4. PART 1
Simulation
• Patient history
• Pre-requisites
• Selection of immobilization devices
• Patient counselling
• Patient positioning
• Scan specifics
• Post Scan
• Data transfer
5. PART 1
Simulation
Patient history:
• Verify patient demographics
• Any history of allergies – previous contrast
(I.V / ORAL _ Barium / Gastrograffin)
• h/o HTN / DM_ to correlate with renal
function
• h/o previous Radiation
• h/o skin conditions: hypo / hypersensitivity
6. PART 1
Simulation
Pre-requisites:
• Renal function – Creatinine clearance
• I.V access
o Aseptic procedure - MANADATORY
o Canula site – Keep in mind patient positioning
o Canula size – Pink is preferred (to ensure
enduring the volume & speed of contrast
injection)
o Fixation of access (don’t be in haste, may
kink the canula leading to contrast
extravasation)
7. PART 1
Simulation
Selection of immobilization devices
• ULTIMATE PRIORITY – Pt is comfortable with the
position maintaining oncological principles
• Types of immobilization devices
• Patient factors to be kept in mind for selection:
Age, Built,
• Tumour factors (Oncologist opinion):
Breast board, Pituitary board, type of Neck rest
17. PART 1
Simulation
Patient counselling:
• Explain clearly in non-medical terms the
entire procedure with the probable
duration; demonstrating the equipment
that we are about to use
• Reassure
• Have signals to indicate any problem
during the course if simulation
18. PART 1
Simulation
Patient positioning:
• Position with decided immobilization device
• Check alignment with lasers,
• Orfit preparation: place fiducials
Heated to adequate temperature
Avoid folds while transferring it from
water-bath onto the patient
Let the orfit cool adequately before removing
it (avoids shrinking-very important)
• Label the orfit legitimately and document the
simulation specifics in the RT record
19. PART 1
Simulation
Scan specifics
• Topogram
• FOV (Select according to the site) – Keep OARs in mind
(Avoids re-simulations)
• Take check scans
• Ensure required alignment
• Appropriate medium (e.g. specific to site- specific to site of
body and manufacturer)
• Contrast:
I.V. – Volume (1.2-1.5ml/kg), rate of infusion; check
patency of canula
Oral - large bowel (previous night);
- small bowel (30-45min prior to initiation of scan
per se)
20. PART 1
Simulation
Data transfer:
• Check scan thoroughly for region of
contrast, any disease progression (local &
distal – Lung/Liver/Bone)
• Get approval from oncologist and transfer
the images to the TPS server (‘PUSH the
images)
22. PART 1
CONTOURING
Target volumes (ICRU 50,62) – GTV
• Gross demonstrable extent and location of the
malignant growth.
• It consists of :
- Primary tumor(GTV primary)
Clinical & radiological
- Metastatic lymphadenopathy(GTV nodal)
- Other metastasis(GTVM)
• If the tumor has been removed prior to
radiotherapy, then no GTV can be defined.
25. PART 1
CONTOURING
Target volumes (ICRU 50,62) – GTV
• Determination of shape, size and location of the GTV
Clinical examination
Inspection, palpation, endoscopy
Various imaging techniques
X-ray, CT, USG, MRI, PET
• Reasons to describe GTV accurately
Staging of the tumor according to the TNM.
To define area requiring adequate dose delivery
for treatment
Regression of GTV used as predictive of tumor
response
26. PART 1
CONTOURING
Target volumes (ICRU 50,62) – GTV
• Gross demonstrable extent and location of the
malignant growth.
• It consists of :
- Primary tumor(GTV primary)
Clinical & radiological
- Metastatic lymphadenopathy(GTV nodal)
- Other metastasis(GTVM)
• If the tumor has been removed prior to
radiotherapy, then no GTV can be defined.
28. PART 1
CONTOURING
Target volumes (ICRU 50,62) – PTV
• Definition:
The PTV is a geometrical concept, and it is defined to
select appropriate beam sizes and beam
arrangements, taking into consideration the net
effect of all the possible geometrical variations and
inaccuracies in order to ensure that the prescribed
dose is actually absorbed in the CTV.
• The PTV can be considered as a 3-D envelope in
which the tumour and any microscopic extensions
reside. The GTV and PTV can move within this
envelope, but not through it.
