Evaluation of differences and dosimetric influences of beam models using golden and multi‐institutional measured beam datasets in radiation treatment planning systems

Abstract

Purpose The beam model in radiation treatment planning systems (RTPSs) plays a crucial role in determining the accuracy of calculated dose distributions. The purpose of this study was to ascertain differences in beam models and their dosimetric influences when a golden beam dataset (GBD) and multi‐institution measured beam datasets (MBDs) are used for beam modeling in RTPSs. Methods The MBDs collected from 15 institutions, and the MBDs' beam models, were compared with a GBD, and the GBD’s beam model, for Varian TrueBeam linear accelerator. The calculated dose distributions of the MBDs' beam models were compared with those of the GBD’s beam model for simple geometries in a water phantom. Calculated dose distributions were similarly evaluated in volumetric modulated arc therapy (VMAT) plans for TG‐119 C‐shape and TG‐244 head and neck, at several dose constraints of the planning target volumes (PTVs), and organs at risk. Results The agreements of the MBDs with the GBD were almost all within ±1%. The calculated dose distributions for simple geometries in a water phantom also closely corresponded between the beam models of GBD and MBDs. Nevertheless, there were considerable differences between the beam models. The maximum differences between the mean energy of the energy spectra of GBD and MBDs were −0.12 MeV (−10.5%) in AcurosXB (AXB, Eclipse) and 0.11 MeV (7.7%) in collapsed cone convolution (CCC, RayStation). The differences in the VMAT calculated dose distributions varied for each dose region, plan, X‐ray energy, and dose calculation algorithm. The ranges of the differences in the dose constraints were −5.6% to 3.0% for AXB and −24.1% to 2.8% for CCC. In several VMAT plans, the calculated dose distributions of GBD's beam model tended to be lower in high‐dose regions and higher in low‐dose regions than those of the MBDs' beam models. Conclusions We found that small differences in beam data have large impacts on the beam models, and on calculated dose distributions in clinical VMAT plan, even if beam data correspond within ±1%. GBD’s beam model was not a representative beam model. The beam models of GBD and MBDs and their calculated dose distributions under clinical conditions were significantly different. These differences are most likely due to the extensive variation in the beam models, reflecting the characteristics of beam data. The energy spectrum and radial energy in the beam model varied in a wide range, even if the differences in the beam data were <±1%. To minimize the uncertainty of the calculated dose distributions in clinical plans, it was best to use the institutional MBD for beam modeling, or the beam model that ensures the accuracy of calculated dose distributions.

Technical note: Point‐by‐point ion‐recombination correction for accurate dose profile measurement in high dose‐per‐pulse irradiation field

“…On the other hand, Tani et al. compared the beam data and the RBDs of nine measurements with CC13, TN31010, and TN31021 chambers, and found that they agreed within 1%, but the deviation of the calculated dose in the water phantom exceeded 2% for the modeled beam 9 . When the RBD is used for beam modeling, it is not important that the RBD agrees from the MBD within 1%, but the important question is whether the calculated dose distribution after beam modeling in the RTPS is the same or not regardless of the input beam data sets (RBD, MBD) for beam modeling.…”

“…3 The characteristics of the detector are important for the accuracy in depth profile measurements. 8,9 Ionization chambers, for example, with low energy dependence are desirable in measuring PDDs. 3 VARIAN TrueBeam linacs (Varian Medical Systems, Palo Alto, CA, USA) are equipped with a flattening filter free (FFF) beam in addition to the conventional flattening filter (FF) beam.…”

Delivery accuracy of VMAT on two beam‐matched linacs provided by accelerated go live service

“…Tani et al compared beam data for 15 TrueBeam linacs and showed good agreement. 3 Sjostrom et al reported that it is not always possible to match linacs and some specific models might be required. 4 Elekta has recently provided Accelerated Go Live (AGL) service.…”

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

“…[7][8][9] Furthermore, significant dose calculation differences have been noted when utilizing automated model generation based on closely corresponding beam commissioning data. 10 In addition, with the prevalence of IMRT planning, multi-leaf collimator (MLC) parameter values take on additional importance. 11,12 Historically, radiation oncology clinics have been required to create and validate unique machine-specific beam models in their treatment planning system (TPS) due to variations in treatment delivery system (TDS) performance.…”

“…Despite this commissioning guidance, articles reporting on dosimetry credentialing results from the Imaging and Radiation Oncology Core (IROC) have demonstrated difficulties in creating an accurate beam model, particularly for highly modulated plans 7–9 . Furthermore, significant dose calculation differences have been noted when utilizing automated model generation based on closely corresponding beam commissioning data 10 . In addition, with the prevalence of IMRT planning, multi‐leaf collimator (MLC) parameter values take on additional importance 11,12 …”