ESTRO 2021 Abstract Book

S282

ESTRO 2021

p=0.038). Use of cisplatin predicted early high frequency (HF) significant SHNL (OR 5.88; 95% CI [2.16, 16.03]; p=0.001). Eighty-nine ears were analyzed for late SNHL. Median follow-up was 36-40 months. Significant progression in SNHL was evident in all frequencies (all p<0.05; Table 1). Both cochlear dose and cisplatin dose were significant independent predictors for late BCT∆4kHz, as well as younger age and better pre-treatment hearing (Table 2). Every 10Gy increase in cochlear Dmean resulted in 7dB BCT∆4kHz (B=0.007 95% CI [0.003, 0.012]; p=0.002). Use of cisplatin was associated with late HF significant SNHL (OR 8.91 (95% CI [2.11-35.6]; p<0.001). In the subgroup of cCRT and iCRT patients, no cisplatin dose dependent ototoxicity was demonstrated. Risk of severe (≥30dB) late HF SNHL increased from 18% to 30% when cochlear constraint was relaxed from 37Gy to 50Gy. No patients in RT alone group developed severe late HF-SNHL (Mean cochlear Dmean 39.6Gy; range 29.4-48.8Gy).

Conclusion SNHL in NPC survivors remained prevalent in modern era. Cochlear radiation dose and cisplatin use showed differential and independent ototoxicity on early and late SNHL in contemporary treatment paradigm. Cochlear dose-dependent ototoxicity was demonstrated. Higher cisplatin dose was not associated with additional ototoxicity. Cochlear dose constraint should be as low as reasonably achievable, especially when cisplatin was part of the treatment. PH-0384 Risk of stroke in nasopharyngeal cancer survivors: a national registry-based,population cohort study T.H. Tan 1 1 National University Cancer Institute, Singapore, Radiation Oncology, Singapore, Singapore Purpose or Objective We aim to determine the risk of stroke and death within 30 days post stroke in nasopharyngeal cancer (NPC) survivors. Materials and Methods We conducted a population-based cohort study of patients diagnosed with NPC from Jan 1, 2005 to Dec 31, 2017. Using the cancer and stroke disease registries and the Singapore general population as the reference population, we report the age-standardized incidence risk differences (SIRDs) ratios (SIRs) and the cumulative incidence of stroke and the standardized mortality risk differences (SMRDs) and ratios (SMRs) for all causes of death within 30 days post stroke for NPC survivors. Results At a median follow up of 48.4 months (IQR 19.8 – 92.9) for 3849 patients diagnosed with NPC, 96 patients developed stroke. The overall SIRD and SIR for stroke was 3.12 (95% CI 2.09 – 4.15) and 2.54 (95% CI 2.06 – 3.10) respectively. The SIRD was highest for the age group 70 – 79 years old (8.84 cases per 1000 person-years (PY); 0.46 – 17.21) while the SIR was highest for the age group 30 – 39 years old (16.41; 6.02 – 35.72). The SIRD and SIR for stage 1 disease was (6.96 cases per 1000 PY; 2.16 – 11.77) and (4.15; 2.27 – 6.96) respectively. The SMRD and SMR for all cause deaths within 30 days of stroke was (3.20 cases per 100 persons; -3.87 – 10.28) and (1.34; 0.69 – 2.35) respectively. Conclusion The overall risk of stroke was markedly elevated in survivors of NPC, especially in Stage 1 disease when compared to the general population. The risk of death within 30 days of stroke was not significantly higher for NPC survivors.

PH-0385 Modulations of salivary microbiota during radiotherapy for head and neck cancer E. Gioscio 1 , N.A. Iacovelli 2 , R. Ingargiola 2 , A. Cavallo 3 , L. De Cecco 4 , S. Alfieri 5 , P. Bossi 5 , N. Facchinetti 2 , M.S.