ESTRO 2021 Abstract Book

S715

ESTRO 2021

In the resected PT patients, the expected proportion of patients with a TTB≥60 was 29.7% for photon and 20.8% for proton RT. After resection, only one out of 14 patients (7.1%) had an TTB≥60 ((p=0.051), compared to the expected proportion based on the photon plans). On average, the observed post-operative TTB was 15 (SEM: 6) after PT, compared to the historical photon cohort in which the observed post-operative TTB was 45 (SEM: 5) . Hospital and ICU stay were also reduced by PT compared to the photon cohort; 12.7 (SEM 1.4) vs. 20.0 (SEM 1.2) and 1.9 days (SEM 0.4) vs. 4.9 (SEM 0.6), resulting in an average cost reduction of about 10,000 euro per patient. Follow up will continuously be updated in our dynamic database. Conclusion In the neo-adjuvant setting, the first results indicate that proton-based nCRT reduces the post-operative TTB compared to historic photon-based nCRT. Moreover, there seems to be a trend towards reduced hospital and ICU stay. PD-0879 Clinical outcomes of neoadjuvant chemoradiation in oesophageal cancer K.S. Chufal 1 , I. Ahmad 1 , A.A. Miller 2 , R. Bajpai 3 , R.L. Chowdhary 1 , A.K. Pahuja 1 , J.S. Sethi 1 , M. Gairola 1 1 Rajiv Gandhi Cancer Institute & Research Centre, Radiation Oncology, New Delhi, India; 2 Illawarra Cancer Care Centre, Radiation Oncology, Wollongong, Australia; 3 Keele University, School of Medicine, Staffordshire, United Kingdom Purpose or Objective To perform an institutional audit of treatment outcomes in patients undergoing neoadjuvant concurrent chemoradiotherapy (NA-CRT) and esophagectomy for oesophagal carcinomas. Materials and Methods After IRB approval (NCT04489368), our cancer registry was queried to retrieve patients who underwent an esophagectomy between January 2010 and December 2020. The inclusion criteria for this analysis were: 1. Squamous Cell Carcinoma/AdenoCarcinoma of the thoracic oesophagus and oesophagogastric junction, who received NA-CRT and esophagectomy. 2. All oncological interventions were delivered at our institution. All patients were re-staged as per the AJCC 8th edition and were retrospectively classified as CROSS- Eligible/Ineligible based on the CROSS investigators' criteria. All patients were treated on a 6MV Linear Accelerator, and elective nodal irradiation was not performed. Dose (Median: 41.4Gy; Range: 40-50.4 Gy) and target volumes at our institution gradually became CROSS-compliant after 2015, and most patients were treated in a single-phase IMRT plan. Similar to RT practice change after 2015, 125 patients received concurrent chemotherapy with Paclitaxel & Carboplatin, delivered weekly. Before 2015, the most commonly delivered chemotherapy was weekly platinum (n = 105) and infrequently, the combination of weekly Cisplatin & 5-FU (n = 24). Most patients underwent surgery (Mckeown’s or Ivor Lewis esophagectomy) within eight weeks after completing NA-CRT (median: 55 days; Range: 26-232 days). Nodal regions in the pathology report were classified as ‘Out-of-Field’ by individually reviewing each patient’s RT plan. The primary endpoints were overall survival (OS), recurrence-free survival (RFS) stratified by pathological response to NA-CRT and CROSS-eligibility. Results A total of 254 patients were included in this analysis with a median follow-up of 53.1 months. The median OS of the entire cohort was 71.4 months & RFS did not reach the median. The OS and RFS of patients achieving complete pathological response did not reach the median and were significantly better than those with residual disease (mOS=29.5 mo, p < 0.0001; mRFS=22.7 mo, p < 0.0001). When stratified by CROSS eligibility, the OS & RFS of CROSS-eligible patients did not reach the median and were significantly better than those deemed ineligible (mOS=32.2 mo, p = 0.005; mRFS=25.1 mo, p = 0.023). Multivariable Cox Proportional Hazards modelling (with backward elimination) yielded the following factors influencing both OS & RFS: Age, In-field Nodal Positivity and Outfield ENE. Additional factors influencing OS were: Sex, CROSS eligibility, Surgical complications and Adventitia Involvement. Additional factors influencing RFS were: Margin Positivity, EQD2 (a/b = 4.9), Residual Nodal disease on PreOp Imaging and Residual Pathological Primary.