High-precision therapy. Pitfalls in dose verification and QA/QC

Firstly, this paper takes up the exposure dose in the intensity modulated radiation therapy (IMRT) using a multileaf collimator (MLC), and describes the dose component derived from the shape of MLC. As the features of the shape, there are arc-like shape and tongue and groove structure at the edge of MLC. It also describes dose decrease due to the tongue and groove effect of a dynamic multileaf collimator (DMLC) in IMRT. Secondly, it describes the effects of the dosimetric leaf gap of MLC, as the modeling parameter of therapy planning equipment toward IMRT, and the setting value of dose transmittance on exposure dose. Furthermore, it touches on dose verification in IMRT, and discusses that it is necessary to sufficiently understand the characteristics of calculated dose and measured value liable to induce dose error, since the dose verification in IMRT is performed through the comparison between the calculated dose (dose at reference points and dose distribution) and measured value. Finally, it takes up the evaluation of beam distribution, and describes the visual evaluation of dose difference or isodose curve, evaluation through distance-to-agreement (DTA) that quantifies the position aberration of the isodose curve, and gamma ray analysis. (A.O.)