Tomotherapy

Tomotherapy
Prof Amin E AAmin
Dean of the Higher Institute of Optics Technology
Prof of Medical Physics
Radiation Oncology Department
Faculty of Medicine
Ain Shams University

2-25
Introduction
❖ The introduction of IMRT has significantly improved the
ability to deliver a highly conformal radiation dose distribution
to a complex target while minimizing collateral damage to
adjacent tissues.
❖ IGRT further improves this by precisely locating a highly
conformal dose distribution with daily verification and with the
potential for daily correction.

Introduction
• The Tomotherapy is
designed to treat the entire
spectrum of radiation
therapy patients with
enhanced speed, precise
performance and ease of
use.
• It is Designed for Simple
or Complex Treatments

Tomotherapy
• Tomotherapy is intensity-modulated rotational radiotherapy
utilizing a photon fan beam.
• Radiation therapy device designed on a CT scanner-based
platform.
• Tomotherapy means: slice therapy coined to describe IMRT
using fan beam.
• Tomo = slice, section (Gk)
• Therapy = treatment

Tomotherapy
 Tomotherapy utilizes a binary collimator to provide the
modulation.
 In helical tomotherapy, the gantry and couch move
simultaneously.

Why Tomotherapy?
❖ Tomotherapy users have the unique ability to use daily CT
imaging to guide treatment based on patient anatomy for that
day, rather than for last week or last month.
❖ Customize delivery for each patient, surrounding the target
with highly-precise radiation delivered from all angles
❖ Minimize radiation exposure to healthy tissue.
❖ If necessary, adapt the treatment plan at any point.

Tomotherapy Concept
❖ Inline short length linac mounted on a continuously rotatable ring
directed at its center.
❖ Thepatient will be slowly translated through the ring.
❖ SoSpiral of slit field Radiation, directed at the patient, which is
modulated bi m-MLC 64 binary leaves. Low dose MVCT
images , virtually eliminates the artifacts.
❖ MVCT[3.5MV]detector mounted opposite to the source for
setup registration , treatment planning and verification
purposes.
❖ 3DCT image guidance before each treatment.

Tomohelical
• Precisely modulate dose intensity-IMRT
• Megavoltage CT- Precise tumor location
• 3 dimensional delivery
• Enables the delivery of thousands of narrow beamlets
directly to the tumor

HELICAL
360˚ Helical
Can irradiate up to a 160 cm long field.

Helical Tomotherapy
• Able to treat multiple tumors at the same time.
• Can irradiate up to a 160 cm long field.
• Shorter and faster treatment.
• Accurate 3D CT Images.
• 360 degree delivery

Helical
Scanning
Helical (Spiral) Tomotherapy
Helical
Fan Beam
Ring
Gantry
Linac
CT
Detector
CT Couch

Re-Engineering Radiotherapy
• Equipment and processes re-engineered for IMRT
• Integration of planning, delivery and verification
• Better leaf resolution
• Simple MLC’s
• More beam directions
• Single energy photon beam
• Better primary shielding
• Tomographic verification
• Helical tomotherapy was the result

• A Highly Integrated
Platform For IMRT
& IGRT
• Integrated solution
for the combination
of IGRT and IMRT
Helical Tomotherapy

Tomotherapy was Designed for IGRT
and IMRT
 Helical fan-beam IMRT or SRS delivery is fast, effective,
and simple.
 CT is the most important imaging modality for
radiotherapy and SRS.

Tomotherapy was Designed for IGRT
and IMRT
 Linac on a CT is better than a CT on a linac.
» ring gantry is more stable than a C-arm gantry.
» CT gantry allows faster rotation.
» no possibility of rotational collisions.
» coplanar delivery is simpler.
 Single energy sufficient.
 Simple binary MLC modulating the fan beam.
 Accurate CT couch.

