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Introduction. COVID radiotherapy requires performance of all radiotherapy (RT) procedures during one site visit due to the infectious nature of the disease. The aim of the study was to develop methods of estimating the delivered dose based on electronic portal image device (EPID) signal during treatment. Material and methods. Electronic portal image device signal was measured as a function of the phantom dose. The dose in 14 COVID patients was estimated for two X6MV beams. Results. The method allows to estimate dose in phantom with uncertainty of 12%. In this case, a systematic error was reported. Therefore, coefficients for clinical data were calculated and used to determine the dose in patients. The mean difference between the dose calculated and the dose measured for the 14 patients was 1%, but the uncertainty of this method was estimated as ±6% Conclusions. The proposed method may be useful in clinical practice as in vivo method. However, due to high uncer- tainty, it should be dedicated to the detection of “big” errors. [ABSTRACT FROM AUTHOR]

Abstract: Background: During a proper execution of dMLC plans, there occurs an undesired but frequent effect of the dose locally accumulated by tissue being significantly different than expected. The conventional dosimetric QA procedures give only a partial picture of the quality of IMRT treatment, because their solely quantitative outcomes usually correspond more to the total area of the detector than the actually irradiated volume. Aim: The aim of this investigation was to develop a procedure of dynamic plans verification which would be able to visualize the potential anomalies of dose distribution and specify which tissue they exactly refer to. Materials & methods: The paper presents a method discovered and clinically examined in our department. It is based on a Gamma Evaluation concept and allows accurate localization of deviations between predicted and acquired dose distributions, which were registered by portal as well as film dosimetry. All the calculations were performed on the self-made software GammaEval, the γ-images (2-dimensional distribution of γ-values) and γ-histograms were created as quantitative outcomes of verification. Results: Over 150 maps of dose distribution have been analyzed and the cross-examination of the gamma images with DRRs was performed. Conclusions: It seems, that the complex monitoring of treatment would be possible owing to the images obtained as a cross-examination of γ-images and corresponding DRRs. [Copyright &y& Elsevier]

Summary: Background: The electronic portal imaging device (EPID) is used for patient setup during radiotherapy sessions. Dosimetric verification is done using ion chambers, diodes and thermoluminescence detectors. In intensity-modulated radiation therapy (IMRT) the dosimetry is a sophisticated and time-consuming task. The simultaneous use of amorphous silicon (aSi) detectors and the transit dosimetry (TD) option in the treatment planning system (TPS) (Eclipse, Varian) enables dosimetric pre-treatment verification of the IMRT plans. Aim: The purpose of this study was to calibrate the EPID and TPS and to evaluate the usefulness of that method for dose verification in IMRT technique. Materials/Methods: The first step was calibration of the aSi EPID mounted on three linear accelerators (Clianc23EXS, Varian). Afterwards, configuration of the calculation algorithm in TPS was carried out. Then dosimetric characteristics of the EPID were investigated. The EPID response depending on the beam mode, treatment time and static square field size was measured. The same measurements were repeated twice for three accelerators and analyzed. Additionally, three IMRT plans were treated for the pre-treatment dose evaluation. The calculated dose matrix was compared with the delivered one. The similarity of the calculated and measured fluency maps was evaluated by means of gamma index and score factor in Eclipse. Results: The linearity of the EPID signal was proven. For both beam modes EPID response is proportional to treatment time and field size, within the considered field size range. Conclusions: The gamma evaluation indicates good correlation between predicted and acquired EPID image, although some differences in a high gradient area were found. We found the EPID-based pre-treatment IMRT verification method to be a good quality assurance (QA) procedure. Quite frequent control of the method and periodic recalibration of the used device are required. [Copyright &y& Elsevier]