Radiotherapy is a primary or an adjuvant treatment for most brain tumor patients for better tumors control and prolong survival [1]. However, cranial irradiation may cause damages to hippocampus (plural: hippocampi), which may induce dementia after they recovered from the disease [2]. To minimise radiation dose to hippocampus becomes a new trend in radiation therapy [3], [4]. This study is to investigate whether traditional coplanar VMAT (CO-VMAT) or proposed non-coplanar VMAT (NC-VMAT) is dosimetrically superior for brain tumor radiotherapy treatment in view of hippocampus sparing.
Both CO-VMAT plan and NC-VMAT plan were generated for 16 brain tumor patients (Glioblastoma: 11, Meningioma: 5) using Varian Eclipse planning system version 15.6. The prescription was to give 54 Gy to PTV in 30 fractions. Dose constraints applied for plan optimization were benchmarked against Radiation Therapy Oncology Group (RTOG). In the CO-VMAT plans, there were 1 full arc (179°-181°) and 2 half arcs. The couch angle for all arcs were 0°. For cases with PTV located at the left side of the brain, the gantry angle for the 2 half arcs were set from 0°to 179° and 179° to 0°. While for cases with PTV on the right side of the brain, the gantry angle of the 2 half arcs were set from 0° to 181°and 181°to 0°. In the NC-VMAT plans, all setting were the same as CO-VMAT plans, except that the couch angle for the 2 half arcs was at 315° for PTV located at the left side of the brain, and 45° for PTV located on the right side of the brain.
Homogeneity index, conformation number, dose to other organs at risk and ipsilateral hippocampus were similar in CO-VMAT and NC-VMAT plans. The maximum dose (D-MaxCH) received by contralateral hippocampus in NC-VMAT is 4Gy lower (p=0.049) than that of the CO-VMAT. The dose received by 40 % of the contralateral hippocampus (D40%CH) in NC-VMAT is 1.46Gy (p=0.003) lower than that of the CO-VMAT. The mean D-MaxCH and mean D40%CH were reduced by 23% and 23.5% respectively in NC-VMAT plans when compared with CO-VMAT.
The NC-VMAT is able to minimize radiation dose to contralateral hippocampus while maintaining good plan quality. The NC-VMAT approach may help to consolidate the development of a new standard of care for brain tumor patients.
Tung Wah College.
Has not received any funding.
All authors have declared no conflicts of interest.