Under the hood
• Linac
• Primary collimator
• Ion chamber
• Jaws
• MLC
• Detector
• Shielding
Monitor
Chambers

Treatment Beam Components
❖ Anenclosed Gantry.
❖ Fixed and rotating assemblies.
❖ Slip ringtechnology.
❖ Linear accelerator.
❖ Primary collimator.
❖ Secondary collimator.
❖ Multi leaf collimator.
❖ MVCTimagingsystem.
❖ Beam stopper.

Design Principles
❖ Designed around a ring gantry
similar to a helical CT scanner.
❖ Non coplanar treatments ruled out
❖ Use of IMRT obviates need for
non coplanar treatment.
❖ Ring gantry maintains its isocenter
to tens of microns as compared to a
millimeter diameter on the best C-
arm Linac gantries1
.

Gantry Specification
❖ Rotates around IEC-Y axis, Continuous 360 degree rotation
with a accuracy of angles within 0.1 Degree.
❖ Gantry Speed B/W 1 & 5.08 RPM for treatment,10 RPM for
imaging with a nominal SSD of 85 cm.
❖ This rotational speed set During the Treatment Planning.
❖ Bore diameter:85cm.
❖ Minimum Rotation Per Minute:1 rpm.
❖ Maximum Rotation Per Minute: 10 rpm.

Linac Shown
Without
Shielding
DetectorBeam Stop
High Voltage
Power Supply
Control
Computer
Magnetron
Pulse Forming
Network and
Modulator
Data Acquisition System
Circulator
Gun Board
Structure

LINAC Design
❖ Standing wave S band LINAC – 2 operating energies
❖ 6 MV photon beam output for treatment
❖ 3.5 MV photon for imaging
❖ No flattening filter
❖ Output increased to 8 Gy/minat center of bore – 2 times that of
periphery
❖ The beam energy spectrum is more constant (< ± 5%)
❖ There is less scatter contamination.
❖ However a beam hardener and electron stopper is provided

Major Specifications
• 6 MV linac
• Up to 8 Gy/min @ axis
• 85 cm diameter gantry bore
• 64 leaves with 6.25 mm resolution @ axis
• 4 cm x 40 cm maximum field @ axis
• Slice field width from 5 mm to 40 mm @ axis
• Minimum beamlet size 5 mm x 6.25 mm @ axis
• Xenon CT detectors with per pulse acquisition
• 0.25 mm precision CT couch
• Leaves 10 cm thick, 95% tungsten alloy
• Primary collimator 22 cm thick 95% tungsten alloy

Major Differences of Tomotherapy
from C-arm Linacs
❖ Field Light: no field light
❖ ODI: no optical distance indicator
❖ MLC: binary modulator
❖ Collimator Rotation: no collimator rotation
❖ Accessories: no accessories
❖ Couch: no rotation, continuous translation
❖ Lasers: green (fixed) and red (movable)lasers
❖ Field Profile: triangular shape (no flattening filter)
❖ Modulation: nearly continuous intensity modulation
❖ Number of Fields: 51 arcs segments instead of 5 to 9 fields
❖ CT Imaged: true CT scanner used for beamline QA

Beam Collimation
❖ Oneset of moveable jaw
❖ Pneumatic, Binary MLC (64 leaves).
❖ 20ms leaf transit time.
❖ Largest field size 5cmX40cm at Isocentre.
❖ Smallest field size 1cmX0.625cm at isocentre

Jaw Characteristics
❖23 cm of 95% tungsten shielding is used in the linac support
fixture and combination of primary collimator and jaws.
❖The average leakage from head is0.01%.
❖Independent Y jaws have been provided – field width 1 – 5 cmat
the isocenter.
❖Output in the fan beam drops dramatically below 1 cm due to loss
of lateral electron equilibrium and partial source occlusion
❖A primary beam stop precludes need for a primary barrier
❖Main scatter is from the beam itself and minimal scatter from the
head.

