Radiation transmission, leakage and beam penumbra measurements of a micro-multileaf collimator using GafChromic EBT film

Abstract

Micro-multileaf collimator systems coupled to linear accelerators for radioneurosurgery treatments require a rigorous dosimetric characterization in order to be used in 3D conformal and intensity modulated stereotactic radiosurgery and radiotherapy applications. This characterization involves high precision measurements of leaf transmission, leakage and beam penumbra through the collimation system and requires the use of detectors with high spatial resolution, high sensitivity and practically no energy dependence. In this work the use of GafChromic EBT radiochromic film to measure the basic dosimetric properties of the m3-mMLC (BrainLAB, Germany) micro-multileaf collimator system integrated to a 6 MV linear accelerator is reported. Results show that average values of transmission and leakage radiation are 0.89 ± 0.07% and 1.08 ± 0.18%, respectively. The 80-20% beam penumbra were found to be 2.83 ± 0.14, 2.62 ± 0.12, 2.77 ± 0.17, 2.88 ± 0.12 and 2.88 ± 0.09 using 9.8, 8.0, 6.0, 4.0 and 2.0 mm square field sizes, respectively, with an average value of 2.80 ± 0.13 mm. These measurements are below the reference values reported by the manufacturer and similar to those reported in the literature for the same type of mMLC using different radiation detectors