Output factor measurement of a dedicated intra-operative radiotherapy (IORT) accelerator using ethanol chlorobenzene (ECB) dosimeter and comparing the results with ionometric dosimetry and monte carlo simulation

Abstract

© 2016, Tehran University of Medical Sciences and Iranian Society of Radiology. Background: The accurate dose delivery in intraoperative radiotherapy (IORT) tightly depends on the precision of measured dose by the ion chamber. Output factor (OF) measurement of dedicated intraoperative electron radiotherapy (IOERT) accelerators using ion chamber faces some technical challenges including determination of Ksat. Objectives: The goal was to evaluate the performance of ethanol chlorobenzene (ECB) dosimeter in measuring the OF of intraoperative electron beam and to compare the results to those of ionometric dosimetry and Monte Carlo simulation. Consequemtly we determined the Ksat of employed ion chamber through comparison of the ECB response to ion chamber. Materials and Methods: LIAC dedicated accelerator (LIAC Sordina SpA, Italy) was used for irradiation. To calculate the Ksat, ECB and Advanced Markus chamber were placed at the depth of maximum dose for different energies of LIAC accelerator. Then, Ksat was calculated through comparison of the obtained results. To measure the OF of electron beam, ECB was placed at the depth of maximum dose for each combination of energy/applicator size, and the absorbed dose was determined. Obtained results were compared to those of Advanced Markus chamber and Monte Carlo simulation. Results: The results of Ksat measurement showed that there is a very good agreement between the practically obtained Ksat and theoretical values determined by Laitano formalism at different energies (the maximum difference between the results was lower than 1%). The results of ECB OF measurement were in accordance to the results of ionometric dosimetry and Monte Carlo simulation (the maximum difference between the results was about 1.5% and 1.7%, respectively). Conclusion: Based on the results, it may be concluded that the ECB dosimeter could be considered as an accurate tool for both OF measurement of intraoperative electron beam and cross calibration of employed ion chambers for absolute dosimetry (determina-tion of the Ksat).