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Dose Variation and Migration Rule of Parotid Gland During Intensity Modulated Radiation Therapy for Nasopharyngeal Carcinoma

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W Wang

W Wang*, H Yang, W Hu, X Wang, W Ding, Taizhou Hospital, Taizhou, Zhejiang

SU-E-CAMPUS-T-2 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To quantify the position of parotid gland (PG) and expound rule of volume and dose changes during the Course of intensity modulated radiation therapy (IMRT) in nasopharyngeal carcinoma patients (NPC).

Methods:A total of 141 CT images from 47 NPC patients (three images for each patient: acquired before treatment, at the 15th fraction and 25th fraction for each patient) who underwent radical IMRT were selected for this retrospective study. The distance between the lateral/medial aspects of PG and midline (DLM and DMM) at the level of odontoid process were measured. The parotid glands were divided into ipsilateral or contralateral base on with or without GTV contour. The variation between plan dose and actual dose were calculated.

Results:The volume reduction of both PG was more in the second half of treatment(SHT) than in the first half of treatment(FHT) (4.68±3.23 cc Vs. 2.46 ±4.55cc for the right PG and 5.96±2.99cc Vs. 2.06 ±2.99cc for the left PG). But, the V30 of bilateral PG decreased more significantly in FHT than SHT( 5.10±16.04% Vs. 1.14 ±21.54% for the right PG and 6.87±15.58% Vs. 0.81 ±15.94cc for the left PG). And the volume of GTVnx and GTVnd decreased more significantly in FHT than SHT(8.23±13.61cc Vs.3.30±8.09cc and 10.27±13.27 Vs.4.88±8.41cc). The DLM and DMM of contralateral PG shifted all medially and laterally both FHT and SHT, respectively. The DLM of ipsilateral PG shifted more medially in the FHT(3.83±1.53mm) than SHT(1.65±2.04mm), and the DMM of ipsilateral PG shifted medially in the FHT(0.80±2.96mm), but laterally in the SHT(2.19±3.96mm).

Conclusion:The reduction of GTV leads to the position change of the parotid gland, which appear more dramatic dose change of the parotid gland in the FHT than SHT.

Funding Support, Disclosures, and Conflict of Interest: This study was supported by Enze Foundation 2013 and had not Disclosures and Conflict of Interest

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