Radiation Protection in Radiotherapy

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Radiation Protection inRadiotherapy
IAEA Training Material on Radiation Protection in
Radiotherapy

• Part 10
• Good Practice including Radiation Protection in
  EBT
• Lecture 3 (cont.) Radiotherapy Treatment Planning

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B. Computerized treatment planning
Patient information
Treatment unit data
Planning
Treatment plan
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The treatment planning process
Individual patient
Radiotherapy treatment units
Beam data radiation quality, PDD, profiles, ...
Patient data CT scan, outlines
Localization of tumor and critical structures
Optimization of source or beam placement
Simulation
Dose calculation
Preparation of treatment sheet and record and
verify data
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A note on inverse treatment planning
Beam data radiation quality, PDD, profiles, ...
Patient data CT scan, outlines
Localization of tumor and critical structures
Definition of dose levels and constraints
Computerized optimization of source or beam
placement
Many iterations to find the optimum solution
Virtual simulation
Dose calculation
Preparation of treatment sheet and record and
verify data
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Treatment planning computer
Individual patient
Radiotherapy treatment units
Beam data radiation quality, PDD, profiles, ...
Patient data CT scan, outlines
Localisation of tumour and critical structures
Optimization of source or beam placement
Simulation
Dose calculation
Preparation of treatment sheet and record and
verify data
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Planning workstation
just a computer box, with highly specialized and
complex software.
ADAC Pinnacle
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B. Computerized treatment planning

• i) Dose calculation algorithms
• ii) A quick tour through a planning system
• iii) Evaluation tools
• iv) Networking and output
• v) Purchase of a planning system

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i) Elements of dose calculation

• Dose calculation algorithm
• Software coding and implementation
• Beam data
• Clinical set-up (data entry options, macros,
  evaluation sheet, hardcopy devices)

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Elements of dose calculation

• Dose calculation algorithm
• Software coding and implementation

• Typically, there is no user control for theses
  features - however it is essential that the user
• is familiar with the physics algorithm
• is aware of its implementation and possible
  software shortcuts
• has tested the algorithm for most possible
  treatment scenarios

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Elements of dose calculation

• Dose calculation algorithm
• Software coding and implementation

Unfamiliarity with set-up of the treatment
planning system has significantly contributed to
the most recent radiotherapy accident in Panama
(compare IAEA report)

• Typically, there is no user control for theses
  features - however it is essential that the user
• is familiar with the physics algorithm
• is aware of its implementation and possible
  software shortcuts
• has tested the algorithm for most possible
  treatment scenarios

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Calculation methods

• Photons
• Kilovoltage (superficial/orthovoltage)
• Megavoltage (60-Co, linear accelerators)
• Electrons
• Brachytherapy

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Photons

• Kilovoltage
• Hand calculation from measured data or lookup
  tables (e.g. BJR Supplement 25, 1996)
• Megavoltage
• correction based methods
• model based methods

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Megavoltage photon dose calculation approaches
Data measured in water and air
Parameterized water data

• Correction based methods
• Reconstitute water data
• Calculate contour corrections
• Calculate inhomogeneity corrections

• Model based methods
• Develop model of each beam (more than 1 model may
  be needed)
• Propagate model into patient data set

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Photon dose calculation approaches
Data measured in water and air
Parameterized water data

• Correction based methods
• Conventional approach
• Measured data used to create data which
  (hopefully) is adequate for patient treatment

• Model based methods
• Most recent planning systems use this
• Measured data only used to tune and verify a beam
  model
• Examples Superposition/convolution Monte Carlo
  Calculations

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Some comments on model based algorithms

• Calculation is from first principles
• The corrections used (e.g. for inhomogeneities)
  typically have no equivalent in hand planning
• Monitor units calculated without direct reference
  to measured data
• Perform better in complex patient than in water
  cube
• Verification and QA more essential!

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Electron dose calculation

• Hand calculation
• Pencil beam (2D ? 3D)
• Phase space evolution
• Monte Carlo Methods

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Monte Carlo Calculations

• The gold standard
• Calculates the path of individual particles using
  random decisions
• Uncertainty depends on number of particles - need
  millions
• Highly computer intensive

Monte Carlo Calculation of ten tracks of 12MeV
electrons
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ii) A tour through a commercial planning system...

