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Organ Doses in a Male Phantom Undergoing High-Dose-Rate Brachytherapy Applied to the Prostate

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C Candela-Juan

C Candela-Juan1*, D Granero2, J Vijande3, F Ballester3, J Perez-Calatayud1, M Rivard4, (1) La Fe University and Polytechnic Hospital, Valencia, Valencia, (2) ERESA, Hospital General Universitario, Valencia, Valencia, (3) University of Valencia, Burjassot, (4) Tufts Medical Center, Boston, MA

WE-C-108-8 Wednesday 10:30AM - 12:30PM Room: 108

Purpose: The aim of this study was to obtain equivalent doses to radiosensitive organs when applying high-dose-rate (HDR) brachytherapy to the prostate using ⁶⁰Co or ¹⁹²Ir sources, and in comparison to external-beam radiotherapy (EBRT) modalities.

Methods: Monte Carlo simulations in Geant4 were performed using a voxelized adult reference man described in Publication 110 by the International Commission on Radiological Protection (ICRP). Point sources of ⁶⁰Co or ¹⁹²Ir with photon energy spectra corresponding to those exiting their capsules were placed in the center of the prostate. Equivalent doses per therapeutic absorbed dose to the prostate were obtained in several radiosensitive organs. Values were corrected to account for realistic source dwell times and positions throughout the prostate. This was repeated for a homogeneous water phantom to assess the adequacy of a homogeneous phantom for HDR brachytherapy dose calculations. Brachytherapy doses were compared to reported values from intensity-modulated radiation therapy (IMRT) and proton therapy.

Results: For the nearest organs considered (bladder, rectum, testes, small intestine, and colon), equivalent doses given by ⁶⁰Co source were smaller than from ¹⁹²Ir. As the distance increased, ⁶⁰Co delivered higher equivalent doses. Relative to ¹⁹²Ir, the dose ratio increased up to a factor 5 for the brain. Differences between the heterogeneous and the water phantom became apparent at distances > 30 cm. For the closest organs, equivalent doses from the three EBRT modalities were within an order of magnitude to equivalent doses deposited by both brachytherapy sources. However, equivalent doses from brachytherapy to the farthest organs were up to two orders of magnitude smaller than EBRT doses.

Conclusion: According to physical considerations, ⁶⁰Co appears dosimetrically advantageous over ¹⁹²Ir sources at close distances, but not for the farthest organs. Equivalent doses to distant healthy organs were lower for brachytherapy than the studied EBRT modalities.

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