ESTRO 2022 - Abstract Book

S121

Abstract book

ESTRO 2022

resectability (Figure 1). The intervention would be deemed tolerable if significant RT-related (grade 3+ CTCAE 5.0) late adverse events occur in less than 20% of patients. We planned to enroll 20 patients based on Wilson’s method for calculation of confidence intervals.

Results We recruited 20 patients. All patients completed the treatment without interruptions. Eight of them had RIS whereas twenty were diagnosed with IFRS. Patients’ characteristics were provided in Table 1. Twelve patients from planned 15 underwent surgery. Two patients with potentially resectable tumors did not undergo surgery due to COVID-related reasons. One patient preferred not to undergo surgery after the preoperative no-boost regimen. The remaining five patients were deemed unresectable at the enrollment and received the simultaneous boost. In five patients who underwent resection, we observed extensive pathological response according to the European Organization for Research and Treatment of Cancer-Soft Tissue and Bone Sarcoma Group recommendations for pathological examination and reporting, namely grade A in two cases and grade C in three cases. In four patients we observed complete radiological response. The median follow-up was 13 months. In 14 patients we noted mild or moderate radiation dermatitis. One patient experienced grade 2 gastrointestinal toxicities. From the late toxicities, we observed restricted limb mobility (grade 1) in one patient and chronic skin ulceration (grade 2) in one patient. None of the patients who developed grade 3 or higher late toxicity. Two patients who received the no-boost regimen and did not undergo resection developed local progression. One patient experienced borderline local relapse after surgery. None of the patients who received the boost regimen developed local progression. Three patients developed distant metastases. One patient was lost to follow-up.

Conclusion Preliminary data suggest that the tolerance of the regimen is acceptable; however, data regarding late toxicity may change during the follow-up period. Boost may play a significant role in achieving local control in non-resected tumors.

MO-0147 Efficacy of perioperative radiotherapy in extraskeletal myxoid chondrosarcoma

J. STELMES 1

1 Oncology Institute of Southern Switzerland, Radiationoncology , Bellinzona, Switzerland

Purpose or Objective