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

              Prescription


                Planning


               Treatment
                   Anwar             2
Objectives
   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

                        Anwar                 3
Contents of the lecture
A. Radiotherapy treatment planning
  concepts
B. Computerized treatment planning




                   Anwar             4
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

                     Anwar                5
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




                     Anwar                6
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

                         Planning

                      Treatment plan
                              Anwar                         7
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.


                         Anwar                 9
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


                    Anwar              10
            Target delineation
              ICRU 50 & 62




 Gross Tumor Volume (GTV) = clinically demonstrated tumor
 Clinical Target Volume = GTV + area at risk (eg. potentially
involved lymph nodes)
                             Anwar                        11
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
                 60
                 40        Critical
                            organ
                 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:                              Critical organ
          High dose to all                    Low dose to most of
          Homogenous dose                      the structure


100%                           100%




                        dose                                 dose


                                Anwar                               13
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?


                    Anwar              15
In practice not
always that clear cut
   ICRU report 62
   Need to understand
    anatomy and
    physiology
   A clinical decision




                          Anwar   16
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.
                                     Anwar                       17
In EBT practice
   Need to know
     where to direct beam to, and
     how large the beam must be and how it
      should be shaped




                       Anwar                  18
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


                       Anwar                 19
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


                   Anwar              20
Minimum patient data required for
external beam planning
   Target location
   Patient outline




                      Anwar         21
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!




                         Anwar                  22
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
                         Anwar                   23
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)
                    Anwar              24
Virtual Simulation
3D Model of
the patient
and the
Treatment
Devices




               Anwar   25
Simulator                                    Rotating
                                              gantry
  Diagnostic
  X-ray tube


 Radiation beam
 defining system



      Simulator couch                  Image intensifier
                                        and X-ray film
                   Nucletron/Oldelft
                                            holder
                           Anwar                   26
Radiotherapy simulator
                        Obtain images and
                         mark beam entry
                         points on the patient




             Anwar                         27
  CT Simulation (Thanks to ADAC)
  Marking the Patient already during CT

Moveable Lasers
     Isocenter
      Position




                  CT images       Isocenter Projection
                       Anwar                 28
Patient marking
                                       Marks on shell

   Create relation
    between patient
    coordinates and
    beam coordinates




                          Tattoos   Skin markers
                       Anwar                       29
Beam placement and shaping
                                    DRR with
                          conformal shielding




 simulator film
 with block



                  Anwar                   42
Tools for optimization of the
radiotherapy approach
   Choice of radiation
    quality
   Entry point
   Number of beams
   Field size
   Blocks
   Wedges
   Compensators

                          Anwar   43
Optimization approaches
                                          beam              Choice of best
         beam                                                beam angle

                                      target                 patient
target


         patient
                                                           wedge



                                      target
                   Use of a beam
                     modifier                    patient


                              Anwar                                    44
Beam number and weighting
                                                   Beam 1
         beam                                               50%
                   100%
                                        50%

target                              Beam 2                  patient


         patient

                                             40%
                          30%                                 10%




                            20%
                                Anwar                                 45
A note on weighting of beams
Different approaches are
possible:
1. Weighting of beams as                    25%
to how much they contribute    25%
                                            40%
                                                       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%
                                      25%



                              Anwar               46
Use of wedges
 Wedged pair
                                        Isodose lines
 Three field
  techniques
                                    patient




    patient     Typical isodose lines
                   Anwar                         47
Beam placement and shaping
   Entry point       a two-dimensional
   Field size            approach?
   Blocks
   Wedges
   Compensators




                   Anwar                  48
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
                       Anwar                 49
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

                           Anwar                    50
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’
                         geometry



             Anwar                              51
Simulator Film
                                     Shows relevant
                                      anatomy
                                     Indicates field
                                      placement and size
                                     Indicates shielding
                                     Can be used as
                                      reference image for
   Field defining wires               treatment
                                      verification

                          Anwar                        52
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,
    compensator)
   Dynamic beam modifiers (dynamic wedge,
    arcs, MLC IMRT)
   Normalization of dose

                           Anwar                    57
Machine data required for
planning
   Depends on
       complexity of treatment
        approaches
       resources available for
        data acquisition
   May be from published
    data or can be acquired
   MUST be verified...


                             Anwar   58
      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
    verification!!!
   Done by physicist
   Some dosimetric equipment
    must be available (water
    phantom, ion chambers, film,
    phantoms,…)
   Documentation essential




                                   Anwar   60
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


                        Anwar                61
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)


                   Anwar              62
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

                           Anwar                   63
                   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                  1
    photons where
    we have
    significant          3           60 Gy            2
    contribution of
    dose to the target
    from many beams
                                         4
        Beam weighting must be factored in !!!

                             Anwar               65
Compensators
   Physical compensators
     lead sheets
     brass blocks
     customized milling

   Intensity modulation
     multiple static fields
     arcs
     dynamic MLC


                          Anwar   66
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

                         Anwar                67
Intensity                             MLC pattern 1




Modulation                                            MLC pattern 2




   Achieved using a
        Multi Leaf Collimator         MLC pattern 3

    (MLC)
   The field shape can be
    altered                                               Intensity
                                                              map
       either step-by-step or
       dynamically while dose is
        delivered
                              Anwar                       68
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.


                      Anwar               69
3D display of
beam
placement
may help to
identify the
structures in
the field.




                Anwar   70
Dose calculation




              Anwar   71
Dose display options




   Isodose lines           Color wash

                   Anwar                72
Isodose display - can be
complex and 3D




              Anwar        73
Anwar   74

								
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