rotational imrt, newer technology in radiotherapy

1. ABHIJIT DAS
2ND YEAR PG
DEPT. OF
RADIOTHERAPY
AHRCC
ARC THERAPY

2. SHIFT OF MACHINES AND
CONCEPT
• The dawn of the 20th century, arc therapy Involving dynamic
field shaping using a multileaf collimator was first described
by Takahashi in 1965.
• 1982,Brahme et al solved an integral equation for a
hypothetical target wrapped around a critical structure and
treated with arc therapy.
• In 1993, another form of IMRT using rotational fan beams,
called Tomotherapy, was Proposed by Mackie et al.
• Intensity modulated arc therapy (IMAT) was introduced by
Cedric X.Yu in 1995

3. THE BASIC CONCEPT OF ARC THERAPY :
• The delivery of radiation from a continuous
rotation of the radiation source and allows the
patient to be treated from a full 360 DEGREE
beam angle.
• Arc therapies have the ability to achieve
highly conformal dose distributions and are
essentially an alternative form of IMRT.

5. A major advantage over fixed gantry IMRT is the improvement in
treatment delivery efficiency due to –
• The Reduction In Treatment Delivery Time .
• The Reduction In MU Usage
(the amount of radiation output per unit of time is referred as monitor
unit).
• Subsequent Reduction Of Integral Radiation Dose To The Rest Of The
Body.
• The Availability Of Extra Time Within A Set To Employ IGRT.

6. ARC-BASED THERAPIES:
 Tomotherapy
 IMAT
 volumetric modulated arc therapy (VMAT)- single arc forms of
IMAT

8. Tomotherapy techniques can be subdivided –
1. axial or serial tomotherapy (where the radiation is delivered
slice by slice)
2. helical tomotherapy (HT) (where the radiation is delivered in a
continuous spiral).
HT has been evaluated in a variety of tumor sites
and it can generally achieve either similar or
improved dose distributions compared with fixed
field IMRT, with variable results on treatment time
comparisons.

11. The TomoHelical delivery mode provides IMRT and
3D CRT treatment delivery in a continuous (360°)
helical pattern, using thousands of narrow
beamlets, which are individually optimized to
target the tumor.
• The TomoDirect delivery mode is a discrete
angle, non-rotational delivery mode.
TomoDirect allows creation of treatment plans
that include between 2 and 12 target-specific
gantry angles. During treatment delivery, all
beams for each target are delivered sequentially
with the couch passing through the bore of the
system at an appropriate speed for each gantry
angle.
HI
ART
SYSTE
M

12. • Tomotherapy - a combination of a CT scanner and a linear accelerator that can
deliver the radiation in a fan-shaped distribution, similar to CT imaging with a
continuously rotating radiation source, while the patient is moved through the
machine.
PARTS DESCRIPTIONS
LINAC 6 MV S-band (3 GHz) linear accelerator
DIRECTION OF ROTATION CLOCKWISE FROM FOOT END /speed varies according to plan.
ENERGY FOR TREATMENT 6 MV photon beam
POWRED BY MAGNETRON
SAD 85 CM
MAXIMUM RADIATION FIELD
LENGTH
150 CM WITH COUCH AT HEIGHT OF ISOCENTER PLANE
TREATMENT VOLUME - Tomohelical 80 Cm (Transverse Diameter) X 135 Cm (Longitudinal)
For Typical Patient Set-up.
Tomodirect 40 Cm (Transverse Diameter) X 135 Cm (Longitudinal)
For Typical Patient Set-up.

13. PARTS DESCRIPTION
ENERGY FOR IMAGING 3.5 MV photon for imaging.
DOSE FOR IMAGING 0.5-3 CGY
DETECTOR SYSTEM 528 channels, single-row xenon ion chamber array
used
for image acquisition
IMAGE RESOLUTION 512X512(0.78 PIXELS)
SCAN TIME TYPICALLY 2 MINUTES PER 10 CM LENGTH AT 4
MM SLICE SPACING.( 2,4,6 mm slicing available)
FIELD OF VIEW (FOV) 40
CM DIAMETER
FIELD OF VIEW (FOV) 40 CM DIAMETER
SOURCE TO DETECTOR
DISTANCE
145 CM
IMAGING

