SU‐FF‐T‐401: Surface Dose Measurement in 6 MeV X‐Ray Beam Using Radiographic Film and TLD

Abstract

Purpose: The purpose of this study was to estimate and compare the surface dose in 6 MV x‐ray beam using TLDs, radiographic film and parallel plate ionization chamber. Method and Materials:_ The surface dose measurements were performed in a 6 MV x‐ray beam of a medical accelerator (Varian 2100 C/D) with X‐Omat V (Ready Pack) radiographic film, LiF thermoluminescence dosimeters (TLD‐100) and parallel plate ionization chamber (PTW) for 10×10 cm field size. The film was placed perpendicular to the beam axis at the surface and at different depths of a solid water phantom, placed 100 cm from the source (SSD=100). The film was calibrated to convert optical density to dose. For TLD measurements, five TLDs were inserted in the center of 2 mm thick Perspex plate and placed at different depths in a solid water phantom. Each TLD was individually calibrated. A Parallel Plate Chamber was placed in a solid water phantom at different depths and the doses were extrapolated to estimate the surface dose. Results: The estimated surface dose with radiographic film was found 17.4% ± 3% and with the TLD technique was found 23% ± 3% relative to maximum dose. The corresponding parallel plate ionization chamber extrapolated dose was 17.8 % ± 2% relative to maximum dose. Conclusion: Radiographic film measurement of surface dose showed good agreement with the parallel plat ionization chamber in this study. With TLD‐100, the measured surface dose was higher than chamber and film measurements due to the positioning of the TLD in the phantom and the inaccuracy of the effective point of measurement.