ESTRO meets Asia 2024 - Abstract Book

S245

Interdisciplinary – Particle Therapy

ESTRO meets Asia 2024

Results:

The average age of patients was 61 at the start of radiotherapy in both cohorts, ranging from 33 to 78 years in the IMPT cohort and 39 to 82 years in the IMRT cohort. The prescription dose was matched, with nine patients in each cohort receiving a total dose of 45 GyRBE, and sixteen patients receiving 50.4 GyRBE. The pelvic bone volume was similar in both groups (p=0.151), with a median volume of 1424 ml (range 916-1653 ml) in the IMPT cohort and 1318 ml (range 1046-1730 ml) in the IMRT cohort. The integral dose in the IMPT cohort was significantly reduced to the pelvic skeleton (23.4 GyRBE vs. 34.3 GyRBE; p<0.001), and the average V 5 Gy, V 10 Gy, and V 20 Gy were reduced by 40%, 41%, and 28%, respectively, compared to the IMRT cohort (p<0.001). The low dose volume was significantly lower, especially for subsite ilium and lower pelvis. Hematotoxicity was significantly more common in the IMRT group (80% vs. 32%; p=0.004), especially hematotoxicity of grade CTCAE II or higher (36% vs. 8%; p=0.037). No patient in the IMPT cohort experienced a grade CTCAE III hematotoxicity compared to four patients in the IMRT cohort. In the IMPT cohort, seven patients who received concurrent chemotherapy received the full dosage. However, in the IMRT cohort, two out of seven patients received incomplete doses of chemotherapy due to hematotoxicity. In the IMPT cohort, 32% of patients experienced SIF. Overall, SIF occurred more frequently with a total dose of 50.4 GyRBE (37.5%) compared to 45 GyRBE (22%). Aside from a trend regarding V 50 Gy to the lumbosacral subsite, no significant predictive dose parameters regarding SIF could be detected.