查看文章

The dosimetric effects from the jaw positioned close to the small field (, , and ) side‐edge generated by a single‐focused multileaf collimator (MLC) were measured and studied. The measurement is important in intensity modulated radiotherapy (IMRT) because generally the jaw cannot perfectly cover all the leaf‐ends in a segment of irregular field. This leads to additional dose contributed by (1) the end surface of the jaw, (2) the leaf‐end, and (3) the inter‐ and intraleaf leakage/transmissions during the dosimetric measurement. Moreover, most of the conventional treatment planning systems ignore these effects in the dose calculation. In this study, measurements were made using a Varian 21 EX linear accelerator with 6 MV photon beam through a MLC containing 120 leaves. Percentage depth dose, beam profile, and output for small fields were measured by varying the jaw at different positions away from the leaf …