A radiation therapy contouring atlas for delineation of the level I-II axilla in the prone position: a single institution experience.
Academic Article
Overview
abstract
PURPOSE: With transition from supine to prone, tenting of the pectoralis major occurs displacing the muscle from the chest wall and shifting the level I-II axillary spaces. For patients whom we aim to treat the level I-II axilla using the prone technique, accurate delineation of these nodal regions is necessary. While different consensus guidelines exist for delineation of nodal anatomy supine, to our knowledge there are no contouring guidelines in the prone position that account for this change in nodal anatomy. METHODS AND MATERIALS: The level I-II nodal contours from the Radiation Therapy Oncology Group (RTOG) breast cancer supine atlas were adapted for prone position by two radiation oncologists and a breast radiologist based on anatomic changes observed from supine to prone positioning on preoperative diagnostic imaging. Forty-three patients from a single institution treated with prone high tangents from 2012 to 2018 were identified as representative cases to delineate the revised level I-II axilla on non-contrast computed tomography (CT) scans obtained during radiation simulation. The revised nodal contours were reviewed by an expanded expert multidisciplinary panel including breast radiologists, radiation oncologists, and surgical oncologists for consistency and reproducibility. RESULTS: Consensus was achieved among the panel in order to create modifications from the RTOG breast atlas for CT-based contouring of the level I-II axilla prone using bone, muscle and skin as landmarks. This atlas provides representative examples and accompanying descriptions for the changes described to the caudal and anterior border of level II, and the anterior, posterior, medial and lateral border of level I. A step-by-step guide is provided for properly identifying the revised anterior border of the level I axilla. CONCLUSIONS: The adaptations to the RTOG breast cancer atlas for prone positioning will enable radiation oncologists to more accurately target the level I-II axilla when the axilla is a target in addition to the breast.
