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Introduction Employing routine dosimetry protocols for intraoperative electron beam needs further refinements to obtain reliable results. In this regard, the performance of some cylindrical and parallel plate ion chambers for both relative and absolute dosimetry of intraoperative electron beam has been evaluated. Materials and methods Four different ion chambers including Semiflex and PinPoint cylindrical chambers as well as Advanced Markus and Roos parallel plate ones were employed for PDD measurement and dose rate determination in reference condition of the electron beam produced by LIAC intraoperative accelerator. The results of PDD measurements were compared with those of Gafchromic EBT2 film. Specific recommendations were followed to determine the chamber correction factors including ks and k Q,Q 0 for absolute dosimetry in intraoperative reference condition. Results There was good agreement between PDDs measured by employed chambers and EBT2 film at all nominal energies. Nevertheless, Advanced Markus chamber had the best performance based on the gamma analysis results. Obtained k Q,Q 0 and ks for studied ion chambers largely differed from expected values by TRS-398 protocol. The difference of measured dose rates at 12 MeV energy by investigated chambers was less than 1.1% and Advanced Markus had the best accordance with pre-set dose rate by manufacture. Conclusion Results showed that ignoring the specific recommended procedures in determining the chamber correction factors causes the overestimation of the measured dose. Therefore, dedicated dosimetry protocol should be developed for high dose per pulse intraoperative electron dosimetry including all of the updated correction factors and deviations from routine ionometric electron dosimetry formalisms.

Objectives Immediately or after head-and-neck (H&N) cancer chemoradiotherapy (CRT), patients may undergone significant sensorineural hearing loss (SNHL) which could affect their quality of life. Radiomic feature analysis is proposed to predict SNHL induced by CRT. Material and methods 490 image features of 94 cochlea from 47 patients treated with three dimensional conformal RT (3DCRT) for different H&N cancers were extracted from CT images. Different machine learning (ML) algorithms and also least absolute shrinkage and selection operator (LASSO) penalized logistic regression were implemented on radiomic features for feature selection, classification and prediction. Also, LASSO penalized logistic model was used for outcome modelling. Results The predictive power of ten ML methods was more than 70% (in accuracy, precision and area under the curve of receiver operating characteristic curve (AUC)). According to the LASSO penalized logistic modelling, 10 of the 490 radiomic features selected as the associated features with SNHL status. All of the 10 features were statistically associated with SNHL (all of adjusted P-values Conclusion CT radiomic analysis proposed in this study, could help in the prediction of hearing loss induced by chemoradiation. Our study also, demonstrates that combination of radiomic features with clinical and dosimetric variables can model radiotherapy outcome such as SNHL.

Purpose Intraoperative radiation therapy (IORT) using electron beam is commonly done by mobile dedicated linacs that have a variable range of electron energies. This paper focuses on the evaluation of the EBT2 film response in the green and red colour channels for IORT quality assurance (QA). Methods The calibration of the EBT2 films was done in two ranges; 0–8 Gy for machine QA by red channel and 8–24 Gy for patient-specific QA by green channel analysis. Irradiation of calibration films and relative dosimetries were performed in a water phantom. To evaluate the accuracy of the film response in relative dosimetry, gamma analysis was used to compare the results of the Monte Carlo simulation and ionometric dosimetry. Ten patients with early stage breast cancer were selected for in-vivo dosimetry using the green channel of the EBT2 film. Results The calibration curves were obtained by linear fitting of the green channel and a third-order polynomial function in the red channel (R2 = 0.99). The total dose uncertainty was up to 4.2% and 4.7% for the red and green channels, respectively. There was a good agreement between the relative dosimetries of films by the red channel, Monte Carlo simulations and ionometric values. The mean dose difference of the in-vivo dosimetry by green channel of this film and the expected values was about 1.98% ± 0.75. Conclusion The results of this study showed that EBT2 film can be considered as an appropriate tool for machine and patient-specific QA in IORT.

Introduction There is a pressing need for a three-dimensional (3D) dosimetry system, appropriate for clinical use, to enable comprehensive verification of the dose distributions typical of modern radiation therapy. Purpose For this aim we introduced a dosimetry system that consist of a polymer gel dosimeter (MAGIC-F) and a prototype of laboratory dedicated level Optical Computed Tomography (OCT) scanner. Materials and methods The OCT was designed and constructed based on a broad beam visible light source and a two-dimensional charge-coupled device (CCD) detector. In this study spatial resolution parameter was determined. One of the methods for evaluating the spatial resolution of an optical CT scanner is to calculate the modulation transfer function (MTF). Results The system could scan a sample around 25 min completely then a set of cross sectional images is reconstructed from projections. The reconstructed images from optical scanner were analyzed to evaluate spatial resolution. The result indicated 10% modulation was 3.6 cycle/mm. That is means the system has sub millimeter resolution. Conclusion It has been observed that the prototype Optical parallel beam scanner is reliable the perspective of resolution for scanning gels for radiotherapy applications. The cost of fabrication scanner is lower than the commercial models. This scanner is a laboratory dedicated level Optical Computed Tomography of course it can be improved and develop in future.