Binary MLC Characteristics
❖Binary MLCs are provided – 2
positions – open or closed
❖Pneumatically driven 64 leaves
Open-close time of 20 ms
❖Width 6.25 mm atisocenter
10 cm thick
❖Interleaf transmission – 0.5% in
field and 0.25% out field
Maximum FOV = 40 cm
LINAC
Cone Beam
Y jaw
Y jaw
Fan Beam
Binary MLC

MLC Specifications
❖ 64binary interlaced leaves with 10 cm
leaf thickness in beam direction.
❖ Leaf width projected to
isocentre:6.25mm.
❖ Leakage :≤0.5%.
❖ Leaf transition time :<40ms.
❖ Travel in longitudinal Direction.
❖ Tungsten material MLC moves with
pneumatic pressure.

MLC’s Oriented in the Sagital Plane

Photon Beam
❖ Single therapy energy spectrum of 6MV.
❖ Dose rate 1000cGy.
❖ D-max 1.5 cm

Beam Characteristics: Projection
❖ For treatment delivery the full rotation is divided into
51projections.
❖ Each projection is characterized by it's own leaf opening
and closing pattern
❖ Each projection covers an arc segment of 7º.
❖ Between each projections all leaves are closed for a short
period of time – highly segmented step and shootapproach.
❖ Constant dose rate for the LINAC assumed – but
monitor chambers have inbuilt safety interlocks

Beam Characteristics: Pitch
❖The rotational fan beams overlap with each point seeing from 2
to 5 rotationsor about 100 to 250 possible beamlets.
❖Three fan beam widths used – 1, 2.5 and 5 cm.
❖Pitch of the delivery: Defined as the fraction of the beam width
that the couch translates (moves in or out) during each rotation of
the gantry
❖The pitch can be defined and helps in offsetting the threading
effect.
❖Typical values for the pitch are 0.25 -0.5

Fan Beam Characteristics
• The fan field width along the longitudinal direction is
continuous from 5 mm to 50 mm.
• There is no field flattening filter in the beam and so the beam
has a higher intensity along the center as compared to either
end.
• The beam without filtration is like the output from a CT
“Bowtie Filter”.
40 cm
1 cmImage Digitized from Kodak XV Film

Profile Along Length of a 1 cm Wide Fan
Beam
Transverse Profile
120
100
80
60
40
20
0
-240 -180 -120 -60 0 60 120 180 240
Distance (mm)
Dose(%)

Off-Axis Energy Dependence
0 1 2 5 6 7
0.010
0.005
0.000
0.020
0.015
0.025
0.030
0.035
0.040
0-5 cm
5-10 cm
10-15 cm
15-20 cm
3 4
Energy [MeV]
0 1 2 5 6
1E-3
0.01
0-5 cm
5-10 cm
10-15 cm
15-20 cm
Photonspectrum
3 4
Energy [MeV]
Tomotherapy has no off axis hardening because of no flattening filte

Couch Characteristics
❖Flat Couch provided allows automatic translations during
treatment
❖Target Length long as 160 cm can be treated – “Cobra
action” of the couch limits the lengthtreatable
❖Manual lateral couch translations possible Automatic
longitudinal and vertical motions possible
❖Possible to treat anywhere within a cylindrical volume 40 cm in
diameter by 160 cm long

Couch
❖ Incorporated with Medical intelligence Indexing System.
❖ Provides Sub-millimetre Positioning accuracy in
translational movements.
❖ Couch catcher to maintain optimal Table sag top position
and to reduce the couch sage from 5mm to 2mm
❖ Couch tolerance maximum weight 0f 200kg

Workstation
Includes:
❖ An operator station Planning station
❖ 32 CPU computer cluster attached to
database server
❖ Treatment machine
❖ Parallel processor architecture for
optimization of thousands of beamlets
involved
❖ System offers no contouring tools – rather
contours have to imported from other TPS

Shielding Requirements
❖ A tomotherapy primary beam shield is:
➢ Reduced in width by a factor of almost 10
➢ Increased in thickness by more than a tenth value layer in
comparison to a conventional accelerator.
➢ Furthermore, the secondary shielding requirements are
enhanced by more than two tenth value layers with
respectto conventional shielding demands.
➢ However primary beam stopper included significantly
reduces room shielding requirements.

