Dosimetric Comparison of Stereotactic Radiation Therapy Planning between Volumetric Modulated Arc Therapy and Helical Tomotherapy in Vestibular Schwannoma

Abstract

Background: Stereotactic radiotherapy (SRT) is an alternative treatment for Vestibular Schwannoma. The advancement of linear accelerator technology and the development of intensity modulated radiotherapy such as Volumetric Modulated Arc Therapy (VMAT) and Helical tomotherapy (HT) techniques that can achieve a high accuracy, a high level of conformity and steep dose gradients to the treatment target and reduce radiation dose to the normal organs. These techniques are an option for Vestibular Schwannoma treatment. Objectives: To compare the dosimetric results of VMAT and HT treatment planning for Vestibular Schwannoma. Materials/Methods: This is a retrospective study of sixteen Vestibular Schwannoma patients who received SRT with Helical tomotherapy. The CT images data with patient's treatment target and normal organs structures were used to create the VMAT plans with total radiation doses of 50–54 Gy (1.8-2Gy/F). Treatment target and organs at risk were constraint follow ICRU 83 report and Quantec guideline respectively. Treatment plan quality evaluation parameters included conformation number (CN), conformality gradient index (CGIg) and homogeneity index (HI). Radiation dose of organs at risk were evaluated by D2, Dmax and Dmean Results: The CN, CGIg and HI between HT and VMAT plans were no statistically significant different (p-value < 0.05). The organs at risk doses of VMAT plan were statistically significant lower than HT plan (p-value < 0.05). These doses of VMAT and HT plans were as follows D2 (Gy) of the brainstem was 44.326±10.528 and 46.339±8.181, D2 (Gy) of optic chiasm was 4.495±3.508 and 8.304±5.829, Dmax (Gy) of optic chiasm was 5.109±4.026 and 8.819±6.085, D2 (Gy) of ipsi-lateral optic nerve was 3.372±1.623 and 7.487±3.770, Dmax (Gy) of ipsi-lateral optic nerve was 3.665±1.837 and 8.174±3.933, D2 (Gy) of contra-lateral optic nerve was 2.147±1.041 and 4.832±2.514, Dmax (Gy) of contra-lateral optic nerve was 2.361±1.154 and 5.122±2.610, Dmean (Gy) of ipsi-lateral globe was 1.781±0.513 and 3.482±1.865, D2 (Gy) of ipsi-lateral globe was 2.778±0.765 and 6.314±1.881, Dmean (Gy) of contra-lateral globe was 1.057±0.551 and 2.749±1.484, D2 (Gy) of contralateral globe was 2.321±0.765 and 5.080±1.483 respectively. Conclusions: There were no statistically significant difference of CN, CGIg and HI between VMAT and HT plans for Vestibular Schwannoma SRT. But VMAT plans provided organs at risk dose statistically significant less than HT plans.