Implementation of Quality Assurance Protocols for an Advanced Linear Accelerator with Volumetric Modulated Arc Therapy Features Using Electronic Portal Imaging Device (EPID)
To use Electronic Portal Imaging Device (EPID), an integral feature of a True Beam linear accelerator (linac) system, for implementing dosimetry based comprehensive Quality Assurance (QA) protocol needed for Volumetric Modulated Arc Therapy (VMAT) modality. Varian makesTrueBeam Version 2.0 linac system with Intensity Modulated Radiotherapy (IMRT), and VMAT treatment modalities were used in the study. The linac is equipped with a Multileaf Collimator (MLC) having 120 leaves (milleniumMLC) and an EPID (aS1000) having mega voltage photon (MV) detector system. The EPID has an active imaging area of 40 cm x 30 cm with 1024 x 768-pixel matrix with a pixel resolution of 0.39 mm. It is capable of capturing 14-bit images at 30 frames per second. We carried out the following QA tests using the EPID:i) Dynamic MLC (DMLC) dosimetry test ii) DMLC positional accuracy test (Picket Fence test) for fixed and rotating gantry modes iii) DMLC positional accuracy test during rotation with intentional errors iv) dose rate and gantry speed tests during RapidArc delivery and v) DMLC leaf speed test during RapidArc delivery. All the tests were analysed with Microsoft Excel application. Deviations of the EPID pixel values from known regions of interest during the various tests with respect to open fields were estimated for accuracy assessment. DMLC dosimetry tests showed a maximum deviation of 0.16 % with respect to reference condition at 0º gantry. The maximum positional accuracy of DMLC was found to be 0.28 mm for fixed gantry and 0.26 mm for rotating gantry. For varying dose rate and gantry speed, the average of the absolute value of all deviations Diff(x) was0.43. The MLC leaf speed variation during RapidArc resulted in the average of the absolute value of all Diff(x) of 0.20. Similar results have been obtained with a film based QA tests. The time taken in performing the above tests with EPID is far less as compared to the conventional methods. EPID based QA tests are reliable and quick. We believe that protocols developed for performing QA tests with EPID can replace the conventional methods of QA. EPID based QA will result in considerable time saving and thus helpful in increasing the patient throughput in a clinic. Also, the quicker and automated QA procedure based on EPID lends itself to better compliance and hence better treatment quality.
Bedford, J. L., & Warrington, A. P. (2009). Commissioning of volumetric modulated arc therapy (VMAT). International Journal of Radiation Oncology Biology Physics, 73(2), 537-545.
Bedford, J. L., Lee, Y. K., Wai, P., South, C. P., & Warrington, A. P. (2009). Evaluation of the Delta4 phantom for IMRT and VMAT verification. Physics in Medicine and Biology, 54(9), N167-176.
Boggula, R., Birkner, M., Lohr, F., Steil, V., Wenz, F., & Wertz, H. (2011). Evaluation of a 2D detector array for patient-specific VMAT QA with different setups. Physics in Medicine and Biology, 56(22), 7163-7177.
Essers, M., de Langen, M., Dirkx, M. L., & Heijmen, B. J. (2001). Commissioning of a commercially available system for intensity-modulated radiotherapy dose delivery with dynamic multileaf collimation. Radiotherapy and Oncology, 60(2), 215-224.
Greer, P. B., & Popescu, C. C. (2003). Dosimetric properties of an amorphous silicon electronic portal imaging device for verification of dynamic intensity modulated radiation therapy. Medical Physics, 30(7), 1618-1627.
Hardcastle, N., Tomé, W. A., Foo, K., Miller, A., Carolan, M., & Metcalfe, P. (2011). Comparison of prostate IMRT and VMAT biologically optimised treatment plans. Medical Dosimetry, 36(3), 292-298.
Klein, E. E., Hanley, J., Bayouth, J., Yin, F. F., Simon, W., Dresser, S., Serago, C., Aguirre, F., Ma, L., Arjomandy, B., Liu, C., Sandin, C., & Holmes, T. (2009). Task Group 142 report: quality assurance of medical accelerators. Medical Physics, 36(9), 4197-4212.
Kumar, R., Sharma, S. D., Deshpande, S., Sresty, N. M., Bhatt, C. P., Amols, H. I., Chourasiya, G., & Mayya, Y. S. (2014). Analysis of patient specific dosimetry quality assurance measurements in intensity modulated radiotherapy: A multi centre study. Journal of Cancer Research and Therapeutics, 10(3), 611-617.
Ling, C. C., Zhang, P., Archambault, Y., Bocanek, J., Tang, G., & LoSasso, T. (2008). Commissioning and quality assurance of RapidArc radiotherapy delivery system. International Journal of Radiation Oncology Biology Physics, 72(2), 575-581.
LoSasso, T. (2008). IMRT delivery performance with a varian multileaf collimator. International Journal of Radiation Oncology Biology Physics, 71(1), S85-S88.
Oliver, M., Ansbacher, W., & Beckham, W. A. (2009). Comparing planning time, delivery time and plan quality for IMRT, RapidArc and Tomotherapy. Journal of Applied Clinical Medical Physics, 10(4), 117-131.
Petoukhova, A. L., Van Egmond, J., Eenink, M. G. C., Wiggenraad, R. G. J., & Van Santvoort, J. P. C. (2011). The ArcCHECK diode array fordosimetric verification of HybridArc. Physics in Medicine and Biology, 56(16), 5411-5428.
Rangaraj, D., Oddiraju, S., Sun, B., Santanam, L., Yang, D., Goddu, S., & Papiez, L. (2010). Fundamental properties of the delivery of volumetric modulated arc therapy (VMAT) to static patient anatomy. Medical Physics, 37(8), 4056-4067.
Rowshanfarzad, P., McGarry, C. K., Barnes, M. P., Sabet, M., & Ebert, M. A. (2014). An EPID-based method for comprehensive verification of gantry, EPID and the MLC carriage positional accuracy in Varian linacs during arc treatments. Radiation Oncology, 9(1), 249-259.
Schreibmann, E., Dhabaan, A., Elder, E., & Fox, T. (2009). Patient‐specific quality assurance method for VMAT treatment delivery. Medical Physics, 36(10), 4530-4535.
Sharma, D. S., Dongre, P. M., Mhatre, V., & Heigrujam, M. (2011). Physical and dosimetric characteristic of high‐definition multileaf collimator (HDMLC) for SRS and IMRT. Journal of Applied Clinical Medical Physics, 12(3), 142-160.
Unkelbach, J., Bortfeld, T., Craft, D., Alber, M., Bangert, M., Bokrantz, R., Chen, D., Li, R., Xing, L., Men, C., Nill, S., Papp, D., Romeijn,E., & Salari, E. (2015). Optimization approaches to volumetric modulated arc therapy planning. Medical Physics, 42(3), 1367-1377.
Van Elmpt, W., McDermott, L., Nijsten, S., Wendling, M., Lambin, P., & Mijnheer, B. (2008). A literature review of electronic portal imaging for radiotherapy dosimetry. Radiotherapy and Oncology, 88(3), 289-309.
Wang, H. C., Chui, C. S., Tsai, H. Y., Chen, C. H., & Tsai, L. F. (2008). Dose deviations caused by positional inaccuracy of multileaf collimator in intensity modulated radiotherapy. Radiation Measurements, 43(2), 925-928.
Winkler, P., Hefner, A., & Georg, D. (2005). Dose‐response characteristics of an amorphous silicon EPID. Medical Physics, 32(10), 3095-3105