Dose distributions of x-ray fields as shaped with multileaf collimators

Abstract

Multileaf collimators (MLC) with various blade widths were simulated using standard cerrobend blocks, and three-dimensional dose computations were carried out to study the resultant radiation field edges. Film measurements made with 6 and 18 MV X-ray beams were compared with calculations that employed a three-dimensional Fourier convolution. The computer simulation was used to study the deviation of the calculated 50% isodose line from the desired geometric field edge using various MLC blade positions. The study suggests that multileaf collimation to the outside of the desired field edge will lead to overdose outside the field, whereas multileaf collimation to the inside of the desired field edge will lead to underdose inside the field.