 Irregular MLC fields dosimetry verification
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Figure 4.2(b) Comparison of MatriXX-measured dose plane (coronal) and PB-calculated dose plane
for a single jaw-defined (10×10) cm2
, 6-MV FFF field in a calibration setup of the MatriXX detector.
Both measured and calculated doses were normalized to 100% at the central axis point. Gamma
results were evaluated based on dose difference of 3% and distance-to-agreement (DTA) of 3 mm.
Dose difference between measurement and calculation at the normalization point is 0.8% for this
calibration setup.
56. Chapter 4 Irregular MLC fields dosimetry verification
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Table 4.1 Reference doses used for calibration of the MatriXX system in dosimetric measurements
for commissioning the pencil beam (PB) algorithm of the iPlan treatment planning system. Measured
2D dose map was compared with the PB-calculated dose map for a field size of (10×10) cm2
in a
calibration setup of the MatriXX detector (dref: 11 cm; SSDref: 89 cm; 100 MU). Differences in the
cental axis dose between the MatriXX measurement and PB dose calculation (Dmeas/Dplan -1) for each
calibration setup for 6 MV and 6 MV FFF photon beams are shown in the table. Measured dose is
larger than the planned dose by less than or equal to 1% in all cases.
6 MV 6 MV FFF
Calibration
date
Reference dose
(cGy)
Dose difference
(%)
Reference dose
(cGy)
Dose difference
(%)
May 10, 2013 80.6 0.5% 78.4 0.8%
May 11, 2013 80.5 0.5% 78.1 0.9%
May 12, 2013 80.5 0.6% 78.0 0.6%
May 13, 2013 80.6 0.1% 78.1 1.0%
May 15, 2013 80.7 0.7% 78.0 0.9%
May 18, 2013 80.5 0.6% 77.7 0.6%
May 19, 2013 80.5 0.4% 77.7 0.6%
4.2 Verification for circular fields
Dose distributions for MLC-defined circular fields were calculated with the
PB dose algorithm. Circular fields of 1, 2, 4, and 8 cm diameter were used. In-
phantom doses were calculated in the phantom body of the I’mRT matrix (ID:
T41010; Plan1). PB-calculated dose distributions were sampled on the array
detector plane with a spatial resolution of 1 mm. They were compared with
the dose distributions measured directly with the MatriXX system. The
comparison results are shown for the four diameter fields in Figures 4.3 to
4.6, for both 6 MV and 6 MV-FFF beams.
Gamma analysis was evaluated based on 3%-dose difference and 3-mm DTA.
For large circular fields with diameters of 2 cm and greater, good agreements
between the MatriXX-measured and PB-calculated dose distributions are
achieved, as shown in Figures 4.3 to 4.5. For the smallest 1-cm diameter
field, the central-axis peak dose measured with the MatriXX detector was
smaller than the PB-calculated peak dose for both 6 MV and 6 MV-FFF
fields, as shown in Figures 4.6(a) and (b), respectively. It is due to the volume
averaging effect of the finite-size ion chambers with cross-sectional areas of
the air cavity of 7-mm diameter. It is also this effect that results in the
measured beam profiles appearing less sharp than the calculated profiles in
the penumbra regions for all diameter fields.
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4.3 Verification for complex “letter” fields
MLC-defined fields shaped as “letters” were created. Dose distributions for
these irregular “letter” fields were calculated with the PB dose algorithm in
the iPlan RT Dose planning system. Four “letter” field shapes were defined
with small field dimesions of the order of (4×4) cm2: (1) “I” shape; (2) “H”
shape; (3) “Z” shape; (4) “N” shape. In-phantom dose distributions were
calculated in the CT body of the I’mRT MatriXX (ID: T41010; Plan2). PB-
calculated dose distributions were sampled on the chambers array plane with
a fine spatial resolution of 1 mm. They were exported to the OmniPro I’mRT
dose analysis software and compared with dose distributions measured
directly with the MatriXX system. The comparison results are shown for the
four “letter” fields in Figures 4.7 to 4.10, for both 6 MV and 6 MV-FFF beams.
