ESTRO 2024 - Abstract Book

S1472

Clinical - Lower GI

ESTRO 2024

single fraction dose of 15 Gy to each of the macroscopic tumor sites, with dose constraints as known in literature for single fractional treatments 3–5 . To minimize the risk of hemorrhage with SBRT and bevacizumab the first two cycles of maintenance therapy were without bevacizumab to ensure a bevacizumab-free interval of at least 28 days before, and 14 days after SBRT. The primary endpoint of the trial was feasibility, defined as 5 out of 6 patients in whom: (1) SBRT was delivered as planned, (2) more than 90% of the planned dose on all disease sites was received in 95% of the planned target volumes (PTV) and (3) the total radiotherapy treatment time would be equal or less than 5 consecutive working days. The secondary endpoint was safety defined as the number of grade II adverse events (AEs) of specific interest, grade III and IV AEs according to CTCAE 5.0 up to 90 days after the last radiation and serious AEs until end of follow-up. Exploratory objectives were progression-free survival, type of progression and overall survival (OS).

Results:

Six patients were included and median follow-up time was 9.6 months. The median age of patients was 53 years and three were female (Table 1). Before initial systemic therapy 26 lesions were identified, of which ten (38%) vanished during systemic treatment and the remaining 16 received radiation. Based on the location, distribution, number and or/size of lesions, curative-intent treatment was considered not feasible.

All endpoints for feasibility were met for all patients. Furthermore, no grade III or grade IV events were reported in the first 90 days. One grade II event of specific interest (‘pain’ any type) had been reported, which was considered non-specific thoracic pain and a relation to the radiation was unlikely. One patient died nine months after SBRT. This was due to recurrence of a rectal tumor and painful abscesses in the pelvis, which was followed by best supportive care. There was no relation to the radiation since the rectal tumor had not been irradiated.