Validation of a new formulism and the related correction factors on output factor determination for small photon fields

(1)Peel Regional Cancer Center, Trillium Health Partners, Mississauga, ON (2) Department of Radiation Oncology, University of Toronto, Toronto, ON (3) Radiation Oncology Dept., Indiana UniversitySchool of Medicine, Indianapolis, IN, USA Introduction It is well known that the small field sizes (≤30 x 30mm 2 ) encountered in stereotactic radiosurgery (SRS) create difficulties in measuring dosimetric data that arise due to lack of charged-particle equilibrium or transient equilibrium (CPE/TCPE) and occlusion of the radiation source. 1, 2 . Furthermore, the choice of detector used for measurements in small field conditions is complicated by the finite size of the detector and non-water equivalence of detector components. 3 Significant variations in measured output factors or total scatter factors using different detectors in the same measurement conditions have been reported. 1, 4-6 If uncorrected, such variations could potentially lead to significant error in delivered dose. 7