ESTRO 2022 - Abstract Book

S1216

Abstract book

ESTRO 2022

Conclusion This innovative technique for ITM in the lower limb resulted in lesion-specific ablation of disease and normal tissue-sparing, with minimal local or systemic adverse effects.

PO-1435 Risk stratification based on whole body tumor burden can refine the role of combining RT and ICIs

J. Kim 1 , J.S. Kim 1 , H. Ko 2 , T.H. Kim 3 , S.H. Choi 4 , W. Sung 5 , S.J. Shin 6 , J.S. Chang 1

1 Yonsei University College of Medicine, Radiation Oncology, Seoul, Korea Republic of; 2 The Catholic University of Korea, Collegeof Medicine, Seoul, Korea Republic of; 3 Eulji University School of Medicine, Radiation Oncology, Seoul, Korea Republic of; 4 Yongin Severance Hospital, Yonsei University College of Medicine, Radiation Oncology, Yongin, Korea Republic of; 5 The Catholic University College of Medicine, Biomedical Engineering, Seoul, Korea Republic of; 6 Yonsei University College of Medicine, Division of Medical Oncology, Department of Internal Medicine, Seoul, Korea Republic of Purpose or Objective Two recent trials showed conflicting findings of adding RT to immune checkpoint inhibitors (ICI) in unselected patients with metastatic disease. Although the current definition of oligometastatic disease is based on the number of metastases and involved organs, little is known about which quantitative methods (lesion number and sum of 2D or 3D measurements) are suitable for better risk stratification in RT and ICI combination trials. Here, we investigated the clinical utility of different quantitative characteristics of metastatic disease in advanced melanoma patients who received pembrolizumab. Materials and Methods 86 patients with metastatic or unresectable malignant melanoma were treated with pembrolizumab between 2015 and 2020. We 3-dimensionally contoured all metastases on available imaging at the time of pembrolizumab initiation. Then, total number of metastases, sum of 10 target lesions per RECIST criteria, 3D volume of total gross tumors and involved organs (liver, lung, brain, and bone) were collected for analysis. The study endpoints included overall survival (OS), progression-free survival (PFS) and PFS-2 (progression after the next line of therapy). Results In total, 1049 metastases were contoured and the average number, 2D-tumor size, and 3D-tumor volume of total metastases before treatment initiation were 12±14/patient, 12.8±20.19 cm/patient, and 94±183 cc/patient, respectively. High correlation between the number of metastatic lesions and baseline 2D-tumor size was observed ( ρ = 0.90), but moderate correlation was seen between the number of metastatic lesions and 3D-tumor volume ( ρ = 0.59). At a median follow-up of