Overall, the MatriXX-measured dose distributions agree well with the PB-
calculated dose distributions for all “letter” fields. Differences of the point
dose at the normalization point in uniform dose region between measurement
and calculation are within 2% for all fields for both 6 MV and 6 MV FFF
beams. The measured point dose is typically smaller than the PB-calculated
dose due to the volume averaging effect of the ion chambers exposed in these
small fields.
Gamma analysis based on 3% dose difference and 3-mm DTA was evaluated
for comparison between MatriXX measurement and PB calculation for these
small “letter” fields. The gamma statistics for each field are shown in Figures
4.7 to 4.10. Gammas with values greater than 1 refer to pixels where typical
sharp dose gradient locates. In comparsion with circular diameter fields
where dose gradients are isotropic in radial directions, the gamma statistics
for these “letter” fields with anisotropic and sharper dose gradients are less
superior. For example, for the “Z” shaped MLC-defined field as shown in
Figure 4.9, measured dose profile agree well with the calculated profile in X-
direction parallel to the MLC leaf motion. However, along the Y-direction
perpendicular to the MLC leaf motion, the measured and calculated dose
profiles differ, particularly in the dip region where the diagonal arm of the
“Z” shape meets the horizontal arm. Similar discrepancy occur in the profiles
for the “N” shaped field, albeit in opposite (X-jaw) direction. Obviously, the
MatriXX detector lacks sufficient resolving power to measure the sharp dose
gradient over a small region. Gamma results can be improved when higher-
resolution, 2D dose detectors are used, such as radiographic or radiochromic
films. Film measurements may follow up to confirm this speculation.
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4.4 Verification for complex “checker-board” fields
“Checker-board” field patterns were created with MLC for further dosimetric
verification for static, complex-shaped fields. Four patterns were designed by
arranging four small MLC-shaped squared fields in orderly fashion. Each
squared field has a dimension of (1.5×1.5) cm2. The “check-board” patterns
were defined within a jaw dimension of (6.4×6.4) cm2. In-phantom dose
distributions were calculated inside the CT body of the MULTICube-MatriXX
dosimetric system with the PB dose algorithm (ID: T41010; Plan 3). The PB-
calculated 2D dose distributions with a spatial resolution of (1×1) mm2 were
exported to the OmniPro-I’mRT dose analysis software for comparison with
direct measurement data. Measured versus calculated dose distributions
along with the gamma analyses are shown in Figures 4.11 to 4.14 for these
four “check-board” field patterns for both 6 MV and 6 MV FFF photon beams.
In comparison, point doses at the normalization point show good agreement
between the MatriXX measurement and PB dose calculation for all four
“checker-board” field patterns, within 2% in general cases and within 3.3% in
the laregest discrepancy. The checker-board patterns were formed with
simpler squared fields with more isotropic dose gradients; therefore, gamma
statistics improve for these fields in comparison with the more anisotropic
dose-varying “letter” fields. More than 98% of the total number of pixels has
gamma value less than 1 for all fields (see Figures 4.11 to 4.14) for both 6 MV
and 6 MV-FFF beams. Gamma values were evaluated based on 3% dose
difference and 3-mm DTA.
