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Treatment Plan Quality Improvement in Head and Neck Radiotherapy Based On New Dose Constraints for the Contralateral (parotid and Submandibular) Glands

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M Kostich

M Kostich*, K Hedrick , S Sutton , B Motley , D Fried , B Chera , S Das , R Adams , P Mavroidis , Univ North Carolina, Chapel Hill, NC


SU-I-GPD-T-405 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To investigate the possibility of reducing the dose to contralateral glands (parotid and submandibular) and superior pharyngeal constrictors after re-optimizing VMAT plans of head and neck cancer patients using newly derived dose constraints.

Methods: Fifteen patients with oropharyngeal squamous cell carcinoma, are analyzed. Of these patients, ten reported xerostomia at 6 and 12 months post radiotherapy based on the PRO-CTCAE scoring system. The original plans were prescribed to 60 Gy using intensity modulated radiotherapy. Dosimetric constraints had been used for the contralateral salivary glands (e.g. mean dose to the contralateral parotid <26Gy). Using newly derived dosimetric constraints for salivary glands and pharyngeal constrictors and the input from the software PlanIQ, the plans of those patients were re-optimized keeping the same dosimetric constraints for the rest of the targets and organs at risk. Subsequently, the D99, D1 and average doses were calculated for each target and OAR in each original and re-optimized plan. The doses of the respective plans were compared between each other and against the clinical goals.

Results: Based on the results of the first four patients, the dosimetric plan evaluation shows that the re-optimized plans give better dosimetric results than the original plans. Specifically, the average differences (new minus original) in the mean dose in the contralateral glands and contralateral parotid alone were -8.5±5.6Gy and -10.3±6.0%, respectively. The reduction in the D99 (minimum dose) of the targets ranged from -0.6 to -1.4 Gy. The differences in the rest of the OARs were small.

Conclusion: The results of the dosimetric analysis indicate that the plans that were optimized with the new dosimetric constraints for the contralateral salivary glands achieved significantly lower doses to those structures without affecting the coverage of the targets or increasing the dose to the rest of the primary OARs beyond their clinical dose constraints.

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