Dosimetric analysis on the efect of tumor motion in IMRT for liver cancer: comparison of TomoTherapy and VMAT using the Delta⁴ Hexa-Motion system

The internal target volume (ITV)-based IMRT method can be used to reduce the efect of respiratory tumor motion. In this study, the efect of tumor motion on the dosimetric accuracy during ITV-based IMRT was investigated. ITV-based IMRT plans for a total of ten cases of liver cancer were prepared in TomoTherapy (Tomo) and volumetric modulated arc therapy (VMAT). Delivery quality assurance (DQA) plans were created using Delta⁴ phantom for the verifcation of dosimetric accuracy of the established Tomo and VMAT plans. DQA measurements were performed in both the static mode and the Hexa-Motion mode by using the Delta⁴ Hexa-Motion system in Tomo and VMAT. In the static mode, the average gamma passing rate (GPR) using a 3% dose diference/3 mm distance-to-agreement criteria was 99.61% in Tomo and 99.35% in VMAT, which confrmed sufcient dosimetric accuracy in both IMRT methods. For the Hexa-Motion measurement, the average GRP result of 90.93% in Tomo was higher than the result of 82.58% obtained in VMAT. In addition, the diference in the GPR results between the static and the Hexa-motion modes in Tomo was 8.68%, which is approximately 8% less than the 16.77% diference in VMAT. This study verifes that the dosimetric error of ITV-based IMRT due to the tumor motion was larger in VMAT than in Tomo. Also, Tomo can be considered to be more suitable than the conventional LINAC-based VMAT method in terms of the dosimetric accuracy of ITV-based IMRT for the treatment of a moving tumor