Abstract
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. 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. 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. 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.
Highlights
MethodsCompared with traditional contouring of the entire parotid glands as organs at risk in imrt for npc, we used a superficial parotid lobe–sparing delineation approach of contouring the superficial parotid lobes as oars
The mean dose to the parotid glands overall decreased by more than 4 Gy in the test plans
The mean dose to the superficial parotid lobes in the test plans was not more than 30 Gy, regardless of clinical stage
Summary
From August 2010 to January 2011, our study, conducted at the Nasopharyngeal Carcinoma Department of Sun Yat-sen University Cancer Center, enrolled 31 newly diagnosed patients with pathology-proven npc. Table i shows the characteristics of the study patients. 2.2 Delineation of Superficial and Deep Lobes of Parotid Glands. In addition to each entire parotid gland, the superficial and deep lobes of the parotids were outlined on every computed tomography slice. The parotid gland is usually divided into a superficial lobe and a deep lobe by the posterior border of the mandible or the facial nerve that threads through it. The superficial lobe covers the front part of masseter muscle’s posterior border anteriorly. We drew the borders of the superficial and deep lobes of the parotids using the facial nerve process and anatomy (Figure 1)
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