MV CT Scans
• MV CT scans are acquired in a helical fashion with the patient in
the treatment position just prior of treatment.
• One full gantry rotation takes 10 s, and therefore the total scan
time is 10 s times the number of slices acquired (regardless of the
slice width).
• The reconstruction of the MV CT image data set starts during
acquisition and takes an additional 2–4 min once the scan is
finished, depending upon the number of slices acquired.
• The resulting MV CT image data set is then fused to the
treatment planning kV CT image data set to obtain the shifts
necessary for precisely aligning the internal treatment target.

Imaging In Tomotherapy
❖ Position with simple, accurate
patient setup.
❖ Delivery with efficient 3D image
guidance for every patient.
❖ Density with consistent image
quality at a low dose.
❖ Dose guided Daily Treatment.

MVCT Imaging Specification
❖ Geometry : Helical Fan Beam.
❖ Image resolution: 512x512(0.76mm Pixels)
❖ Dose/MVCT image : 0.5-3cGy [Depending on resolution and
body thickness & acquisition Pitch]
❖ Detector Configuration : 528 channels ,single row xenon ion
chamber array used for image acquisition.
❖ Field of view: 39 cm diameter.
❖ Source to detector distance: 140 cm.
❖ Image reconstruction with filtered back projection algorithm.
❖ Image reconstruction in Real Time slice by slice at time.

Imager Characteristics
❖Arc-shaped xenon detector has 738 channels, each with two
ionization cavities filled with xenon gas and divided by 0.32mm
tungsten septa.
❖The detector array has a 110 cm radius of curvature
❖540 out of 738 channels are used for the MVCT image
reconstruction.
❖The source to detector distance is 145 cm.
❖Majority of photon beam interacts with tungsten septae which
also prevent detector cross talk – greater effeciency
❖FOV = 40 cm

Image Characteristics
❖ Maximum number of slices = 80
❖ Allows higher image resolution than cone beam MV CT (3
cm diameter with 3% contrast difference)
❖ Tissue heterogeneity calculations can be done reliably on the
CT images as scatter is less (HU more reliable per pixel)
❖ Not affected by High Z materials (implant) Dose
0.3 – 3 Gy depending on slice thickness
❖ 3 imaging modes: Coarse (12 mm), Normal (8 mm) and fine
(4 mm) thickness.

Image Characteristics
• FOV of 40 cm available in the tomotherapy MVCT system may
lead to a degradation of image quality because the tissue outside
the FOV is not properly accounted for in the reconstruction
process
• Typical result is ‘bowl’ artifacts - the reconstructed CT values are
increased in the peripheral regions of the images
• However sufficient information for checking setup even if the
MV- CT image width is half that of the patientthickness.

Cone beam CT vs Tomo MV CT
❖ Cone beam CT on C-arm gantry designs restricted to 1rotation
per second due to collisional considerations
❖ In Tomotherapy CT length of 1.2 cm can be imaged in 10 secor
1 rotation
❖ Acquisition occurs automatically
❖ In KV cone beam CT takes 1.7 min to acquire 285projections
and few minutes to reconstruct
❖ However, this effort would yield 256 slices, almost twice as
many slices per minute as the tomotherapyunit.

