Abstract
A superposition/convolution GPU‐accelerated dose computation algorithm (the Calculator) has been recently incorporated into commercial software. The algorithm requires validation prior to clinical use. Three photon energies were examined: conventional 6 MV and 15 MV, and 10 MV flattening filter free (10 MVFFF). For a set of IMRT and VMAT plans based on four of the five AAPM Practice Guideline 5a downloadable datasets, ion chamber (IC) measurements were performed on the water‐equivalent phantoms. The average difference between the Calculator and IC was −0.3 ± 0.8% (1SD). The same plans were projected on a phantom containing a biplanar diode array. We used the forthcoming criteria for routine gamma analysis, 3% dose–error (global (G) normalization, 2 mm distance to agreement, and 10% low dose cutoff). The γ (3%G/2 mm) average passing rate was 98.9 ± 2.1%. Measurement‐guided three‐dimensional dose reconstruction on the patient CT dataset (excluding the Lung) resulted in a similar average agreement rate with the Calculator: 98.2 ± 2.0%. The mean γ (3%G/2 mm) passing rate comparing the Calculator to the TPS (again excluding the Lung) was 99.0 ± 1.0%. Because of the significant inhomogeneity, the Lung case was investigated separately. The calculator has an alternate heterogeneity correction mode that can change the results in the thorax for higher‐energy beams (15 MV). As this correction is nonphysical and was optimized for simple slab geometries, its application leads to mixed results when compared to the TPS and independent Monte Carlo calculations, depending on the CT dataset and the plan. The Calculator vs. TPS 15 MV Guideline 5a IMRT and VMAT plans demonstrate 96.3% and 93.4% γ (3%G/2 mm) passing rates respectively. For the lower energies, which should be predominantly used in the thoracic region, the passing rates for the same plans and criteria range from 98.6 to 100%. Overall, the Calculator accuracy is sufficient for the intended use.
Highlights
It is the current standard of practice in the United States that for each radiotherapy treatment course involving intensity modulated, inversely planned dose delivery (IMRT/VMAT), a patient-specific quality assurance procedure has to be performed to ensure that the calculated dose distribution is reasonably accurate.[1]
Patient specific IMRT QA was performed by projecting the treatment plan on a phantom containing a dosimeter and comparing the measured sample of the 3D dose distribution with calculations.[3]
We critically examine and validate a fast, independent 3D dose calculator as an additional tool that potentially could be incorporated in the IMRT/VMAT QA process
Summary
It is the current standard of practice in the United States that for each radiotherapy treatment course involving intensity modulated, inversely planned dose delivery (IMRT/VMAT), a patient-specific quality assurance procedure has to be performed to ensure that the calculated dose distribution is reasonably accurate.[1]. Patient specific IMRT QA was performed by projecting the treatment plan on a phantom containing a dosimeter and comparing the measured sample of the 3D dose distribution with calculations.[3] As the inversely planned techniques matured and became the mainstay of radiotherapy, alternative dose verification techniques started to be actively explored Those included electronic portal imaging device (EPID)-based dosimetry,[4,5] calculation-based reconstruction from the accelerator log files,[6,7] including harvesting aperture shapes (but not fluence) from the EPID,[8] or just a straightforward recalculation by an independent dose engine.[9,10,11,12,13] Each method has its advantages and disadvantages, and none is capable of catching every possible mode of failure,[10] including catastrophic events
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