Brachytherapy at IST Results from an atypical Comparison Project

1. Brachytherapy 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

2. Comparison Projects were approved by the CB/TSB as a milestone 2000 March 2000 The group decided to contribute to the milestone Letters of intent were presented to the TSB by the experiments April 2000 Work on the Comparison Project started May 2000 First resultspresented at the ICCR conference Proposals were presented to the TSB June 2000 First results shown to the TSB September 2000 Further results presented at the ESTRO conference The status of comparison projects is presented at the Geant4 Workshop October 2000 Further results presented at the Calor2000, MC2000, AIRO conferences and Geant4 workshop December 2000 Code to be released as an advanced example 2001 Publications History

3. What 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

4. Brachytherapy 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

5. Monte 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

6. Comparisons with data Full simulation of the radioactive source Simulated water  (photon attentuation coefficient) Comparison of NIST data with Geant4 Standard electromagnetic package and Low Energy extensions results Simulation of a simple set-up 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

7. Comparisons 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

8. Photon attenuation coefficient, Water Comparison of Geant4 LowE/standard e.m. processes and NIST data (Statistical errors are smaller than dot size)

9. Photon attenuation coefficient, Fe Comparison of Geant4 LowE/standard e.m. processes and NIST data (Statistical errors are smaller than dot size)

10. Photon 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)

11. Description 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

12. Simulation 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

13. Investigated 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

14. Investigated quantities: isodoses • The simulated dose deposition data can also be used to derive isodoses

15. Products of this Comparison Project • Tests of Geant4LowE/standard e.m. processes • Tests of the Geant4Radioactive Decay Module • A physics test (m/r) to become part of regular LowE testing • AnAdvanced Exampleto be released to the user communities • Theportingof Geant4 2.0 to Windows/Cygnus • 4 common presentations atconferencesso far • 2 commonpublicationsin preparation (+ IST group’s ones) • A widepromotionof Geant4 in the medical environment • A contribution totechnology transfer

16. Conclusions 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!