IAEA Training Material on Radiation Protection in Radiotherapy
Radiation Protection in
Radiotherapy
Part 10
Good Practice including Radiation
Protection in EBT
Lecture 3 (cont.): Radiotherapy Treatment Planning
C. Commissioning



Complex procedure depending very much on
equipment
Protocols exist and should be followed
Useful literature:


J van Dyk et al. 1993 Commissioning and QA of treatment
planning computers. Int. J. Radiat. Oncol. Biol. Phys. 26: 261-273
J van Dyk et al, 1999 Computerised radiation treatment planning
systems. In: Modern Technology of Radiation Oncology (Ed.: J
Van Dyk) Chapter 8. Medical Physics Publishing, Wisconsin,
ISBN 0-944838-38-3, pp. 231-286.
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
2
Acceptance testing and
commissioning
Acceptance testing: Check that the system conforms with
specifications.
 Documentation of specifications either in the tender, in
guidelines or manufacturers’ notes – may test against
standard data (e.g. Miller et al. 1995, AAPM report 55)
 Subset of commissioning procedure
 Takes typically two weeks
Commissioning: Getting the system ready for clinical use
 Takes typically several months for modern 3D system
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
3
Some equipment required
Scanning beam data acquisition system
 Calibrated ionization chamber
 Slab phantom including
inhomogeneities
 Radiographic film
 Anthropomorphic phantom
 Ruler, spirit level

Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
4
Commissioning
A. Non-dose related components
B. Photon dose calculations
C. Electron dose calculations
(D. Brachytherapy - covered in part 11)
E. Data transfer
F. Special procedures
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
5
A. Non-dose components


Image input
Geometry and scaling of





Digitizer,
Scans
Output
Text information
Anatomical structure information


CT numbers
Structures (outlining tools, non-axial
reconstruction, “capping”,…)
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
6
Electron and photon beams
Description (machine, modality, energy)
 Geometry (Gantry, collimator, table,
arcs)
 Field definition (Collimator, trays, MLC,
applicators, …)
 Beam modifiers (Wedges, dynamic
wedges, compensators, bolus,…)
 Normalization

Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
7
B. Photon calculation tests

Point doses
TAR, TPR, PDD, PSF
 Square, rectangular and irregular fields
 Inverse square law
 Attenuation factors (trays, wedges,…)
 Output factors


Machine settings
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
9
Photon calculation tests (cont.)

Dose distribution

Homogenous








Profiles (open and wedged)
SSD/SAD
Contour correction
Blocks, MLC, asymmetric jaws
Multiple beams
Arcs
Off axis (open and wedged)
Collimator/couch rotation
Radiation Protection in Radiotherapy
PTW waterphantom
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
10
Photon calculation tests (cont.)
 Dose distribution
 Inhomogeneous
 Slab geometry
 Other geometries
 Anthropomorphic phantom
 In
vivo dosimetry at least for the
first patients
 Following the incident in Panama, the IAEA
recommends a largely extended in vivo dosimetry
program to be implemented
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
11
C. Electron calculation

Similar to photons, however, additional:




Bremsstrahlung tail
Small field sizes require special consideration
Inhomogeneity has more impact
It is possible to use reference data for
comparison (Shui et al. 1992 “Verification
data for electron beam dose algorithms” Med.
Phys. 19: 623-636)
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
12
E. Data transfer
Pixel values, CT numbers
 Missing lines
 Patient/scan information
 Orientation
 Distortion, magnification

All needs verification!!!
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
13
F. Special procedures







Junctions
Electron abutting
Stereotactic procedures
Small field procedures (e.g. for eye
treatment)
IMRT
TBI, TBSI
Intraoperative radiotherapy
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
14
Sources of uncertainty







Patient localization
Imaging (resolution, distortions,…)
Definition of anatomy (outlines,…)
Beam geometry
Dose calculation
Dose display and plan evaluation
Plan implementation
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
15
Typical accuracy required (examples)





Square field CAX:
1%
MLC penumbra: 3%
Wedge outer beam:
5%
Buildup-region: 30%
3D inhomogeneity
CAX: 5%
From AAPM TG53
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
16
Typical accuracy required (examples)
Note:
Uncertainties have
two components:
Dose (given in %)
Location (given in
mm)
Radiation Protection in Radiotherapy