14. • The beam from the accelerator is collimated by a multileaf collimator
consisting of 64 leaves each of which project a shadow of 6.25 mm at the
patient generating a total fan beam width of 40 cm. (pneumatically driven)
• By using a separate collimation ("jaws") system above the multileaf
collimators, the "slice thickness" can range between 0.5 to 5 cm. it is a
specially designed machine for helical, fan beam delivery.
• multileaf collimation system is specifically designed to minimize leaf
transmission and interleaf leakage - important considerations for narrow
beam, multislice delivery procedures. Average MLC leakage - 0.25% (typical)
• Axis of travel is in one direction.(IEC-y axis)

15. Radiation Characteristics
One of the key differences is the lack of flattening filter, which makes the dose more
uniform at greater depths. As a result of this, the photon fluence profile is shaped
differently when compared to a traditional radiotherapy system. the conical shape of
the profile implies that there will be an increased average dose rate - thus reducing
the imaging time & No scatter outside the field

17. Procedures descriptions
3-D Imaging. standard diagnostic imaging equipment or CT-simulators
Definition of
Target Volume and
Organs at Risk
contour the target volume as well as the organs at risk. This
could be done at the CT-simulator or on a conventional 3-D treatment
planning computer---> after the image data set has been transferred to the
treatment planning system.
Tomotherapy Co-
registration
a rigid-body adjustment that will only provide translational, rotational, pitch and yaw
calculations. The Registration process allows the user to define structures for co-
registration including the Whole Image (Mutual information with no thresholding), Bone
and Tissue Technique (pixel threshold > 0.3 g/cm3), or a Bone Technique (pixel threshold >
1.1 g/cm3) as the focus for registration. N.B- The simplest thresholding methods replace
each pixel in an image with a black pixel if the image intensity is less than some
fixed constant T (that is, ), or a white pixel if the image intensity is greater than
that constant
Data Transfer to
Planning
Computer
planning computer which will perform the delivery optimization
calculations

18. PLANNING
AND DOSE
DELIVERY
the full gantry rotation is divided into 51 projections.
Each projection is characterised by its own leaf opening
pattern and covers an arc segment of approximately 7°.
The available rotation period may be between 15 and
60 s (typically around 20 s). As such, each projection takes
between 0.2 and 1 s with all leaves shut for a short
time between projections. The delivery assumes
constant dose rate of the linac.

19. Optimized
Planning.
The tomotherapy treatment planning system provides "inverse
planning" capabilities.
Three factors are predefined before starting the calculations:

20. 1.Pitch : 2.Modulation Factor: 3.Field width:
The pitch factor is defined as couch
movement per rotation in units of
the FBT(fan beam thickness).
The MF represents the ratio
of maximum leaf opening time
to the mean leaf opening time
of all MLC leaves, which open in
a projection
The FBT is achieved a compromise
between fast treatment times
and dose modulation in the
superior/inferior direction
• The smaller the pitch factor, the
longer the treatment time.
• a small pitch improves the
capability of dose modulation and
the ability to deliver high doses per
fraction.
• A potential problem with large
FBT and large pitch is the dose
distribution away from the central
axis. The beam divergence will
cause variations in overlap
between adjacent rotations, which
increase with distance from the
axis of rotation. -‘THREAD EFFECT
• MF is proportional to the
overall treatment time, and
with typical physical
constraints for the
tomotherapy delivery,
• can be selected between 1
and approximately 6.
• A small MF results in short
treatment times and is
adequate for relatively
symmetrical targets close to
the central axis of the patient.
. A large FBT results in larger
volumes covered in any projection
and a higher central axis dose
output while it reduces the scope
for conformality and detailed dose
modulation in cranio/caudal
direction of the patient.
Kissick et al showed a pitch factor of 0.86/integer number (e.g., 0.43, 0.287, 0.215, etc.) minimises
the thread effect).

