Radiation dose to the brachial plexus in nasopharyngeal carcinoma treated with intensity-modulated radiation therapy: An increased risk of an excessive dose to the brachial plexus adjacent to gross nodal disease.

This retrospective study aimed to evaluate the dose to the brachial plexus in patients with nasopharyngeal carcinoma (NPC) treated with intensity-modulated radiation therapy (IMRT). Twenty-eight patients were selected and the brachial plexus was delineated retrospectively. Brachial plexus adjacent/not adjacent to nodes were defined and abbreviated as BPAN and BPNAN, respectively. Dose distribution was recalculated and a dose-volume histogram was generated based on the original treatment plan. The maximum dose to the left brachial plexus was 59.12-78.47 Gy, and the percentage of patients receiving the maximum dose exceeding 60, 66 and 70 Gy was 96.4, 57.1 and 25.0%, respectively; the maximum dose to the right brachial plexus was 59.74-80.31 Gy, and the percentage of patients exposed to a maximum dose exceeding 60, 66 and 70 Gy was 96.4, 64.3 and 39.3%, respectively. For the left brachial plexus, the maximum doses to the BPANs and the BPNANs were 72.84±3.91 and 64.81±3.47 Gy, respectively (p<0.001). For the right brachial plexus, the maximum doses to the BPANs and the BPNANs were 72.91±4.74 and 64.91±3.52 Gy, respectively (p<0.001). The difference between the left BPANs and the left BPNANs was statistically significant not only for V60 (3.60 vs. 1.01 cm(3), p=0.028) but also for V66 (1.26 vs. 0.11 cm(3), p=0.046). There were significant differences in V60 (3.68 vs. 1.16 cm(3), p<0.001) and V66 (1.83 vs. 1.23 cm(3), p=0.012) between the right BPANs and the right BPNANs. In conclusion, a large proportion of patients were exposed to the maximum dose to the brachial plexus exceeding the Radiation Therapy Oncology Group-recommended restraints when the brachial plexus was not outlined. The BPANs are at a significantly higher risk of receiving an excessive radiation dose when compared to the BPNANs. A further study is underway to test whether brachial plexus contouring assists in the dose reduction to the brachial plexus for IMRT optimization.