2. IMRT is the product of advances in RT technology.
Aims to deliver radiation more precisely to the tumour while
relatively limiting dose to the surrounding normal tissues.
The purpose of the presentation is to discuss IMRT, its
applications and comparison with other RT method.
3. Conventional radiotherapy treatment are delivered with
radiation beams that are of uniform intensity across the field .
Wedge or compensators are used to modify the intensity
profile to offsets contour in irregularities and produce more
uniform composite dose distributions such as in techniques
using wedges.
This process of changing beams intensity profile to meet the
goal of a composites plan is called intensity modulation.
4. Intensity Modulated Radiotherapy is a special
form of 3D-CRT, where conformal dose delivery can be
enhanced by generating a non-uniform photon fluence
within each beam, calculated by treatment planning
system designed to meet specified dosimetric objectives.
5. IMRT
Intensity Modulated
Radiotherapy is a special
form of 3D-CRT conformal dose
delivery can be enhanced by
generating a non-uniform
photon fluence within each
beam, calculated by an inverse
treatment planning process
designed to meet specified
dosimetric objectives.
3DCRT
3 Dimensional Conformal
Radiotherapy is the use of 3
dimensional anatomical
information to plan and deliver
treatment so that the resultant
dose distribution conforms as
closely as possible to the target
volume in 3 dimensions with
minimum dose to the
surrounding normal tissue.
6. Better normal tissue sparing
Complex target shapes
Less toxicity
Possibly higher dose to target
More dose in a fraction
7. A treatment planning computer system that can calculate non
uniform fluence maps for multiple beams directed from different
directions to minimizing dose to the critical normal structures.
A system of delivering the no uniform fluence as planned.
8. To deliver high dose to
tumour.
While normal tissue should
receive minimal dose as
much as possible.
The further NTCP curve is
to the right of TCP curve,
larger is the therapeutic
ratio.
9. Positioning &
Immobilization
Image acquisition
& Registration
Delineation of Target
Volumes & Organs at risk
Plan evaluation,
comparison &
selection
Treatment
Delivery
Quality
Assurance
Decide dose to PTV
Beam arrangement
Field shaping
Beam modification
Dose calculation
Select technique
Dose constraints
Beam arrangement
Plan generation
3DCRT
‘Forward
Planning’
IMRT
‘Inverse
Planning’
10. Vital component of conformal treatment.
• Thermoplastic sheets
• Polyurethane foam
• Vacuum forming mold
Must be attached
reproducibly on
patients !
11.
12. Multislice CT Scanner
With a flat couch-top
Laser localization system
Precisely controllable
couch movements.
Simulation software
allows segmentation, contouring and
generates DRRs, 3D volumes and
isoceneters
Components
14. CT Scan is most commonly used procedure, even other
modalities after special advantages in imaging certain types
of tumours and locations.
15. The CT image
CT numbers are used to
calculated electron
density
Other Imaging
modalities
MRI
PET
SPECT
MRS
16. The reference cut is defined
Individual CT slices are used
to create a 3 dimensional
image which can be viewed in
coronal and sagittal planes.
17. It is a process of correlation different image data to identify
corresponding structures or region.
Image fusion is the seamless mixing up of two image sets of
the same patient, it may be two different image modalities.
Same modality in which image sets are taken at different
point of time.
18. Co-Registration
Surface based / Image based / Point
based.
Fused Images
Allows superior
outlining of targets in
selected areas.
19. 1
1
Siemens medical
Solutions that help
Non-Small Cell Carcinoma
Soft Tissue Window Lung Window
Courtesy of Universitaets-Klinikum Essen
Soft tissue window Lung window FDG - PET
Green outline: CT only Red outline: CT& FDG
PET provides functional
information to an
anatomical scan
Combined PET-CT Scanners
reduce setup discrepancies
Information from PET can can help modify PTV volumes
20. It refers to slice by slice delineation of anatomic regions of
interest.
The segmented regions can be rendered in different colours
and can be viewed in beams eye view configuration or in
other planes using digital reconstruction radiographs
21. Usually the body and the
bones are contoured
first specialized images
segmentation features -
automatic process
Digitally Reconstructed
Radiographs (DRRs) –
place fields according to bony
landmarks
Verify with portal imaging
Fast DRRs – virtual fluoroscopy
Digital Composite
Radiographs (DCRs) –
View different ranges of CT
numbers – soft tissue, skin
marks
22. GTV – the gross palpable/ visible/
demonstrable extent and
localization of tumor
CTV – the volume containing GTV
and/ or subclinical microscopic
malignant disease
PTV – geometrical concept that takes
into account the net effect of all
possible geometrical variations, in
order to ensure that the prescribed
dose is actually absorbed in the CTV.