6 MV Linac Electron beam
Target
Whole treatment head rotates
around y -axis, with an SAD of 85
cm
x
z
y
Binary multileaf collimator
y-jaws
Photons
Principle of Operation
A short 6 MV linac is
collimated by jaws
and a binary
multileaf collimator.
The treatment head
rotates on a gantry in
the x/z plane while a
patient is
continuously
translated through the
bore of the machine
in the y-direction –
the therapy analogue
of spiral CT

Different Moods Of Tomotherapy
There are two moods of tomotherapy
❖Helical tomotherapy
❖Direct tomotherapy

Helical Tomotherapy Treatment Delivery
Mode
• The gantry rotates around
the patient in Helical
tomotherapy delivery
mode, delivering
radiation in a continuous
spiral pattern

Helical Tomotherapy Treatment
Delivery Mode
• The Helical tomotherapy delivery mode provides IMRT and 3D
CRT treatment delivery in a continuous (360°) helical pattern.
• The Helical tomotherapy mode is suited to the majority of
clinical situations, where rotational delivery and beam
modulation enhance target dose conformality and uniformity.
• The user is able to create a treatment plan that defines dose goals
and constraints for target and avoidance structures, the level of
modulation for the plan, as well as the fractionation schedule.

Helical Tomotherapy Treatment
Delivery Mode
• During treatment delivery, the linear accelerator completes
multiple 360° rotations around the patient while the couch passes
through the bore of the system, initiated by a single turn of the
operator console key.
• The field width varies during delivery to increase dose gradient
outside the.
• Targets of up to 135 cm in length can be treated, with no need to
reposition the patient and with no field junctioning.

Direct Tomotherapy Treatment Delivery
Mode
• Multiple discrete
gantry angles
(between 2 – 12
angles) can be
used in Direct
tomotherapy
delivery mode

Mode
• Direct tomotherapy delivery mode provides IMRT and 3D
CRT treatment via a discrete angle, non-rotational delivery
mode.
• Direct tomotherapy allows creation of treatment plans that
include between 2 and 12 target-specific gantry angles.
• Direct tomotherapy complements Helical tomotherapy in
situations where a fixed-angle delivery is most appropriate.

Mode
• During treatment delivery, beams are delivered sequentially with
the couch passing through the bore of the system at an appropriate
speed for each beam.
• The complete treatment delivery is initiated by a single turn of the
operator console key.
• The field width varies during delivery to increase dose gradient
outside the.
• Targets of up to 135-160 cm in length can be treated, with no need
to reposition the patient and with no field junctioning.

Adaptive Radiotherapy (ART) With
Tomotherapy
❖ The precise Adaptive Radiation therapy System allows to
track delivered dose relative to the planned dose over the
entire course of multi-fraction treatment using the MVCT
data and the patient positioning system.
❖ It provides tools to aid in the efficient generation of new
treatment plans for patients currently or previously under
treatment.

The Treatment Process
• Patient is set up on table to moveable lasers (2 min)
• High energy CT scan performed in the Tx Position (3 Min)
• New images are fused with planning CT images (3 Min)
• Adjustments are made for patient position (2 min)
• Treatment is delivered (10 Min)

Simplicity of Tomotherapy
Tomotherapy Conventional RT
Designed for Image-Guided IMRT Designed for Conventional RT Processes
Single Photon Energy Dual Mode Multiple Energy
Simple MLC Complex MLC
No Collimator Rotation Collimator Rotation
No Couch Rotation One or Two Axes of Couch Rotation
Simple CT Detector 2D Electronic Portal Imager
System Integration Multi-Component Integration

Simplicity of Tomotherapy
❖No Electrons
❖No Wedges.
❖No Couch Angles.
❖No collimator angles.
❖No MLC Shapes.
❖No Field light.

Treatment Delivery Efficiency
❖ Faster Image Acquisition:- 10 rpm gantry rotation
increased from the 6 rpm.
❖ 40%shorter Scan Time:-
❖ 6Second Beam on Warm up decreased from 10 sec.
❖ 15%Reduced the treatment Delivery Time.
❖ 1000 MU/min dose rate increased from850MU/min.

