Superficial parotid lobe-sparing delineation approach: a better method of dose optimization to protect the parotid gland in intensity-modulated radiotherapy for nasopharyngeal carcinoma

Purpose We used a superficial parotid lobe-sparing delineation approach for dose optimization with better protection for the parotid glands in intensity-modulated radiotherapy (IMRT) for nasopharyngeal carcinoma (NPC) patients. Methods Compared with traditional contouring of the entire parotid glands as organs at risk (OARS) in IMRT for NPC, we used a superficial parotid lobe-sparing delineation approach of contouring the superficial parotid lobes as oars. Changes in dose to the parotid glands, the targets, and other OARS were evaluated. Results The mean dose to the parotid glands overall decreased by more than 4 Gy in the test plans. Impressively, the mean dose to the superficial parotid lobes in the test plans was not more than 30 Gy, regardless of clinical stage. In T1-3 NPC patients, the dose distributions for targets were not significantly different in the control plans and the test plans. However, for some T4 patients, the dose distributions for targets and brainstem in the test plans could not meet clinical requirements. Conclusions The superficial parotid lobe-sparing delineation approach can significantly lower the mean dose to the entire parotid and to the superficial parotid lobe in T1-3 NPC patients, which would be expected to result in less xerostomia and better quality of life for those patients.