Neurovascular-Sparing MR-Guided Adaptive Radiotherapy in Prostate Cancer; Defining the Potential Population for Erectile Function-Sparing Treatment. Issue 7 (23rd May 2022) - Teunissen, Frederik R.
ABSTRACT: Background: Magnetic resonance-guided adaptive radiotherapy (MRgRT) enables neurovascular-sparing treatment for localized prostate cancer (PCa). The aim of this treatment is preservation of erectile function by sparing the neurovascular bundles, the internal pudendal arteries, the corpora cavernosa, and the penile bulb. Internal pudendal arteries, corpora cavernosa, and penile bulb sparing can generally be achieved in all patients, but NVB sparing can be challenging due to its proximity to the prostate and is therefore dependent on tumor location. PCa patients that have sufficient erectile function at baseline and favorable tumor characteristics might benefit from this treatment. Currently, it is unclear what proportion of patients are eligible for neurovascular-sparing treatment and to what extent this is technically feasible. Aim: To define the eligibility and technical feasibility for neurovascular-sparing MRgRT in intermediate-risk localized PCa patients. Methods: A consecutive series of men that received 5 × 7.25 gray (Gy) MRgRT for localized PCa were included. Baseline erectile function was assessed using the International Index of Erectile Function (IIEF)-5 questionnaire. Additionally, the ability of sparing the neurovascular bundles was assessed in all patients. Per neurovascular-sparing protocol, the dominant intraprostatic lesion with a 4 mm isotropic margin should receive 34.44 Gy in ≥ 99% of the volume (i.e., high-dose area). When the high-dose area directly borders or overlaps the NVB because of a dorsolateral position of the dominant intraprostatic lesion, sparing of the NVB was considered not feasible on that side. Outcomes: Patient-reported IIEF-5 baseline questionnaires and the technical feasibility of NVB sparing were assessed. Results: Of the 102 men that completed the IIEF-5 questionnaire at baseline, 49.0% of patients reported to have an IIEF-5 score of ≥ 17. In those patients, the NVB could technically have been spared bilaterally in 20.0% and unilaterally in 68.0%. Clinical Implications: Our findings define the potential population for neurovascular-sparing MRgRT for localized PCa and indicate the proportion in which the NVB can technically be spared. Strength & Limitations: The major strength of this study is the prospective collection of data. The limitations include that the neurovascular-sparing feasibility definition is based on pre-clinical planning data. Conclusion: A substantial group of 49.0% of patients in our study had mild or no erectile dysfunction at baseline. Of these patients, the NVB could technically have been spared bilaterally in 20.0% and unilaterally in 68.0% during MRgRT. Trials need to assess the effect of neurovascular-sparing MRgRT on erectile function.