Sparing the neurovascular bundle in prostate radiotherapy: A dosimetric study

Prostate radiotherapy is associated with a high prevalence of erectile dysfunction (ED). Nerve-sparing prostatectomy techniques demonstrate reduced postoperative ED rates, suggesting a similar benefit may be achievable with neurovascular bundle (NVB) sparing radiotherapy. This feasibility planning study aims to comparatively evaluate various NVB sparing techniques described in the literature. This was a retrospective feasibility planning study evaluating NVB sparing techniques for localized prostate cancer treated with moderate hypofractionation of 60 Gy in 20 fractions. The Volumetric Modulated Arc Therapy (VMAT) plans compared different NVB sparing strategies: (1) Standard prostate treatment without sparing of the NVBs (SPT), (2) bilateral NVB sparing (BNS) plan, (3) BNS with reduced Planning Target Volume (PTV) margins (BSRM), and (4) unilateral NVB sparing (UNS) plan. NVB target goals were V53Gy < 70% and D_max < 57Gy. Dose-volume histogram endpoints were compared to the SPT plan with a Wilcoxon signed-rank test. NVB sparing plans significantly reduced radiation dose to the NVB. UNS showed the greatest NVB sparing with a relative dose reduction of 10.3%, 99.1%, and 3.4% (p<0.001) for D_max, V57Gy, and V53Gy, respectively. BNS had smaller NVB reductions compared to UNS, and BSRM had similar NVB sparing to BNS but greater sparing of the penile bulb, corpus cavernosa, and rectum. All sparing techniques significantly reduced PTV coverage, and while achieving PTV V57Gy > 99% was not possible with NVB sparing, PTV V57Gy remained >95% for all plans. NVB sparing radiotherapy can significantly reduce dose to the NVB; however, there is a compromise of reduced PTV coverage with unilateral sparing allowing for the greatest reduction. These findings highlight the need for further clinical investigation to establish optimal NVB dose constraints that balance improved erectile function outcomes with effective tumor control.