UCLA

Purpose: High-dose-rate (HDR) prostate brachytherapy delivers a heterogeneous dose distribution throughout the prostate gland. There is however limited information regarding the spatial distribution of this dose heterogeneity. To this end, we analyzed the magnitude and location of intraprostatic dose heterogeneity in HDR prostate brachytherapy. Methods and Materials: Five consecutive prostate cancer patients treated with HDR were analyzed. Based on CT-simulation images, each prostate was divided into three sections (apex, base, and mid-gland). These were further subdivided into eight symmetrical sections to give a total of 24 sections. Dose-volume histograms were analyzed from V100-V200% for these 24 sections comparing the means of individual regions, left vs right, apex vs base vs mid-gland, lateral vs medial, and anterior vs posterior. A separate analysis on dose as a function of individual region volume was also performed. Results: Analyses comparing the 24 regions showed a maximum 62% difference (range, 21.9-83.9%) at V130% and 19.9% (1.9-20.8%) at V200%. Seven regions were significantly decreased and one significantly elevated from V130-V180% when compared with the mean. The means for lateral sections were 1.57-fold higher than medial sections from V110-V200% (. p < 0.0001). The dose at the base was significantly higher than the rest of the gland from V120-V200 (V150, 35.6±16.2% vs 20.9±13.1%, p < 0.0001). Conclusions: There is significant intra-prostatic dose heterogeneity in prostate HDR brachytherapy. This is most notable in the increased dose to base and lateral portions of the gland. Further studies are needed to determine the impact of heterogeneity on clinical outcomes.