Toward Prostate Cancer Contouring Guidelines on Magnetic Resonance Imaging: Dominant Lesion Gross and Clinical Target Volume Coverage Via Accurate Histology Fusion

Authors

Eli Gibson, Robarts Research Institute
Glenn S. Bauman, The University of Western OntarioFollow
Cesare Romagnoli, The University of Western Ontario
Derek W. Cool, The University of Western Ontario
Matthew Bastian-Jordan, The University of Western Ontario
Zahra Kassam, The University of Western Ontario
Mena Gaed, Robarts Research Institute
Madeleine Moussa, The University of Western Ontario
José A. Gómez, The University of Western Ontario
Stephen E. Pautler, The University of Western Ontario
Joseph L. Chin, The University of Western Ontario
Cathie Crukley, Robarts Research Institute
Masoom A. Haider, Sunnybrook Health Sciences Centre
Aaron Fenster, Robarts Research Institute
Aaron D. Ward, The University of Western Ontario

Document Type

Article

Publication Date

9-1-2016

Journal

International Journal of Radiation Oncology Biology Physics

Volume

96

Issue

1

First Page

188

Last Page

196

URL with Digital Object Identifier

10.1016/j.ijrobp.2016.04.018

Abstract

Purpose Defining prostate cancer (PCa) lesion clinical target volumes (CTVs) for multiparametric magnetic resonance imaging (mpMRI) could support focal boosting or treatment to improve outcomes or lower morbidity, necessitating appropriate CTV margins for mpMRI-defined gross tumor volumes (GTVs). This study aimed to identify CTV margins yielding 95% coverage of PCa tumors for prospective cases with high likelihood. Methods and Materials Twenty-five men with biopsy-confirmed clinical stage T1 or T2 PCa underwent pre-prostatectomy mpMRI, yielding T2-weighted, dynamic contrast-enhanced, and apparent diffusion coefficient images. Digitized whole-mount histology was contoured and registered to mpMRI scans (error ≤2 mm). Four observers contoured lesion GTVs on each mpMRI scan. CTVs were defined by isotropic and anisotropic expansion from these GTVs and from multiparametric (unioned) GTVs from 2 to 3 scans. Histologic coverage (proportions of tumor area on co-registered histology inside the CTV, measured for Gleason scores [GSs] ≥6 and ≥7) and prostate sparing (proportions of prostate volume outside the CTV) were measured. Nonparametric histologic-coverage prediction intervals defined minimal margins yielding 95% coverage for prospective cases with 78% to 92% likelihood. Results On analysis of 72 true-positive tumor detections, 95% coverage margins were 9 to 11 mm (GS ≥ 6) and 8 to 10 mm (GS ≥ 7) for single-sequence GTVs and were 8 mm (GS ≥ 6) and 6 mm (GS ≥ 7) for 3-sequence GTVs, yielding CTVs that spared 47% to 81% of prostate tissue for the majority of tumors. Inclusion of T2-weighted contours increased sparing for multiparametric CTVs with 95% coverage margins for GS ≥6, and inclusion of dynamic contrast-enhanced contours increased sparing for GS ≥7. Anisotropic 95% coverage margins increased the sparing proportions to 71% to 86%. Conclusions Multiparametric magnetic resonance imaging–defined GTVs expanded by appropriate margins may support focal boosting or treatment of PCa; however, these margins, accounting for interobserver and intertumoral variability, may preclude highly conformal CTVs. Multiparametric GTVs and anisotropic margins may reduce the required margins and improve prostate sparing.