Radiotherapy Treatment Planning - PowerPoint by opza81

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									Radiotherapy Treatment Planning
Treatment planning is the task to make
sure a prescription is put into practice
in an optimized way



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   Understand the general principles of
    radiotherapy treatment planning
   Appreciate different dose calculation
   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
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

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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
   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


                      Treatment plan
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ii. Patient information required
   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
 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
                 120                                    three different
                                                        treatment techniques
                 100                                    (red, blue and green)
    Volume (%)

                                                        in terms of dose to
                 80                                     the target and a
                                                        critical structure
                 40        Critical
                                                        Target dose
                       0       20      40     60   80
                                      Dose (Gy)

Dose Volume Histograms are a way to
     summarize this information
  The ideal DVH
      Tumor:                              Critical organ
          High dose to all                    Low dose to most of
          Homogenous dose                      the structure

100%                           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
   ICRU report 62
   Need to understand
    anatomy and
   A clinical decision

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In many organs, dose and volume
effects are linked - eg.
                                        Dose             Rectal
Boersma*   et al.,                      (Gy)             volume(%)
classified the
following                               >65              40
(Dose,Volume) regions
to be regions of high                   >70              30
risk for developing
rectal bleeding:                        >75              5

*Int.   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
   In radiotherapy practice the target is
    localized using diagnostic tools:
     Diagnostic procedures - palpation, X-ray,
     Diagnostic procedures - MRI, PET, SPECT
     Diagnostic procedures - CT scan, simulator

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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
   Target location
   Patient outline

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Diagnostic tools which could be
used for patient data acquisition
   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
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Virtual simulation
 All aspects of simulator work are
  performed on a 3D data set of the
 This requires high quality 3D CT data of
  the patient in treatment position
 Verification can be performed using
  digitally reconstructed radiographs
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Virtual Simulation
3D Model of
the patient
and the

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Simulator                                    Rotating
  X-ray tube

 Radiation beam
 defining system

      Simulator couch                  Image intensifier
                                        and X-ray film
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Radiotherapy simulator
                        Obtain images and
                         mark beam entry
                         points on the patient

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  CT Simulation (Thanks to ADAC)
  Marking the Patient already during CT

Moveable Lasers

                  CT images       Isocenter Projection
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Patient marking
                                       Marks on shell

   Create relation
    between patient
    coordinates and
    beam coordinates

                          Tattoos   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
   Choice of radiation
   Entry point
   Number of beams
   Field size
   Blocks
   Wedges
   Compensators

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Optimization approaches
                                          beam              Choice of best
         beam                                                beam angle

                                      target                 patient


                   Use of a beam
                     modifier                    patient

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Beam number and weighting
                                                   Beam 1
         beam                                               50%

target                              Beam 2                  patient


                          30%                                 10%

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A note on weighting of beams
Different approaches are
1. Weighting of beams as                    25%
to how much they contribute    25%
to the dose at the target      30%                     10%
2. Weighting of beams as
to how much dose is
incident on the patient

These are NOT the same                20%

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Use of wedges
 Wedged pair
                                        Isodose lines
 Three field

    patient     Typical isodose lines
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Beam placement and shaping
   Entry point       a two-dimensional
   Field size            approach?
   Blocks
   Wedges
   Compensators

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Beam placement and shaping
   Entry point       Multiple beams
   Field size        Dynamic delivery
   Blocks            Non-coplanar
   Wedges            Dose compensation
   Compensators       (IMRT) not just
                       missing tissue
                      Biological planning

    This is actually a 3D approach
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Target Localization
   Diagnostic procedures - palpation, X-ray,
   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
                        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’

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Simulator Film
                                     Shows relevant
                                     Indicates field
                                      placement and size
                                     Indicates shielding
                                     Can be used as
                                      reference image for
   Field defining wires               treatment

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iii. Machine data requirements for
treatment planning
   Beam description (quality, energy)
   Beam geometry (isocentre, gantry, table)
   Field definition (source collimator distance,
    applicators, collimators, blocks, MLC)
   Physical beam modifiers (wedges,
   Dynamic beam modifiers (dynamic wedge,
    arcs, MLC IMRT)
   Normalization of dose

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Machine data required for
   Depends on
       complexity of treatment
       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
   …from vendor or
    publications (eg BJR 17 and
    25) - this requires
   Done by physicist
   Some dosimetric equipment
    must be available (water
    phantom, ion chambers, film,
   Documentation essential

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Machine data availability
   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

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Machine data summary
   Need to include all beams and options
    (internal consistency‫ ,القوام، اللزوجة‬conventions,
    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
Weight (eg for OHS restrictions on lifting)
From single to multiple beams
   Mainly an issue
    for megavoltage                  1
    photons where
    we have
    significant          3           60 Gy            2
    contribution of
    dose to the target
    from many beams
        Beam weighting must be factored in !!!

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   Physical compensators
     lead sheets
     brass blocks
     customized milling

   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

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Intensity                             MLC pattern 1

Modulation                                            MLC pattern 2

   Achieved using a
        Multi Leaf Collimator         MLC pattern 3

   The field shape can be
    altered                                               Intensity
       either step-by-step or
       dynamically while dose is
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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
may help to
identify the
structures in
the field.

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Dose calculation

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Dose display options

   Isodose lines           Color wash

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Isodose display - can be
complex and 3D

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