Interrater agreement of contouring of the neurovascular bundles and internal pudendal arteries in neurovascular-sparing magnetic resonance-guided radiotherapy for localized prostate cancer

F.R Teunissen,R.C Wortel,F.J Wessels,A Claes,S.M.G Van De Pol,M.J.A Rasing,R.P Meijer,H.H.E Van Melick,J.C.J De Boer,H.M Verkooijen,J.R.N Van Der Voort Van Zyp

doi:10.1016/j.ctro.2021.11.005

Abstract

Background and purposeRadiation damage to neural and vascular tissue, such as the neurovascular bundles (NVBs) and internal pudendal arteries (IPAs), during radiotherapy for prostate cancer (PCa) may cause erectile dysfunction. Neurovascular-sparing magnetic resonance-guided adaptive radiotherapy (MRgRT) aims to preserve erectile function after treatment. However, the NVBs and IPAs are not routinely contoured in current radiotherapy practice. Before neurovascular-sparing MRgRT for PCa can be implemented, the interrater agreement of the contouring of the NVBs and IPAs on pre-treatment MRI needs to be assessed. Materials and methodsFour radiation oncologists independently contoured the prostate, NVB, and IPA in an unselected consecutive series of 15 PCa patients, on pre-treatment MRI. Dice similarity coefficients (DSCs) for pairwise interrater agreement of contours were calculated. Additionally, the DCS of a subset of the inferior half of the NVB contours (i.e. approximately prostate midgland to apex level) was calculated. ResultsMedian overall interrater DSC for the left and right NVB was 0.60 (IQR: 0.54 – 0.68) and 0.61 (IQR: 0.53 – 0.69) respectively and for the left and right IPA 0.59 (IQR: 0.53 – 0.64) and 0.59 (IQR: 0.52 – 0.64) respectively. Median overall interrater DSC for the inferior half of the left NVB was 0.67 (IQR: 0.58 – 0.74) and 0.67 (IQR: 0.61 – 0.71) for the right NVB. ConclusionWe found that the interrater agreement for the contouring of the NVB and IPA improved with enhancement of the MRI sequence as well as further training of the raters. The agreement was best in the subset of the inferior half of the NVB, where a good agreement is clinically most relevant for neurovascular-sparing MRgRT for PCa.

Highlights

Erectile dysfunction is a common adverse effect of external beam radiation therapy (EBRT) for localized prostate cancer (PCa) [1]
The prostate is located adjacent to neural structures and in close proximity to vascular structures responsible for erectile function such as the neuro vascular bundles (NVBs), the internal pudendal arteries (IPAs), the corpora cavernosa (CCs), and the penile bulb (PB) [2]
Assessment of the interrater agreement of the contours of the neurovascular bundle (NVB) and the IPA on pre-treatment Magnetic Resonance Imaging (MRI) resulted in a median overall Dice similarity coefficient (DSC) of 0.60 (IQR: 0.54 – 0.68) and 0.61 (IQR: 0.53 – 0.69) for the left and right NVB respectively and 0.59 (IQR: 0.53 – 0.64) for the left and 0.59 (IQR: 0.52 – 0.64) for the right IPA

Summary

Introduction

Erectile dysfunction is a common adverse effect of external beam radiation therapy (EBRT) for localized prostate cancer (PCa) [1]. Radiation damage to neural and vascular tissue, such as the neurovascular bundles (NVBs) and internal pudendal arteries (IPAs), during radiotherapy for prostate cancer (PCa) may cause erectile dysfunction. Before neurovascular-sparing MRgRT for PCa can be implemented, the interrater agreement of the contouring of the NVBs and IPAs on pre-treatment MRI needs to be assessed. Materials and methods: Four radiation oncologists independently contoured the prostate, NVB, and IPA in an unselected consecutive series of 15 PCa patients, on pre-treatment MRI. The agreement was best in the subset of the inferior half of the NVB, where a good agreement is clinically most relevant for neurovascular-sparing MRgRT for PCa

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Conclusion