21. Creation
of
Verificati
on Data
consists of the expected beam intensity at the
detector array for each gantry angle and couch
position. This intensity pattern is referred to as a
"sinogram" because each point irradiated in the
patient maps a sine wave pattern at the CT
detector as the gantry revolves. Sinograms can
actually be obtained for various processes
including a CT sinogram as described above, an
MLC sinogram, a registration sinogram, a
verification sinogram and a planned detector
sinogram. each is implemented in a very
specialized manner to address a specific task.

22. A sinogram is an array of pencil beam intensity values as a function of gantry
angle (horizontal axis in this Figure). Each vertical row corresponds to one
angular view.
A point object that is straight and parallel to the z-axis will appear as one cycle of
a sinusoidal curve when the gantry revolves by 360 degrees.

23. Procedures descriptions
Pre-Treatment
Megavoltage CT
Tomotherapy
Delivery.
Delivery
Verification.
While the patient is being treated, the detector array is
actively measuring the radiation transmitted through the patient (for
each pulse of the linac). This is used to determine actual radiation
incident on the patient and can be used to verify dose delivery during or
after treatment
Dose
Reconstruction.
Using the incident radiation fluence delivered to the patient and the CT
information that was obtained before the treatment, the dose actually
deposited in the patient can be computed and compared to the planned
dose. If necessary, corrections can be made to subsequent fractions

24. pros cons
Total Body
Irradiation
(TBI)
greater control over the dose
distribution and to spare organs that
may be at risk.
HT provided excellent conformal lung
sparing with mean doses not
exceeding 10 Gy.
Helical Tomography (HT) for TBI is
that it can’t be used when the body
length of the patient exceeds 145
cms.
Whole
brain
helical
Tomothera
py
Whole brain helical tomotherapy is a
possible treatment option for patients
suffering from malignant melanoma
with four or more brain metastases.-
hippocampal sparing
All HT plans had a higher dose brain
Exposure.
Inoperable
Lung
Cancer
Tomotherapy could produce
acceptable coverage for the target
while decreasing the mean dose to
sensitive surrounding areas such
U
S
E

26. • Intensity Modulated Arc therapy where
the following three parameters are
modulated simultaneously:
1. Gantry rotation
2. Dose rate
3. Leaf speed
• Like tomotherapy, IMAT is delivered in an arc manner.
• Instead of using rotating fan beams as in tomotherapy, IMAT uses
rotational cone beams of varying shape to achieve intensity
modulation.

27. • Cedric x.Yu concept:
1. with the increase in the number of gantry angles, the number of intensity
levels at each gantry angle can be Reduced without degrading plan quality.
2. plan quality is a function of the total number of quanta defined as the
product of the number of beam angles and the number of intensity levels. ( it is
the total number of aperture shape variations that determines the plan quality).
• Based on this fact a single arc with sufficient number of apertures variations would
be able to create the optimal treatment plans.
• Because linear accelerator at the time can not vary the dose rate dynamically
during gantry rotation. Most previous works on single arc IMAT was under the
assumption that the machine dose rate has to be constant during arc rotation.

28. Beamlet-Based Inverse Planning:
• Two-step approach to treatment planning:
1. Fluence map optimization–Delivery constraints ignored
2. Leaf sequencing –Accounts for delivery constraints
Aperture-Based Optimization:
• A One-step process:
1. Contour-based planning:
• Anatomy contour-based
• Isodose contour-based
2.Direct Aperture Optimization

29. DAO Optimization :
• Introduction of an automated planning system in which the
traditional intensity optimization is bypassed, and instead
directly optimize the shapes and the weights of the
apertures. -------‘‘direct aperture optimization.
• All of the MLC delivery constraints are included in the
optimization.

30. • The leaf settings and the aperture intensities are optimized simultaneously
using a simulated annealing algorithm.
• The DAO algorithm takes as input 1.beam angles, 2.beam energies, and 3.
number of apertures per beam angle.
• The algorithm then cycles through all of the variables, which are to be
optimized. These variables are 1.the leaf positions for each aperture and 2.
the weight assigned to each aperture.

