Premium
Experimental verification of a Monte Carlo‐based MLC simulation model for IMRT dose calculation
Author(s) -
Tyagi Neelam,
Moran Jean M.,
Litzenberg Dale W.,
Bielajew Alex F.,
Fraass Benedick A.,
Chetty Indrin J.
Publication year - 2007
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2428405
Subject(s) - monte carlo method , imaging phantom , collimator , collimated light , head and neck , dosimetry , radiation treatment planning , linear particle accelerator , intensity modulation , nuclear medicine , optics , beam (structure) , physics , computer science , mathematics , radiation therapy , medicine , radiology , laser , statistics , surgery , phase modulation , phase noise
Inter‐ and intra‐leaf transmission and head scatter can play significant roles in intensity modulated radiation therapy (IMRT)‐based treatment deliveries. In order to accurately calculate the dose in the IMRT planning process, it is therefore important that the detailed geometry of the multi‐leaf collimator (MLC), in addition to other components in the accelerator treatment head, be accurately modeled. In this paper, we have used the Monte Carlo method (MC) to develop a comprehensive model of the Varian 120 leaf MLC and have compared it against measurements in homogeneous phantom geometries under different IMRT delivery circumstances. We have developed a geometry module within the DPM MC code to simulate the detailed MLC design and the collimating jaws. Tests consisting of leakage, leaf positioning and static MLC shapes were performed to verify the accuracy of transport within the MLC model. The calculations show agreement within 2% in the high dose region for both film and ion‐chamber measurements for these static shapes. Clinical IMRT treatment plans for the breast [both segmental MLC (SMLC) and dynamic MLC (DMLC)], prostate (SMLC) and head and neck split fields (SMLC) were also calculated and compared with film measurements. Such a range of cases were chosen to investigate the accuracy of the model as a function of modulation in the beamlet pattern, beamlet width, and field size. The overall agreement is within 2 % ∕ 2 mm of the film data for all IMRT beams except the head and neck split field, which showed differences up to 5% in the high dose regions. Various sources of uncertainties in these comparisons are discussed.