The characteristics of Gafchrommic™ EBT film for dosimetric verification for high energy photon beams

Abstract

The objectives of this research are to study the characteristics of GafchromicTM EBT film for 6 MV x-ray photon beams and to verify isodose distribution of advanced radiation treatment techniques. The characteristics of Epson perfection V700 flat-bed color CCD were studied for the response, repeatability, reproducibility and color band of scanner. The characteristics of GafchromicTM EBT film were investigated for speed of film development, polarization, uniformity, field size, dose rate and repeatability rate effect. The percentage depth dose and beam profile were measured and compared with the data from ionization chamber. The comparisons of fluence map measured by film and calculated by Eclipse treatment planning were observed for two nasopharynx caner and one brain tumor. The response of Epson perfection V700 flat-bed color CCD in term of pixel value and net optical density showed the polynomial curve. The variations of scanner reproducibility and repeatability were within 1.0% and 1.1%, respectively. The GafchromicTM EBT film was best evaluated in the red channel of the Epson perfection V700 scanner. The optical density growths with time seem to stabilize after 4 hours and increasing up to ±7 %. The effect of EBT film polarization at 900 and 2700, with 50 cGy delivered dose was up to 24% difference when compared with orientation at 00. The variation of EBT film uniformity was ±7 % at 400 cGy. The film responses did not depend on the dose rate and repeatability rate. The difference of percentage depth dose between EBT film and CC13 ionization chamber was 3.11% for 2×2 cm2 field size at 5 cm depth. The deviation of beam profile between EBT film and CC13 ionization chamber was presented at region of off-axis and high dose gradient. The fluence map measured by GafchromicTM EBT and calculated by Eclipse planning system of two nasopharynx cancer and one brain tumor were compared with the criterion of 3% dose difference and 3 mm distance to agreement. The two plans showed over 90% passed but one plan was below 90%. The characteristics of scanner should be studied before examined the characteristics of GafchromicTM EBT film. The characteristics of film such as speed of film development, polarization effect and uniformity were very important because of the stability time of net optical density and the direction of non-polarization effect should be selected. The uniformity of film affected to dose distribution verification, it should be corrected before scanning the film. Then, the GafchromicTM EBT films can be implemented to verify isodose distribution of advanced radiation treatment techniques.