SU‐E‐T‐690: Fast Monte Carlo Treatment Planning for Prostate Brachytherapy: A Comparison with VariSeed

Abstract

Purpose: Treatment planning for prostate Brachytherapy with seeds uses mainly the TG43 algorithm for dose calculations. It doesnˈt take into account the interseed attenuations (known as the interseed effect) due to its complexity. A fast Monte Carlo dose calculation engine, taking into account the interseed effect, has been developed, using the MCNP5 code. Methods: Three MC techniques were used to calculate the dose distributions of the prostate implants: MCOSST, FMCT and MCOSSIT. The two last techniques take into account the interseed effect. IsoSeed (Bebig) seeds were chosen for this work. A 3D comparison has been performed to validate the new MC techniques for 8 patients. Dose distributions are compared on each ultrasound imaging slide. Moreover, a DVH comparison is also performed for some organs. Results: The interseed effect was investigated by comparing MCOSST with FMCT. It leads to the appearance of cold spots in the planar dose distribution which varies from 4% to 6%. It depends on number, position and composition of seeds. Moreover, the interseed effect becomes more important as the number of implanted seeds increases. We can especially notice it at the end of the strand and also behind set of seeds implanted each 5 mm in the same plane. DVH comparison between VariSeed and MC techniques was also performed. VariSeed overestimates the average dose deposited in the prostate by 3% up to 5%. MCOSSIT can be considered being a more accurate and faster (2–3 sec) calculation method in a near future as it taks into account the interseed effect and can also be applied on line Conclusions: MCOSSIT is a new calculation technique of dose distribution for prostate Brachytherapy that can be used for all types of seeds. All these advantages make from MCOSSIT very accurate and fast system for online permanent brachytherapy of the prostate.This work is submited by UCL University to get a patent.