Patient-specific IMRT verification using independent fluence-based dose calculation software: experimental benchmarking and initial clinical experience

Dietmar Georg, Markus Stock, Bernhard Kroupa, Jörgen Olofsson, Tufve Nyholm, Anders Ahnesjö, Mikael Karlsson
2007 Physics in Medicine and Biology  
Experimental methods are commonly used for patient-specific intensitymodulated radiotherapy (IMRT) verification. The purpose of this study was to investigate the accuracy and performance of independent dose calculation software (denoted as 'MUV' (monitor unit verification)) for patient-specific quality assurance (QA). 52 patients receiving step-and-shoot IMRT were considered. IMRT plans were recalculated by the treatment planning systems (TPS) in a dedicated QA phantom, in which an experimental
more » ... 1D and 2D verification (0.3 cm 3 ionization chamber; films) was performed. Additionally, an independent dose calculation was performed. The fluence-based algorithm of MUV accounts for collimator transmission, rounded leaf ends, tongueand-groove effect, backscatter to the monitor chamber and scatter from the flattening filter. The dose calculation utilizes a pencil beam model based on a beam quality index. DICOM RT files from patient plans, exported from the TPS, were directly used as patient-specific input data in MUV. For composite IMRT plans, average deviations in the high dose region between ionization chamber measurements and point dose calculations performed with the TPS and MUV were 1.6 ± 1.2% and 0.5 ± 1.1% (1 S.D.). The dose deviations between MUV and TPS slightly depended on the distance from the isocentre position. For individual intensity-modulated beams (total 367), an average deviation of 1.1 ± 2.9% was determined between calculations performed with the TPS and with MUV, with maximum deviations up to 14%. However, absolute dose deviations were mostly less than 3 cGy. Based on the current results, we aim to apply a confidence limit of 3% (with respect to the prescribed dose) or 6 cGy for routine IMRT verification. For off-axis points at distances 0031-9155/07/164981+12$30.00 © 2007 IOP Publishing Ltd Printed in the UK Ahnesjö A, Weber L, Murman A, Saxner M, Thorslund I and Traneus E 2005 Beam modeling and verification of a photon beam multisource model Med. Phys. 32 1722-37 Baker C R, Clements R, Gately A and Budgell G J 2006 A separated primary and scatter model for independent dose calculation of intensity modulated radiotherapy Radiother. 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doi:10.1088/0031-9155/52/16/018 pmid:17671348 fatcat:k36g7jiz7fgm7ozq4662lwhgga