Multileaf collimator interleaf transmission

Multileaf collimators (MLCs) have advanced past their original design purpo se as a replacement for held shaping cerrobend blocks. Typically, MLCs inco rporate an interlocking tongue-and-groove design between adjacent leaves to minimize leakage between leaves. They are beginning to be used to provide intensity modulation for conformal three-dimensional radiation therapy. It is possible that a critical target volume may receive an underdose due to t he region of overlap if adjacent leaves are allowed to alternate between th e open and closed positions, as they might if intensity modulation is emplo yed. This work demonstrates the magnitude of that effect for a commercially available one-dimensional temporally modulated MLC. The magnitude of the t ransmission between leaves as a function of leaf separation was also studie d, as well as the transmission as a function of leaf rotation away from the source. The results of this work were used for the design of a tomotherapy MLC, The radiation leakage considerations for a tomotherapy MLC are discus sed. (C) 1999 American Association of Physicists in Medicine. [S0094-2405(9 9)01702-2].