Initial dosimetric evaluation of SmartArc - a novel VMAT treatment planning module implemented in a multi-vendor...

We performed an initial dosimetric evaluation of SmartArc - a novel VMAT planning module for Philips Pinnacle treatment planning system. A test suite of structure sets and dose objectives provided by the AAPM for multi-institutional comparison of IMRT dosimetry was used. A total of fifty plans were successfully delivered. The effect of control point spacing on dosimetric accuracy was investigated. When calculated with the 4 masculine spacing, the overall mean point dose errors measured with an ion chamber were 0.5+/-1.4 and -0.3+/-1.4% for the PTV and OAR, respectively. The gamma(3%,3mm) passing rate, measured for absolute dose with a biplanar diode array, was 98.2+/-1.6% (range 94.5-99.9%). Ninety percent of the passing rate values were above 97.7%. With the 6 masculine control point spacing, the highly modulated plans exhibited large dosimetric errors, while the results were still acceptable for the simpler cases. The data show that the practical accuracy of the small-arc approximation, which is at the heart of VMAT dose calculations, depends not only on the control point spacing, but also on the size and relative position of the MLC openings corresponding to the consecutive control points. The effect of the minimum allowed separation between the opposing leaves was found to be minimal. It appears that 4 masculine control point spacing may be a good compromise between calculation speed and accuracy. However each institution is encouraged to establish its own treatment planning guidelines based on the case complexity and acceptable error level.