[A study of collimator scatter factors of rectangular irradiation fields using the virtual source plane]

Kim introduced the geometric weighting factor concept into the field mapping method, and estimated collimator scatter factors of rectangular fields by correcting collimator exchange effects. The source plane is present at a specific position in the field mapping method, and, accordingly, the geometric weighting factor is constant. In this study, we changed the position of the source plane based on the measurement results, and we estimated the collimator factors of rectangular fields using the field mapping method. A geometric weighting factor at which the measured collimator scatter factors optimally fitted a square collimator scatter factor was calculated in each field. Collimator scatter factors can be accurately calculated recursively by changing the geometric weighting factor, resulting in altering the position of the source plane, as in this method.