Prostate brachytherapy postimplant dosimetry: a comparison of prostate quadrants

Abstract

Purpose : To investigate postimplant dosimetry for different regions of the prostate gland in patients treated with transperineal 125Iodine brachytherapy implants for low- and intermediate-risk prostate cancer. Methods and Materials : Two hundred eighty-four patients treated with permanent interstitial prostate brachytherapy comprised the study population. A nonuniform, urethral-sparing algorithm was used to plan all patients. Prostate contours were outlined on postimplant CT images. Prostate volumes were then divided into four quadrants: anterior-superior quadrant (ASQ), posterior-superior quadrant (PSQ), anterior-inferior quadrant (AIQ), and posterior-inferior quadrant (PIQ). Dose-volume histograms (DVHs) were calculated for the whole prostate and each quadrant. Results : The mean postimplant V 100 ± 95% confidence (the percent prostate volume encompassed within the isodose surface comprising the prescription dose = 144 Gy) for the ASQ was 78.5 ± 1.9, which was significantly lower than that of the PSQ, AIQ, and PIQ in which the V 100 ± 95% confidence values were 94.9 ± 0.8, 92.6 ± 1.2, and 98.7 ± 0.3, respectively. The mean V 100 ± 95% confidence for the whole prostate was 90.4 ± 0.8. Mean values for V 150 and D 90 (the minimum dose in Gy received by 90% of the target volume) for the four quadrants and the whole prostate showed similar results. Conclusions : Underdosed areas of the planning target volume (PTV), if present, were largely confined to the ASQ, which received a significantly lower dose, on average, compared to the other three quadrants of the prostate.