Evaluation of dosimetric accuracies of gated step-and-shoot IMRT using Dynalog data

Abstract

Gated intensity modulated radiation therapy is often used for a lung cancer treatment. We investigated dosimetric accuracies of delivered radiation from each segment due to lag effect of beam on and off by a gating system varying dose rate from 100 to 600 MU/min. 7 ports step-and-shoot lung IMRT study which is planned with the direct machine parameter optimization (DMPO) option in Pinnacle3 and the respiration signals acquired from the Real-time position management (RPM) system of the home-made moving phantom were tested. We analyzed Dynalog file since all information of MLC including leaves position and delivered dose is recorded in that file. The discrepancies between the planned MUs and delivered MUs increased along with an increase of dose rate, even more than 0.5 MU. However there was no significant additional error due to gating system comparing with ungated cases. MLC controller communication delay time was more serious for both cases. © 2009 Springer-Verlag.