Acquisition of small field electron dosimetry data using ion chamber Gafchromic® EBT3 film and development of GUI for treatment parameters calculation

摘要

Small electron field is a preferential choice of the oncologists in case of the treatment of small superficial lesions (scars). Small field electron dosimetry is necessary to perform prior to the treatment to assure the accuracy of the dose delivery. The main objectives of this work is to acquire small field electron dosimetric data with narrow circular cutouts and to develop the graphical user interface on the basis of this acquired data to extract desired field parameters from the data. Results show that as the cutout size become smaller, percentage depth dose shifts towards surface due to the lack of lateral scatter equilibrium. Thus surface dose is increased i.e. the depth of maximum dose (dmax) is reduced. Similarly the depth of 90% isodose level is decreased as well as the range (i.e. R50 and Rp). Whereas the x-ray contamination is increased with decrease in cutout diameter, field size coverage for 90% isodose curve and the relative output factor is decreased. Results of the radiochromic films were not up to expectations because of the existence of air pockets as the acquisition was performed with solid water phantom slabs. It is, therefore, suggested to use these films in real water. Based on experimental data, GUI enables us to find treatment parameters i.e. energy, cutout dimension, margins, bolus thickness, monitor units etc.