Room: Exhibit Hall | Forum 3
Purpose: We propose real-time tumor-tracking volumetric modulated arc therapy (RT-VMAT). In RT-VMAT, three-dimensional position of the internal fiducial marker is calculated by means of X-ray fluoroscopy. Treatment beam irradiation is enabled only when the fiducial marker is within the gating window (GW). This study investigated the irradiation time and residual motion of the target during irradiation in order to reveal the clinical feasibility.
Methods: RT-VMAT plans were implemented on 5 cases of lung and 3 cases of liver that underwent SBRT with multiple fixed fields. Dose prescriptions were 40 Gy in 4 fractions and 48 Gy in 8 fractions to 95 % of the PTV for lung and liver, respectively. 6MV-FFF photon beam with dose rate of 600 MU/min was used. Partial arcs from ipsilateral side were used. Irradiation time and residual motion range of the target were evaluated for several GW size by using actual tumor trajectory data. Ratio of prolongation of irradiation time by RT-VMAT compared with non-gating irradiation was examined. Residual motion range was defined as the 95% range of accumulated frequency of the target dislocation during beam delivery.
Results: In all treatment planning for RT-VMAT, dosimetric goals were achieved. In lung cases, estimated irradiation time of RT-VMAT with GW size of Â±2 mm was 4.1Â±1.4 times longer than that of non-gating. In liver cases, prolongation of irradiation in RT-VMAT was estimated to be 2.5Â±0.3 times. In lung cases, residual motion range was reduced to 2.1Â±0.2 mm from 8.5Â±4.2 mm by RT-VMAT. The liver cases were also similar. In RT-VMAT, positional error of beam irradiation could be reduced despite the motion amplitude although irradiation time was increased. It is expected that inter-play effect can be ignored in RT-VMAT with appropriate GW size.
Conclusion: The results showed the clinical feasibility of RT-VMAT.
Not Applicable / None Entered.