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Purpose: Prostate brachytherapy sometimes requires the volume receiving >150% of the prescribed dose (V150) to be >50% to obtain satisfactory coverage. There has been concern expressed that high V150 may be associated with higher rates of urinary retention and morbidity., Methods and Materials: We reviewed 207 consecutive cases of prostate brachytherapy treated with palladium 103 ((103)Pd; n = 140) or iodine 125 ((125)I; n = 67). Prescribed doses for (103)Pd monotherapy and boost were 124 and 90 Gy, respectively; for (125)I, the corresponding doses were 160 and 120 Gy. Patients were evaluated at baseline, 1 month, 3 months, and every 6 months thereafter., Results: Median follow-up at the time of analysis was 18 months. For (103)Pd, the mean intraoperative volume and V150 were 30.3 cm(3) and 72%, respectively; corresponding values for (125)I were 38.3 cm(3) and 59%, respectively. Two of the patients treated with iodine and 9 treated with palladium experienced acute urinary retention, which was not statistically significant (P = .48). The rectal V100 for (103)Pd was significantly less than that for (125)I (P < .001). The mean baseline, 1-month, and 12-month American Urologic Association (AUA) scores for (103)Pd were 8.5, 19.7, and 8.2, respectively; for (125)I, the values were 7.4, 17.1, and 13.4, respectively. At 12 months, the AUA scores returned to baseline in the (103)Pd-treated patients, whereas scores in (125)I-treated patients remained elevated (P = .005). High V150 did not appear to cause undue risk of urinary retention or morbidity based on logistic regression analysis of patients treated with monotherapy performed with either isotope., Conclusions: The risk of urinary retention was low, despite high V150 values for both isotopes. In patients treated with brachytherapy alone, no significant increase in urinary morbidity was seen in relation to V150. AUA scores returned to baseline in (103)Pd-treated patients at 1 year, whereas (125)I-treated patients demonstrated continued elevation., (Copyright © 2015 American Society for Radiation Oncology. Published by Elsevier Inc. All rights reserved.)