83. Chapter 4 Irregular MLC fields dosimetry verification
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4.5 Verification for complex “number” fields
Lastly, “number” fields shaped by the high-definition MLC’s of the TrueBeam
1 unit were used in dosimetric verification for single, irregularly MLC-shaped
fields. Nine “number” fields with shapes ranging from numbers “1” to “9”
were created by the MLC (ID: T41010; Plan04). Two sets of these 9 “number”
fields were formed based on the font sizes of the numbers: (1) Large font size
group with jaws-defined field dimensions of the order of (4×7) cm2 and (2)
Small font size group with jaws-defined field dimensions of the order of (2×4)
cm2. In-phantom dose distributions were calculated in the CT body of the
solid-water embedded MatriXX detector (ID: T41011). PB-calculated dose
distributions were sampled on the chambers array plane with a fine spatial
resolution of 1 mm. They were exported to the OmniPro I’mRT dose analysis
software and compared with dose distributions measured directly with the
MatriXX system. The comparison results are shown for the 9 “number” fields
with two font size ranges in Figures 4.15 to 4.23, parts (a) and (b) for 6 MV
beams with large and small font sizes, respectively, and parts (c) and (d) for 6
MV-FFF beams with large and small font sizes, respectively.
Comparison shows that MatriXX-measured dose distributions agree well
with the PB-dose distributions for all larger-sized “number” fields. Difference
in the normalization point dose between measurement and calculation is
small, within 2.2%. Distribution of gamma values based on 3% dose
difference and 3-mm DTA varies depending on the complexity of the field
shape. For round figure configurations (such as numbers “6” and “8”), gamma
statistics are excellent with more than 97% of the total number of pixels with
gamma values less than 1. For figure configurations with high irregularity
(e.g., numbers “2” and “5”), gamma distributions slightly degrade primarily
due to very steep dose gradients which cannot be adequately measured with
the current finite-resolution MatriXX system.
As shown in Figures 4.15 to 4.23, when the field configurations were reduced
by ½ in size of the order of (2-4) cm, discrepancies between the measured and
PB-calculated dose distributions, including the normalization point doses, are
more significant. These results demonstrate the limitation of the currently
used MatriXX system for use in dosimetry verification for small fields. The
smaller spatial resolution of 7 mm for this dosimeter prevents its application
to dosimetry for fields as small as 2 cm, unless the field shapes are uniform
or rounded like configurations of “6” and “8” as shown in parts (b) and (d) of
Figures 4.20 and 4.22, respectively. For such small and highly irregular field
shapes, it is recommended to use high-resolution films to evaulate 2D dose
distributions and a small-field ion chamber to evaulate an in-phantom point
dose located in a uniform dose region.
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4.6 Summary
In summary, a total of 42 plans for single, static, MLC-defined complex fields
were used in commissioning the PB dose algorithm of the iPlan RT Dose
treatment planning system (21 plans for 6 MV beam and 21 identical plans
for 6 MV FFF beams). 2D isodose distributions with fine spatial resolution of
(1×1) mm2 were calculated with the PB algorithm for each plan and compared
with the dose distributions measured directly with the ion-chamber arrays
(MatriXX) dosimetery system.
The accuracy of the commissioned PB dose calculation algorithm is evaluated
from a comparison of the measured and calculated dose distributions in two
aspects: (1) Point dose difference; (2) Gamma (γ) map analysis. Point dose
difference refers to the percentage difference in the absolute dose at a point of
normalization in a phantom between the measurement and PB calculation.
Gamma map analysis evaluates difference in relative isodose distributions
between the measurement and PB calculation in terms of dose and distance.
These QA results for each plan were evaluated and are presented in the
corresponding figure in this chapter.
QA results (i.e., point dose difference and gamma analysis) of all plans are
summarized in the form of frequency histograms in Figure 4.24 to evaluate
the peformance of the PB dose calculation algorithm. Out of a total 42 plans,
76% and 93% of all plans have point dose difference between measurement
and calculation within ±2% and ±3%, respectively. In addition, 74% of all
plans have more than 97% of all pixels passing the gamma values (less than
1) based on the criteria of 3% dose difference and 3-mm DTA. The median
percentage of pixel population meeting the gamma criteria is 97.2%. In
conclusion, agreements between the measured and PB-calculated dose
distributions are good for single, MLC-shaped complex fields. The PB dose
algorithm is validated for these fields.
