Clinical Implementation of Portal Dosimetry—Establishing Action Levels

Abstract

The aim of this investigation was to better understand the trends in agreement between the portal dose prediction (PDP) and the measured dose for dynamic multileaf collimator (dMLC) intensity modulated radiation therapy (IMRT), with the goal of setting clinical action levels and establishing methods to improve agreement between PDP and measured dose for IMRT fields.  In this work, we evaluated three scalar indices for 152 treatment plans (1152 treatment fields): maximum gamma (g_max), average gamma (g_avg), and percent of the field area with a gamma value greater than 1.0 (g_% > 1).  These data were used to set clinical action levels in our clinic.  Action levels are based on the institutional mean and standard deviations.  In addition, several strategies were considered to improve agreement between measured dose and PDP, the most effective of which was recalculating the fields at lower dose rates.