31. 1.Highly conformal IMRT plans with only 3 to 5 apertures per beam.
2.Delivery in traditional 15 minute time slots.
3.The user has complete control over the complexity.
4.Provides optimal aperture shapes and weights.
5.No leaf sequencing.
6.Can be used for IMAT treatment planning.
Direct Aperture Optimization
Benefits

32. Small number of apertures can produce large number of intensity
levels
N= Number of intensity levels
n= Number of apertures
For 3 apertures, 7 intensities
For 4 apertures, 15 intensities
For 5 apertures, 31 intensities
For 6 apertures, 63 intensities

33. 3 Separate
Rotations with
Different Intensities
Per Rotation
Yields 7 Unique Intensity Levels

34. Otto developed a single arc IMAT algorithm that he referred to as
Volumetric Modulated Arc Therapy (VMAT), using this DAO algorithm.

35. IMAT to VMAT
New Developments
Delivery Control Systems
Elekta and Varian have introduced new linac control systems that will
systems that will be able to change the MLC leaf positions and dose
rate while the gantry is rotating.
Elekta - PreciseBeam Infinity® [can be delivered using single or
multiple arcs]
• Varian -RapidArc® [RapidArc always uses single arc to deliver
treatment]
• Philips Medical Systems, Inc - SmartArc
Both are using the term Volumetric Modulated Arc Therapy

36. VMAT Plan Design:
• Single arc vs. Multi-arc delivery
• Coplanar vs. Noncoplanar
Single vs. Multi Arc:
• Increasing the number of arcs provides
additional flexibility in shaping the dose
distribution.
• The key questions are which cases benefit
from the use of multiple arcs and what
number of arcs should be used

37. ADVANTAGES:
(Over Tomotherapy)
(1) IMAT does not need to move the patient during treatment and avoid
abutment issues seen with serial tomotherapy;
(2) IMAT retains the ability of using Non-coplanar beams and arcs, which has
value for brain and head / neck tumors;
(3) IMAT uses a conventional linac, thus complex rotational IMRT treatments
and simple palliative treatments can be delivered with the same treatment
unit.

38. • Varian: Eclipse RapidArc
• Philips: Pinnacle SmartArc
• Elekta : ERGO++
• Elekta: Monaco VMAT
• Nucletron : Oncentra MasterPlan VMAT
Inverse Planning

40. basic arc
parameters, e.g
arc length and
couch angle
coarse
segments
around the
arc
are generated
The fluence maps
are converted to
MLC segments,
two per angle.
MLC segments are filtered, evenly
redistributed around the arc, and
interpolated segments are added to reach
a final fine arc spacing
resulting segments are optimized using
machine parameter optimization to
satisfy dose volume objectives and leaf
motion, dose
rate, and gantry speed constraints.
To limit computation
time, initially
optimized intensity
maps with a coarse
angular resolution,
then convert to MLC
segments, and
redistribute the
segments around the
arc at a finer
resolution.
Optimized fluence maps are
converted to MLC leaf and jaw
segments using a conversion
algorithm that produces segments
with leaf motion that travels from
one side of the target to the other,
also known as sliding window.
Arc Sequencing

41. • The algorithm uses a simulated annealing based optimization and
minimizes the discrepancy between the optimized and sequenced
intensity maps. (fluence map)
• The algorithm iteratively changes the leaf positions and aperture
weights and rejects any change that and aperture weights and rejects
any change that violates an VMAT delivery constraint.
Arc Sequencing

42. • Gantry speed and dose rate must constant
throughout each arc.
• All beam weights within an arc must be equal.
IMAT Constraints:

43. Interconnectedness of Adjacent Beam Shapes:
Leaf motion between adjacent angles is limited by leaf Leaf
motion between adjacent angles is limited by leaf travel
speed and gantry rotation speed.

44. Electron arc therapy
a special radio-therapeutic technique in which a rotational electron beam is used to treat
superficial tumour volumes that follow curved surfaces.
the technique is well known and accepted as clinically useful in the treatment of certain
tumours, it is not widely used because it is relatively complicated and its physical
characteristics are poorly understood
The dose distribution in the target volume depends in a complicated fashion on the
electron beam energy, field width, depth of the isocentre, source to axis distance (SAD),
patient curvature, tertiary collimation and field shape as defined by the secondary
collimator.
Two approaches electron pseudo arc (series of
overlapping
stationary electron fields)
continuous rotating
electron beam.

