SWIMRT: a graphical user interface using sliding window algorithm to construct fluence map machine file

Abstract

A house-made computer program, SWIMRT to construct ?multi-leaf collimator (MLC) machine? file for IMRT fluence maps was developed using MATLABâ and the sliding window algorithm. The user can either import a fluence map with a graphical file format created by an external treatment planning system such as Pinnacle3, or create his own fluence map using the matrix editor in the program. Through comprehensive calibrations of the dose and dimension of the imported fluence field, the user could use associated image processing tools such as field resizing and edge trimming to modify the imported map. When the processed fluence map was suitable, a ?MLC machine? file would be generated for our Varian 21 EX linear accelerator (linac) with a 120-leaf Millennium MLC. This machine file was transferred to the MLC console of the linac to control the continuous motions of the leaves during the beam irradiation. An IMRT field was then irradiated with the 2D intensity profiles, and the irradiated profiles were compared to the imported or modified fluence map. This program has been verified and tested using film dosimetry and uncertainties to note: (1) the mechanical limitation due to the leaf width and maximum traveling speed, and (2) the dosimetric limitation due to the leaf leakage/transmission and penumbra effect. As the fluence map could be edited, resized and processed according to the requirement of a study, SWIMRT was found essential in studying and investigating the IMRT technique using the sliding window algorithm. Using this program, future work on the algorithm may include redistributing the time space between segmental fields to enhance the fluence resolution, and readjusting the timing of each leaf during delivery to avoid small fields.