Square field CAX:
1%
MLC penumbra: 3%
Wedge outer beam:
5%
Buildup-region: 30%
3D inhomogeneity
CAX: 5%
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
17
Time and staff requirements for
commissioning (J Van Dyk 1999)
Photon beam: 4-7 days
 Electron beam: 3-5 days
 Brachytherapy: 1 day per source type
 Monitor unit calculation: 0.3 days per
beam

Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
18
Some ‘tricky’ issues


Dose Volume Histograms - watch sampling,
grid, volume determination, normalization
(1% volume represents still > 10E7 cells!)
Biological parameters - Tumour Control
Probability (TCP) and Normal Tissue
Complication Probability (NTCP) depend on
the model used and the parameters which
are available.
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
19
Commissioning summary





Probably the most complex task for RT
physicists - takes considerable time and training
Partial commissioning needed for system
upgrades and modification
Documentation and hardcopy data must be
included
Training is essential and courses are available
Independent check highly recommended
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
20
Quick Question:
What ‘commissioning’ needs to be done for a hand
calculation method of treatment times for a superficial
X Ray treatment unit?
Superficial beam








HVL
Percentage depth dose (may be look up table)
Normalization point (typically the surface)
Scatter (typically back scatter) factor
Applicator and/or cone factor
Timer accuracy
On/off effect
Other effects which may affect dose (e.g. electron
contamination)
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
22
Quality Assurance of a treatment
planning system


QA is typically a subset of commissioning
tests
Protocols:



As for commissioning and:
M Millar et al. 1997 ACPSEM position paper.
Australas. Phys. Eng. Sci. Med. 20 Supplement
B Fraas et al. 1998 AAPM Task Group 53: QA for
clinical RT planning. Med. Phys. 25: 1773-1829
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
23
Aspects of QA (compare also
part 12 of the course)
Training - qualified staff
 Checks against a benchmark reproducibility
 Treatment verification
 QA administration

Communication
 Documentation


Awareness of procedures required
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
24
Quality Assurance
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
25
Quality Assurance
Check prescription
Radiation Protection in Radiotherapy
Hand calculation of
treatment time
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
26
Frequency of tests for planning (and
suggested acceptance criteria)

Commissioning and significant upgrades


Annual:




See above
MU calculation (2%)
Reference plan set (2% or 2mm)
Scaling/geometry input/output devices (1mm)
Monthly


Check sum
Some reference test sets
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
27
Frequency of tests (cont.)

Weekly


Each time system is turned on


Input/output devices
Check sum (no change)
Each plan



CT transfer - orientation?
Monitor units - independent check
Verify input parameters (field size, energy, etc.)
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
28
Treatment planning QA summary
Training most essential
 Staying alert is part of QA
 Documentation and reporting necessary
 Treatment verification in vivo can play
an important role

Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
29
Quick Question:
How much time should be spent on treatment
planning QC?
Staff and time requirements
(source J. Van Dyk et al. 1999)
Reproducibility tests/QC: 1 week per
year
 In vivo dosimetry: about 1 hour per
patient - aim for about 10% of patients
 Manual check of plans and monitor
units: 20 minutes per plan

Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
31
QA in treatment planning
The planning system
Plan of a patient
QA of the system
Radiation Protection in Radiotherapy
QA of the plan
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
32
QC of treatment plans

Treatment plan:
Documentation of






treatment set-up,
machine parameters,
calculation details,
dose distribution,
patient information,
record and verify
data
Radiation Protection in Radiotherapy

Consists typically of:




Treatment sheet
Isodose plan
Record and Verify
entry
Reference films
(simulator, DRR)
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
33
QC of treatment plans
Check plan for each patient prior to
commencement of treatment
 Plan must be

Complete from prescription to set-up
information and dose delivery advise
 Understandable by colleagues
 Document treatment for future use

Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
34
Who should do it?
Treatment sheet checking should involve
senior staff
 It is an advantage if different professions
can be involved in the process
 Reports must go to clinicians and the
relevant QA committee

Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
35
Example for physics treatment sheet
checking procedure
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
Check prescription (energy/dose/fractionation is everything signed ?)
Check prescription and calculation page for consistency: Isocentric (SAD) or fixed distance (SSD) set-up ? Are all
necessary factors used? Check both,dose/fraction and number of fractions.
Check normalisation value (Plan or data sheets).
Check outline, separation and prescription depth.
Turn to treatment plan: Does it look ok ? Outline ? Bolus ? Isocentre placement and normalisation point ? Any concerns
regarding the use of algorithms near surfaces or inhomogeneities? Would you expect problems in planes not shown ?
Prescription ?
Check and compare with treatment sheet calculation page: treatment unit and type, field names, weighting, wedges,
blocks, field size (FS), focus surface distance (FSD), Tissue Air Ratio (TAR) (if isocentric treatment) - is this consistent
with entries in treatment log page?
Electrons only: …
Photons only: …
Check shadow tray factor, wedge factor. Are any other attenuation factors required (e.g. couch, headrest, table tray...) ?
Check inverse square law factor (in electron treatments: is the virtual FSD appropriate?)
Calculate monitor units. Is time entry ok ?
Check if critical organ (e.g. spinal cord, lens, scrotum) dose or hot spot dose is required. If so, is it calculated correctly ?
Suggest in vivo dosimetry measurements if appropriate. Sign calculation sheet (if everything is ok).
Compare results on calculation page with entries in treatment log.
Check diagram and/or set up description: is there anything else worth to consider ?
Sign top of treatment sheet (specify what parts where checked if not all fields were checked).
Contact planning staff if required. Sign off physics log book.
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
36
Example for physics treatment sheet
checking procedure
1. Check prescription (energy/dose/fractionation is
everything signed ?)
2. Check prescription and calculation page for
consistency: Isocentric (SAD) or fixed distance (SSD)
set-up ? Are all necessary factors used? Check
both,dose/fraction and number of fractions.
3. Check normalisation value (Plan or data sheets).
4. Check outline, separation and prescription depth.
5. Turn to treatment plan: Does it look ok ? Outline ?
Bolus ? Isocentre placement and normalisation point ?
Any concerns regarding the use of algorithms near
surfaces or inhomogeneities? Would you expect
problems in planes not shown ? Prescription ?
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
37
Example for physics treatment sheet
checking procedure (cont.)
6.
7.
8.
9.
10.
11.
12.
Check and compare with treatment sheet calculation page:
treatment unit and type, field names, weighting, wedges,
blocks, field size (FS), focus surface distance (FSD), Tissue
Air Ratio (TAR) (if isocentric treatment) - is this consistent with
entries in treatment log page?
Electrons only: …
Photons only: …
Check shadow tray factor, wedge factor. Are any other
attenuation factors required (e.g. couch, headrest, table
tray...) ?
Check inverse square law factor (in electron treatments: is the
virtual FSD appropriate?)
Calculate monitor units. Is time entry ok ?
Check if critical organ (e.g. spinal cord, lens, scrotum) dose or
hot spot dose is required. If so, is it calculated correctly ?
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
38
Example for physics treatment sheet
checking procedure (cont.)
13. Suggest in vivo dosimetry measurements if
appropriate. Sign calculation sheet (if everything is
ok).
14. Compare results on calculation page with entries in
treatment log.
15. Check diagram and/or set up description: is there
anything else worth to consider ?
16. Sign top of treatment sheet (specify what parts
where checked if not all fields were checked).
17. Contact planning staff if required. Sign off
physics log book.
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
39
Treatment plan QA summary
Essential part of departmental QA
 Part of patient records
 Multidisciplinary approach

Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
40
Quick Question:
What advantages has a multidisciplinary
approach to QC of treatment plans?
Did we achieve the objectives?




Understand the general principles of
radiotherapy treatment planning
Appreciate different dose calculation
algorithms
Be able to apply the concepts of optimization
of medical exposure throughout the treatment
planning process
Appreciate the need for quality assurance in
radiotherapy treatment planning
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
42
Overall Summary




Treatment planning is the most important step
towards radiotherapy for individual patients as such it is essential for patient protection as
outlined in BSS
Treatment planning is growing more complex
and time consuming
Understanding of the process is essential
QA of all aspects is essential
Radiation Protection in Radiotherapy
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
43
Any questions?
Question:
Please label and discuss the following processes in
external beam radiotherapy treatment.
Question:
Diagnostic tools
1
Patient
2
4
6
3
5
Treatment
planning
Radiation Protection in Radiotherapy
Treatment unit
Part 10, lecture 3 (cont.): Radiotherapy treatment planning
46