A comparison study on various low energy sources in interstitial prostate brachytherapy

Purpose: Low energy sources are routinely used in prostate brachytherapy. ¹²⁵I is one of the most commonly used sources. Low energy ¹³¹Cs source was introduced recently as a brachytherapy source. The aim of this study is to compare dose distributions of ¹²⁵I, ¹⁰³Pd, and ¹³¹Cs sources in interstitial brachytherapy of prostate.

Material and methods: ProstaSeed ¹²⁵I brachytherapy source was simulated using MCNPX Monte Carlo code. Additionally, two hypothetical sources of ¹⁰³Pd and ¹³¹Cs were simulated with the same geometry as the ProstaSeed ¹²⁵I source, while having their specific emitted gamma spectra. These brachytherapy sources were simulated with distribution of forty-eight seeds in a phantom including prostate. The prostate was considered as a sphere with radius of 1.5 cm. Absolute and relative dose rates were obtained in various distances from the source along the transverse and longitudinal axes inside and outside the tumor. Furthermore, isodose curves were plotted around the sources.

Results: Analyzing the initial dose profiles for various sources indicated that with the same time duration and air kerma strength, ¹³¹Cs delivers higher dose to tumor. However, relative dose rate inside the tumor is higher and outside the tumor is lower for the ¹⁰³Pd source.

Conclusions: The higher initial absolute dose in cGy/(h.U) of ¹³¹Cs brachytherapy source is an advantage of this source over the others. The higher relative dose inside the tumor and lower relative dose outside the tumor for the ¹⁰³Pd source are advantages of this later brachytherapy source. Based on the total dose the ¹²⁵I source has advantage over the others due to its longer half-life.