Different treatment planning strategies for whole-brain radiation therapy with simultaneous integrated boost for multiple brain metastases to protect neurocognitive function with hippocampal sparing

Abstract

PURPOSE: The aim of this study is to provide the dosimetric evaluation of the compound therapeutic concept of hippocampal avoidance for the whole brain radiotherapy (WBRT) with a simultaneous integrated boost (SIB) in patients with multiple brain metastases more than 3. MATERIALS AND METHODS: Ten patients with multiple brain metastases previously treated with conventional WBRT followed by SIB on Radixact Tomotherapy Unit were selected. The whole-brain (WB) clinical target volume was generated by contouring the WB and excluding the hippocampal avoidance structure for the sake of WBRT while plan optimization of both approaches was performed with the aim of delivering 95% of the WB and receiving the prescription dose of 30 Gy; in addition, planning target volumes (PTVs) were given 45 Gy using SIB technique in 10 fractions. Dmax ≤16 Gy and D100% ≤9 Gy for hippocampi and V37 Gy for the WB-PTVs were evaluated in this study as well. RESULTS: The D95% was 44.8 ± 0.15 Gy in helical tomotherapy (HT) which was calculated as 44.9 ± 0.11 Gy in volumetric modulated arc therapy (VMAT) plan. The volume receiving 37 Gy for brain-PTV was 3% ± 0.55% in HT and 10% ± 1.55% in the VMAT plan. The D2% and D100% values of hippocampi were calculated <2 Gy in HT plan compared to the VMAT plan. CONCLUSION: Techniques used in both plans are feasible. However, the VMAT plan owns the ability to deliver SIB dose to each individual metastasis as well while it adequately delivers WBRT and conformably spares the hippocampus. On the negative side, providing the dosimetric criteria of hippocampus is not possible in some cases due to the close proximity of tumor locations to the hippocampus.

Keywords

• helical tomotherapy
• hippocampal sparing
• multiple brain metastases
• volumetric arc radiation therapy
• wbrt