Whole Brain Irradiation With Hippocamus Protection On Tomotherapy HDA Device

Abstract

Purpose: In this study, treatment planning and hippocampus dose were evaluated by hippocampus-protected radiotherapy planning in whole brain irradiation with Helical Tomotherapy plan. Materials and Methods: In the study, magnetic resonance and computed tomography images were used to contour the PTV, the whole brain, hippocampus and structures at risk (OAR). The optimization volume was drawn by giving a 5 mm margin to the hippocampus. Planning parameters were 1.25 cm jaw width, 3 modulation factors and 0.215 pitch factors. Direction block definitions were entered for the right and left lenses from the structures at risk. Dose calculation was made with the fine dose grid. The dose prescription for the PTV was defined as 30 Gy in 10 fractions. In the PTV evaluation; while the dose received by the 95% volume, Homogeneity Index (HI) and Conformity Index (CI) were evaluated for homogeneity, the RTOG 0933 (Radiation Therapy Oncology Group) protocol was taken as a reference for the structures at risk, and the maximum and median doses of the hippocampus were evaluated considering the reference studies for the hippocampus. Findings and Conclusion: In the whole brain irradiation performed with the helical tomotherapy device while preserving the hippocampus, it was observed that 95% of the PTV volume covered the targeted dose. The parameters indicating the quality of the plan were calculated as HI= 0.21 and CI=1.05. It was observed that the eyes and lenses were below the tolerance doses specified in RTOG. It was found that the maximum and mean doses of the hippocampus were high compared to the reference studies. Since the tomotherapy device allows rapid dose reduction and target dose homogeneity, the hippocampus can be preserved in whole brain irradiation.