Adaptive magnetic resonance-guided neurovascular-sparing radiotherapy for preservation of erectile function in prostate cancer patients

Abstract

Background and purpose: Erectile dysfunction is a common adverse effect of external beam radiation therapy for localized prostate cancer (PCa), likely as a result of damage to neural and vascular tissue. Magnetic resonance-guided online adaptive radiotherapy (MRgRT) enables high-resolution MR imaging and paves the way for neurovascular-sparing approaches, potentially lowering erectile dysfunction after radiotherapy for PCa. The aim of this study was to assess the planning feasibility of neurovascular-sparing MRgRT for localized PCa.

Materials and methods: Twenty consecutive localized PCa patients, treated with standard 5×7.25 Gy MRgRT, were included. For these patients, neurovascular-sparing 5×7.25 Gy MRgRT plans were generated. Dose constraints for the neurovascular bundle (NVB), the internal pudendal artery (IPA), the corpus cavernosum (CC), and the penile bulb (PB) were established. Doses to regions of interest were compared between the neurovascular-sparing plans and the standard clinical pre-treatment plans.

Results: Neurovascular-sparing constraints for the CC, and PB were met in all 20 patients. For the IPA, constraints were met in 19 (95%) patients bilaterally and 1 (5%) patient unilaterally. Constraints for the NVB were met in 8 (40%) patients bilaterally, in 8 (40%) patients unilaterally, and were not met in 4 (20%) patients. NVB constraints were not met when gross tumor volume (GTV) was located dorsolaterally in the prostate. Dose to the NVB, IPA, and CC was significantly lower in the neurovascular-sparing plans.

Conclusions: Neurovascular-sparing MRgRT for localized PCa is feasible in the planning setting. The extent of NVB sparing largely depends on the patient's GTV location in relation to the NVB.

Keywords: Erectile dysfunction; Erectile function sparing; Localized prostate cancer; MR-Linac; MRgRT; Neurovascular-sparing.

Fig. 1

Example of the contours of the neurovascular bundle of a single study patient. Abbreviations: NVB = neurovascular bundle. A: transverse plane; B: sagittal plane; C: coronal plane.

Fig. 2

Example of neurovascular-sparing 5×7.25 Gy MRgRT plan dose distribution in 3 patients representing the 3 neurovascular bundle-sparing scenarios. Abbreviations: GTV = gross target volume; PTV = planning target volume; NVB = neurovascular bundle; IPA = internal pudendal artery. A: NVB constraint met bilaterally (40% of patients); B: NVB constraint met unilaterally (40% of patients); C: NVB constraint not met (20% of patients).

Fig. 3

Population-median DVH curves for the neurovascular-sparing 5×7.25 Gy MRgRT plans (n = 20) and the standard 5×7.25 Gy MRgRT plans (n = 20). Abbreviations: PTV = planning target volume; GTV = gross tumor volume; NVB = neurovascular bundle; NS = neurovascular-sparing; IPA = internal pudendal artery; CC = corpus cavernosum; PB = penile bulb. Femur, NVB, IPA, and CC: n = 40 (left and right side are combined); NVB constraint met in NS plan: n = 24; NVB constraint not met in NS plan: n = 16. *Standard 5×7.25 Gy MRgRT dose prescription to PTV was 34.4 Gy in ≥ 99.0% (no separate clinical target volume or GTV + 4 mm prescription). Dose constraints for bladder, rectum, sphincter, and femur were identical for the neurovascular-sparing and standard plans. Population-median DVH curves with 95% confidence intervals are displayed in Supplementary Material 2.