Title: Brachytherapy at IST Results from an atypical Comparison Project
1Brachytherapy at ISTResults from an atypical
Comparison Project
- Stefano Agostinelli1,2, Franca Foppiano1,
Stefania Garelli1, Matteo Tropeano1 - 1National Institute for Cancer Research and
2Physics Dept. Univ. of Genova - Petteri Nieminen Maria Grazia Pia
2History
3What is brachytherapy?
- Brachytherapy is a medical therapy used for
cancer treatments - Radioactive sources are used to deposit
therapeutic doses near tumors while preserving
surrounding healthy tissues
After-loading unit
- In HDR endocavitary brachytherapy
- a radioactive source, for example 192Ir, is used
- the source moves along catheters inserted in
natural cavities of the body, e.g. vagina or
bronchi this allows the deposition of the
therapeutic tumor dose right where it is needed - the source track is programmed by an
after-loading unit
Catheter along which source moves
4Brachytherapy treatment planning
- A typical vaginal treatment plan source moves
along a single catheter
A typical intra-uterine treatment plan the
source moves along 3 catheters
5Monte Carlo for brachytherapy
- Monte Carlo simulation topics for brachytherapy
- Dose calculation
- Computation of dose deposition kernels for
treatment planning dose calculation algorithms
based on convolution/superposition methods - Separation of primary, first scatter and multiple
scatter components for complex dose deposition
models - Computation of other model-dependent parameters,
e.g. anisotropy function - Accurate computation of dose deposition in high
gradient regions (i. e. near sources) - Verification of experimental calibration
procedures
6Comparisons with data
Full simulation of the radioactive source
Simulation of a simple set-up
- Simulated water ???
- (photon attentuation coefficient)
- Comparison of NIST data with Geant4
- Standard electromagnetic package
- and Low Energy extensions results
Comparison with in-house experimental data and
certifications of the supplying company
Low Energy/Standard e.m. Physics packages ESA
Radioactive Decay Module
Tests of
7Comparisons with full source simulation
Anisotropy Comparisons with published reference
treatment planning data
Air kerma rate at various distances Comparisons
with measurements of the air kerma rate at IST,
following the Protocol for the Basic Dosimetry in
Radiotherapy with Brachytherapy Sources of the
Italian Association of Biomedical Physics
Isodoses Comparisons with tabulated isodoses for
superficial brachytherapy applicators
8Photon attenuation coefficient, Water
Comparison of Geant4 LowE/standard e.m. processes
and NIST data
(Statistical errors are smaller than dot size)
9Photon attenuation coefficient, Fe
Comparison of Geant4 LowE/standard e.m. processes
and NIST data
(Statistical errors are smaller than dot size)
10Photon attenuation coefficient, Pb
Comparison of Geant4 LowE/standard e.m. processes
and NIST data
Photons are all absorbed with Standard below 100
keV
(Statistical errors are smaller than dot size)
11Description of ?-Selectron 192Ir source
- Geant4 allows complete flexible description of
the real geometry
- 192Ir energy spectrum
- currently described as monochromatic at 356 keV
- will soon be described by the ESA Geant4
RadioactiveDecay class
12Simulation of dose deposition in water
- The simulated source is placed in a 30 cm water
box - The dose deposition is investigated in the
longitudinal plane - The plane is partitioned in 1 million 1mm3 voxels
- A minimum of 10 millions photons are generated on
the 4? solid angle
?-Selectron 192Ir source
Longitudinal plane partitioned in cells
13Investigated quantities anisotropy
- The dose deposition is not isotropic due to
source geometry and auto-absorption,
encapsulation and shielding effects - Anisotropy can be described by a simple angular
function which can be computed by re-sampling our
simulated voxels grid calculations
14Investigated quantities isodoses
- The simulated dose deposition data can also be
used to derive isodoses
15Products of this Comparison Project
- Tests of Geant4 LowE/standard e.m. processes
- Tests of the Geant4 Radioactive Decay Module
- A physics test (m/r) to become part of regular
LowE testing - An Advanced Example to be released to the user
communities - The porting of Geant4 2.0 to Windows/Cygnus
- 4 common presentations at conferences so far
- 2 common publications in preparation ( IST
groups ones) - A wide promotion of Geant4 in the medical
environment - A contribution to technology transfer
16Conclusions and future goals
- This Comparison Project has already generated
valuable products - The activity of the experimental group and of the
Geant4 collaborators are fully integrated, with
mutual benefit - Further developments and comparisons are planned
in the next weeks
- More realistic description of 192Ir source energy
spectrum with the new Geant4 RadioactiveDecay
class - Comparison with in-house data
- Simulation of shielded brachytherapy applicators
Many thanks to Gabriele Cosmo and Alessandro
Brunengo for their invaluable help!