Commissioning of a micro-MLC (mMLC) for Stereotactic Radiosurgery / 의학물리

ABSTRACT

The 4 bank mico-MLC (mMLC; Acculeaf, Direx, Isral) has been commissioned for clinical use of linac based stereotactic radiosurgery. The geometrical parameters to control the leaves were determined and comparisons between measured and calculated by the calculation model were performed in terms of absolute dose (cGy/100 MU). As a result of evaluating calculated dose for various field sizes and depths of 5 and 10 cm in water in the geometric condition of fixed SSD (source to surface distance) and fixed SCD (source to chamber distance), most of differences were within 1% for 6 MV and 15 MV x-rays. The penumbral widths at the isocenter were approximately evaluated to 0.29~0.43 cm depending on the field size for 6 MV and 0.36~0.51 cm for 15 MV x-rays. The average transmission and leakage for 6 MV and 15 MV x-rays were 6.6% and 7.4% respectively in single level of leaves fully closed. In case of dual level of leaves fully closed the measured transmission is approximately 0.5% for both 6 MV and 15 MV x-rays. Through the commissiong procedure we could verify the dose characteristics of mMLC and approximately evaluate the error ranges for treatment planning system.