Parameter optimization in HN-IMRT for Elekta linacs

Abstract

Planning and delivery in HN-IMRT has been challenging for Elekta linacs because of numerous machine limitations.  Direct aperture optimization (DAO) algorithms have had success in simplifying the planning process and improving plan quality.  Commercial adaptations of DAO allow for widespread use in many clinics, however clinical validation of these methods is still needed.  In this work we evaluated Pinnacle³ commercial software for HN-IMRT on Elekta linacs.  The purpose was to find a set of planning parameters that are applicable to most patients and optimal in terms of plan quality, delivery efficiency and dosimetric accuracy.  Four types of plans were created for each of 12 patients: ideal fluence optimization (FO), conventional two-step optimization (TS), segment weight optimization (SW) and direct machine parameter optimization (DMPO). Maximum number of segments (NS) and minimum segment area (MSA) were varied in DMPO.  Results showed DMPO plans have the best optimization scores, dosimetric indices and the most consistent IMRT output among patients.  At larger NS (?80), plan quality decreases with increasing MSA as expected, except for MSA