Clinical Implications
• More complex target volumes can be delivered and still spare
critical volumes.
• Complex prescriptions or “dose painting”.
• Higher dose/fraction can be delivered to the tumor and still have
low dose and dose/fraction to critical tissues.
• Conformal avoidance.
• More accurate setup of the patient.
• Better verification that delivery is correct.
• Have a basis to repair dose distributions.
• Adaptive radiotherapy.

Tomotherapy Utilization At Treatment
❖ Complex cases with targets in close proximity to OARs
❑ Head &Neck
❑ Breast (Comprehensive nodal irradiation)
❖ Extended fields
❑ Pelvic or Para-aortic CSI
❖ Special Cases
❑ Spine Tumours
❑ Pediatric Cancers.

Uses Of Tomotherapy
• Tomotherapy can be used for any form of cancer at any stage
including:
• Mesothelioma
• Currently the only treatment for Mesothelioma
• Gynecologic cancers
• Endometrium, Cervix,Ovarian
• Bone cancer/marrow
• Breast, prostate, lung, liver, colon, anus, pancreas, lymph nodes,
throat, stomach, and digestive system.
• Head and neck cancers
• Spares salivary glands

Generated H&N Plan
Nasopharyngeal
tumor

Multiple Tumors
Several bone metastases of
breast cancer. Lesions in the
third left rib, os sacrum and
lumbar

From Dr. An Liu
Total Marrow
Irradiation
Using
Tomotherapy

Other Innovative Treatments
Tomotherapy Will Enable
• Stereotactic radiotherapy (and radiosurgery) to the body.
• Irradiate entire nodal chains with conformal avoidance.
• Repairing the dose distributions from other modalities, e.g., poor seed
implants.
• Combined brachytherapy and IMRT.
• Bone marrow ablation while sparing visceral organs.
• Whole-skin irradiation using IMRT.
• Probability-based prophylactic radiotherapy.
• Swiss-cheese-like dose distributions in normal tissue (3-D grid therapy).
• Great change in breast radiotherapy.

• CT scanner-like gantry allows for continuous delivery
• Allows for single treatment fields
• No junctions
• Even dose distribution
• Shorter and faster treatment
• Condensed treatment period, due to a higher dose of radiation
• Results in up to a 50% reduction in treatment days
What Makes Tomotherapy Unique?

•Precise tumor dose
• Pattern of movement is calculated before treatment
• Conforms to the tumor and avoids critical structure and
normal tissue
•Fewer side effects
• Excellent tumor contouring minimizes radiation to normal tissue,
minimizing secondary cancer
• Faster recovery times

•Able to treat multiple tumors at the same time.
• TomoTherapy may be a treatment alternative for individuals who
have already gone through radiation treatments and have been
told they cannot receive any more treatment
•Daily 3D CT Imaging
• Improves accuracy
• Ensures treatment effectiveness
• Minimizes side effects
• Uses IGRT (Image guided radiation therapy)

• Sophistocated MLC
• Opens and closes quickly to permit, or block, the
passage of radiation, dividing the radiation beams into
many smaller beamlets
• 360 degree delivery
• More beam directions
• Exceptional dose distribution to the tumor

What Makes Tomotherapy Unique
❖ Patient can be treated up to 135cm,with no reposition, no
field matching
❖ Faster Treatment deliver because of dose rate 1000cGy/min
❖ Precise tumor dose.
❖ Sophisticated Multi leaf collimator.
❖ 360degree delivery.
❖ CTScanner like gantry allows for continuous delivery.

❖ The ring gantry of a Tomotherapy unit exploits this (ring)
structural stability resulting in an isocentric precision of 0.2
mm, 5x better than typical arm-gantry systems.
❖ It is well recognized that increasing the number of fields can
improve the overall dose conformality.
❖ In typical arm gantry-based IMRT, selection of the most
effective gantry angles may not be obvious.
❖ This can result in the loss of useful directions prior to the
initiation of optimization.
Advantages of Tomotherapy

❖ In tomotherapy IMRT, the optimizer has full access to 360° of
rotation.
❖ One of the weaknesses of MLCs is that most of them are
motorised making them prone to motor breakdown, positional
inaccuracies, and velocity fluctuations.
❖ However, binary MLCs, such as the 64-leaf system of
tomotherapy, are inherently much more reliable since the
sensors need to read only in open or closed positions.

