1. Planning systems in
Radiotherapy
WFO Schmidt
Institute for Radio-Oncology
Donauspital Vienna

2. Contents
Who is Mr. Schmidt ?
Handbook for Teachers and Students, IAEA, May
2003
Chapter 7: Clinical Treatment Planning in External Beam
Radiotherapy
Chapter 11: Computerized Treatment Planning Systems for
External Beam Radiotherapy
AAPM Rep 85 (2004): Tissue inhomogeneity
corrections for megavoltage Photon Beams
Remark: this is a selection of some topics – not a
total view of all aspects dealing with planning !

3. Personal data
Dosimetry & Radioprotection at Inst
Nucl Phys, Univ. Vienna 1977-1984
Medical Physics in Radiotherapy at
the Univ. Vienna 1984 - 1995
Medical Physics in Radiotherapy at
the Donauspital Vienna since 1995
PACS since 1993 in Diagnostics
Stepping now into image fusion and
image-guided radiotherapy (IGRT)

4. My relation to
planning systems (TPSs):
I do not develop planning systems but I´m an advanced and
interested user. Main interest is to get new (and good) system
into routine.
systems working in our institute at present:
CORVUS 6.1 PROWESS
HELAX 6.2 Vs. 3.2
XiO (CMS) PLATO
Vs 4.2 Vs14.2

5. What I will not talk about:
specialized systems for:
Brachytherapy Stereotactic radiosurgery
with linac or GammaKnife
Orthovoltage therapy
Tomotherapy
IMRT
Intraoperative therapy
Dynamic MLC D-shaped beams
Total Body Irradiations Electron beam arc
therapy
MicroMLC
Total Skin Electron
Irradiations

6. Development of TPSs
„historical“ dates:
~1980 :1D-planning (by hand) ~ 2000: 4D: taking also
patient movement into
~1980 – 1990: 2D-planning account
with computers, CT starts
„Parallel“ developments:
From ~1990: 2.5D-systems
Inverse planning
Eg missing knowledge how to
handle scatter
MonteCarlo-methods
New algorithms (pencil-beam,
convolution/superposition,...)
~1995: Real 3D available,
getting exact

7. Clinical Treatment Planning:
Definition of Volumes
Definitions of GTV, CTV,
ITV, PTV, OAR,... not
discussed here
Dose specifications:
Min/max dose
Mean dose
ICRU-point
not discussed here but
play an important role
when comparing planning
from different systems !

8. Clinical Treatment Planning:
Patient data for 2D-planning
Single patient contour,
eventually with lead wire
markers, is transferred to
a sheet of paper
Simulation radiographs
are taken for each field
OARs identified and their
position identified on
radiographs
Irregular field calculation
Clarkson algorithm

9. Clinical Treatment Planning:
Patient data for 3D-planning
CT-data (5-10mm for thorax,
5mm pelvis, 3mm H&N)
External contour on each slice
Volumes drawn by oncologist
OARs fully outlined !!! (DVHs)
Other imaging information
(fusion)
Knowledge of inhomogeneities
Comparison of radiographs with
DRRs

10. Clinical Treatment Planning:
Treatment simulation
Determination of patient
treatment position
Identification of TVs & OARs
Determination and
verification of field geometries
Generation of radiographs for
comparison with portfilms/PI
Acquisition of patient data for
further planning

11. Clinical Treatment Planning:
Patient positioning, immobilization
Immobilization devices
have 2 fundamental roles:
Immobilising patient
Reproducing patient position
from CT/simulator and
between fractions
Usually for Head and H&N
Additional devices (eg
vacuum-based) needed for
special treatments

12. Clinical Treatment Planning:
Localization, Beam Geometries
Localisation of (mostly
invisible) PTVs and OARs
Setting up and positioning
the patient
Taking geometrical data (FSD,
angles, fieldsizes,...
Taking radiographs
Taking pictures (digitally)
Taking data for irregular
fields (eg with lead wires)

13. Clinical Treatment Planning:
CT-Patient Data - Advantages
Excellent soft tissue contrast
Easy contouring
Electron density planning
TVs and OARs can easily be
identified
Scout views
Position of TVs relative to
bony anatomy
fields conform TVs much
better

14. Clinical Treatment Planning:
Virtual Simulation
Prior to scanning marking of a
reference isocenter
TVs and OARs are outlined
directly at the CT
Use of standard beam geometries
or unorthodox techniques
Defining the ICRU-point in the
PTV
Patient first is adjusted to the
reference isocenter (stable
markers), then the ICRU-point is
set into the isocenter by moving
the table to calculated coordinates Large opening necessary
Best >80cm

15. Clinical Treatment Planning:
Virtual Simulation - DRRs
Digitally reconstructed
radiographs from CT-
dataset
Mandatory for
comparing patient
images with portfilms or
portal images
Oftehn combined with
Beam´s Eye Views
(BEVs)

16. Clinical Treatment Planning:
Virtual Simulation - BEVs
BEVs are projections of the
treatment beam axes onto
(mostly) a DRR
DRRs ideally should be
transferred through image
networks – but they contain
colors !
Definition of new standard for
radiotherapy – DICOM RT !

