Brachytherapy radiation doses to the neurovascular bundles

Purpose: To investigate the role of radiation dose to the neurovascular bun dles (NVB) in brachytherapy-related impotence. Methods and Materials: Fourteen Pd-103 or I-125 implant patients were studi ed. For patients treated with implant alone, the prostate and margin (clini cal target volume [CTV]) received a prescription dose of 144 Gy for I-125 o r 115 Gy for Pd-103, Two patients received Pd-103 (90 Gy) with 46 Gy supple mental external beam radiation (EBRT), Axial CT images were acquired 2 to 4 hours postoperatively for postimplant dosimetry, Because the NVBs cannot b e visualized on CT, NVB calculation points were determined according to pre viously published anatomic descriptions. Bilateral NVB points were consider ed to lie posterior-laterally, approximately 2 mm from the prostatic capsul e. NVB doses were recorded bilaterally, at 0.5-cm intervals from the prosta tic base. Results: For Pd-103, the average NVB doses ranged from 150 Gy to 260 Gy, or 130% to 226% of the prescription dose. For I-125, the average NVB dose ran ged from 200 Gy to 325 GS, or 140% to 225% of the prescription dose. These was no consistent relationship between the NVB dose and the distance from t he prostatic base. To examine the possible effect of minor deviations of ou r calculation points from the true NVB location, we performed NVB calculati ons at points 2 mm medial or lateral from the NVB calculation point in 8 pa tients. Doses at these alternate calculation points were comparable, althou gh there was greater variability with small changes in the calculation poin t if sources were located outside the capsule, near the NVB calculation poi nt. Three patients who developed early postimplant impotence had maximal NV B doses that far exceeded the average values. Conclusions: In the next few Sears, we hope to clarify the role of high NVB radiation doses on potency, by correlating NVB dose calculations with a la rge number of patients enrolled in an ongoing I-125 versus Pd-103 trial for early-stage patients, for whom detailed dosimetric and potency data are be ing collected prospectively. In the future, we anticipate that NVB doses ma y be incorporated into dosimetry guidelines to maximize tumor control and m inimize treatment-related morbidity, (C) 2000 Elsevier Science Inc.