ESTRO 2023 - Abstract Book

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ESTRO 2023

generated by adding a 5 mm margin. Therefore, the PRV dose received by 0.5 cc (D0.5cc, the maximum dose delivered to 0.5 cc) was also evaluated. For quantitative evaluation between PLANref and PLANeval, the difference of the shortest distance (delta shortest distance) and D0.5cc (delta D0.5cc) was calculated. Spearman correlation test was used to analyze the association between delta shortest distance and delta D0.5cc. The paired differences were analyzed with paired Wilcoxon signed-rank tests. Results The median shortest distance in PLANref was 2.1 mm (interquartile range: IQR:0-3.8) in the gastro-duodenum, 16.5 mm (8.8-20.6) in the small intestine, and 19.0 mm (9.8-29.2) in the large intestine (Figure 1). The median D0.5cc of PRV in PLANref was 32.0 Gy (IQR: 31.7-32.4) in the gastro-duodenum, 25.6 Gy (18.9-29.9) in the small intestine, and 19.7 Gy (16.3 28.5) in the large intestine. In spearman correlation test, significant association between delta shortest distance and delta D0.5cc was found in the small (correlation coefficients r=-0.638, p<0.001) and large intestine (r=-0.621, p<0.001), but not in the gastro-duodenum (r=0.024, p=0.866) (Figure 2)

Conclusion The gastro-duodenum is more likely to receive high-dose, possibly due to its proximity to the GTV. Prediction of daily gastro-duodenum dose was suggested to be difficult solely from the shortest distance in daily CT images.

PO-1390 Definitive radiotherapy in T1N0M0 esophageal cancer: a multicenter retrospective study (KROG 21-10)

J.Y. Song 1 , B.H. Kim 2 , M.K. Kang 3 , J.W. Chung 4 , J. Kim 5 , S.H. Moon 6 , Y. Suh 6 , J.H. Kim 7,7 , H.J. Kim 8,1 , Y.S. Kim 9 , W. Park 10

1 Seoul National University Hospital, Department of Radiation Oncology, Seoul, Korea Republic of; 2 Seoul Metropolitan Government-Seoul National University Boramae Medical Center, Department of Radiation Oncology, Seoul, Korea Republic of; 3 Kyungpook National University, Department of Radiation Oncology, Daegu, Korea Republic of; 4 Chonnam National University Hwasun Hospital, Department of Radiation Oncology, Hwasun, Korea Republic of; 5 Asan Medical Center, Department of Radiation Oncology, Seoul, Korea Republic of; 6 Proton Therapy Center, National Cancer Center Korea, Department of Radiation Oncology, Goyang, Korea Republic of; 7 Keimyung University Dongsan Medical Center, Department of Radiation Oncology, Daegu, Korea Republic of; 8 Inha University Hospital, Department of Radiation Oncology, Incheon, Korea Republic of; 9 Jeju National University Hospital, Department of Radiation Oncology, Jeju, Korea Republic of; 10 Chungbuk National University Hospital, Department of Radiation Oncology, Cheongju, Korea Republic of Purpose or Objective In this study, we aimed to assess the failure pattern and survival outcomes and to analyze the optimal treatment field of definitive RT for T1N0M0 ESCC. Materials and Methods We performed a retrospective analysis in a multi-institutional cohort of patients with histologically confirmed T1N0M0 ESCC. We included patients who underwent RT with definitive aim from 2010 to 2019. Patterns of failure were demonstrated as in-field locoregional, out-field locoregional and distant metastasis, according to the radiation field, along with the mortality data. In the survival analysis, endpoints such as recurrence free survival, cancer-specific survival, locoregional recurrence free survival and overall survival, and their association with clinicopathologic risk factors were analyzed. We performed a propensity score matching in the cT1b patients to adjust for the heterogeneity of tumor grade and chemotherapy use. Results A total of 138 patients were included with a median follow-up of 32.4 months, and there were 20 cT1a, 94 cT1b and 24 cT1, not otherwise specified (cT1x) patients. The rates of locoregional and any failure were 25.0% and 30.0% for cT1a and 22.3% and 24.5% for cT1b patients. Among 94 cT1b patients, 55 patients received elective nodal irradiation (ENI) and 39