Abstract
Purpose: HybridArc is a new treatment modality that combines dynamic conformal arcs and intensity modulated beams in a single inverse‐optimized plan. The aim of this work is to evaluate the dosimetric accuracy of HybridArc, in iPlan RT Dose 4.5 (BrainLAB) using a cylindrical diode array (ArcCHECK, Sun Nuclear Corporation). Methods: HybridArc plans for various sites (intracranial and extracranial) were constructed. After that the dose distributions were recalculated for the cylindrical ArcCHECK diode array with Monte Carlo(MC) and Pencil Beam (PB) dose algorithms in iPlan. Measurements of these dose distributions were performed with the 6 MV photon beams of a Novalis accelerator (BrainLAB) using the ArcCHECK device without and with an insert containing an ionization chamber. The measurements were evaluated using gamma criteria of various degrees of stringency (dose difference/distance to agreement: 2%/2mm, 3%/3mm and 5%/3mm).Results: For the HybridArc plans studied here, good agreement between the ArcCHECK measurements and the MC calculations is observed (pass rates of 95%, 99% and 100% for 2%/2mm, 3%/3mm and 5%/3mm, respectively). The results are similar to the quality assurance measurements that are routinely carried out at our institution for IMRT plans, which are calculated with the PB algorithm. However, agreement between HybridArc PB calculations and measurements is less satisfactory (pass rates of 69%, 85% and 91% for 2%/2mm, 3%/3mm and 5%/3mm, respectively). This is probably due to the limited angular resolution of the PB dose calculation (10 degree discretization) Conclusions: MC dose calculations and ArcCHECK measurements of HybridArc plans showed good agreement, even when evaluated with the most stringent 2%/2mm gamma criterion. PB calculations significantly differ from the ArcCHECK measurements so that the MC algorithm is found to be superior to the PB algorithm in calculation of the HybridArc plans. However, use of a finer angular resolution may improve the PB results significantly.
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