Radiotherapy Treatment Planning
Treatment planning is the task to make
sure a prescription is put into practice
in an optimized way
Prescription
Planning
Treatment
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Objectives
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Understand the general principles of
radiotherapy treatment planning
Appreciate different dose calculation
algorithms
Understand the need for testing the treatment
plan against a set of measurements
Be able to apply the concepts of optimization
of medical exposure throughout the treatment
planning process
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Contents of the lecture
A. Radiotherapy treatment planning
concepts
B. Computerized treatment planning
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The need to understand
treatment planning
IAEA Safety Report Series 17 “Lessons
learned from accidental exposures in
radiotherapy “ (Vienna 2000):
 About 1/3 of problems directly related to
treatment planning!
 May affect individual patient or cohort of
patients

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A. Basic Radiotherapy Treatment
Planning Concepts
i. Planning process overview
ii. Patient data required for planning
iii. Machine data required for planning
iv. Basic dose calculation
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i. Planning process overview

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Combine machine parameters and individual patient
data to customize and optimize treatment
Requires machine data, input of patient data,
calculation algorithm
Produces output of data in a form which can be used
for treatment (the ‘treatment plan’)
Patient information
Treatment unit data
Planning
Treatment plan
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ii. Patient information required

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Radiotherapy is a localized treatment of
cancer - one needs to know not only the dose
but also the accurate volume where it has
been delivered to.
This applies to tumor as well as normal
structures - the irradiation of the latter can
cause intolerable complications. Again, both
volume and dose are important.
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One needs to know
Target location
 Target volume and shape
 Secondary targets - potential tumor
spread
 Location of critical structures
 Volume and shape of critical structures
 Radiobiology of structures

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Target delineation
ICRU 50 & 62
 Gross Tumor Volume (GTV) = clinically demonstrated tumor
 Clinical Target Volume = GTV + area at risk (eg. potentially
involved lymph nodes)
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It all comes down to the correct
dose to the correct volume
Comparison of
three different
treatment techniques
(red, blue and green)
in terms of dose to
the target and a
critical structure
120
Volume (%)
100
80
60
Critical
organ
40
20
Target dose
0
0
20
40
60
80
Dose (Gy)
Dose Volume Histograms are a way to
summarize this information
The ideal DVH

Tumor:

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
High dose to all
Homogenous dose
100%
Critical organ

Low dose to most of
the structure
100%
dose
dose
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Need to keep in mind
Always a 3D problem
 Different organs may respond differently
to different dose patterns.
 Question: Is a bit of dose to all the
organ better than a high dose to a small
part of the organ?

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In practice not
always that clear cut

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ICRU report 62
Need to understand
anatomy and
physiology
A clinical decision
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In many organs, dose and volume
effects are linked - eg.
Boersma*
et al.,
classified the
following
(Dose,Volume) regions
to be regions of high
risk for developing
rectal bleeding:
*Int.
Dose
(Gy)
Rectal
volume(%)
>65
40
>70
30
>75
5
J. Radiat. Oncol. Biol. Phys., 1998; 41:84-92.
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In EBT practice

Need to know
where to direct beam to, and
 how large the beam must be and how it
should be shaped

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Target design and reference
images

In radiotherapy practice the target is
localized using diagnostic tools:
Diagnostic procedures - palpation, X-ray,
ultrasound
 Diagnostic procedures - MRI, PET, SPECT
 Diagnostic procedures - CT scan, simulator
radiograph

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Selection of treatment approach
Requires training and experience
 May differ from patient to patient
 Requires good diagnostic tools
 Requires accurate spatial information
 May require information obtained from
different modalities

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Minimum patient data required for
external beam planning

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Target location
Patient outline
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Diagnostic tools which could be
used for patient data acquisition
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CT scanner, MRI, PET scanner, US,…
Simulator including laser system, optical
distance indicator (ODI)
Many functions of the simulator are also
available on treatment units as an alternative
- simulator needs the same QA!
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Note on the role of simulation

Simulator is often used twice in the
radiotherapy process
Patient data acquisition - target localization,
contours, outlines
 Verification - can the plan be put into
practice? Acquisition of reference images
for verification.


Simulator may be replaced by other
diagnostic equipment or virtual
simulation
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Virtual simulation
All aspects of simulator work are
performed on a 3D data set of the
patient
 This requires high quality 3D CT data of
the patient in treatment position
 Verification can be performed using
digitally reconstructed radiographs
(DRRs)

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Virtual Simulation
3D Model of
the patient
and the
Treatment
Devices
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Simulator
Rotating
gantry
Diagnostic
X-ray tube
Radiation beam
defining system
Simulator couch
Nucletron/Oldelft
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Image intensifier
and X-ray film
holder
26
Radiotherapy simulator

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Obtain images and
mark beam entry
points on the patient
27
CT Simulation (Thanks to ADAC)
Marking the Patient already during CT
Moveable Lasers
Isocenter
Position
CT images
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Isocenter Projection
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Patient marking
Marks on shell

