C. Jiang1, T. McWilliams2, Z. Belal1, E. S. Lebow3, H. G. Hubbeling1, J. D. Kolker1, S. Nagda1, G. Kurtz1, and M. Alonso-Basanta1; 1Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, 2Biostatistics Analysis Center, University of Pennsylvania, Philadelphia, PA, 3Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY
Purpose/Objective(s): The incidence of brain metastases (BM) is increasing. Radiotherapy (RT) options include whole brain RT (WBRT) and stereotactic radiosurgery (SRS), although both have limitations including neurocognitive toxicity and intracranial failures, respectively. For patients with significant intracranial disease burden predominantly in the posterior fossa, there is opportunity to strike a more favorable therapeutic balance. Here, we report our experience with whole posterior fossa radiotherapy (WPFRT) with or without supratentorial SRS. We hypothesized that WPFRT is a safe RT option that can obviate the need for WBRT in well-selected patients. Materials/
Methods: This is a single institution retrospective study of =18-year-old patients with BM who received palliative WPFRT between 6/2011 and 12/2023. Clinical and RT details were extracted from the electronic medical record. Associations between categorical variables were assessed using Chi-squared and Fisher’s Exact tests, as appropriate. The Kaplan-Meier method was used to assess overall survival (OS), time to progression (TTP), and progression free survival (PFS), measured from the last fraction of WPFRT. A log-rank test was used to assess survival differences between groups. Results: 21 patients were included, of whom 48% had prior overlapping RT, 43% had known leptomeningeal disease, and 52% had an ECOG performance status of 3. Median age was 61 and mean follow-up was 8.2 months. The most common malignancies were lung (38%) and breast (24%). The mean number of posterior fossa and supratentorial metastases were 4.6 and 2.5, respectively. Dose was 20-30 Gy in 5-10 fractions, and 29% received concurrent supratentorial SRS. During WPFRT, most frequently observed grade 2 acute toxicities were fatigue (33%), nausea (14%), and headache (10%). There was one acute grade 3 toxicity (cerebellar hemorrhage) and 1 possible late toxicity (cognitive decline). Median OS was 4.2 months (range 0-75.9 months). After WPFRT, 24%, 29%, 33%, and 52% of patients had known progression in the leptomeninges, supratentorial brain, posterior fossa, and extracranial body. Median time to leptomeningeal progression was 7.2 months, median time to extracranial progression was 4.9 months, and median time to posterior fossa or supratentorial progression were both 5.8 months. Those with >5 supratentorial metastases were more likely to receive concurrent SRS (100% vs. 16.7%, p=0.015) and have worse supratentorial PFS (median 1.4 vs. 4.2 months, p = 0.024) compared to patients with <5 metastases. Pre-existing leptomeningeal disease and development of grade 2-3 acute toxicities adversely impacted OS (p<0.05). 9 patients received another course of RT, of which 4 were WBRT. Conclusion: WPFRT is a tolerable RT option for patients with notable intracranial disease predominantly in the posterior fossa, even in a heavily pre-treated cohort with poor performance status. 19% of patients subsequently received WBRT.
