Bertelsen, Anders3; Hansen, Christian Rønn3; Johansen, Jørgen3; Brink, Carsten3
1 Oncology, Department of Clinical Research, Det Sundhedsvidenskabelige Fakultet, SDU2 Det Sundhedsvidenskabelige Fakultet, SDU3 Oncology, Department of Clinical Research, Det Sundhedsvidenskabelige Fakultet, SDU
Background: A few planning systems are currently able to plan volumetric modulated arc therapy (VMAT). The VMAT algorithm in Pinnacle3 TM is called SmartArc. The capability of SmartArc to create complex VMAT plans for the head and neck (H&N) region was tested. Materials and Methods: This retrospective planning study included 11 patients with oropharyngeal or hypopharyngeal cancer previously treated with IMRT by utilization of the Pinnacle treatment planning system and Elekta Synergy accelerators. Doses between 50 Gy and 68 Gy were prescribed to relevant Planning Target Volumes (PTV) as specified by the DAHANCA recommendations. The patients were re-planned with VMAT by use of the SmartArc algorithm in Pinnacle3 TM 8.9c (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 sparing of the organs at risk (OAR) by VMAT compared to the IMRT plan. The VMAT plans were compared to the original IMRT plans by evaluation of 1) dose-volume histograms (DVH) of targets and organs at risk 2) monitor units 3) treatment time and 4) the dose measured with a Delta4 phantom from Scandidos. Results: For all 11 patients, it was possible to achieve clinically acceptable treatment plans based on one single arc which satisfied the re-planning objectives. On average, VMAT used less monitor units compared to IMRT. Delivering the VMAT plans on an Elekta Synergy accelerator the mean treatment time was 250 s which was a 40 % reduction in treatment time compared to IMRT treatments. For all plans, the Delta4 dose measurement showed that more than 97 % of the measurement points satisfied a gamma criterion of 3 mm and 3 % of 2 Gy. CONCLUSION: With SmartArc it was possible in one single arc to achieve the same target coverage and sparing of OAR as achieved with IMRT. VMAT provided more conformal treatment plans compared to the original IMRT plans. Thus. with VMAT the high-dose volumes in the surrounding normal tissues are decreased which potentially reduces the normal tissue complication probability. On average the VMAT plans used fewer MUs compared to IMRT. This reduces the scattered dose to the patient. VMAT reduced the treatment time by ~40 % compared to IMRT. Finally, all VMAT plans were successfully delivered on an Elekta Synergy accelerator with geometric acceptable dose distributions.