Create relation
between patient
coordinates and
beam coordinates
Tattoos
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Skin markers
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Beam placement and shaping
DRR with
conformal shielding
simulator film
with block
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Tools for optimization of the
radiotherapy approach
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Choice of radiation
quality
Entry point
Number of beams
Field size
Blocks
Wedges
Compensators
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Optimization approaches
Choice of best
beam angle
beam
beam
target
patient
target
patient
wedge
target
Use of a beam
modifier
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patient
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Beam number and weighting
beam
Beam 1
100%
50%
50%
target
patient
Beam 2
patient
40%
30%
10%
20%
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A note on weighting of beams
Different approaches are
possible:
1. Weighting of beams as
to how much they contribute
to the dose at the target
2. Weighting of beams as
to how much dose is
incident on the patient
25%
40%
25%
25%
30%
These are NOT the same
10%
20%
25%
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Use of wedges
Wedged pair
 Three field
techniques

Isodose lines
patient
patient
Typical isodose lines
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Beam placement and shaping
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Entry point
Field size
Blocks
Wedges
Compensators
a two-dimensional
approach?
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Beam placement and shaping
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Entry point
Field size
Blocks
Wedges
Compensators
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Multiple beams
Dynamic delivery
Non-coplanar
Dose compensation
(IMRT) not just
missing tissue
Biological planning
This is actually a 3D approach
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Target Localization



Diagnostic procedures - palpation, X-ray,
ultrasound
Diagnostic procedures - MRI, PET, SPECT
Diagnostic procedures - CT scan,
simulator radiograph
Allows the creation of Reference Images for
Treatment Verification:
Simulator Film, Digitally Reconstructed Radiograph
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Simulator image
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During ‘verification
session’ the treatment
is set-up on the
simulator exactly like it
would be on the
treatment unit.
A verification film is
taken in ‘treatment’
geometry
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Simulator Film
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Field defining wires
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Shows relevant
anatomy
Indicates field
placement and size
Indicates shielding
Can be used as
reference image for
treatment
verification
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iii. Machine data requirements for
treatment planning
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Beam description (quality, energy)
Beam geometry (isocentre, gantry, table)
Field definition (source collimator distance,
applicators, collimators, blocks, MLC)
Physical beam modifiers (wedges,
compensator)
Dynamic beam modifiers (dynamic wedge,
arcs, MLC IMRT)
Normalization of dose
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Machine data required for
planning

Depends on
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complexity of treatment
approaches
resources available for
data acquisition
May be from published
data or can be acquired
MUST be verified...
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Quick Question:
Who is responsible for the
preparation of beam data for the
planning process?
Acquisition of machine data

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…from vendor or
publications (eg BJR 17 and
25) - this requires
verification!!!
Done by physicist
Some dosimetric equipment
must be available (water
phantom, ion chambers, film,
phantoms,…)
Documentation essential
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Machine data availability
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Hardcopy (isodose charts, output factor
tables, wedge factors,…) - for emergencies
and computer break downs
Treatment planning computer (as above or
beam model) - as standard planning data
Independent checking device (eg. mu
checks) - should be a completely
independent set of data
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Machine data availability
Hardcopy (isodose charts, output factor
tables, wedge factors,…)
 Treatment planning computer (as above
or beam model)
 Independent checking device (eg. mu
checks)

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Machine data summary
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Need to include all beams and options
(internal consistency‫ اللزوجة‬،‫القوام‬, conventions,
collision ‫ تصادم‬protection, physical limitations)
Data can be made available for planning in
installments as required
Some data may be required for individual
patients only (eg. special treatments)
Only make available data which is verified
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Quick Question:
What data is available for physical
wedges in your center?
This should include at least:
Wedge angle - and how it is defined
Wedge output modification factor - and to which depth
and field sizes it applies
The field sizes for which the wedge can be used
Beam hardening? Maybe a new beam must be
defined by TMRs or percentage depth dose
Profiles in both directions (wedged and un-wedged the latter is affected by divergence related profile
changes)
Weight (eg for OHS restrictions on lifting)
From single to multiple beams

Mainly an issue
for megavoltage
photons where
we have
significant
contribution of
dose to the target
from many beams
1
3
2
60 Gy
4
Beam weighting must be factored in !!!
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Compensators

Physical compensators
lead sheets
 brass blocks
 customized milling

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Intensity modulation
multiple static fields
 arcs
 dynamic MLC
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Intensity modulation
Can be shown to allow optimization of
the dose distribution
 Make dose in the target homogenous
 Minimize dose out of the target
 Different techniques

physical compensators
 intensity modulation using multi leaf
collimators
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Intensity
Modulation
MLC pattern 1
MLC pattern 2
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
Achieved using a
Multi Leaf Collimator
(MLC)
The field shape can be
altered


either step-by-step or
dynamically while dose is
delivered
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MLC pattern 3
Intensity
map
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iv. Basic dose calculation

Once one has the target volume, the
beam orientation and shape one has to
calculate how long a beam must be on
(60-Co or kV X-ray units) or how many
monitor units must be given (linear
accelerator) to deliver the desired dose
at the target.
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3D display of
beam
placement
may help to
identify the
structures in
the field.
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Dose calculation
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Dose display options
Color wash
Isodose lines
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Isodose display - can be
complex and 3D
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