Dosimetric analysis and clinical outcomes of brachial plexus as an organ-at-risk in head-and-neck cancer patients treated with intensity-modulated radiotherapy

Objectives: To document the dose received by brachial plexus (BP) in patients treated with intensity-modulated radiotherapy (IMRT) for head-and-neck squamous cell carcinoma (HNSCC) and report the incidence of brachial plexopathy. Methods: Newly diagnosed patients of HNSCC treated with radical or adjuvant IMRT were included in this retrospective study. No dosimetric constraints were applied for BP maximum dose equivalent dose (EQD2 α/β = 3). Patients with minimum 6-month follow-up were included and patients with suspicion of plexopathy were evaluated further. Results: Sixty-seven patients were eligible and 127 BP were analyzed. The mean BP maximum dose (BP_max) was 62.4 Gy (+6.9), while mean BP volume was 28.1 cc (+4.1). Proportion of patients receiving BP_max >66 and >70 Gy were 34.7% and 14.2%. The mean BP_max for T4 tumors was significantly higher than T1 tumors (65 vs. 57.5 Gy, P = 0.005) but when adjusted for N-category, T-category was not independently significant in accounting for BP_max >66 or >70 Gy. Mean BP_max for N0 versus N2+ was 59.8 versus 65.6 Gy (P = 0.0001) and N1 versus N2+ was 61.6 versus 65.6 Gy (P = 0.018). After adjusting for T-category, patients with N2+ had a mean 4.2 Gy higher BP_max than N0-N1 (P = 0.0001). Stage III-IV patients had a mean six Gy higher BP_max doses than Stage I-II disease (P = 0.0001). With a median follow-up of 28 months (interquartile range 16-42), no patient had brachial plexopathy. Conclusion: Clinically significant plexopathy was not seen in spite of majority having over 2-years follow-up and a third of patients having dose above the recommended tolerance. Only nodal category independently influenced dose to the brachial plexii.