PII S0360-3016(00)00746-X CLINICAL INVESTIGATION Prostate A COMPARISON OF RADIATION DOSE TO THE NEUROVASCULAR BUNDLES IN MEN WITH AND WITHOUT PROSTATE BRACHYTHERAPY- INDUCED ERECTILE DYSFUNCTION GREGORY S. MERRICK, M.D.,* ² WAYNE M. BUTLER,PH.D.,* ANTHONY T. DORSEY, M.S.,* JONATHAN H. LIEF,PH.D.,* ‡ AND JOSEPH G. DONZELLA, B.S.* *Schiffler Cancer Center, Wheeling Hospital, Wheeling, WV; ² The George Washington University Medical Center, Division of Radiation Oncology and Biophysics, Washington, DC; ‡ Wheeling Jesuit University, Wheeling, WV Purpose: The etiology of erectile dysfunction after definitive local therapy for carcinoma of the prostate gland represents a multifactorial phenomenon including neurogenic compromise, venous insufficiency, local trauma, and psychogenic causes. It has been suggested that impotence after prostate brachytherapy is a consequence of excessive radiation dose to the neurovascular bundles (NVB). Herein we evaluate the potential relationship between radiation dose to the NVB and the development of erectile dysfunction following prostate brachytherapy. Methods and Materials: The radiation dose to the NVB was evaluated for 33 patients who developed erectile dysfunction (ED) following brachytherapy plus 21 additional patients who were potent before and subsequent to brachytherapy. Of the 54 patient study group, the median follow up was 37 months, and 25 patients were managed with 125 I as a monotherapeutic approach and 29 received 103 Pd as a boost following 45 Gy of external beam radiation therapy. Radiographic localization of the NVB was performed via a two-dimensional geometric model that placed 3-NVB calculation points on the left and right posterolateral side of each 5-mm CT slice. Parameters evaluated included dose–surface histograms, dose parameters via point doses on each slice, the magnitude of the dose in relationship to the distance from the base, and the relationship between NVB radiation dose in patients with and without ED, patient response to sildenafil and case sequence number. Results: In terms of percent prescribed minimum peripheral dose (% mPD), there was no significant difference in mean neurovascular bundle dose between potent and impotent patients, between the isotopes ( 125 I or 103 Pd), mono- or boost therapy, or side of the prostate for which the overall average was 217%  55% of mPD. There was also no significant dosimetric difference in terms of response to sildenafil based on a multivariate analysis which included % mPD and various dose thresholds and side of the gland. The dose distribution over the length of the prostate rose smoothly from the base and apex to peak at midgland in 125 I implants while 103 Pd implants had a relatively constant dose over the length of the prostate. Considering the calculation grid as forming a 6-mm wide ribbon along each side of the prostate, the average patient had 70 mm 2 area receiving at least 300% of mPD. Conclusion: In this study, no relationship between radiation dose to the NVB and the development of post brachytherapy erectile dysfunction was discernible. Such a difference may become evident with additional follow-up. If long-term brachytherapy-induced erectile dysfunction is related to the radiation dose to the NVB, the ultimate preservation of potency following prostate brachytherapy may be markedly inferior to what has been reported. Nevertheless, the majority of this patient population responded favorably to sildenafil. © 2000 Elsevier Science Inc. Prostate, Brachytherapy, Neurovascular bundles, Erectile dysfunction, Sildenafil. INTRODUCTION Erectile dysfunction has been estimated to affect up to 30 million American men (1). Transperineal ultrasound guided prostate brachytherapy with or without moderate dose ex- ternal beam radiation therapy results in impotence in 6 –53% of cases (2– 6). The etiology of erectile dysfunction after definitive local therapy for carcinoma of the prostate gland represents a multifactorial phenomenon including neurogenic compromise, venous insufficiency, local trauma, and psychogenic causes. Merrick et al. (7), recently reported the efficacy of sildenafil citrate (Viagra) in prostate brachy- therapy patients with erectile dysfunction; 80.6% of all patients responded favorably to such treatment. Comparable results with external beam radiation therapy-induced impo- tence have recently been reported (8, 9). Men undergoing bilateral nerve-sparing prostatectomy, but not unilateral nerve-sparing or non–nerve-sparing procedures, have been reported to respond favorably to sildenafil (10). These re- sults suggest the necessity of bilateral nerve integrity for response to sildenafil. Lepor et al. (11), correlated impo- Reprint requests to: Dr. Gregory S. Merrick, Schiffler Cancer Center, Wheeling Hospital, 1 Medical Park, Wheeling, WV 26003-6300. E-mail: schifonc@wheelinghosp.com Accepted for publication 14 June 2000. Int. J. Radiation Oncology Biol. Phys., Vol. 48, No. 4, pp. 1069 –1074, 2000 Copyright © 2000 Elsevier Science Inc. Printed in the USA. All rights reserved 0360-3016/00/$–see front matter 1069