MO‐DE‐210‐07: Investigation of Treatment Interferences of a Novel Robotic Ultrasound Radiotherapy Guidance System with Clinical VMAT Plans for Liver SBRT Patients

Abstract

Purpose:To evaluate the proportion of liver SBRT cases in which robotic ultrasound image guidance concurrent with beam delivery can be deployed without interfering with clinically used VMAT beam configurations.Methods:A simulation environment incorporating LINAC, couch, planning CT, and robotic ultrasound guidance hardware was developed. Virtual placement of the robotic ultrasound hardware was guided by a target visibility map rendered on the CT surface. The map was computed on GPU by using the planning CT to simulate ultrasound propagation and attenuation along rays connecting skin surface points to a rasterized imaging target. The visibility map was validated in a prostate phantom experiment by capturing live ultrasound images of the prostate from different phantom locations. In 20 liver SBRT patients treated with VMAT, the simulation environment was used to place the robotic hardware and ultrasound probe at imaging locations indicated on the visibility map. Imaging targets were either entire PTV (range 5.9–679.5 ml) or entire GTV (range 0.9–343.4 ml). Presence or absence of mechanical collisions with LINAC, couch, and patient body as well as interferences with treated beams were recorded.Results:For PTV targets, robotic ultrasound guidance without mechanical collision was possible in 80% of the cases and guidance without beam interference was possible in 60% of the cases. For the smaller GTV targets, these proportions were 95% and 85% correspondingly. GTV size (1/20), elongated shape (1/20), and depth (1/20) were the main factors limiting the availability of non‐interfering imaging positions.Conclusion:This study indicates that for VMAT liver SBRT, robotic ultrasound tracking of a relevant internal target would be possible in 85% of cases while using treatment plans currently deployed in the clinic. With beam re‐planning in accordance with the presence of robotic ultrasound guidance, intra‐fractional ultrasound guidance may be an option for 95% of the liver SBRT cases.This project was funded by NIH Grant R41CA174089.