Measurement Of Scatter Factors For Small Photon Fields Using Gaf chromic EBT۲ Film

Introduction: Small field dosimetry is challenging for radiotherapy dosimetry. measurement of the output factor in the air and water (Sc, Scp) is one of the input parameters for commissioning of treatment planning systems and beam modeling. The aims of this study are to measured Sc,Scp for small fields with EBT۲ and Ion chamber and design a appropriate mini-phantom for small fields dosimetry with EBT۲ film. Materials and Methods: output factors in air and water were measured for Siemens linear accelerator ۶Mv energy and fields sizes (۱-۲۰cm) which irradiated by ۲۰۰MU. Measurements were performed using a gafchromicfilm EBT۲ and ۰.۶cc Farmer ion chamber and then the results were compared with Report of AAPM Group۷۴ and TG۱۵۵. For lateral electron equilibrium and electron contamination removal, two top of the water and Cerrobend were designed for film dosimetry and plexiglass buildup cap for Farmer chamber was applied. Results: It was observed that In-air output factors increased with field size, and this increase in Cerrobend top is less than water top and Farmer dosimeter.Sc measured in small field is good agreement with data TG۷۴ (۰.۵%), also Scp result were compared with data TG۱۵۵(۴.۱%), and the response of the film to the Ion chamber isalso in good agreement showed (۲.۴%). Conclusion: EBT۲ film in measured output factors in air and wayer for small field as a good alternative to ion chamber dosimeters known as a standard dosimeter.

کلیدواژه ها:

Output factor ، (Sc) ، (Scp) ، miniphantom ، small field ، gafchromic film EBT۲