ESTRO 2021 Abstract Book

S849

ESTRO 2021

Materials and Methods Retrospective descriptive study of 36 patients diagnosed with head and neck cancer treated with RT ± QT between November 2018 and December 2020. During treatment, all patients received oral L-glutamine, 14g every 8 hours. The radiation oncologist evaluated weekly the degree of mucositis. The CTCAE v5.0 scale was used to assess acute toxicity. Results Treatment with glutamine was initiated at a median of 16 days prior to RT ± QT. With a median follow-up of 14 months, we analyzed our sample constituted by 75% males and 25% females, mean age was 63 years. The tumor locations by frequency were larynx 26.5%, oral cavity 23.5%, unknown origin with cervical lymph node metastases 17.6%, nasopharynx 11.8%, oropharynx 8.8% and parotid 8.8% . Locally advanced tumors represented 83.34% of our group. All patients received intensity modulated radiotherapy (IMRT), 62.9% radical treatment (69.96Gy) and 37.1% adjuvant treatment (60-66Gy). Cervical lymph node levels were irradiated in 94.4% of the patients and, within these, 88.2% bilaterally. The 58.3% received concomitant QT (cisplatin or cetuximab). Mucositis was observed in the oral cavity, larynx and/or pharynx at completion of RT ± QT: 5.7% G0, 45.7% G1, 31.4% G2, 17.1% G3. At first month: 19.4% G0, 47.2% G1, 30.6% G2, 2.8% G4. At three months we did not observe any severe mucositis grade (G3, G4), highlighting that 60% of them presented G0. At 6 months only a 15.4% still presented mucositis G1. We noticed that 11% of the patients continued showing mild dysphagia a year after finishing antineoplastic treatment. Conclusion Oral glutamine is being investigated to prevent oral and esophageal mucositis secondary to antineoplastic therapies. The administration of glutamine during treatment with RT ± QT in head and neck cancer patients could reduce the duration and severity of mucositis. This results may improve adherence to treatment and quality of life of our patients, although future studies are needed to support these results. Purpose or Objective Definitive chemoradiotherapy (CRT) is standard of care for nasopharyngeal carcinoma. Due to the tumor localization and concomitant platinum-based chemotherapy, hearing impairment is a frequent complication, without defined dose-threshold. The widely accepted QUANTEC constraint for the cochlear tolerance dose of 45 Gy is associated with an expected complication rate of <30%. In this study, we aimed to achieve the maximum possible cochleae sparing. Materials and Methods Treatment plans of 20 patients, treated with CRT (6 IMRT and 14 VMAT) based on the QUANTEC organs-at-risk constraints were investigated. The cochleae were re-delineated independently by two radiation oncologists, whereas target volumes and other organs at risk (OARs) were not changed. The initial plans, aiming to a mean cochlea dose <45 Gy, were re-optimized with VMAT, using 2-2.5 arcs without compromising the dose coverage of the target volume. Mean cochlea dose, PTV coverage, Homogeneity Index (HI), Conformity Index (CI) and dose to other OAR were compared to the reference plans. NTCP models were performed for tinnitus and hearing loss. Wilcoxon signed-rank test was used to evaluate differences, a p-value <0.05 was considered significant. Results The re-optimized plans achieved a statistically significant lower dose for both cochleae (median dose for left and right 14.97 Gy and 18.47 Gy vs. 24.09 Gy and 26.05 Gy respectively, p<0.001) compared to the reference plans, without compromising other plan quality parameters. The median NTCP for tinnitus of the most exposed sites was 11.3% (range: 3.52 – 91.1%) for the original plans, compared to 4.60% (range: 1.46 – 90.1%) for the re- optimized plans (p<0.001). For hearing loss, the median NTCP of the most exposed sites could be improved from 0.03% (range: 0 – 99.0%) to 0.00% (range: 0 – 98.5%, p<0.001). Conclusion A significantly improved cochlea sparing beyond current QUANTEC constraints is feasible without compromising the PTV dose coverage in nasopharyngeal carcinoma patients treated with VMAT. Based on NTCP analyses, such an exposure would reduce the probability of both tinnitus and hearing loss significantly. Not a single quality parameter was inferior in the cochlea-optimized plans, while the median number of monitor units and the beam-on time of the optimized plans were reasonable. These findings highlight the practicability of intensive cochlea sparing for daily routine. As there appears to be no threshold for hearing toxicity after CRT, this should be considered for future treatment planning. The clinical effect of this optimization should be evaluated in the future prospective trials. PO-1020 Cochlea sparing optimized radiotherapy for nasopharyngeal carcinoma E. Vu 1 , E. Lamaj 1 , J. van Timmeren 1 , C. Leonardi 1 , I. Pytko 1 , L. Marc 1 , M. Guckenberger 1 , P. Balermpas 1 1 University Hospital Zurich, Radiation Oncology, Zurich, Switzerland