29. PART 1
CONTOURING
Target volumes (ICRU 50,62) – PTV
AFFECTED BY :
• Size and shape of the GTV & CTV
• Effects of internal motions of organs and the
tumor
• Treatment technique (beam orientation and
patient fixation, daily setup errors)
• Intra-fractional errors (During a single session)
• Inter-fractional errors (From one session to
another)
30. PART 1
CONTOURING
Volumes (ICRU 50,62) – Treated volume
• Definition:
It is the volume enclosed by an isodose surface
that is selected and specified by the radiation
oncologist as being appropriate to achieve the
purpose of treatment (palliation or cure).
• Usually taken as the volume enclosed by the
95% isodose curve.
• Ideally dose should be delivered only to the PTV
but due to limitations in the radiation treatment
technique.
31. PART 1
CONTOURING
Volumes (ICRU 50,62) – Treated volume
• Reasons for identification of Treated Volume
are :
The shape and size of the Treated Volume
relative to the PTV is an important
optimization parameter.
Recurrence within a Treated Volume but
outside the PTV may be considered to be a
“true”, “in-field” recurrence due to
inadequate dose and not a “marginal”
recurrence due to inadequate volume.
33. PART 1
CONTOURING
Volumes (ICRU 50,62) – Irradiated volume
• Definition:-
It is the volume that receives a dose
considered
• significant in relation to normal tissue
tolerance
• Usually taken as the volume enclosed by
the 50% isodose curve.
• It depends on the treatment technique
used.
35. PART 1
CONTOURING
VOLUMES – ICRU 62
• Gives more detailed recommendations on the
different margins that must be considered to account
for anatomical & geometrical variations &
uncertainties.
• PTV has been separated into two components: an
internal margin and set-up margin.
• Classified organs at risk depending on response to
radiation.
• Defined planning organ at risk volume (PRV)
• Report dose to the OAR/PRV
• Introduced conformity index
• Gives recommendations on graphics
36. PART 1
CONTOURING
VOLUMES – ICRU 62
• PTV has been separated into two components: an internal
margin and set-up margin.
37. PART 1
CONTOURING
VOLUMES – ICRU 62
• PTV has been separated into two components: an internal
margin and set-up margin.
38. PART 1
CONTOURING
VOLUMES – ICRU 62
• PTV has been separated into two components: an internal
margin and set-up margin.
39. PART 1
CONTOURING
VOLUMES – ICRU 62
• PTV has been separated into two components: an internal
margin and set-up margin.
40. PART 1
CONTOURING
VOLUMES – ICRU 62
• PTV has been separated into two components: an internal
margin and set-up margin.
41. PART 1
CONTOURING
• INTERNAL MARGIN
A margin that must be added to the CTV to compensate for
expected physiologic movements and the variations in size,
shape and position of the CTV during therapy in relation to
the Internal Reference Point and its corresponding
Coordinate System. Motion is associated with adjacent
respiratory and digestive organs.
• INTERNAL TARGET VOLUME (ITV)
It is the margin given around the CTV to compensate for all
variations in the site, size and shapes of organs and tissues
contained in or adjacent to CTV.
These may result from respiration, different fillings of the
bladder and rectum, swallowing, heart-beat, movements of
bowel etc.
42. PART 1
CONTOURING
• SET-UP MARGIN ( SM )
It is the margin that must be added to account specifically
for uncertainties (inacuracies and lack of reproducibility) in
patient positioning and aligment of the therapeutic beams
during treatment planning and through all treatment
sessions.
