Investigation into the Pinnacle SmartArc Module for VMAT Planning

This study describes the early investigation of a new VMAT planning module developed by Philips for the Pinnacle TPS. The Pinnacle solution for VMAT planning, SmartArc, was evaluated for example prostate patients including inverse planning, export, delivery and verification. The quality of verification was investigated as the gantry spacing of the arc used in the final dose calculation on the TPS was varied. The inverse planning was performed using the same objectives as for our established prostate IMRT programme. Verification of the treatment plan was performed using the Delta4 phantom (Scandidos, Sweden) on an Elekta Synergy linac. The robustness of delivery to machine faults such as gantry overshoots, prf drop-outs, beam interruptions, and communication drop-outs was investigated. SmartArc was able to produce clinically acceptable plans that were at least comparable to the standard IMRT plans. The time for delivery was around 100 seconds compared to 220 seconds for the IMRT plans, mostly due to the separate loading of each step-and-shoot IMRT beam compared to a single button push for VMAT. The quality of the verification was strongly influenced by the gantry spacing of the final dose calculation on Pinnacle, with <60% of pixels with a Γ<1 using a 2mm/2% tolerance for 8° spacing compared to >90% when using 4° for the final gantry spacing. However, the time for delivery increased from ~1.6 min to ~2.2min when the final gantry spacing was reduced. Repeat deliveries with a large range of faults and terminations induced did not degrade the delivered solution highlighted the robustness of the linac delivery. The SmartArc module developed within the Pinnacle TPS is able to produce clinically acceptable plans, provided a final gantry spacing of ≤4° is employed.