Hippocampal Sparing in Whole Brain Radiotherapy with Simultaneous Integrated Boost for Brain Metastasis – Feasibility and Neurocognitive Function Assessment

Abstract

Introduction: Whole Brain Radiation Therapy (WBRT) is a standard in most of patients with brain metastasis. Hippocampus is being recognized as organ at risk to maintain neurocognitive functions and hippocampal sparing WBRT has been started. Further, WBRT followed by Boost shows better local control compared with WBRT alone. The present study is done to evaluate the feasibility of sparing the hippocampus and assessment of neurocognitive function treated with WBRT with boost in brain metastasis.
Materials and Methods: All patients with brain metastasis were recruited and followed between December 2022 and January 2025. Inclusion criteria: Pathologic proven diagnosis of solid tumor malignancy; Age ≥ 18; KPS ≥ 70; Mini Mental State Examination (MMSE) ≥ 18; RPA class I or II; One or more brain lesions. Exclusion Criteria - Previously treated patients of brain tumors or leptomeningeal disease by MRI and/or cerebrospinal fluid cytology. Baseline and follow up (at 0,3 and 6 months) neurological cognitive functions were assessed using Mini-Mental State Examination (MMSE) and Hopkins Verbal Learning Test-Revised (HTLV-R). Patients underwent radiotherapy with hippocampal sparing with dose fractionation of 30Gy to the whole brain-PTV (PTV30) and 45Gy to the boost-PTV (PTV45) using simultaneous integrated boost in 10 fractions. Dosimetric parameters of PTV and OARs were assessed. Statistical analysis was analysed using unpaired t-Test: two – samples of unequal variances, to calculate level of significance (P< 0.05 taken as significant).
Results: 23 patients with brain metastasis were recruited and followed. The mean age 55.34 years and seen more in females (sex ratio 1:1.9). Common primary sites were lung (43.47%) followed by breast (26.08%) with headache (73.9%) as commonest clinical presentation. The metastatic lesions were more common in supratentorial region (60.9%), commonest lobe being frontal (39.1%). Oligometastasis was seen in 91.3%. PTV dosimetry - Conformity index was 1.28 ± 0.34 and homogeneity index was 0.063 ± 0.021. Dosimetric parameters of all OAR’s were achieved except PRV Brainstem and Optic Chiasma in several cases. Hippocampal sparing achieved in 21 patients- Dmax 13.72±1.84 Gy, Dmin 9.16±1.5 Gy, Dmean 11.26±2.08 Gy. Degree of impairment has no change in 17 patients in MMSE, (p=0.52) at 6 months and no significant decline or improvement in HVLT-R score from baseline.
Conclusion: Hippocampal sparing whole brain radiotherapy with simultaneous integrated boost can be an efficient therapeutic option for patients with brain metastasis to spare neurocognitive functions and may be associated with improved local tumor control.