• These uncertainties depend on factors like :
Variations in pt. positioning
Mechanical uncertainties of the equipment (sagging of
gantry, collimators, and couch)
Dosimetric uncertainties
Transfer set-up errors from CT & simulator to the treatment
unit
Human factors
44. PART 1
CONTOURING
OARs & PRV:
ORGANS AT RISK(“CRITICAL NORMAL STRUCTURES”):
• The normal tissues (e.g., spinal cord) whose
radiation sensitivity may significantly influence
treatment planning and/or prescribed dose
PLANNING ORGAN at RISK VOLUME (PRV):
• The volume obtained by adding a margin to OAR
to account for variations in position of OARs due
movement and uncertainties in set up
• Its analogous with that of PTV
45. PART 1
CONTOURING
ORGANS AT RISK(“CRITICAL NORMAL STRUCTURES”):
Functional Sub-Unit concept:
The tissues of an OAR can be considered to be
functionally organized as either ‘serial’ / ‘parallel’/
‘serial-parallel (mixed)’
For OARs with a high ‘relative seriality’
(e.g. ,spinal cord),a dose above tolerance limit
to even a small volume of OAR is deleterious
For OARs with a low ‘relative seriality’ (e.g. ,lung /)
the most important parameter is the relative size of
the volume that is irradiated above the tolerance level
48. ORGANS AT RISK
(“CRITICAL NORMAL STRUCTURES”):
Serial – Dose is more important; DMx
Parallel – Volume receiving more the tolerance
dose is more important; Dmn >>DMx
Mixed – Keep both in mind
PART 1
CONTOURING
- OARs
66. PART 2
• Isocentre
• Contours
• Planning
• Data Documentation
• Generation of DRRs
• Lasers / Markings
• Verification
• Film processing
SIMULATION / TREATMENT PREPARATION
67. PART 2
Isocentre
Isocentre:
• Isocentre is the point in space about which the gantry
of the linear accelerator, the treatment head of the
linear accelerator, and the couch rotate
o Mechanical Isocentre is the point in space about
which the linear accelerator and couch rotate
o Radiation Isocentre is the point where the radiation
beams intersect if the gantry, collimator or couch is
rotated
o These two points need not be the same although
ideally, they should be
68. PART 2
Isocentre
During normal operations, the
radiation isocentre is defined
by a set of laser guides that
are positioned at the side of
the bunker and on the linear
accelerator itself. The junction
of all these laser beams is the
location of the isocentre
69. PART 2
Generation
of DRR
DRR: Digitally Reconstructed Radiograph
• An image generated from CT scan data by mapping
average CT values computed along ray lines drawn from a
“virtual source” of radiation to the location of a “virtual
film”
• DRR is essentially a calculated (i.e., computer-generated)
port film that serves as a simulation film.
• The quality of the anatomic image is not as good as the
simulation radiograph, but it contains additional useful
information such as the outlined target area, critical
structures, and beam aperture defined by blocks or MLC.
74. PART 2
LASERS /
MARKINGS
2D Simulator :
• Skin tattoo:
Aseptic precautions mandatory
Use of proper technique** (direction of poking/depth of
poking etc.)
Don’t use more ink
• Fiducials (Both 2d & 3D):
Use fresh ones for each patient
Be cautious while placing as there is a chance of
systemic error (due to parallax error)-always cross
check after application
**DOI: 10.4103/2278-330X.96502
75. PART 2
LASERS /
MARKINGS
• LASERS:
To aid us in patient position at simulation / treatment
Always make sure the QA is done daily for LASERS and
proceed the day
Always use LASERs for positioning to minimise errors
Role of lasers D1 of treatment (applying shifts from
fiducials to move to planning Isocentre)
QA – 2mm maximum acceptable tolerance; inform your
oncologist and physicist in case of any deviation from it
80. PART 2
Verification
Day 1 of
TREATMENT:
1. Position the
patient according
to the simulation
notes and verify
all the criteria
(e.g., knee rest
position/umbilicus
position)
81. PART 2
Verification
Day 1 of TREATMENT:
2. Apply the shifts given by the physicist so that the
isocenter assumed at simulation position matches the
planning isocenter rendering initiation of treatment
82. PART 2
Verification
Day 1 of TREATMENT:
3. Image verification:
X-ray / Cone beam CT (practical)
If within tolerance – continue
If beyond – inform Oncologist
(we follow 3 days average and apply shift)
Course of TREATMENT:
Weekly once / twice image verification of set up
and if varying significantly – resimulate and plan if
required keeping in to minimise any treatment
interruptions
83. SUCCESS IS THE ABILITY TO
MOVE FROM ONE FAILURE
TO ANOTHER WITHOUT
LOSS OF ENTHUSIASM…
WINSTON CHURCHILL
SUCCESS & FAILURE are only RELAYS’ in the JOURNEY but not
endpoints … .
and the definition varies with the perspective of the definer..
12$
Notes de l'éditeur
**
EXPLANATION:
If we mark the teeth bite wrong on day of sim – systemic
If Patient is not counselled on the importance of properly positioning the bite there might be intra / inter-fractional variations in position of mouth bite and shift of target or OAR leading to random error
