Development and Validation of a Standardized Method for Contouring the Brachial Plexus: Preliminary Dosimetric Analysis Among Patients Treated With IMRT for Head-and-Neck Cancer

Purpose: Although Radiation Therapy Oncology Group protocols have proposed a limiting dose to the brachial plexus for patients undergoing intensity-modulated radiotherapy for head-and-neck cancer, essentially no recommendations exist for the delineation of this structure for treatment planning. Methods and Materials: Using anatomic texts, radiologic data, and magnetic resonance imaging, a standardized method for delineating the brachial plexus on 3-mm axial computed tomography images was devised. A neuroradiologist assisted with identification of the brachial plexus and adjacent structures. This organ at risk was then contoured on 10 consecutive patients undergoing intensity-modulated radiotherapy for head-and-neck cancer. Dose-volume histogram curves were generated by applying the proposed brachial plexus contour to the initial treatment plan. Results: The total dose to the planning target volume ranged from 60 to 70 Gy (median, 70). The mean brachial plexus volume was 33 ± 4 cm³ (range, 25.1-39.4). The mean irradiated volumes of the brachial plexus were 50 Gy (17 ± 3 cm³), 60 Gy (6 ± 3 cm³), 66 Gy (2 ± 1 cm³), 70 Gy (0 ± 1 cm³). The maximal dose to the brachial plexus was 69.9 Gy (range, 62.3-76.9) and was ≥60 Gy, ≥66 Gy, and ≥70 Gy in 100%, 70%, and 30% of patients, respectively. Conclusions: This technique provides a precise and accurate method for delineating the brachial plexus organ at risk on treatment planning computed tomography scans. Our dosimetric analysis suggest that for patients undergoing intensity-modulated radiotherapy for head-and-neck cancer, brachial plexus routinely receives doses in excess of historic and Radiation Therapy Oncology Group limits.