Assessment of Brachial Plexus Dose and Associated Toxicity in Nasopharyngeal Carcinoma Radiotherapy

Introduction Radiation plexopathy is known to depend on various parameters, and is rarely reported in head&neck cancers. While literature suggests dose constraints of 60-66 Gy, our study aimed to evaluate late brachial plexopathy after primary chemoradiotherapy for locally advanced nasopharyngeal carcinoma with IMRT, and determine the maximum tolerated dose. Methods Between May 2015 and March 2020, a retrospective cohort of 50 patients with a history of previously irradiated nasopharyngeal cancer was identified. All patients underwent definitive treatment using IMRT at recommended curative doses. Clinical and treatment-related characteristics were collected, and all cases were reviewed for symptoms of radiation-induced brachial plexopathy. Verbal informed consent was obtained from all patients prior to their inclusion in the study. Results Of the 50 patients, 98% received concurrent chemoradiotherapy. The mean age at treatment was 44 years. All patients received a minimum dose of ≥ 60 Gy. The median maximum dose to the BP (BPMax) was 73.57Gy (ranges: 61.47 Gy-82.64 Gy). Among patients with nodal involvement, 86% received a minimum dose of ≥ 66 Gy. A correlation study with N-category showed a significant increase in BPmax dose with increasing nodal stage. The median BPmax for patients with level III/IV lymph nodes (75.19 Gy) was higher than for those with level I/II involvement (69.19 Gy) (P = 0.0001). All patients had a minimum follow-up of two years, with a median follow-up duration of 36 months (ranges: 22 – 68 months). Five patients reported clinical symptoms of acute or late brachial plexopathy, but none had confirmation via MRI or electromyography. The analysis showed a significant difference in the dose received by 0.03 cm 3 of the volume across the different nodal stages (p < 0.05). As the nodal stage increases (N2, N3), the dose to this volume tends to exceed 70 Gy (p < 0.05). Dosimetric data related to the levels of nodal involvement revealed significant differences between groups (p < 0.05). Conclusion In this cohort of nasopharyngeal cancer patients treated with IMRT and concurrent chemoradiotherapy, Higher nodal stages, especially level III/IV, were associated with increased doses, but symptomatic plexopathy remained rare. These results support careful dose planning in advanced nodal disease.