PURPOSETo validate that DMPO model for "one step" algorithm can reduce the total MLC segments number, we compare the dosage distribution of "one-step" algorithm with "two-step" algorithm for generating IMRT MLC segments.

METHODSOn the platform of "Pinnacle 8.0h" version radiation treatment planning system developed by Philips, we respectively select one head and neck tumor case, one thorax tumor case and one abdomen tumor case, by means of designing seven fields IMRT planning, then utilized "one-step" algorithm and "two-step" algorithm to optimize and generate IMRT MLC segments, and then calculated dosage distribution, evaluated dosage distribution lines and DVH diagram, in order to compare the two MLC segment groups generated by the two different algorithm.

RESULTFor the three IMRT plans selected by us, the number of MLC segments generated by "two-step" algorithm appear to be larger than "one-step" algorithm but dosage distribution seems to be worse than the latter.

DISCUSSIONFor utilizing the "Pinnacle" plan system to design IMRT plan, "one-step" algorithm with "DMPO" definitely can effectively reduce the number of MLC segments, what's more, the result of dosage distribution seems to be better.