45. angle ß concept
• offers a semiempirical technique for treatment planning for electron arc therapy.
The characteristic angle ß for an arbitrary point A on the patient’s surface & is
measured between the central axes of two rotational electron beams
positioned in such a way that at point A the frontal edge of one beam crosses
the trailing edge of the other beam.

46. • The angle ß is uniquely determined by
three treatment parameters: f,(SAD) ,
d, (the depth of the isocentre) and w,
the field width.
• Electron beams with combinations of
d and w that given the same
characteristic angle ß actually exhibit
very similar radial PDDs, even though
they may differ considerably in
individual d and w Thus the PDDs for
rotational electron beams depend
only on the electron beam energy and
on the characteristic angle ß.

47. DIFFICULTY:
• Photon contamination:
the photon contribution from all beams is added at the isocentre and
the isocentre might be placed on a critical structure.
• field shape of the moving electron beam defined by secondary
collimators. (homogeneity of dose)
1.cylindrical geometry (e.g. the chest wall), the field width can be
defined by rectangular photon collimators.
2.a spherical geometry (e.g. the scalp), a custom built secondary
collimator defining a nonrectangular field of appropriate shape has to
be used to provide a homogeneous dose in the target volume

48. Prostate cancer is one of the most common tumour sites treated with IMRT
worldwide, VMAT is new alternative.
IMRT
VMAT

49. STUDY PATIENTS OUTCOME
Palma et
al
10 1.The lowest doses to the OARs were achieved in the VMAT plans, which required
42% fewer MU compared with the fixed field IMRT plans
2. improved OAR sparing (improved rectal wall sparing)
MSKCC 11 1. improved rectal wall sparing with a resultant improved Normal Tissue
Complication Probability (NTCP) of rectal wall by 1.5%,
2. lower doses to the bladder wall (not statistically significant) and femoral heads
Ost et al 12 reducing the dose to the rectum.(V50 Gy was 45% in the 7-field IMRTvs32% in
VMAT,
p=0.001)
Kopp et
al
RapidArc
292 1. VMAT and IMRT similar PTV coverage (VMAT less homogeneous). VMAT –
slightly higher D2%
2. VMAT better than IMRT (sparing of rectum at high doses, bladder, femoral
heads, penile bulb)
Yoo et al
RapidArc
10 1. Primary plans – IMRT better than VMAT (PTV coverage, conformity). Boost
plans – similar PTV coverage, homogeneity; IMRT had worse conformity
compared to VMA
2. OAR: Boost plans – IMRT and DA VMAT better than SA VMAT. Higher integral
doses to body with VMA

50. This variation regarding target volume homogeneity and conformity could be
due to a number of factors:
• The number of arcs used in the VMAT plans (in general, double arc plans can
achieve higher conformity and homogeneity compared with single arc plans).
• The type of VMAT optimization approach and the number of fields used in
the fixed field IMRT plans.
• PTV coverage. (prostate/prostate and seminal vesicles/prostate +nodal
burden)

51. PROS AND CONS:
1. VMAT plans generally use fewer MU (up to 65% fewer) compared with fixed field IMRT.
2. improved efficiency of VMAT delivery with a reduction in treatment delivery times.
3. intrafraction motion may be of particular relevance in prostate radiotherapy as there may
be significant changes in rectal and bladder volumes within the time period required to
deliver an IMRT fraction.
4. Prostate has lower α/ß ratio, thus hypofractionated schedule may be better, so faster
VMAT delivery may be attractive solution.
5. It is worth noting that the optimisation and dose calculation times for VMAT planning are
longer compared with fixed field IMRT (up to x 4)

