In-gantry or remote patient positioning? Monte Carlo simulations for proton therapy centers of different sizes

Purpose: We estimated the potential advantage of remote positioning (RP) vs. in-room positioning (IP) for a proton therapy facility in terms of patient throughput. Materials and methods: Monte Carlo simulations of facilities with one, two or three gantries were performed. A sensitivity analysis was applied by varying the imaging and setup correction system (ICS), the speed of transporters (for RP) and beam switching time. Possible advantages of using three couches (for RP) or of switching the beam between fields was also investigated. Results: For a single gantry facility, an average of 20% more patients could be treated using RP: ranging from +45%, if a fast transporter and slow ICS were simulated, to -14% if a slow transporter and fast ICS was simulated. For two gantries, about 10% more patients could be treated with RP, ranging from +32% (fast transporter, slow ICS) to -12% (slow transporter, fast ICS). The ability to switch beam between fields did not substantially influence the throughput. In addition, the use of three transporters showed increased delays and therefore a slight reduction of the fractions executables. For three gantries, RP and IP showed similar results. Conclusions: The advantage of RP vs. IP strongly depends on ICS and the speed of the transporters. For RP to be advantageous, reduced transport times are required. The advantage of RP decreases with increasing number of gantries.