Comparative Dosimetric Evaluation of Tomotherapy with a 1-cm Field Width versus Volumetric-modulated Arc Therapy for Whole-brain Radiotherapy with Hippocampal Avoidance

Background: Hippocampal-avoidance whole-brain radiotherapy (HA-WBRT) reduces radiation dose to the hippocampal neural stem-cell niche, helping preserve neurocognitive function in patients with brain metastases. Objective: The objective of this study is to compare tomotherapy using a 1-cm field width with four-arc volumetric-modulated arc therapy (VMAT) for HA-WBRT. Materials and Methods: Twenty patients prescribed 30 Gy in 10 fractions were planned on both platforms. Hippocampi were contoured on T1-weighted magnetic resonance imaging according to the RTOG 0933 atlas. Tomotherapy plans used a 1-cm jaw, pitch 0.500, and modulation factor 1.5–2.0, while VMAT plans used 6 MV photons with one coplanar and three noncoplanar arcs. Plan quality, hippocampal and organ-at-risk (OAR) doses, treatment efficiency, and deliverability (3%/3 mm gamma analysis) were compared. Results: Planning target volume coverage was comparable (V95%: 96.67% ± 0.57% vs. 96.53% ± 0.73%; P = 0.28). Tomotherapy achieved superior homogeneity and conformity (both P < 0.001), with significantly lower hippocampal Dmax, Dmean, D40%, V10 Gy, and bilateral lens and globe doses (all P < 0.001). Gamma pass rates exceeded 95% for both techniques. VMAT provided shorter beam-on time (2.62 ± 0.25 vs. 12.21 ± 0.99 min) and lower monitor units (MU) (786.5 ± 74.9 vs. 12440.5 ± 992.9; both P < 0.001). Conclusion: Tomotherapy with a 1-cm field width provides superior hippocampal sparing, plan quality, and OAR protection while maintaining equivalent target coverage. VMAT achieves substantially faster treatment delivery with fewer MU, offering an alternative when shorter treatment times are preferred.