Program Information
Cluster Pattern Analysis for Alternative High Dose Rate Brachytherapy Sources 75Se, 169Yb, and 153Gd
G Famulari*, S Enger , McGill University, Montreal, Quebec
Presentations
SU-I-GPD-T-6 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To evaluate the spatial distribution of energy deposition sites for alternative radiation sources proposed for high dose rate brachytherapy (⁷⁵Se, ¹⁶⁹Yb, ¹⁵³Gd), a high energy source (¹⁹²Ir), a low energy source (¹²⁵I), and a reference radiation (⁶⁰Co).
Methods: Brachytherapy sources were modelled as point sources located in the center of a spherical water phantom with a radius of 40 cm using the Geant4 Monte Carlo toolkit. The kinetic energy of all primary, scattered and fluorescence photons interacting in a scoring volume were tallied at various depths from the source. Electron tracks were generated by sampling the photon interaction spectrum, and tracking all the interactions down to 10 eV following the initial Compton or photoelectric interaction using the event-by-event capabilities of Geant4-DNA. The relative frequency of energy deposition clusters of at least 2 energy deposition events and the mean cluster order (MCO) were obtained through random sampling of interaction points and overlaying scoring volumes with 2 nm diameter within the associated volume of the tracks. Each of the tracks were sampled numerous times to keep standard deviations below 0.2 %.
Results: The relative frequency of clusters of at least 2 energy deposition events with respect to ⁶⁰Co was 1.024, 1.038, 1.061, 1.082, and 1.077 for ¹⁹²Ir, ⁷⁵Se, ¹⁶⁹Yb, ¹⁵³Gd, and ¹²⁵I, respectively. The MCO for ¹⁹²Ir, ⁷⁵Se, ¹⁶⁹Yb, ¹⁵³Gd and ¹²⁵I was 1.320, 1.326, 1.334, 1.342, and 1.340, respectively. The relative frequency of clusters and MCO generally increased with increasing distance from the source.
Conclusion: The relative frequency of clusters within the distance corresponding to the width of a DNA strand can provide a prediction on the difference in initial double strand break (DSB) yields induced by these radiation sources.
Funding Support, Disclosures, and Conflict of Interest: The authors acknowledge partial support by the NSERC Discovery Grant (number 241018), CREATE Medical Physics Training Network Grant (number 432290), and Simone and Morris Fast Award for Oncology.
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