❖ In addition, the MLC motion is extremely rapid, opening and closing
within 20 ms, and the dwell time at each position can be
automatically varied from 1 to 400 ms.
❖ The combination of number of control points, gantry directions, and
dwell times yields substantial flexibility in generating an optimized
distribution.
❖ This allows an almost infinite dynamic range of intensities, not only
for every angle, but also for every point in the target volume from that
angle.
❖ IMRT without a wide dynamic range of intensities will always be
inferior.

❖ The maximum field size for typical accelerators without the
need for junctions is less than 40×40 cm2.
❖ Larger fields for IMRT require complex junctions and/or
extended SSD.
❖ With Tomotherapy, fields of up to 160 cm in length can be
treated without the need for junctions.
❖ Will be able to use Tomotherapy for total marrow Irradiation.

❖ The imaging chain of tomotherapy allows a full 38 cm diameter
imaging ring.
❖ The detector (511 Xenon ion chambers) serves a dual purpose:
❖ Imaging and patient positioning
❖ Can obtain quantitative dose values, allowing the delivery to
be validated.
❖ Reconstruction of the actual dose can then be calculated on the
acquired 3D CT data set.

Advantages Of Tomotherapy
There is also the considerable potential for radiobiological gain.
In Tomotherapy every cell receives its full complement of dose
in less than 2 minutes. In conventional accelerators the time
from first to last photon may be 20 min or more allowing
significant tumour cell recovery.

❖Less functionality in Tomotherapy but this translates into
shorter commissioning time and reduced QA burden.
❖Can use existing linac bunker. Inherent beam-stopper in Tomo.
❖Can (possibly) use Mobile Tomotherapy instead of an overspill
bunker when replacing Oncors. Could be a cheaper alternative
and improve patient throughput and staff skill levels.

• Integration of planning, delivery and verification.
• Potentially easier to commission and calibrate.
• Dose reconstruction eliminates need for on-going patient-specific
dosimetry measurements.
• Fewer planning decisions and optimization may be automated.
• High dose rate (8 Gy/min).

• Higher dose/fraction more feasible because normal tissue can be
more easily avoided.
• Easier patient setup.
• No couch rotation reducing possibility of collision.
• Tomographic verification images are more easy to interpret than
planar portal images.
• Impact of delivery errors can be reduced.
• Increased primary collimation so less staff irradiation per patient.

Major Advantages highlighted
• Applicable where highly conformal dose distributions are
required.
• Also considered useful for long segment and multiple target
involvement or in targets in close proximity to criticalorgans
• Image guidance for precise treatment of difficult targets in
difficult patients.
• MV-CT advantage in reducing bony targets
Possibility of dose guided radiotherapy

Summarising The Advantages Of
Tomotherapy
Given the superior design of the imaging / delivery hardware, the
construction and speed of the MLC, the integrated design and less
QA, it is clear that the tomotherapy approach to IMRT will lead
the way in the future.

LIMITATIONS
❖ Only coplanar beams
❖ Constant tx parameters
➢ Gantry speed
➢ Table speed
➢ Beam width(affects longitudinal modulation)
➢ Dose rate
❖ No static beam for simple case
❖ Only 6MV & no electrons
❖ Hot dose & Interval

DISADVANTAGES
❖ Manual radiation is not possible.
❖ Allshould be CT based.
❖ Nointra-fractional image guidance.
❖ Summation of total integral dose will be more.
❖ Diagnostic CT scanner is needed for planning.

Tomotherapy

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