17. Clinical Treatment Planning:
Conventional vs. Virtual Simulation
Better soft tissue contrast in
CT
DRRs and BEVs in CT
Setting anatomical landmarks
Patient has only to be present
at the CT – much shorter !
Do you still need a
conventional simulator if you
have your own CT ?
Radiographs from treatment
setup are fine !

18. Clinical Treatment Planning:
Image Fusion
MRI offers better
contrast esp in soft
tissues, but
MRI cannot be used for
planning
Image fusion is standard
now in all modern TPSs
Other modalities also
important (eg PET, US) MRI CT

19. Clinical Treatment Planning:
Simulation - Summary

20. Clinical Treatment Planning:
Simulation – Summary (cont.)

21. Clinical Treatment Planning:
Treatment Aids - Wedges
Wedge angles are defined at the 50% isodose line perpendicular
to the central beam (sometimes in 10cm !!)
Wedge factor: dose-ratio in 10cm depth with/without wedge
HEEL: thick end; TOE: thin end (Error source !)
Typical usage for compensation or to avoid overdosage

22. Clinical Treatment Planning:
Treatment Aids–Bolus, Compensators
Bolus: tissue equivalent
material
To increase the surface dose
To compensate missing
tissue
Compensator: made of
almost any material from wax
to lead
Gets new drive now, better
calculaton algorithms, better
3D-cutting devices
bolus – compensator
IMRT ?
difference

23. IMRT with compensators at the WSP Vienna
F. Sommer1, H. Wetzel1, WFO. Schmidt2, M. Bobek1,
B. Riemer1, I. Wedrich1, B. Hirn1
1 Inst for Radio-Oncology, Wilhelminenspital Vienna; 2 Inst for Radio-Oncology,
Donauspital Vienna
HVL- measurement Oct 27, 2001
Roses-Metal und Tin-grain (grainsize ~ 0.5mm)
100,0
90,0
% (100%=without perspex)
80,0
70,0
60,0
50,0
40,0
30,0
20,0
10,0
0,0
0 1 2 3 4 5 6 7 8
cm compensator thickness
Future Work:
Installation of CMS-planning
system for IMRT-compensators
Comp. planning/measurement
with films and storage foils
checks of production accuracy
First patients expected in 2004 at a Mevatron (6MV) without MLC

24. Clinical Treatment Planning:
Oblique Incidence, Inhomogeneities
Different correction methods, partially integrated into planning
systems, but mostly rough and may produce large errors
Isodose shift method
Effective attenuation coefficient method
TAR method
Equivalent TAR method

25. Clinical Treatment Planning:
Beam Combinations Usual
1 beam
Parallel opposed beams
Multiple coplanar beams
Rotational beams
Multiple non-coplanar
beams
IMRT ? Positioning of adjacent beams

26. Clinical Treatment Planning:
Hand Control of Plans
Institute for Radio- Oncology
HOSPITAL
LINAC -- ISOZENTRIC
Nobody loves it ! Physics´ Planning
Patient + Reg.Nr Techn: Date :
Physicians have to sign
Physicist : Date :
what they say ! Peak voltage (MV) :
F1 F2 F3 F4
Focus-skin-distance FSD (cm) :
Dosimetrists or technicians
Fieldsize in reference distance (cm*cm) :
Reference depth d (cm) :
see it as an unnecessary
Wedge angle (°) :
Irregular field with perspex (y/n) :
piece of work only
Ref. dose Dref / fract/field in ICRU-point (Gy) :
Physician :
Reference value (Monitorunits/Gy for 10*10 - field; isocentric) RV= MU/Gy =
Physicists have to run for Gantry angle :
data and signatures – and
2* a* b
FLeq =
(a + b)
always have to answer the Equivalent field :
Outputfactor OF (Tab) :
question: is it really Wedge-factor WF (Tab) :
Tray-factor TF (Tab) :
necessary ? 100
Μ = D ref * RV **
1
*
TMR-value for d, FLeq (Tab) :
1
TMR WF TF OF
*
1
Monitor-units necess.:

