In the present study, we describe a method based on the analysis of the dynamic MLC log files (DynaLog) generated by the controller of a Varian linear accelerator in order to perform patient‐specific IMRT QA. The DynaLog files of a Varian Millennium MLC, recorded during an IMRT treatment, can be processed using a MATLAB‐based code in order to generate the actual fluence for each beam and so recalculate the actual patient dose distribution using the Eclipse treatment planning system. The accuracy of the DynaLog‐based dose reconstruction procedure was assessed by introducing ten intended errors to perturb the fluence of the beams of a reference plan such that ten subsequent erroneous plans were generated. In‐phantom measurements with an ionization chamber (ion chamber) and planar dose measurements using an EPID system were performed to investigate the correlation between the measured dose changes and the expected ones detected by the reconstructed plans for the ten intended erroneous cases. Moreover, the method was applied to 20 cases of clinical plans for different locations (prostate, lung, breast, and head and neck). A dose‐volume histogram (DVH) metric was used to evaluate the impact of the delivery errors in terms of dose to the patient. The ionometric measurements revealed a significant positive correlation false(normalR2=0.9993false) between the variations of the dose induced in the erroneous plans with respect to the reference plan and the corresponding changes indicated by the DynaLog‐based reconstructed plans. The EPID measurements showed that the accuracy of the DynaLog‐based method to reconstruct the beam fluence was comparable with the dosimetric resolution of the portal dosimetry used in this work false(3normal%/3 mmfalse). The DynaLog‐based reconstruction method described in this study is a suitable tool to perform a patient‐specific IMRT QA. This method allows us to perform patient‐specific IMRT QA by evaluating the result based on the DVH metric of the planning CT image (patient DVH‐based IMRT QA).PACS number: 87.55.Qr

BackgroundThe software PRIMO for the Monte Carlo simulation of radiotherapy linacs could potentially act as a independent calculation system to verify the calculations of treatment planning systems. We investigated the suitability of the PRIMO default beam parameters to produce accurate dosimetric results for 6 MV photon beams from Varian Clinac 2100 linacs and 6 MV flattening–filter–free photon beams from Varian TrueBeam linacs.MethodsSimulation results with the DPM algorithm were benchmarked against a published reference dosimetry dataset based on point measurements of 25 dosimetric parameters on a large series of linacs. Studied parameters (for several field sizes and depths) were: PDD, off–axis ratios, and output factors for open fields and IMRT/SBRT–style fields. For the latter, the output factors were also determined with radiochromic film and with a small–sized ionization chamber. Benchmark data, PRIMO simulation results and our experimental results were compared.ResultsPDD, off–axis ratios, and open–field output factors obtained from the simulations with the PRIMO default beam parameters agreed with the benchmark data within 2.4% for Clinac 2100, and within 1.3% for TrueBeam. Higher differences were found for IMRT/SBRT–style output factors: up to 2.8% for Clinac 2100, and up to 3.3% for TrueBeam. Experimental output factors agreed with benchmark data within 1.0% (ionization chamber) and within 1.9% (radiochromic film).ConclusionsPRIMO default initial beam parameters for 6 MV photon beams from Varian Clinac 2100 linacs and 6 MV FFF photon beams from Varian TrueBeam linacs allowed agreement within 3.3% with a dosimetry database based on measurements of a high number of linacs. This finding represents a first step in the validation of PRIMO for the independent verification of radiotherapy plans.Electronic supplementary materialThe online version of this article (10.1186/s13014-018-1076-0) contains supplementary material, which is available to authorized users.

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