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An Investigation of the Relationship Between Xerostomia and Parotid Gland Dose Based On CBCT

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j lou

J Lou1, C Ma2 , P Huang1 , J Chen2 , G Yu1 , Y Liang2 , H Li2 , Y Yin2 , D Li1* , (1) Shandong Normal University, Jinan, Shandong Province, China (2) Shandong Cancer Hospital Affiliated to Shandong University, Jinan, Shandong Province, China


SU-H4-GePD-I-3 (Sunday, July 30, 2017) 4:30 PM - 5:00 PM Room: Imaging ePoster Lounge

Purpose: To investigate the correlation between parotid gland (PG) dosimetric factors and xerostomia, and determine selection criteria to decrease PG |∆Dmean| for nasopharyngeal carcinoma (NPC).

Methods: Fifteen NPC patients treated with Intensity-modulated radiation therapy were enrolled in this study. Among these fifteen patients, five suffered from xerostomia and the rest had good prognosis. Each patient underwent weekly cone beam CT (CBCT) during the entire treatment. The deformable image registration of planning CT and weekly CBCT was used to overriding the Hounsfield Units (HU) value of the CBCT. The modified CBCT (mCBCT) was introduced to estimate the delivered dose. Beams from each patient’s treatment plan were applied to each weekly mCBCT to construct the dose distribution. Weekly doses were summed together to obtain the accumulated dose.

Results: Thirty PGs of 15 patients were analyzed. PG overdose was observed in twelve patients (12/15). PG overdose in patients with xerostomia has no clear increase. The increase of PG Dmean between planning and delivery was 1.6 Gy, ranged from -6.9 to +11.9 Gy. This difference was statistically significant (r=0.876, p=0.024). For patients with xerostomia, the planning dose was 32.7±2.8 Gy, the delivered dose was 34.3±4.2 Gy, and the overdose from planning was 1.7±2.3 Gy. For patients without xerostomia, the planning dose was 31.3±8.3 Gy, the delivered dose was 32.9±8.5 Gy, and the overdose from planning was 1.6±4.1 Gy. The Pearson correlation between |∆Dmean| and initial PG volume, initial planning PG Dmean, and dose deviation in the first fraction were .264 (p=.158), .098 (p=.294) and .678 (p=.000).

Conclusion: No statistically significant dosimetric difference was found between patients with and without xerostomia. Elder patients with high dose deviation in the first fraction are supposed to be given special attention.

Funding Support, Disclosures, and Conflict of Interest: This research was partially funded by the National Natural Science Foundation of China (NO.61471226), Natural Science Foundation for Distinguished Young Scholars of Shandong Province (NO. JQ201516).We also thank the supporting of Taishan scholar project of Shandong Province.

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