Abstract
BackgroundTo create an arc therapy plan, certain current general calculation algorithms such as pencil-beam calculation (PBC) are based on discretizing the continuous arc into multiple fields to simulate an arc. The iPlan RT™ treatment planning system incorporates not only a PBC algorithm, but also a more recent Monte Carlo calculation (MCC) algorithm that does not need beam discretization. The objective of this study is to evaluate the dose differences in a homogenous phantom between PBC and MCC by using a three-dimensional (3D) diode array detector (ArcCHECK™) and 3DVH software.MethodsA cylindrically shaped ‘target’ region of interest (ROI) and a ‘periphery ROI’ surrounding the target were designed. An arc therapy plan was created to deliver 600 cGy to the target within a 350° rotation angle, calculated using the PBC and MCC algorithms. The radiation doses were measured by the ArcCHECK, and reproduced by the 3DVH software. Through this process, we could compare the accuracy of both algorithms with regard to the 3D gamma passing rate (for the entire area and for each ROI).ResultsComparing the PBC and MCC planned dose distributions directly, the 3D gamma passing rates for the entire area were 97.7% with the gamma 3%/3 mm criterion. Comparing the planned dose to the measured dose, the 3D gamma passing rates were 98.8% under the PBC algorithm and 100% under the MCC algorithm. The difference was statistically significant (p = 0.034). Furthermore the gamma passing rate decreases 7.5% in the PBC when using the 2%/2 mm criterion compared to only a 0.4% decrease under the MCC. Each ROI as well as the entire area showed statistically significant higher gamma passing rates under the MCC algorithm. The failure points that did not satisfy the gamma criteria showed a regular pattern repeated every 10°.ConclusionsMCC showed better accuracy than the PBC of the iPlan RT in calculating the dose distribution in arc therapy, which was validated with the ArcCHECK and the 3DVH software. This may suggest that the arc step of 10° is too large in the PBC algorithm in the iPlan RT.
Highlights
To create an arc therapy plan, certain current general calculation algorithms such as pencil-beam calculation (PBC) are based on discretizing the continuous arc into multiple fields to simulate an arc
To calculate a 180° arc, the pencil-beam calculation (PBC) algorithm of iPlan RTTM (BrainLAB, Heimstetten, Germany) planning system uses 19 beams, which are each separated from neighboring beams by a beam angle of 10°
We evaluated the accuracy of the Monte Carlo calculation (MCC) and the PBC algorithm of the iPlan RT software in arc therapy by using a 3D volumetric diode array detector and the 3DVH software
Summary
To create an arc therapy plan, certain current general calculation algorithms such as pencil-beam calculation (PBC) are based on discretizing the continuous arc into multiple fields to simulate an arc. Rotational arc radiation therapy has attracted great interest in the modern radiation therapy era Several techniques such as dynamic arc therapy, intensity-modulated arc therapy (IMAT), volumetric arc therapy (VMAT) and helical tomotherapy have been developed [1,2,3]. To calculate a 180° arc, the pencil-beam calculation (PBC) algorithm of iPlan RTTM (BrainLAB, Heimstetten, Germany) planning system uses 19 beams, which are each separated from neighboring beams by a beam angle of 10°. This method is not continuous, and it is sometimes necessary to increase the number of beams to improve the accuracy of the dose distribution [5]. The MCC method will be more accurate than current TPSs for arc therapy [6]
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