Study of radiochromic film dosimetry on gamma knife

This article explored the properties of radiochromic films in monitoring radiation covering the relationships of time and film reaction, dosimetry linearity, energy dependency and angle dependency. The films were clinically applied in measuring the output dose factors of gamma knife; furthermore, the results were compared with those of the Monte Carlo simulations. This experiment used the Leksell B (Leksell Gamma Knife Type B) gamma knife, MD-55 radiochromic films and the Monte Carlo OMEGA/BEAM simulation program. In this experiment, the Cs-137 radioactive source and the x-ray machine used were from the National Radiation Standard Laboratory (NRSL) and the Co-60 radioactive source was from the National Yang-Ming University. The Monte Carlo method was used to calculate the in-phantom dosimetry and then the measurements of gamma knife output factors were performed with the radiochromic films with high spatial resolutions to verify the accuracy of the calculations and treatment plans. For the output factors of the 18, 14 and 8 mm gamma knife collimator helmet, the respective results from the radiochromic film measurements, Monte Carlo OMEGA/BEAM simulations and Elekta were all within experiment deviations, but for the 4 mm output factor, the measurement value was 2% lower compared with Elekta's value. The results showed that the radiochromic films did make an explicit measurement instrument for the dosimetry quality verification and the treatment output of the 3-D positioning radiation surgery gamma knife.