The use of EPID-measured leaf sequence files for IMRT dose reconstruction in adaptive radiation therapy.

For intensity modulated radiation treatment (IMRT) dose reconstruction, multileaf collimator (MLC) log files have been shown applicable for deriving delivered fluence maps. However, MLC log files are dependent on the accuracy of leaf calibration and only available from one linear accelerator manufacturer. This paper presents a proof of feasibility and principles in (1) using an amorphous silicon electronic portal imaging device (aSi-EPID) to capture the MLC segments during an IMRT delivery and (2) reconstituting a leaf sequence (LS) file based on the leaf end positions calculated from the MLC segments and their associated fractional monitor units. These EPID-measured LS files are then used to derive delivered fluence maps for dose reconstruction. The developed approach was tested on a pelvic phantom treated with a typical prostate IMRT plan. The delivered fluence maps, which were derived from the EPID-measured LS files, showed slight differences in the intensity levels compared with the corresponding planned ones. The dose distribution calculated with the delivered fluence maps showed a discernible difference in the high dose region when compared to that calculated with the planned fluence maps. The maximum dose in the former distribution was also 2.5% less than that in the latter one. The EPID-measured LS file can serve the same purpose as a MLC log files does for the derivation of the delivered fluence map and yet is independent of the leaf calibration. The approach also allows users who do not have access to MLC log files to probe the actual IMRT delivery and translate the information gained for dose reconstruction in adaptive radiation therapy.

[1]  Joao Seco,et al.  Evaluation of two methods of predicting MLC leaf positions using EPID measurements. , 2006, Medical physics.

[2]  Lei Xing,et al.  Evaluation of on-board kV cone beam CT (CBCT)-based dose calculation , 2007, Physics in medicine and biology.

[3]  R I MacKay,et al.  Use of an amorphous silicon electronic portal imaging device for multileaf collimator quality control and calibration , 2005, Physics in medicine and biology.

[4]  James F Dempsey,et al.  Validation of dynamic MLC-controller log files using a two-dimensional diode array. , 2003, Medical physics.

[5]  M C Kirby,et al.  Verification of dynamic multileaf collimation using an electronic portal imaging device. , 2000, Physics in medicine and biology.

[6]  D. Yan,et al.  Adaptive radiation therapy , 1997, Physics in medicine and biology.

[7]  Lei Xing,et al.  Formulating adaptive radiation therapy (ART) treatment planning into a closed-loop control framework , 2007, Physics in medicine and biology.

[8]  Ping Xia,et al.  Communication and sampling rate limitations in IMRT delivery with a dynamic multileaf collimator system. , 2002, Medical physics.

[9]  Indrin J Chetty,et al.  Synchronized dynamic dose reconstruction. , 2006, Medical physics.

[10]  J. Dempsey,et al.  An extensive log-file analysis of step-and-shoot intensity modulated radiation therapy segment delivery errors. , 2004, Medical physics.

[11]  P. Lambin,et al.  A global calibration model for a-Si EPIDs used for transit dosimetry. , 2007, Medical physics.

[12]  J Wong,et al.  Adaptive modification of treatment planning to minimize the deleterious effects of treatment setup errors. , 1997, International journal of radiation oncology, biology, physics.

[13]  G J Budgell,et al.  Use of an amorphous silicon EPID for measuring MLC calibration at varying gantry angle. , 2008, Physics in medicine and biology.

[14]  S Webb,et al.  Adapting IMRT delivery fraction-by-fraction to cater for variable intrafraction motion , 2008, Physics in medicine and biology.

[15]  Ron S Sloboda,et al.  Quality assurance measurements of a-Si EPID performance. , 2004, Medical dosimetry : official journal of the American Association of Medical Dosimetrists.

[16]  Fang-Fang Yin,et al.  Dosimetric feasibility of cone-beam CT-based treatment planning compared to CT-based treatment planning. , 2006, International journal of radiation oncology, biology, physics.

[17]  Lei Xing,et al.  Development of a QA phantom and automated analysis tool for geometric quality assurance of on-board MV and kV x-ray imaging systems. , 2008, Medical physics.

[18]  Lei Xing,et al.  Quantitative measurement of MLC leaf displacements using an electronic portal image device. , 2004, Physics in medicine and biology.

[19]  M Partridge,et al.  Independent verification using portal imaging of intensity-modulated beam delivery by the dynamic MLC technique. , 1998, Medical physics.

[20]  L. Xing,et al.  Retrospective IMRT dose reconstruction based on cone-beam CT and MLC log-file. , 2008, International journal of radiation oncology, biology, physics.

[21]  Jan-Jakob Sonke,et al.  Leaf trajectory verification during dynamic intensity modulated radiotherapy using an amorphous silicon flat panel imager. , 2004, Medical physics.

[22]  Maarten L P Dirkx,et al.  Fast and accurate leaf verification for dynamic multileaf collimation using an electronic portal imaging device. , 2002, Medical physics.

[23]  Automatic detection of single MLC leaf positions with corrections for penumbral effects and portal imager dose rate characteristics. , 1997, Physics in medicine and biology.

[24]  R. Mackay,et al.  Improving IMRT quality control efficiency using an amorphous silicon electronic portal imager. , 2005, Medical physics.

[25]  Jan-Jakob Sonke,et al.  3D in vivo dose verification of entire hypo-fractionated IMRT treatments using an EPID and cone-beam CT. , 2008, Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology.

[26]  J. Mechalakos,et al.  Use of EPID for leaf position accuracy QA of dynamic multi-leaf collimator (DMLC) treatment. , 2004, Medical physics.

[27]  L Kumaraswamy,et al.  Automatic verification of step-and-shoot IMRT field segments using portal imaging. , 2003, Medical physics.

[28]  R D Wiersma,et al.  Examination of geometric and dosimetric accuracies of gated step-and-shoot intensity modulated radiation therapy. , 2007, Medical physics.

[29]  Philippe Lambin,et al.  Treatment verification in the presence of inhomogeneities using EPID-based three-dimensional dose reconstruction. , 2007, Medical physics.

[30]  M van Herk,et al.  Comparison of ghosting effects for three commercial a-Si EPIDs. , 2006, Medical physics.

[31]  B. McCurdy,et al.  Dosimetric investigation and portal dose image prediction using an amorphous silicon electronic portal imaging device. , 2001, Medical physics.

[32]  G H Olivera,et al.  The use of megavoltage CT (MVCT) images for dose recomputations , 2005, Physics in medicine and biology.

[33]  D L McShan,et al.  Calibration and quality assurance for rounded leaf-end MLC systems. , 2001, Medical physics.

[34]  M van Herk,et al.  Radiation field edge detection in portal images. , 1991, Physics in medicine and biology.