121. Chapter 4 Irregular MLC fields dosimetry verification
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0
2
4
6
8
10
12
14
(-4%,-3%) (-3%,-2%) (-2%,-1%) (-1%,0%) (0%,1%) (1%,2%) (2%,3%) (3%,4%)
Point dose difference (%)
Numberofplans
0
2
4
6
8
10
12
[93%,94%) [94%,95%) [95%,96%) [96%,97%) [97%,98%) [98%,99%) [99%,100%)
Percentage of pixels in passing (γ < 1) range
Numberofplans
Figure 4.24 Frequency histograms summarizing quality assurance (QA) results of a total 42 plans
with single, static, MLC-defined irregular fields for both 6 MV and 6 MV FFF beams. The top
histogram shows number of plans with difference of the normalization point dose between the
MatriXX measurement and the PB calculation in 1%-difference interval. The bottom histogram
shows the number of plans with total number of pixels (in percentage) having γ less than 1 in various
percentage ranges from 93% to 100%.
122.
123. Chapter 5 Patientspecific plans dosimetry verification
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5. Dosimetric verification for patient-specific treatment plans
Validation of the iPlan pencil beam (PB) dose calculation algorithm extends
from application to single, static MLC-defined fields to application to patient-
specific treatment plans. The accuracy of the PB algorithm was investigated
in the iPlan RT Dose platform for two radiosurgery-dedicated techniques: (1)
Static Conformal Fields (SCF) technique and (2) Dynamic Conformal Arcs
(DCA) technique. Patient-specific treatment plans with multiple planning
target volumes (PTV) were used for the SCF and DCA techniques with both 6
MV and 6 MV FFF photon beams from the Varian’s TrueBeam 1 system. In-
patient dose distributions were calculated with the PB algorithm using the
non-uniform density CT image data set for the particular patient.
To verify the accuracy of the PB dose calculation model, each treatment plan
was mapped to the CT body phantom (ID: T41011) of the MultiCube-MatriXX
dosimetry system. The calculated in-phantom dose distributions on the plane
of the ion-chambers array were compared with the corresponding 2D planar
dose distributions measured directly with the MatriXX system. Both absolute
doses and gamma distributions were evaluated for validation purpose. Figure
5.1 shows the beam setup for the SCF and DCA radiosurgical techniques for
in-phantom dose calculation and verification.
124. Chapter 5 Patientspecific plans dosimetry verification
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Figure 5.1 In-phantom dose calculation and verification geometry for two radiosurgical techniques:
(a) Static Conformal Fields (SCF) technique and (b) Dynamic Conformal Arcs (DCA) technique with
6 MV and 6 MV FFF beams from the TrueBeam 1 linac. Dose distributions were calculated with the
pencil beam (PB) algorithm in a CT body phantom of the MatriXX dosimeter (ID: T41011). The PB-
calculated dose distributions on the plane of the ion-chambers array were compared directly with the
same 2D planar dose distributions measured directly with the MatriXX system to validate the dose
calculation accuracy of the PB model.
The MatriXX system was mounted on the special Brainlab 6D robotic couch
for dosimetry verification of the SCF and DCA techniques. Given that some
treatment fields were incident into the MatriXX body through the treatment
couch, a model of the couch with the associated electron density information
was incorporated in the in-phantom dose distributions calculation with the
PB algorithm (see Figure 5.1). Both SCF and DCA radiosurgical techniques
are characterized by multiple non-coplanar fields. This means both the
gantry and the couch are rotated at specific planned angular positions for
treatment irradiation. The MatriXX system is set up with a particular couch
position during verification. Some combined gantry-couch angular positions
may result in a collision of the MatriXX detector with the gantry and thus
should not be incorporated in associated treatment plans. Table 5.1 shows the
range of gantry angles of collision clearance for a set of couch angles available
for use in the SCF and DCA radiosurgical techniques.
