Treatment planning considerations for prostate implants with the new linear RadioCoil? 103Pd brachytherapy source

Abstract

Recently various linear source models, like 103Pd RadioCoil?, have been introduced to overcome the shortcomings of traditional ?seed? type interstitial prostate brachytherapy implants, such as migration and clumping of the seeds. However, the existing prostate treatment planning systems have not been updated to perform dose calculation for implant with linear sources greater than 1.0 cm in length. In these investigations two new models have been developed for 3D dose calculation for a prostate implant with linear brachytherapy sources, using the commercially available treatment planning systems. The proposed models are referred as Linear-Segmented-Source (LSS) model and Point-Segmented-Source (PSS) model. The calculated dose distributions obtained by these models for single linear source have been validated by their comparison with the Monte Carlo simulated data. Moreover, these models were used to calculate the dose distributions for a multi-linear source prostate implant and the results were compared to ?seed? type implants. The results of these investigations show that the LSS model better approximates the linear sources than PSS model. Moreover, these models have shown a better approximation of the dose distribution from a linear source for 0.5 cm source segments as compared to 1.0 cm source segments. However, for the points close to the longitudinal axis of the source located outside the region bounded by the active length, both the models show differences of approximately ± 15 %. These deficiencies are attributed to the limitations of the TG43 formalism for elongated sources.