52. study N site outcome
Verbak-
el
et al
12 Nasopharynx
oropharynx
hypopharynx
Both has similar PTV coverage. DA VMAT better than SA VMAT and IMRT
for homogeneity.
Parotid dose lower with DA VMAT (by average 2Gy) compared with SA
VMAT and IMRT.
Vanetti
et al
29 Oropharynx,
hypo pharynx
Larynx
VMAT better than IMRT at sparing spinal cord (D2%, mean dose),
brainstem (D2%, mean dose) and parotid glands (mean dose).
DA VMAT better than SA VMAT.
VMAT – lower integral doses to body.
Cleme-
nte
et al
8 Oropharynx HT better than VMAT and IMRT for coverage of elective
PTV/ homogeneity. VMAT better than IMRT in conformity (no difference
in homogeneity).
HT – lower doses to brain, parotid, oral mucosa, oesophagus.
VMAT and IMRT lower doses to mandible.
VMAT – slightly lower mean dose to ipsilateral parotid gland
compared with IMRT.
HEAD AND NECK CANCER
RADIOTHERAPY

53. PROS AND CONS:
 In the post-operative pharyngeal patients, PTV coverage was inferior
in the single arc VMAT plan compared with the IMRT plan. The double
arc plan was equivalent to IMRT and triple arc was superior in terms of
PTV coverage and homogeneity.(Guckenberger et al)
 In primary pharyngeal patients, both single arc and double arc VMAT
plans were inferior to the IMRT plan, while the triple arc plan was
equivalent.
 In the paranasal sinus group, all VMAT plans were inferior to the IMRT
plan for dose coverage, particularly in the region between the
orbits.(Guckenberger et al)
 The mean dose to the lenses in this group was also higher in the VMAT
plans compared with the IMRT plans.

54. Central nervous system tumours
Radiotherapy for intracranial tumours can be challenging owing to the
proximity of these tumours to numerous critical structures.
Benign lesions:
cranial tumours where long life expectancies are predicted raises the need for
highly conformal techniques to reduce radiation dose to the surrounding
normal tissue.
LESIONS TRIALS TARGET OAR
Benign
lesions
Acoustic
neuroma,
meningioma,
pituitary
adenom
Fogliata
et al
RapidArc
VMAT and HT slightly
better
than IMRT for PTV
coverage
(D99%, D98%)
VMAT and IMRT better than HT
at sparing OARs (brainstem,
optic structures
Acoustic neuroma
(radiosurgery
single 12.5Gy
Lagerwaard
et al
RapidArc
Similar PTV coverage.
VMAT better than DCA for
conformity
VMAT and 5DCA – similar
maximum doses for cochlea,
brainstem, trigeminal nerve

55. MALIGNANT LESION
Wagner
et al
Rapidarc
High grade
glioma
VMAT slightly
better than IMRT for
conformity (both VMAT
and IMRT better than
CRT)
VMAT slightly better than IMRT
and 3D-CRT for OAR sparing
(chiasm, brainstem)
VMAT –highest mean dose to normal
brain and V5Gy of healthy
tissue
shaffer
et al
RapidArc
High grade
glioma
Similar PTV coverage,
conformity and
homogeneity
VMAT better than IMRT at sparing
lateralised OARs (retina, lens,
optic nerves).
No significant differences in sparing of
centralised OARs (brainstem, chiasm).
VMAT – higher mean dose to normal brain
(by 12%
Lagerwaar
d
et al
RapidArc
Brain
metastases
integrated plans (VMAT)
significantly better than
summated plans for
conformity
Smaller volume of normal brain receiving
Low dose radiation
Integrated plans (VMAT) – higher
maximum
dose to lenses

56. Lung cancer
• EARLY STAGE LUNG CANCERS : Stage I non-small cell lung cancer (NSCLC) SBRT has emerged as
an alternative treatment option to surgical resection for patients who are medically
inoperable, giving excellent local control rates (up to 95%).
• usually delivered with hypofractionated radiotherapy schedules and using multiple non-
coplanar fixed beams occasionally combined with dynamic arcs.
• IMRT and HT have also been evaluated using this approach. These techniques can
improve dose conformity compared with conventional radiotherapy, but at the expense of
prolonged delivery time.
McGrath
et al
Stage Ia NSCLC
(SBRT 48 Gy in
12 fraction)
VMAT better than 3D-CRT for
conformity at 80% and 50%
isodose levels. No difference
in homogeneity
IMAT better than 3D-CRT at sparing lung
(V20 Gy, V12.5 Gy, V10 Gy, V5 Gy). No
significant difference in mean dose to other
OAR
Ong
et al
Stage I NSCLC
SBRT 54Gy in 3
fractions 55Gy
in 5 fractions
/60Gy in 8 #
VMAT better than 3D-CRT,
DCA and IMRT for
conformity at 80% and
60% isodose level.
VMAT better sparing of chest wall
(V45Gy, V30Gy, V20Gy) compared to 3D-CRT
VMAT – higher lung doses (V20Gy,V5Gy)
compared with 3D-CRT

