ESTRO 2025 - Abstract Book

S539

Clinical - Breast

ESTRO 2025

2609

Digital Poster Impact of targeted therapy on symptomatic radiation necrosis risk in breast cancer cases treated with SRS for brain metastases at a single institution Aditya Mittal 1 , Revathy Krishnamurthy 1 , Rima Pathak 1 , Tabassum wadasadawala 1 , Rajiv Sarin 1 , Purvi Haria 2 , Arpita Sahu 2 1 Radiation oncology, Tata Memorial Hospital, Mumbai, India. 2 Radiodiagnosis, Tata Memorial Hospital, Mumbai, India Purpose/Objective: To investigate the influence of targeted therapy on the risk of developing symptomatic radiation necrosis ( SRN) after stereotactic radiosurgery (SRS) for brain metastases from breast cancer. Material/Methods: Of the 51 consecutive breast cancer patients screened with 1-3 brain metastases who received LINAC based SRS between 2018 to 2023, 48 cases with at least 3-month post SRS follow up MRI were included in this analysis. Diagnosis of SRN was confirmed through imaging reviews conducted by a multidisciplinary team comprising two neuroradiologists and one radiation oncologist. SRN risk was computed, and significant predictors were identified through univariate and multivariate analyses. Results: SRS was single fraction of 15-24 Gy in 8 cases and multifraction in 40 cases - 27/3# in 24 and 30 Gy/5# in 7 cases. Targeted therapy was given in 26 cases - AntiHer2 in 21, CDK4/6 in 3 and Olaparib in 2 cases. SRN was seen in 29.2% cases with 1-, 2- and 3-year probability being 6.2%, 20.7%, and 29.1%, respectively. Of various risk factors, targeted therapy emerged as a major risk factor for SRN with 43.4% of such patients developing SRN as compared to 13.7% cases who did not receive targeted therapy post SRS (p=0.029). For patients on targeted therapies, SRN probability at 1, 2, and 3 years was 15%, 43%, and 77%, versus 7%, 17%, and 58% for those not receiving targeted treatments. Other variables, including age, comorbidities, SRS fractionation regimens and other dosimetric parameters were not significantly associated with SRN, possibly due to the limited cohort size. As expected, excellent 2-year local intracranial control at the SRS site of 81.3% was achieved with 37.2% cases having distal intracranial progression in the brain outside the SRS region. For patients experiencing local recurrence or distal progression, 39.5% required salvage treatments, including re-irradiation with whole-brain radiation therapy or repeat SRS.

Conclusion: Our cohort of consecutive cases treated with SRS in the modern era shows the significant impact of targeted therapies on the risk of SRN, consistent with findings from some prior studies [1]. This underscores the importance of close follow up and integrated management strategies. These findings highlight the delicate balance between