125. Chapter 5 Patientspecific plans dosimetry verification
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Table 5.1 Range of gantry angles at given couch angles used in the SCF and DCA radiosurgical
techniques devoid of the gantry collision with the MatriXX system mounted on the Brainlab 6D
robotic treatment couch. Note that this data applies to the MatriXX system set up at a particular
couch position (Vertical: 11.07 cm; Longitudinal: 111.42 cm; Lateral: 1000.00 cm; Rotation: 0.00°).
If the MatriXX system is changed to a different setup position, this data may vary.
Couch angle (°) Range of gantry angle (°) avoiding collision
90° (179°, 310°) counter‐clockwise (ccw)
75° (179°, 310°) ccw
60° (179°, 305°) ccw
45° (179°, 300°) ccw
30° (179°, 295°) ccw
15° (179°, 181°) ccw
0° (179°, 181°) ccw
345° (179°, 181°) ccw
330° (70°, 181°) ccw
315° (60°, 181°) ccw
300° (55°, 181°) ccw
285° (50°, 181°) ccw
270° (45°, 181°) ccw
5.1 Two-brain-metastases plan verification
Treatment plan (ID: 169073) of a patient with two brain metastases (anterior
and posterior) was used to verify the accuracy of dose calculation of the PB
algorithm for SCF and DCA radiosurgical treatments. The anterior brain
metastasis PTV (PTVa) has a volume of 12.3 cm3 with the equivalent radius
of 1.4 cm and was prescribed with a total dose of 22.5 Gy in a single fraction.
The posterior brain metastasis PTV (PTVp) has a volume of 3.8 cm3 with the
equivalent radius of 1 cm and was prescribed with a single fractionated dose
of 30 Gy. Figures 5.2 and 5.3 show the field setups of both the SCF and DCA
radiosurgical techniques used in treating the PTVa and PTVp, respectively.
In-patient 3D dose distributions calculated with the PB dose algorithm in the
three orthogonal (axial; sagittal; coronal) planes are also displayed (in color
wash form) in the figures. The corresponding treatment parameters used for
both radiosurgical techniques were summarized in the setup reports printed
from a commissioned Record-and-Verify Oncology information system
(ARIA®; Varian; USA). Figure 5.4 and 5.5 shows the ARIA-printed setup
forms for the SCF and DCA techniques used to treat the anterior PTV and
posterior PTV, respectively, in this patient plan (ARIA ID: T41010; Course
ID: C5-169073).
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Figure 5.2 Beam setup of two radiosurgical techniques: (a) SCF and (b) DCA for dose calculation
with the PB algorithm in a patient-specific treatment plan (ID: 169073). All fields are isocentrically
setup at an anterior planning target volume (PTVa) prescribed with a single fractionated dose of 22.5
Gy. The PB-calculated 3D dose distributions are shown in the form of colorwash and isodose lines
(10%, 30%, 50%, 80%, 90%, and 95%).
127. Chapter 5 Patientspecific plans dosimetry verification
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Figure 5.3 Beam setup of two radiosurgical techniques: (a) SCF and (b) DCA for dose calculation
with the PB algorithm in a patient-specific treatment plan (ID: 169073). All fields are isocentrically
setup at a posterior planning target volume (PTVp) prescribed with a single fractionated dose of 30
Gy. The PB-calculated 3D dose distributions are shown in the form of colorwash and isodose lines
(10%, 30%, 50%, 80%, 90%, and 95%).
128. Chapter 5 Patientspecific plans dosimetry verification
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Figure 5.4 Aria-printed setup report summarizing the treatment parameter used for in-phantom verification with the MatriXX system for the SCF and
DCA techniques used in conjunction with the PB dose calculation algorithm to treat the anterior planning target volume (PTVa) of the test patient case
(ID: 169073).
129. Chapter 5 Patientspecific plans dosimetry verification
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Figure 5.5 Aria-printed setup report summarizing the treatment parameters used for in-phantom verification with the MatriXX system for the SCF
and DCA techniques used in conjunction with the PB dose calculation algorithm to treat a posterior planning target volume (PTVp) of a test patient
case (ID: 169073).
