Anatomical Contouring Guidelines and Dosimetric Analysis of Brachial Plexus Segments for Patients Treated by Intensity-Modulated Radiotherapy for Head and Neck Cancer

Objective: Develop anatomical contouring guidelines for segments of the brachial plexus and determine whether specific regions receive higher doses to possibly further reduce the risk of nerve injury.

Materials and Methods: The study consisted of 10 patients with nasopharyngeal cancer treated by intensity-modulated radiotherapy (IMRT) to 70 Gy. Both CT and MRI were used to identify segments of the brachial plexus. The following contouring instructions were devised: (1) The roots extend from the lateral aspect of the spinal canal to the space between the anterior and middle scalenes. (2) The trunks run between the anterior and middle scalenes and course posterosuperior to the subclavian artery. (3) The divisions lie posterior to the clavicle and adjacent to the subclavian artery. (4) The cords form at the lateral border of the first rib. (5) The branches start at the lateral border of the pectoralis minor. A mixed model analysis of variance and Tukey's test compared differences in dose received by each segment.

Results: Each segment of the brachial plexus received significantly different maximum and mean doses, except for the maximum doses to the roots and trunks. The roots and trunks received the highest maximum (68 Gy) and mean (61 Gy) doses, respectively.

Conclusions: The delineation of brachial plexus segments is feasible using our proposed guidelines. Dosimetric analysis, suggesting that the roots and trunks are exposed to the highest levels of radiation during head and neck IMRT, may have important clinical implications and further refine treatment planning.