ESTRO 2025 - Abstract Book

S723

Clinical - CNS

ESTRO 2025

a significantly improved OS compared to the infratentorial BM group (35.3 months vs. 24.2 months, p=0.021). In the non-infratentorial BM group, resection of BM before RT(p=0.027), targeted therapy(p<0.001) and immunotherapy following the RT initiation (p=0.009) were independent factors influencing OS, but the method of RT did not impact OS(p=0.361). In the infratentorial BM group, age(p=0.001), targeted therapy following the RT initiation(p=0.010), existence of extracranial metastases(p<0.001) and the RT method(p=0.002) were independent factors influencing OS. Within the infratentorial BM group, patients receiving whole-brain radiotherapy (WBRT) had worse OS than those receiving WBRT with simultaneous integrated boost (WBRT+SIB) and stereotactic radiotherapy (SRT) (WBRT vs. WBRT+SIB: HR= 2.164, 95%CI 1.190 - 3.935, p=0.011; WBRT vs. SRT: HR=3.297, 95%CI 1.695 - 6.412, p<0.001). However, there was no significant difference in OS between SRT and WBRT+SIB(SRT vs. WBRT+SIB: HR=0.656, 95%CI 0.309 – 1.393, p=0.273). The incidence of grade 3-4 acute brain radiation reactions did not differ between the groups with and without infratentorial BM (21.6% vs. 18.4%, p=0.766). Conclusion: The presence of infratentorial BM was associated with inferior OS compared to only supratentorial BM in non-small cell lung cancer. Additionally, local high-dose delivery of BM (SRT or WBRT+SIB) can improve OS for patient with infratentorial involvement of BM. References: 1. Dou Z, et al. The Infratentorial Localization of Brain Metastases May Correlate with Specific Clinical Characteristics and Portend Worse Outcomes Based on Voxel-Wise Mapping. Cancers. 2021;13:324. 2. Graham PH, et al. Randomized comparison of whole brain radiotherapy, 20 Gy in four daily fractions versus 40 Gy in 20 twice-daily fractions. Int J Radiat Oncol Biol Phys. 2010;77:648–54. 3. Burri SH, et al. Brain metastases treated with radiosurgery alone: an alternative to whole brain radiotherapy? Neurosurgery. 2004;54:1033–4; author reply 1034-1035. 4. Routman DM, et al. The growing importance of lesion volume as a prognostic factor in patients with multiple brain metastases treated with stereotactic radiosurgery. Cancer Med. 2018:757–64. Keywords: Infratentorial brain metastases, WBRT Digital Poster Impact of Stereotactic Radiosurgery Doses on Local Control and Radiation Necrosis in Metastatic Brain Lesions: A Comparative Study Mohammad Mukahal 1 , Abdullah Alzibdeh 1 , Tariq Alrawajih 2 , Hadeel Asfour 3 , Ala'a Khanfar 4 , Mohammad Alsmairat 1 , Abdelatif Almousa 1 , Ahmad KH Ibrahimi 1 1 Radiation Oncology, King Hussein Cancer Center, Amman, Jordan. 2 Primary care, Ministry of Health, Amman, Jordan. 3 Pulmonary and Critical Care, Chicago Ridge Medical Center, Chicago, USA. 4 Research Department, King Hussein Cancer Center, Amman, Jordan Purpose/Objective: This study aimed to evaluate and compare the efficacy of different stereotactic radiosurgery (SRS) prescription doses on local control rates of intact brain metastases, in addition to the association between SRS doses and radiation necrosis risk. Material/Methods: A retrospective review was conducted on patients who were treated between 2018 to 2023 at a single institution with SRS at doses of 20 Gy, 22 Gy, or 24 Gy. A one-way ANOVA was used to analyze differences in lesion volumes across dose groups. The effects of radiation doses on local control and radiation necrosis were first evaluated using univariate analysis. Subsequently, multivariate analysis, including logistic regression, was conducted to assess the 3323