57. Lung cancer
• EARLY STAGE LUNG CANCERS : Stage I non-small cell lung cancer (NSCLC) SBRT has emerged as
an alternative treatment option to surgical resection for patients who are medically inoperable,
giving excellent local control rates (up to 95%).
• usually delivered with hypofractionated radiotherapy schedules and using multiple non-coplanar
fixed beams occasionally combined with dynamic arcs.
• IMRT and HT have also been evaluated using this approach. These techniques can improve dose
conformity compared with conventional radiotherapy, but at the expense of prolonged delivery
time.
McGrath
et al
Stage Ia NSCLC
(SBRT 48 Gy in
12 fraction)
VMAT better than 3D-CRT for
conformity at 80% and 50%
isodose levels. No difference
in homogeneity
IMAT better than 3D-CRT at sparing lung
(V20 Gy, V12.5 Gy, V10 Gy, V5 Gy). No
significant difference in mean dose to other
OAR
Ong
et al
Stage I NSCLC
SBRT 54Gy in 3
fractions 55Gy
in 5 fractions
/60Gy in 8 #
VMAT better than 3D-CRT,
DCA and IMRT for
conformity at 80% and
60% isodose level.
VMAT better sparing of chest wall
(V45Gy, V30Gy, V20Gy) compared to 3D-CRT
VMAT – higher lung doses (V20Gy,V5Gy)
compared with 3D-CRT
doses to the chest wall in this study were
significantly
lower in the VMAT plans, but at the cost of increased
dose to the lungs.

58. Brock
et al
Stage I
NSCLC
SBRT 60Gy
in
8 fraction
1. non-coplanar and VMAT better than co-planar
for PTV coverage.
2. Non-coplanar CRT better than coplanar CRT for
lung V11Gy (no significant difference for V20Gy).
A RECENT STUDY BY Holt A, van Vliet-Vroegindeweij C, Mans A, Belderbos JS,
Damen EM.:
The VMAT plans used double partial arcs avoiding the contralateral lung. While PTV
coverage was similar between all three techniques, both non-coplanar IMRT and
coplanar VMAT performed better then coplanar IMRT in reducing dose to healthy
lung tissue.

59. Pelvic malignancies (lower gastrointestinal tract)
Site Inference Studies problems
Anal
cancer
DA VMAT slightly better than
SA VMAT and IMRT in PTV
coverage & OAR like penile
bulb, external geniatalia.
A significant reduction in MU
(of up to 70%) and treatment
time.
Clivio et al
Vieillot et al
Stieler et al
the paucity of data for conventional IMRT
in anal cancer
Rectal
cancer
No significant difference in
bladder sparing.
VMAT significantly better
than 3D-CRT for conformity
No difference PTV coverage
Richetti et
al

60. • IMAT was one of the first arc techniques evaluated for whole abdomino-pelvic radiotherapy
(WAPRT) in the treatment of relapsed ovarian cancer.
GYNECOLOGICAL CANCERS
STUDY RESULTS AND INFERENCE
Wong et al two anterior arcs were sufficient in treating the target volume adequately with
acceptable sparing of OARs.
Cozzi et al
VMAT
with five-
field
conventio
nal fixed
field IMRT
• show similar target
volume coverage with
improved homogeneity
& conformity with
VMAT
• E.g: rectum, mean dose
andV40 Gy in the VMAT
plans were 36.3 Gy &
51.5%, respectively,
compared with 42.5 Gy
and 78.7% in the IMRT
plans
• The increase in the number of fields can improve the
quality of the IMRT plans leading to less differences
with the VMAT plans, but it takes higher MU and longer
treatment time.
• Brachytherapy has advantage of organ immobilization
with very steep dose gradients and highly conformal
dose distributions, which are not currently matched by
IMRT techniques - therefore, the general consensus is
that IMRT or VMAT will not replace the role of
brachytherapy in gynaecological cancers

