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Reduced Expected Risk for Xerostomia After Radiotherapy for Head and Neck Tumors Based On New Dose Constraints for the Contralateral (parotid and Submandibular) Glands

P Mavroidis

P Mavroidis*, M Kostich , K Hedrick , B Chera , D Fried , L Marks , S Das , University of North Carolina, Chapel Hill, NC


SU-I-GPD-T-249 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To investigate the possibility of reducing the reported rates of xerostomia by using newly derived dose constraints for the contralateral parotid and submandibular glands during the optimization of the VMAT plans of patients with head and neck tumors.

Methods: Ten patients with oropharyngeal squamous cell carcinoma, who received de-intensified 60Gy intensity modulated radiotherapy are analyzed. Most of the patients reported xerostomia 12 months post radiotherapy based on the PRO-CTCAE scoring system. In the original plans, dosimetric constraints had been used for the contralateral parotid alone. Using newly derived dosimetric constraints for salivary glands and the input from the software PlanIQ, the plans of those patients were re-optimized using the same dosimetric constraints for the rest of the targets and organs at risk. Subsequently, the TCP and NTCP values of the different targets and organs at risk (OAR) of the two sets of plans were calculated and compared along with the P+ index, which is the probability of achieving tumor control without normal tissue complications.

Results: Based on the results of the first four patients, the radiobiological plan evaluation shows that the re-optimized plans give better results than the original plans in terms of expected clinical outcome. Specifically, the average difference (new minus original) in P+=15.3±9.9%, total TCP=0.6±1.7% and total NTCP=-15.8±10.3%. The difference observed mainly stems from the lower NTCP values of the contralateral parotid and submandibular glands (combined) (34.7% vs. 52.9%). The TCP and NTCP differences to the rest of the targets and OARs ranged between 0.0% to 2.4%.

Conclusion: The findings of the analysis indicate that the plans that were optimized with the new dosimetric constraints for the salivary glands achieved equivalent expected tumor control with significantly lower risk for xerostomia associated to the contralateral parotid and submandibular glands, while preserving the sparing of the primary OARs.

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