Background: A few planning systems are currently able to plan volumetric modulated arc therapy (VMAT) which can be delivered on Elekta and Varian accelerators. Pinnacles version of a VMAT algorithm is called SmartArc. SmartArcs capability to modulate complicated treatment plans is to be tested. Materials and Methods: This retrospective planning study includes 10 oropharyngis c. patients previously treated with IMRT by utilization of Pinnacle treatment planning system and Elekta Synergy accelerators. Doses between 50 and 68 Gy were prescribed to relevant PTVs as specified by the DAHANCA recommendations. The patients were re-planned with VMAT by use of the SmartArc algorithm in Pinnacle (research version). The collapsed cone dose engine was used for final dose calculation. One constraint for the re-planning study was to use only one single arc to create deliverable plans. The objectives were to achieve similar or better target coverage and sparring of organs at risk (OAR) as achieved in the IMRT plan. The VMAT plans were compared to the original IMRT plans by evaluation of 1) treatment time, 2) monitor units (MU) 3) DVH for targets and OAR and 4) the dose measured with a Delta4 phantom from Scandidos. Results: For all 10 patients it was possible to achieve clinically acceptable treatment plans based on one single arc which fulfilled the re-planning objectives. In average the VMAT and IMRT plans used the same number of MU. The VMAT plans were delivered on an Elekta Synergy accelerator. The treatment time was in average ~200s which is a 50 percent reduction in treatment time compared to IMRT treatments. For all plans the Delta4 dose measurement showed that more than 90 % of the measurement point satisfied a gamma criterion of 3mm and 3% of max dose. Conclusion: With SmartArc it was possible in one single arc to achieve the same target coverage and sparring of OAR as achieved with IMRT. The VMAT plans used the same number of MU as the IMRT plans. Both IMRT and VMAT plans were delivered on an Elekta Synergy accelerator with acceptable dose precision. VMAT reduced the treatment time by approximately 50% compared to IMRT.
Dansk Selskab for Klinisk Onkologi. Årsmøde 2009, 2009