Evaluation of candidate template beam models for a matched TrueBeam treatment delivery system

Abstract

Purpose: To explore candidate RayStation beam models to serve as a class-specific template for a TrueBeam treatment delivery system. Methods: Established validation techniques were used to evaluate three photon beam models: a clinically optimized model from the authors' institution, the built-in RayStation template, and a hybrid consisting of the RayStation template except substituting average MLC parameter values from a recent IROC survey. Comparisons were made for output factors, dose profiles from open fields, as well as representative VMAT test plans.Results: For jaw-defined output factors, each beam model was within 1.6% of expected published values. Similarly, the majority (57-66%) of jaw-defined dose curves from each model had a gamma pass rate >95% (2% / 3 mm, 20% threshold) when compared to TrueBeam representative beam data. For dose curves from MPPG 5.a MLC-defined fields, average gamma pass rates (1% / 1 mm, 20% threshold) were 92.9%, 85.1%, and 86.0% for the clinical, template, and hybrid models, respectively. For VMAT test plans measured with a diode array detector, median dose differences were 0.6%, 1.3%, and 1.1% for the clinical, template, and hybrid models, respectively. For in-phantom ionization chamber measurements with the same VMAT test plans, the average percent difference was −0.3%, −1.4%, and −1.0% for the clinical, template, and hybrid models, respectively. Conclusion:Beam model templates taken from the vendor and aggregate results within the community were both reasonable starting points, but neither approach was as optimal as a clinically tuned model, the latter producing better agreement with all validation measurements. Given these results, the clinically optimized model represents a better candidate as a consensus template. This can benefit the community by reducing commissioning time and improving dose calculation accuracy for matched TrueBeam treatment delivery systems.

IMRT QA result prediction via MLC transmission decomposition

“…Once that was completed, points belonging to the tongue and groove zone were then assigned to one of the three subgroups: paired, exposed, or neglected. Similarly, specific points belonging to open field were reassigned to the calibration classification if their assignment changed after applying RayStation's position calibration 12 . The assignment criteria for the seven classifications are provided in Table 2.…”

“…Similarly, specific points belonging to open field were reassigned to the calibration classification if their assignment changed after applying RayStation's position calibration. 12 The assignment criteria for the seven classifications are provided in Table 2.…”

“…In this work, it is based on the standard 120 leaf Millennium MLC on a TrueBeam (Varian Medical Systems, Palo Alto, California) c-arm treatment delivery system and the corresponding institution's beam model within the RayStation 8B treatment planning system. 12 In this model, the MLC is considered to have zero height and is represented as a 2D transmission array. It is sufficient to treat the MLC geometry of each control point as lying in a rectangular plane, the extent of which is defined by the jaw positions.…”

“…We utilized a clinically optimized TrueBeam model for a flattened 6 MV (X06F) beam. 12 The three coefficients of the calibration function (offset, gain, and curvature),tip width,tongue and groove width,and transmission parameter values are summarized in Table 1.…”

Golden beam data provided by linear accelerator manufacturers should be used in the commissioning of treatment planning systems

“…In light of this, time may be better invested in creating a personalised, optimal model based on comprehensive commissioning of the machine. This has been shown as the best approach by Hansen et al [ 18 ] who compared a clinical model, a Raystation model and a hybrid IROC-Raystation model.…”