27. Clinical Treatment Planning:
Dose Statistics
Describing not the
spatial information but:
Min dose to the PTV
Max dose to the PTV
Mean dose to PTV
Dose received by at least
95% of the volume
Volume irradiated by at
least 95% of the
prescribed dose

28. Clinical Treatment Planning:
Dose Volume Histograms (DVHs)
Computer is summing voxels
of known size in a certain
dose range
Direct or differential DVHs
Cumulative or integrals
DVHs Differential DVH
Cumulative DVHs are more
popular
But always keep in mind:
DVH (one line) also means
loss of spatial informaTION
Cumulative DVH

29. Clinical Treatment Planning:
Portal Imaging
Fluoroscopic detectors
like simulator image
intensifier
Ionisation chamber
detectors
Amorphous silicon
detectors
Like fluoro detectors, light
photons from metal plate
produce electron- hole pairs
in the photodiodes whose
quantity is proportional to the
intensity and is „translated“
into an image

30. Clinical Treatment Planning:
Portal Films
Localisation films (fast
films)
Generally produce better
images
Good for small fields or
complex arrangements
Verification films (slow
films)
Esp. for larger fields
Single/double exposure

31. Computerized TPS for External
Beam Radiotherapy (EBRT)
Typical TPS hardware
Central Processing Unit (CPU)
Graphics display (typically 17“ – 21“), sometimes 2 monitors
Memory and archiving functions (floppies, CDs, ODs, DVDs,
rewritable harddisks, tapes,...)
Digitizing devices (digitizers, scanners,...)
Output devices (printers, plotters,...)
Uninterruptable Power Supplies (UPS)
Communications hardware (networks, modem,...)
Air conditioning !

32. Computerized TPS for EBRT
Configurations Possible
Smaller TPSs normally
have a stand-alone lay-
out
But also some communi-
cation necessary for eg CTs
and/or data transfer
Backup ?
Larger systems operate in
a hospital-wide network
Backing up on servers
Specially trained personal
necessary

33. Computerized TPS for EBRT
Calculation Algorithms
Proper understanding of manual dose calculation is
mandatory !
Some listing of chronological development in ICRU 42
Present approach is to decompose the radiation beam
into primary and secondary (scatter) components.
Convolution/superposition algorithms
Pencil beam algorithms
MonteCarlo methods

34. Computerized TPS for EBRT
Beam Modifiers
Photons: Electrons:
Jaws (eventually moving Cones or movable
jaws) collimators
Blocks (mostly made Shielding for irregular
from lead or low melting
metal-compositions fields with perspex
blocks or Rose´s metal
MLC with/without backuo – Take care on burning
leafs) the skin at block edges
Wedges
Bolus materials
Compensators
...
...

35. Computerized TPS for EBRT
Data Acquisition – Machine Data
Have to be entered prior to entering scanned
curves
Gantry-, couch-, collimator-, jaw- and table-
movements, wedge directions and their limits
Data for MLC, blocks, trays,...
Electron cone data
This work is often underestimated and leads
to avoidable errors !

36. Computerized TPS for EBRT
Data Acquisition – Beam Data
Beam data required must be well understood
Also, how the system works with them internally !
Photon scanning data typically contain depth doses and
profiles with/without wedges and blocks.
Scanning measurements for electrons are more difficult !
Non-scanning data like peak- or total scatter factors as
well as absolute doses normally are measured with
chambers and controlled with a second device.
Data entry possible via digitizing tablet, keyboard or
electronically
Data-fitting outside the planning system is dangerous !

37. Computerized TPS for EBRT
Commissioning and QA
EN 62083 !
Comparison of input and output data !
Hardcopy of all curves, archiving in a logbook
Control of hardware, eg digitizing tablet
Control of communication, eg R&V system, CT, cutter
Make your own plans (eg with oblique incidence or a
combination photons/electrons) and try to verify it.
..........

38. Computerized TPS for EBRT
Commissioning and QA (cont)
Spot checks eg for determination of correct wedge
calculation
Written documentations of normalization and beam-
weightings for usual plannings
Same for DVHs and plan optimization
Training (eg user meetings) and documentation for
hard- and software
I don´t like software changes by modem !
Scheduled QA (daily. weekly, monthly,...)

39. AAPM 85
TG 65,
Aug ´04

40. AAPM 85, list of
TPS Vendors and Algorithms