ESTRO 2024 - Abstract Book

S2112

Clinical - Sarcoma, skin cancer, melanoma

ESTRO 2024

this distance is to allow enough space for dose falloff between the two different dose levels from 50Gy down to 20Gy. Treatment was delivered twice weekly for a total of 5 fractions (Figure 1).

Figure 1. Images showing the volumes and isodose lines using PABR technique.

Patient demographics, tumour characteristics, tumour response, clinical outcomes and toxicities were recorded. The primary endpoints of this study were symptomatic and structural response rates. Secondary endpoints were local progression-free survival (LPFS), overall survival (OS), distant progression-free survival (DPFS) and acute and late toxicity rates.

Results:

A total of eighteen patients were included. Median age was 73(65-75). 44% of patients were ECOG 2-3. 61% of patients had stage IV disease. Most tumours were histologically high-grade (94%). All patients had tumours ³ 5cm (T2 17%, T3 39%, T4 44%) with a median tumour absolute volume of 985cm3 (769-3023). Prior to treatment with PABR, five patients (28%) had previous radiotherapy in the same area and 8 patients (44%) did not respond or had progressive disease with previous systemic therapy. There were 10 sarcomas subtypes treated, the most common of which are dedifferentiated liposarcomas (33%), leiomyosarcomas (22%), and myxoid liposarcomas (11%). The most common location was in the retroperitoneum (50%) followed by the non-retroperitoneal intraabdominal location (16%). The most common symptom for initially symptomatic patients (n=14) was pain (86%). The most common radiotherapy regimen was 20Gy in 5 fractions to the whole tumour with an intratumoral boost dose of 50Gy (83%). After a median follow-up of 11 months, 89% of patients exhibited a partial response, and 11% had stable disease, with a mean absolute tumour volume reduction of 48.8%. All patients who were initially symptomatic experienced symptomatic response (Figure 2). The 1-year OS, LPFS and DPFS were 65%, 83% and 35%, respectively. Most local progressions were in-field (80%) and occurred at the tumour periphery. The median time to local progression was