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

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... 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. Oncol. 80 385-90 Chen Z, Xing L and Nath R 2002 Independent monitor unit calculation for intensity modulated radiotherapy using the MIMiC multileaf collimator Med. Phys. R and Huq M S 2005 A dose verification method using a monitor unit matrix for dynamic IMRT on Varian linear accelerators Phys. Med. Biol. 50 5641-52 Clarkson J R 1941 A note on depth doses in fields with irregular shape Br. J. Radiol. 14 265-7 Dutreix A, Svensson H, Bjärngard B E, Bridier A, Mijnheer A and Shaw J 1997 Monitor unit calculation for high energy photon beams ESTRO Booklet no. 3 Ezzell G A, Galvin J M, Low D, Palta J R, Rosen I, Sharpe M B, Xia P, Xiao Y, Xing L and Yu C X 2003 IMRT subcommittee; AAPM Radiation Therapy committee. Guidance document on delivery, treatment planning, and clinical implementation of IMRT: report of the IMRT Subcommittee of the AAPM Radiation Therapy Committee Med. Phys. 30 2089-115 Georg D, Kroupa B, Winkler P and Potter R 2003 Normalized sensitometric curves for the verification of hybrid IMRT treatment plans with multiple energies Med. Phys. 30 1142-50 Georg D, Olofsson J, Künzler T and Karlsson M 2004 On empirical methods to determine scatter factors for irregular MLC shaped beams Med. Phys. 31 2222-9 Gillis S, De Wagter C, Bohsung J, Perrin B, Williams P and Mijnheer B J 2005 An inter-centre quality assurance network for IMRT verification: results of the ESTRO QUASIMODO project Radiother. Oncol. 76 340-53 Hounsell A R and Wilkinson J M 1997 Head scatter modeling for irregular field shaping and beam intensity modulation Phys. Med. Biol. 42 1737-49 Kung J H, Chen G T and Kuchnir F K 2000 A monitor unit verification calculation in intensity modulated radiotherapy as a dosimetry quality assurance Med. Phys. 27 2226-30 Leybovich L B, Sethi A and Dogan N 2003 Comparison of ionization volumes for IMRT absolute dose verification Med. Phys. 30 119-1123 Linthout N, Verellen D, Van Acker S and Storme G 2004 A simple theoretical verification of monitor unit calculation for intensity modulated beams using dynamic mini-multileaf collimation Radiother. Oncol. 71 235-41 Low D A, Gerber R L, Mutic S and Purdy J A 1998 Phantoms for IMRT dose distribution measurement and treatment verification Int. Monitor unit calculation for Monte Carlo treatment planning Phys. Med. Biol. 49 1671-87 Mijnheer B, Olszewska A, Fiorino C, Hartmann G and Knöös T 2004 A practical guide to quality control of brachytherapy equipment ESTRO Booklet no. 8 Naqvi S A, Sarfaraz M, Holmes T, Yu C X and Li X A 2001 Analysing collimator structure effects in head-scatter calculations for IMRT class fields using scatter raytracing Phys. Med. Biol. 46 2009-28 Nyholm T, Olofsson J, Ahnesjö A and Karlsson M 2006a Photon pencil kernel parameterisation based on beam quality index Radiother. Oncol. 78 347-51 Nyholm T, Olofsson J, Ahnesjö A and Karlsson M 2006b Modelling lateral beam quality variations in pencil beam kernel based photon dose calculations Phys. Med. Biol. 51 4111-8 Olofsson J, Georg D and Karlsson M 2003 A widely tested model for head scatter influence on photon beam output Radiother. Oncol. 67 225-38 Olofsson J, Nyholm T, Georg D, Ahnesjö A and Karlsson M 2006a Evaluation of uncertainty predictions and dose output for model based dose calculations in photon beams form multiple linacs Med. Phys. 33 2548-56