ESTRO 2025 - Abstract Book

Brachytherapy - Gastro-intestinal, paediatric brachytherapy, miscellaneous

S178

ESTRO 2025

fSRs

IORT

50 Gy (28.4-59Gy)

Median BED (a/ß=10) at PTV margin (3mm)

48 Gy (48-59.5Gy) =5x6 Gy (R0) or 5x7 Gy (R1)

=20Gy (13.4-30Gy) on surface of applicator

Results: We analyzed 129 patients receiving 137 radiation treatments of a resection cavity (fSRS:72/75; ioRT:57/62). Median FU was 8 months. Both groups did not show significant differences regarding age, RPA class, size and number of mets. With regard to histology the fSRS group had more breast cancer and less NSCLC patients compared to the IORT group. Median Paddick Conformity Index of the fSRS treatment plans was 0.73 (0.29-0.91). Patients characteristcs: HSRT IORT patients 72 5 lesions 75 62 age 64 years (34-87 years) 64 years (39-88 years)

1= 10 (13.9%) 2= 54 (75.0%) 3= 8 (11.1%)

1= 8 (14.0%) 2= 41 (72.0%) 3= 8 (14.0%)

RPA class

median number of metastasis per patient

1

(1-4)

1

(1-4)

1-year overall survival (fSRS: 60.1% (95%CI 47.0-70.9%) vs ioRT: 58.5% (95%CI 43.9-70.5%) p=0.415), local control (fSRS: 89.0% (95% CI 75.2-95.4%) vs. ioRT: 86.8% (95% CI 71.0-94.3%) p=0.706) and LMD rate (fSRS:15.3% (95% CI 7.0 31.4%) vs. ioRT: 16.5% (95% CI 7.7-33.4%) p=0.745) showed no significant difference. But Patients treated with ioRT showed significantly lower 1-year rates of RN (ioRT: 3.7% (95% CI 0.5-23.5%) vs. fSRS: 21.8% (95% CI 11.7-39.2%) p=0.0002). This was true for asymptomatic and symptomatic RN (fSRS: 14.7% vs. SRS: 1.8%) Conclusion: ioRT treatment of the resection cavity shows similar oncological outcome as postoperative fSRS regarding overall survival and local control after resection of BM, with significantly lower rates of RN.

Keywords: IORT, Cavity RT, CNS

1355

Proffered Paper

Real-world comparison of MR-Based brachytherapy dose escalation with total neoadjuvant therapy or chemoradiation in rectal preservation (NCT06252142) Rahul Krishnatry 1,2 , Aditi Jain 1,2 , Vikas Ostwal 3,2 , Mufaddal Kazi 4,2 , Purvi Haria 5,2 , Shivakumar Gudi 1,2 , Anant Ramaswamy 3,2 , Prabhat Bhargav 3,2 , Reena Engineer 1,2 1 Radiation Oncology, Tata Memorial Centre, Mumbai, India. 2 HBNI, HBNI University, Mumbai, India. 3 Medical Oncology, Tata Memorial Centre, Mumbai, India. 4 Surgical Oncology, Tata Memorial Centre, Mumbai, India. 5 Radiology, Tata Memorial Centre, mumbai, India