Dosimetric verification of micro‐MLC based intensity modulated radiation therapy

A methodology for the dosimetric verification of micro‐multileaf collimator (mMLC) based intensity modulated radiation therapy (IMRT) plans intended for stereotactic applications is described. The method is similar to that of conventional IMRT patient‐specific quality assurance (QA) with some notable exceptions, particularly, mechanical tests that verify the mMLC positioning with respect to the isocenter and individual leaf calibration prior to use. Relative dosimetry measurements are performed with radiographic film, a commercial film‐scanning system and a dose‐image registration program. Film dosimetry results are within [Formula: see text] of calculated distributions or within 2.0 mm distance to agreement. Absolute dosimetry measurements are performed with a small volume ion chamber and a commercially available stereotactic phantom. The cumulative dose from all beams is within [Formula: see text] of the prescribed dose. Large deviations may be observed from individual beams since the smaller IMRT fields tend to have very few high‐dose and low‐gradient regions. An independent program that examines the treatment mMLC file is used to estimate the central axis dose from each beam and provide a dose image that can be assessed alongside the intended fluence distribution prior to treatment. Tolerances for relative and absolute dosimetry of mMLC‐based IMRT treatments are tighter than what is typically reported for conventional MLC‐based IMRT. Also, the time commitment for the IMRT QA is slightly longer than of conventional MLC‐based IMRT due to QA processes that check the mechanical alignment of the mMLC device with the laser and radiation isocenter. PACS Number: 87.53Dq, 87.53Ly, 87.53Tf