ESTRO 2023 - Abstract Book

S543

Sunday 14 May 2023

ESTRO 2023

generated to examine the effect of several parameters on PFS and on OS; Cox regression models were used to determine predictors of PFS and OS. Results Between 2003 and 2021, 181 patients (pts) were included. Patients were re-irradiated with SRS (n = 75; 41.4%), f-SRT (n = 63; 34.8%), PT (n = 31; 17.1%) and conventional radiotherapy (n = 12; 6.7%). 78 pts were identified with WHO Grade I disease, 65 pts had Grade II disease, and 10 pts had Grade III disease. 28 pts who had no histologic sampling were grouped with Grade I patients for further analysis. Median age at re-irradiation was 62 (range, 20-89) and median KPS was 90 (range, 60-100). After a median follow-up of 4.6 years (interquartile range 1.7-6.8), 3-year PFS was 51.6% and 3-year OS 72.5%. At UVA Ki67 >5% (HR 2.81, 95% CI 1.48-5.34, p=0.002) and WHO grade > I (HR 3.08, 95% CI 1.80-5.28, p< 0.001) were negatively correlated with PFS, whereas f-SRT (HR 0.32, 95% CI 0.19-0.55, p<0.001), longer time to reRT (HR 0.37, 95% CI 0.21-0.67, p=0.001) and higher tumor BED (HR 0.45 95% CI 0.27-0.76, p=0.003) were positively correlated with PFS. At multivariate Cox analysis only f-SRT, time to reRT and tumor BED maintained their statistically significant prognostic impact on PFS (HR 0.36, 95% CI 0.21-0.64, p<0.001; HR 0.38, 95% CI 0.20-0.72, p=0.003 and HR 0.47 95% CI 0.26-0.83, p=0.01, respectively, Fig.1 ). Concerning toxicity, larger tumor GTV had a statistically significant higher risk of acute and late toxicity (p=.0.004 and p=0.005 respectively, Fig. 2 ).