Small field dosimetry and analysis of flattening filter free beams in true beam system

Abstract

The purpose of this study was to report the dosimetric characteristics of the small fields in flattening filter free (FFF) beams (output measurements, profile analysis, surface dose and consistency) generated by medical linear accelerator and its variation with respect to flattened beams (FB). Surface doses were obtained for field sizes 1 × 1-40 × 40 cm(2). Field width and penumbra were analyzed for field sizes 1 × 1-40 × 40 cm(2). To take output factors for small fields, diode and micro chamber were used and data was taken at a source-to-surface distance (SSD) and extended SSD. Consistency checked for the dosimetric data for 1 year. Surface doses were higher in FFF compared with FB up to 20 × 20 cm(2) field size. Measured field sizes were slightly lesser in FFF and penumbra values were increased with respect to field size in both FB and FFF. For small fields, diode values have shown more promising results than micro chamber. Small field output measurements at nominal SSD and extended SSD were well in agreement with each other. FFF beams showed good data consistency in 1 year duration. Small field dosimetry, surface dose, profile analysis and consistency of FFF beams in FFF photon beams were derived and data shown good consistency during 1 year duration.