Development of EPID-based Real time Dose Verification for Dynamic IMRT

Authors: Todsaporn Fuangrod, Daryl J. O'Connor, Boyd MC McCurdy, Peter B. Greer

Abstract:

An electronic portal image device (EPID) has become a method of patient-specific IMRT dose verification for radiotherapy. Research studies have focused on pre and post-treatment verification, however, there are currently no interventional procedures using EPID dosimetry that measure the dose in real time as a mechanism to ensure that overdoses do not occur and underdoses are detected as soon as is practically possible. As a result, an EPID-based real time dose verification system for dynamic IMRT was developed and was implemented with MATLAB/Simulink. The EPID image acquisition was set to continuous acquisition mode at 1.4 images per second. The system defined the time constraint gap, or execution gap at the image acquisition time, so that every calculation must be completed before the next image capture is completed. In addition, the <=-evaluation method was used for dose comparison, with two types of comparison processes; individual image and cumulative dose comparison monitored. The outputs of the system are the <=-map, the percent of <=<1, and mean-<= versus time, all in real time. Two strategies were used to test the system, including an error detection test and a clinical data test. The system can monitor the actual dose delivery compared with the treatment plan data or previous treatment dose delivery that means a radiation therapist is able to switch off the machine when the error is detected.

Keywords: real-time dose verification, EPID dosimetry, simulation, dynamic IMRT

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1055435

References:

[1] van Elmpt, W., L. McDermott, et al. (2008). "A literature review of electronic portal imaging for radiotherapy dosimetry." Radiotherapy and Oncology 88: 289-309.
[2] McDermott, L. N., M. Wendling, et al. (2007). "Replacing pretreatment verification with in vivo EPID dosimetry for prostate IMRT." Int J Radiat Oncol Biol Phys 67(5): 1568-77.
[3] Mans, A., M. Wendling, et al. (2010). "Catching errors with in vivo EPID dosimetry." Med Phys 37(6): 2638-44.
[4] Bogdanich, W. (2010). "Radiation Offers New Cures, and Ways to Do Harm." From http://www.nytimes.com/2010/01/24/health/24radiation.html
[5] McCurdy, B. M. and P. B. Greer (2009). "Dosimetric properties of an amorphous-silicon EPID used in continuous acquisition mode for application to dynamic and arc IMRT." Med Phys 36(7): 3028-39.
[6] Low, D. A., W. B. Harms, et al. (1998). "A technique for the quantitative evaluation of dose distributions." Med Phys 25(5): 656-61.
[7] Stock, M., B. Kroupa, et al. (2005). "Interpretation and evaluation of the gamma index and the gamma index angle for the verification of IMRT hybrid plans." Phys Med Biol 50(3): 399-411.
[8] Jiang, S. B., G. C. Sharp, et al. (2006). "On dose distribution comparison." Phys Med Biol 51(4): 759-76.