Implementing Volumetric Modulated Arc Therapy (VMAT): Initial dosimetric results for retrospective patient study

Abstract

Purpose: The aim of this work is to compare and evaluate the quality of treatment techniques: step-and shoot intensity modulation (IMRT) with Volumetric Modulated Arc Therapy (VMAT). Methods: Two different VMAT (VMAT-2°, VMAT-4°) and step-and-shoot 7-field IMRT (IMRT-7F) plans were retrospectively created for patients undergoing radiotherapy for prostate cancer. Plans were compared in terms of efficiency, number of monitor units and dose volume parameters. Finally, measured and calculated dose distributions for complete VMAT treatment plans were compared and evaluated. Results: The number of monitor units per treatment fraction was similar for VMAT-2°, VMAT-4° and IMRT-7F techniques with mean values of 540 MU ± 40 MU, 505 MU ± 37 MU and 514 MU ± 61 MU, respectively. VMAT has been shown to reduce the time required for RT delivery. The representative dose value measured by an ionization chamber measurement in the high-dose region differed by -2.1 %, -2.4 % and -0.7 % for VMAT-2°, VMAT-4° and IMRT-7F compared to data from the TPS. Conclusion: VMAT and IMRT-7F provided quality dose distributions with acceptable target coverage and similar normal tissue sparing. © 2009 Springer-Verlag.