Abstract ID: 16060 Title: Fast Monte Carlo treatment planning for prostate brachytherapy: a comparison with VariSeed
Purpose: Treatment planning for prostate Brachytherapy with seeds uses mainly the TG43
algorithm for dose calculations. It doesn’t 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.
Funding Support, Disclosures, and Conflict of Interest:
This work is submited by UCL university to get a patent