= ITV + setup margin (for setup
variations)
ITV – the CTV + the
internal margin (for normal
body movements)
23. Contour all normal structures of relevance
In IMRT : what is not contoured, the program
cannot shield
Margins around the OAR for
geometric variations ?
24. 1. How many beams? – IMRT usually require more
than 4 beams
2. Coplanar or Non-
coplanar?
Use the Room’s Eye View (REV) to
get a practical idea about the
geometry of beam placement.
25. Even in IMRT, you
have to decide the
beam arrangement.
Mainly coplanar
beams are used,
although non-
coplanar beams
are possible
26. - automatic margins around PTV
(different margins in each co-
ordinate axis?)
MLCs are used to shape the field
around the PTV
- Use the Beam’s Eye View (BEV)
to place MLCs – take into account
structures to be shielded
28. Dose constraints have to be set to both target volumes and organs
at risk. Appropriate priorities must be set for each volume.
Practical issues :
Don’t set impossible constraints. Set appropriate priorities.
First start with constraints to a few structures – then improve the
plan by adding more constraints.
29.
30. In the Plan Evaluation mode of a treatment planning
system, look at the doses received by each structure
of interest.
31. Evaluate the dose distribution characteristics of one
or more plans using dose volume histograms (DVH)
The cumulative (integral)
DVH represents a
cumulative frequency
distribution of the dose
integrated over the VOI.
In the differential DVH,
the ordinate represents
the absolute or relative
volume which receives the
dose specified on the
abscissa within a specified
range of dose.
Rectum
Bladder
PTV
PTV
32. Always verify the anatomical dose distribution slice by
slice, in order to identify where underdosage or
overdosage is occurring.
Overdosage : 117%
Underdosage: <90%
33. An optimal plan should deliver tumouricidal dose to the entire tumour
and spare all the normal tissue.
To achieve quantitative biological endpoint ,model have been
developed involving biological indices such asTCP and normal tissue
complication probability.
Dose distributions of competing plan are evaluated by viewing isodose
curves in individual slices, orthogonal planes or 3D isodose surface.
35. Based on inverse planning
initially , a ct scan is performed on the affected region.
radiation oncologist defines the ptv.
enters the plan criteria ; max dose ,mini dose, desired
limiting dose and a dose volume histogram.
Then ,an optimisation program is run to find the treatment
plan which best matches all the input criteria.
37. 1. The fluence
map is
generated
2. A special software converts it
into a compensator file
3. A computerized milling
machine creates a Styrofoam
mold
4. The mold is filled with the
compensator material (eg. Tin
granules, brass cubes, cerrobend) and
the compensator box can be attached
to the wedge slot.
38. Rotating Slit Beam
Temporally modulated
slit MLC with 1 or 2
banks. Nomos MIMiC
Attached to a linac or dedicated systems
Serial tomotherapy
Helical tomotherapy
39. 1. Static Mode (Step & Shoot)
=
Mainly delivered in 2 ways: static & dynamic MLCs
The intensity pattern is decomposed into a number of static
segments, each of uniform intensity
The number of intensity levels determine the complexity or
the smoothness of the delivered fluence.
40. 2. Dynamic mode (Sliding window)
3. Intensity Modulated Arc Therapy (IMAT)
4. Volumetric Modulated Arc Therapy (VMAT)
The beam stays ON, and the MLC
leaves move continuously at
variable speeds
dose rate is also modulated to
achieve efficient delivery
When viewed from BEV, a
narrow slit slides across the
beam from one edge to other –
sliding window
41. Static Mode
(Step & Shoot)
Dynamic mode
(Sliding window)
• Conceptually simpler
• No need to control individual
leaf speeds
• interrupted treatments are
easier to resume
• Easier to verify intensity
patterns in each subfield
• Fewer MUs
• Regions with zero dose are
more easily delivered
• Smoothly varying intensities
• Only one field per beam
direction
• Less time consuming
42. 1. Check beam
data transfer
2. Position &
Immobilize
3. Match/Change
isocenter with lasers
4. Visually verify
MLC positions
5. Take Portal
images
6. Match with DRRs
in EPID software
43. MORE COMPLEXITY
NEED FOR NEW EQUIPMENTS
MORE NEED FOR QA
LONGERTREARMENTTIMES
HIGHER RISK OF GEOGRAPHICAL MISS
