ESTRO 2022 - Abstract Book

S926

Abstract book

ESTRO 2022

initiation, 100 (46%) were treated with antibiotics during (C)RT. The most frequent indication of antibiotics prescription was single-shot antibiotic prophylaxis before port catheter implantation (n=132). Peritherapeutic antibiotics administration significantly worsened both PFS (median 10 vs. 24 months, p <0.05) and OS (median 26 vs. 36 months, p <0.05), while pretherapeutic usage had no effect. This effect was found pronounced in the cohort of patients aged <75 years (median PFS 10 vs. 44 months, p <0.05, and median OS 26 vs. 54 months, p <0.05), whereas there was no significant difference among older patients ( ≥ 75 years). Conclusion Peri- but not pretherapeutic antibiotic usage was associated with reduced PFS and OS in HNSCC patients receiving (C)RT. In the future, microbiome analyses may help to better understand the mechanisms underlying the observed effects of antibiotic use in HNSCC patients receiving (C)RT.

PO-1090 Late toxicity-related symptoms and fraction dose affect decision regret in HNC patients

M. Koeksal 1 , L. Saur 1 , C. Dejonckheere 1 , F. Far 2 , S. Strieth 3 , F.A. Giordano 1

1 University Hospital, Department of Radiation Oncology, Bonn, Germany; 2 University Hospital, Department of Oral, Maxillofacial and Plastic Surgery, Bonn, Germany; 3 University Hospital, Oral, Maxillofacial and Plastic Surgery, Bonn, Germany Purpose or Objective Decision regret reflects patient satisfaction with treatment choice and is greatly associated with overall quality of life. This study aims to identify patient and therapy characteristics and late toxicity-related symptoms of adjuvant radiotherapy resulting in decision regret in patients with head and neck cancer. Materials and Methods In this cross-sectional study, patients completed a questionnaire during a telephone interview, including the Decision Regret Scale (DRS) and several symptom-related items. Results 108 patients were included. After adjuvant radiotherapy, 40.5% reported no regret, 30.1% showed mild regret, and 29.4% moderate to strong regret. Along with a lower single fraction dose, the severity of multiple late toxicity-related symptoms correlated strongly with decision regret. The strongest correlations were with limitations in everyday life and pain. Patients experiencing emotional distress scored higher on the DRS. Conclusion Based on these findings, it is recommended that patients undergoing adjuvant radiation receive psychosocial support and adequate treatment of late toxicity-related symptoms. When confronted with different therapeutic options, radiotherapy with a higher single fraction dose (i.e., hypofractionation) is preferred, due to the subsequent reduced regret as well as emotional distress experienced by patients. 1 KLES Dr Prabhakar Kore Hospital and MRC, Radiation Oncology, Belgaum, India; 2 KLES Dr Prabhakar Kore Hospital and MRC, Medical Oncology, Belgaum, India Purpose or Objective Precision radiotherapy is the essence of modern day treatment for head and neck cancers, which utilizes accurate delineation of target volumes for accurate dose delivery. Volumetric measurement of the tumour depicts the number of clonogenic cells present and thus can predict the treatment outcomes. This volume defined as GTV in the routine radiotherapy planning has been limited for mere contouring purpose and its potential as prognostic factor is less explored. Materials and Methods The data of 150 patients of head and neck cancer undergoing IMRT and weekly cisplatin (40mg/m 2 ) between April 2015 and December 2019 at our Institution were retrospectively analyzed. GTVp (primary), GTVn (node) and GTVcombo (primary + node) contoured on eclipse treatment planning system version 13 were used to generate the volumetric parameters. The prognostic value of these tumour volumes with respect to treatment outcomes was analyzed using SPSS version 16. Results Median age at presentation was 58.5 years. 73% were male. 42.6%, 36.6% and 20.6% had Oropharynx, Hypopharynx and Larynx primaries respectively. 16%, 62%, 19% and 3% had T2, T3, T4a and T4b disease; 32%, 23%, 41% and 3% had N0, N1, N2 and N3 disease respectively. 50% had stage III disease. Mean GTVp was 44.5cc (range 2.4 – 169.3), mean GTVn was 13.4cc (range 0 – 156.1) and mean GTVcombo was 57.9cc (range 2.4 – 227.2). All patients completed 70Gy in 33-35 fractions; median chemotherapy cycles were 6. 64% had complete response (CR). Comparison of GTV with CR rates was done using Pearson Chi-Square test, GTVp <30cc had better CR rates than GTVp >30cc (82.6% v/s 51.9%, p=0.00), GTVn <4cc had better CR rates than GTVn >4cc (74% v/s 58.4%, p=0.04) and GTVcombo <50cc had better CR rates than GTVcombo >50cc (81.5% v/s 47.8%, p=0.00). At median follow up of 21.4 months (range 3 – 71) OS was 60% and median OS was 32.3 months. PO-1091 GTV as prognostic marker in head and neck cancer - Time to redefine GTV beyond contouring I. Ahmed 1 , S. Krishnamurthy 1 , R. Bhise 2 , R. Sagar 1 , B. Balaji 1 , A. Devi 1 , V. Banu 1