Session Item

Hippocampal sparing whole-brain radiotherapy (HS-WBRT) technique has shown a significantly lower memory decline in 4-months assessment compared to standard WBRT with comparable local control of disease. The aim of the present study is to retrospectively evaluate intra and extra-hippocampal recurrences of disease in our HS-WBRT cohort, evaluating the association with clinical, pathological and radiological variables.

Data were retrospectively collected from a cohort of patients (pts) who underwent HS-WBRT from 2016 to 2021. Inclusion criteria were: 1) diagnosis of BM; 2) Karnofsky Performance Status (KPS)> 60; 3) life expectancy more than 6 months; 4) available brain magnetic resonance imaging (MRI) before RT; 5) signed written informed consent. Treatment was performed using TomoHelical scheduled in 30 Gy in 10 or 12 fractions or 25 Gy in 10 fractions (Figure 1). Oncological outcomes were clinically and radiologically assessed every 3 months after the end of HS-WBRT. First, Kaplan-Meier plots depicted oncological outcomes rates and univariable and multivariable Cox regression models focused on predictors of local progression. Encephalic progression-free survival was analyzed considering as competing risks systemic progression and death before first radiological assessment. Toxicity was graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events version 4.0.

One-hundred and nineteen pts matched inclusion criteria. Eighty-eight percent had KPS 90-100, 12% KPS 60-80. More represented primaries were NSCLC (39%) and breast (53%). The majority of patients had ≥ 10 BM. Median dose to hippocampus was 7.6 Gy (range 6.41, 12.5), median volume was 2.03 cc (range 0.64, 4.95) and median maximum dose was 13.4 Gy (range 8.74, 27.1) (Figure 1). Most of pts (60%) underwent concomitant systemic therapies. Forty patients (34%) experienced a brain recurrence. Of them, 57% were exclusively extra-hippocampal and 40% had intra-hippocampal involvement. Forty-two percent were oligoprogression (maximum 5 lesions), and 16 involved hippocampi. Median time to recurrence was 7 months (range 0-23). After a median follow up of 17.15 months (range 0-49), 74% of patients were dead. Patients who underwent concomitant systemic therapy (n=71) were stratified according to the treatment (chemotherapy vs others) and results showed a benefit for not chemo systemic treatments in terms of OS and any PFS (p= < .001), but not in terms of local control (p= .12) (Figure 2). No acute toxicities ≥ G2 were observed on the entire cohort.

Given the growing potential for prolonged survival with metastatic disease, identifying strategies to reduce treatment-associated side effects is of increasing significance. In the present study, according with published literature, HS-WBRT shows a durable intracranial disease control. A small risk of additional intra-hippocampal recurrence seems to be justified by memory preservation reported in numerous studies on HS-WBRT.