• A series of screen shots from Theraplan Plus
• An example, mainly to illustrate a planning
  session

Many modules and options
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All commences with creating a patient
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Anatomy of the patient must be defined

• May be
• outlines
• CT scans
• Can be
• one slice
• many slices
• Here 21 slices in 1cm distance are created

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Creation of external contours on all slices -
this is not required if a CT scan is available
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Creation of internal organs
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A patient outline is filled with target
structures (CTV) and other organs of interest
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Points of interest are added (these could be
dosimetric reference points and dose point
relevant to effects in normal structures
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Inhomogeneities are added

• If appropriate
• Here a low density is associated with lung
• In case of a CT scan these are typically
  automatically created by the system

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Full screen layout - can be customized
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Making the CTV into a planning target volume
(PTV) by including margins
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CTV becomes PTV...
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A radiation beam is added...
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Physicians eye view and Beams eye view (BEV)
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Parameters for the beam are defined...
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The dose calculation grid

• Determines how detailed the dose distribution is
  calculated
• Usually around 2 to 5mm
• Depends on treatment situation
• Increases calculation time dramatically

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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 calculation
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Dose calculation
4MV
10MV
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Calculation with and without contour correction
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Addition of a beam modifier - here a 45degree
dynamic wedge
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Inhomogeneity correction turned on
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Beams eye view

• A useful tool
• Green - the beam
• Blue and red - the target
• Pink - a critical structure
• Allows beam shaping and the creation of blocks

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Creation of an opposing beam A parallel opposed
pair (POP)
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The resulting dose distribution
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Dose display options
Color wash
Isodose lines
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A third beam with multileaf collimator blocking
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Information on the beams
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Dose to the points of interest
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Changing the beam weighting...
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Changing the beam weighting and adding
wedges creates a homogenous dose distribution in
the target
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Normalization - where do we connect a dose
distribution with absolute dose...
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A complex dose delivery in a 90deg arc...
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iii) Other planning tools

• Three dimensional displays
• Dose Volume Histograms
• Virtual simulation
• Digitally reconstructed radiographs

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From two dimensions to three

• 3D data input
• 3D visualisation
• Non coplanar beam placement
• 3D dose computation
• New evaluation tools (DRRs, DVH)

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Isodose display - can be complex and 3D
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Dose display tools
Dose volume histograms (DVHs)
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Dose volume histogram
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Digitally reconstructed radiographs

• Better target definition
• Beam shaping
• Benchmark for treatment (what the computer
  thinks is really happening)

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Contouring and localisation ? virtual simulation
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all this needs verification

• Do the dimensions and volumes match?
• Is orientation in image transfer preserved (left
  and right may be difficult to distinguish in a
  brain scan!)
• Dont forget the mundane tools - wooden or
  plastic rulers may shrink

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Quick Question

• What advantages would three dimensional treatment
  planning have over two dimensional approaches?

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iv) Planning as part of a network
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Data transferandnetwork
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Protect network from others (fire wall!) and
still allow access e.g. for remote diagnostics
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Output for treatment and documentation

• Isodose plan
• DVH, DRR
• Treatment sheet
• Blocks, MLC
• Compensators, IMRT
• Verification data

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BSS, appendix II.31

• Records must be kept for a period specified by
  the Regulatory Authority (in RT this may be up to
  30 years)
• Records must include
• Planning volume
• Max and min dose
• Doses to other relevant organs
• Fractionation
• Overall treatment time

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Examples for data to be kept Isodose display
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need for electronic record keeping

• Less space required
• Potentially easier to access
• Problems with hardware and software
• Who can still read 5 1/4 inch disks?
• Who can access WordStar PC documents just 10
  years old
• Is not only the plan but also the beam data kept
  which was used to produce the plan?

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Planning tools summary

• Make use of all available diagnostic tools for
  planning
• Dramatic improvements in computing
• New evaluation tools
• Networking
• Record keeping

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v) Purchase of a treatment planning system

• Assessment of need
• Request for information
• Demonstrations/presentations
• Tender?
• Selection criteria

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Considerations

• Existing system?
• Special techniques (stereotactic, HDR brachy,
  TBI,)
• Workload, number of workstations
• Need for visualisation/clinical evaluation (DRRs,
  DVH,
• Treatment units available (MLC, dynamic wedge,
  IMRT, )

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Typical hardware

• Processor memory hard disk
• Floppy disk, tape, CD ROM, optical disk
• Keyboard, mouse, joystick
• High resolution graphics monitor and card
• Laser printer, color plotter
• Network card

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Typical software

• Physics data entry including brachytherapy
• Utility for patient data entry
• File manager for patient files
• Contour tools
• Video display for interactive beam placement
• Dose calculation
• Isodose display
• Hardcopy, archiving and backup

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Tender document (J van Dyk)

• Objectives
• Definitions
• Summary of essentials
• Regulations, standards, code of practice
• Vendor guarantees
• Vendor references/information
• Purchase/payment
• Installation/acceptance

• Specifications
• Hardware
• Software
• Network/Interface
• Planning software/calculations
• Documentation/training
• Service/parts
• Environmental requirements power, air
  conditioning

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Purchase summary

• Assess needs first
• Assess resources available (staffing, training,
  equipment, )
• Assess budget ongoing!

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Quick Question

• Please estimate the cost of a modern 3D treatment
  planning system include both investment and
  on-going costs.

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Please estimate the cost of a modern 3D treatment
planning system include both investment and
on-going costs.

• Investment
• Hardware US150,000.-
• Software US200,000.-

• Ongoing costs per year
• Hardware US40,000.-
• Software maintenance US20,000 (no new features!)

Very, very rough estimates!