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

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

Clin Transl Radiat Oncol. 2021 Nov 14:32:29-34. doi: 10.1016/j.ctro.2021.11.005. eCollection 2022 Jan.

Authors

Affiliations

¹ Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, the Netherlands.
² Department of Oncological Urology, University Medical Center Utrecht, Utrecht, the Netherlands.
³ Department of Radiology, University Medical Center Utrecht, Utrecht, the Netherlands.
⁴ Department of Urology, St. Antonius Hospital, Nieuwegein, Utrecht, the Netherlands.
⁵ Imaging and Oncology Division, University Medical Center Utrecht, Utrecht, the Netherlands.
⁶ Utrecht University, Utrecht, the Netherlands.

Abstract

Background and purpose: 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. 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 methods: Four 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.

Results: Median 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.

Conclusion: We 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.

Keywords: CC, corpus cavernosum; CT, computed tomography; DSC, Dice similarity coefficient; EBRT, external beam radiation therapy; Erectile function sparing; GRRAS, Guidelines for Reporting Reliability and Agreement Studies; Gy, gray; IPA, internal pudendal artery; IQR, interquartile range; Internal pudendal artery (IPA); Interrater agreement; Localized prostate cancer (PCa); MRI, magnetic resonance imaging; MRgRT, magnetic resonance-guided adaptive radiotherapy; Magnetic resonance-guided radiotherapy (MRgRT); NCCN, National Comprehensive Cancer Network; NVB, neurovascular bundle; Neurovascular bundle (NVB); Neurovascular-sparing; OAR, organs at risk; PB, penile bulb; PCa, prostate cancer; PTV, planning target volume.