Prescription dose in permanent seed prostate implants

Abstract

Recently, seeds have been introduced for prostate permanent seed implants. This type of seed has a relatively short half‐life of 9.7 days and has its most prominent emitted photon energy peaks in the 29–34 keV region. Traditionally, 145 and 125 Gy have been prescribed for and seed prostate implants, respectively. Since both the half‐life and dosimetry characteristics of seed are quite different from those of and , the appropriate prescription dose for seed prostate implant may well be different. This study was designed to use a linear quadratic radiobiological model to determine an appropriate dose prescription scheme for permanent seed prostate implants. In this model, prostate edema was taken into consideration. Calculations were also performed for tumors of different doubling times and for other related radiobiological parameters of different values. As expected, the derived prescription dose values were dependent on type of tumors and types of edema. However, for prostate cancers in which tumor cells are relatively slow growing and are reported to have a mean potential doubling time of around 40 days, the appropriate prescription dose for permanent seed prostate implants was determined to be: if the experiences of seed implants were followed and if the experiences of seed implants were followed.