61. Breast cancer mortality is decreasing owing to a combination of factors including earlier
diagnosis via screening and improvements in therapy.
Johansen
et al
Breast (chest wall and
nodes including internal
mammary nodes
VMAT and IMRT better than CRT for conformity.
& homogeneity.
VMAT and IMRT better than CRT at sparing ipsilateral lung.
CRT – lowest doses to contralateral lung.
VMAT – lowest doses to contralateral breast
Nicolini
et al
Breast (Bilateral, SIB to
tumour bed)
VMAT better than IMRT at sparing heart and lungs (medium-high dose
level).
for lungs, IMRT better at sparing at low dose levels.
VMAT – higher mean and integral dose to healthy tissue
Qiu et al Breast (partial breast
radiotherapy
VMAT better than 3D-CRT at sparing ipsilateral normal
breast tissue, ipsilateral lung.
Popescu
et al
breast (+regional nodes
including
Internal mammary
node
VMAT – lower mean dose to healthy tissue but higher V5Gy compared
with 3D-CRT and IMRT.
Breast cancer

62. • The increased risk of secondary malignancy secondary to low dose radiation is currently not
accurately quantifiable but should be borne in mind when deciding on the treatment strategy
or radiation technique for patients.
• IMRT will still play an important role in breast radiotherapy, particularly within the setting of
partial breast dose escalation for high-risk disease, which is currently being investigated in the
IMPORT-HIGH trial.
• partial arcs can be used in case of use of VMAT.
• While inverse planned IMRT is necessary for complex target volumes, simpler forward planned
techniques using multiple segmented tangential fields may be able to produce acceptable dose
distributions for less complex cases while also minimizing low dose radiation to surrounding
normal tissue.

63. • Arc therapy is an alternative form of IMRT in which continuous rotation of the
radiation source allows the patient to be treated from a full 360 DEGREE beam
angle
• Mainly three types: Tomotherapy, IMAT, volumetric modulated arc therapy
(VMAT)- single arc forms of IMAT
• Tomotherapy - a combination of a CT scanner and a linear accelerator that
can deliver the radiation in a fan-shaped distribution, where patient moves
continuously through gantry. Simultaneous MVCT & KVCT imaging is
available.
• lack of flattening filter makes the dose more uniform at greater depth resulting
in an increased average dose rate - thus reducing the imaging time & No scatter
outside the field.
• The intensity pattern created by expected beam intensity at the detector array
for each gantry angle and couch position, is referred to as a "sinogram" which is
used in verification data in tomotherapy.

64. • Intensity Modulated Arc therapy where the following three parameters are
modulated simultaneously: Gantry rotation ,Dose rate ,Leaf speed.
• Instead of using rotating fan beams as in tomotherapy, IMAT uses
rotational cone beams.
• Introduction of DAO helps to bring the concept of VMAT .
• Elekta and Varian have introduced new linac control systems:
PreciseBeam Infinity & RapidArc respectively
• It is of two types: Single arc vs. Multi-arc delivery & Coplanar vs. Noncoplanar
• multi arcs gives flexibility in treatment planning.
• Advantage over tomo is : not to move the patient during treatment delivery/can
use non coplanar beams/no new machine installment

65. • For treating superficial tumors electron arc therapy is used but it is technically difficult thus
not popular.
• Prostate & head-neck cancers are highly discussed topics in VMAT and tomotherapy since
critical structure avoidance is necessary along with dose escalation.
• In prostate intrafractional motion ,rectal and bladder wall sparing and hypofractionated RT
is of special mention . double arc plans can achieve higher conformity and homogeneity
compared with single arc plans.
• Similarly in head and neck double or even triple arc plan supersedes imrt which is superior
to single arc plan.
• In Paranasal sinus all VMAT plans were inferior to the IMRT.
• partial arcs can be used in case of use of VMAT in breast RT
• general consensus is that IMRT or VMAT will not replace the role of brachytherapy in
gynaecological cancers