Dosimetric characterization of radioactive sources employed in prostate cancer therapy

Three types of radiation sources are employed currently in the radiation treatment of prostate cancer, namely, external, implant, and high-dose-rate (HDR) sources using an afterloader method. The present article provides a detailed dosimetric characterization of several commercially available implant sources and an HDR source employing the same stochastic code and dataset.

The radioactive implants considered are (125)I seeds: models 6701, 6702 and 6711, (103)Pd seed: model 200, and a high-dose-rate (192)Ir source: microSelectron-HDR model V7.0x. Detailed modeling of the sources and their associated X-rays and gamma rays has been carried out using the stochastic code MCNP4C. A sensitivity study has been conducted to quantify effects of varying the composition and density of the tissue equivalent material, and a dosimetric comparison is made for different media (tissue equivalent, solid-water, water, and air). Furthermore, a set of measurements using thermoluminescent dosimeters has been done to provide experimental validation of some of the calculational results obtained.

Effectively, high-precision dosimetric values (Monte-Carlo statistical 1-sigma error <1%) are provided in tabulated form over a wide range to enable therapy planning as well as to check numerical values calculated by other methods. A subset of calculated dosimetric values has been experimentally validated by using thermoluminescent dosimeters.

A detailed comparison of results obtained for the radial dose distribution function, anisotropy factor, and dose rate constant as defined in the TG-43 protocol has indicated reasonable agreement with the values reported in the literature.