Measurement Of Scatter Factors For Small Photon Fields Using Gaf chromic EBT2 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 EBT2 and Ion chamber and design a appropriate mini-phantom for small fields dosimetry with EBT2 film. Materials and Methods: output factors in air and water were measured for Siemens linear accelerator 6Mv energy and fields sizes (1-20cm) which irradiated by 200MU. Measurements were performed using a gafchromicfilm EBT2 and 0.6cc Farmer ion chamber and then the results were compared with Report of AAPM Group74 and TG155. 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 TG74 (0.5%), also Scp result were compared with data TG155(4.1%), and the response of the film to the Ion chamber isalso in good agreement showed (2.4%). Conclusion: EBT2 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.