ESTRO 2021 Abstract Book

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ESTRO 2021

discriminative power. The calibration plot (Figure 1) showed unsatisfactory predictive accuracy.

Conclusion The nomogram proposed by Sun et al. should be used with great caution in stage II NPC patients in the IMRT era. The benefit of the addition of CCRT to IMRT remained controversial. T category, N category, and TN category were not predictive of OS. Future studies are awaited to identify high-risk subgroups who might benefit from CCRT. PO-1017 Outcome of proton therapy for salivary gland cancer and NTCP risk analysis for xerostomia/dysphagia N. Bachmann 1 , M. Walser 1 , C. Tully 1 , A. Köthe 1 , D. Leiser 1 , N. Bizzocchi 1 , D.C. Weber 1,2,3 1 Paul Scherrer Institute, Center for Proton Therapy, Villigen, Switzerland; 2 Inselspital, University Hospital Bern, Radiation Oncology, Bern, Switzerland; 3 University Hospital of Zürich, Radiation Oncology, Zürich, Switzerland Purpose or Objective Radiation therapy (RT) for salivary gland tumors (SGTs) is routinely performed either as definitive or postoperative treatment. However, the toxicities of such a treatment regime can be substantial, not limited to but including severe dysphagia and xerostomia. The dose distribution in pencil beam scanning proton therapy (PBSPT) allows for a minimization of dose delivered to organs at risk (OARs). This potentially results in less toxicity compared to photon RT. A risk calculation for specific toxicities is possible by the use of normal tissue complication probability (NTCP) models. Therefore, we aimed to report the clinical outcome after PBSPT and to perform an NTCP calculation of xerostomia and dysphagia through comparison of PBSPT and photon plans of patients with SGTs. Materials and Methods We retrospectively reviewed 26 patients who received PBSPT for SGT between 2009 and 2020 at our institute. Acute and late toxicities were recorded according to CTCAE v.4.1. Overall survival (OS), local control (LC) and distant control (DC) were estimated with the Kaplan-Meier method. An isotoxic volumetric modulated arc