Evaluation of the Portal Imaging System Performance for an Elekta Precise Linac in Radiotherapy

Document Type: Original Paper


1 Medical Physics Research Center, Mashhad University of Medical Sciences, Mashhad, Iran.

2 Medical Physics Research center, Mashhad University of Medical Sciences, Mashhad, Iran


Introduction: Electronic portal imaging devices (EPIDs) provide two- and three-dimensional planar and volumetric cone beam images to improve the accuracy of radiation treatment delivery. Periodic quality assurance (QA) of EPIDs is essential for dosimetric verification in radiotherapy. In this study, a QA program was implemented to evaluate the function of the EPID to be confident in applying corrections for the uncertainty of patient set-up.
Material and Methods: Firstly, the safety features were verified, and the uniformity of EPID response was evaluated using flat panel detector. Additionally, the contrast and spatial resolutions of the EPID were assessed using detail counting of the Los Vegas phantom images by visualization method and measuring the modulation transfer function using edge technique, respectively. Moreover, a combination of smoothing methods was used for optimal use of edge detection algorithm for the noisy portal images. Finally, the location of the central ray on the EPID surface at different gantry angles was determined to evaluate the mechanical stability of the supporting arm.
Results: The safety interlocks were found to be functional.The EPID response variation was less than 3% according to the results obtained from the detector. The contrast resolution met the recommended tolerance; however, the visualization method was widely observer-dependent. The value of f50 for spatial resolution was 0.401±0.005 lp/mm for the photon energy of 6 MV. The supporting arm deviation was within ±1 mm.
Conclusion: The periodic QA of image guidance system gave confidence to apply the corrections for set-up in clinic.


Main Subjects

  1. O'Daniel JC, Garden AS, Schwartz DL, Wang H, Ang KK, Ahamad A, et al. Parotid gland dose in intensity-modulated radiotherapy for head and neck cancer: is what you plan what you get?. International Journal of Radiation Oncology* Biology* Physics. 2007;69(4):1290-6.
  2. Bedford JL. Treatment planning for volumetric modulated arc therapy. Medical physics. 2009;36(11):5128-38.             
  3. Fredh A, Korreman S, af Rosenschöld PM. Automated analysis of images acquired with electronic portal imaging device during delivery of quality assurance plans for inversely optimized arc therapy. Radiotherapy and Oncology. 2010;94(2):195-8.             
  4. Kirby M, Glendinning A. Developments in electronic portal imaging systems. The British journal of radiology. 2014.  
  5. Van Herk M, Meertens H. A matrix ionisation chamber imaging device for on-line patient setup verification during radiotherapy. Radiotherapy and Oncology. 1988;11(4):369-78.             
  6. Heijmen B, Pasma K, Kroonwijk M, Althof V, De Boer J, Visser A, et al. Portal dose measurement in radiotherapy using an electronic portal imaging device (EPID). Physics in medicine and biology. 1995;40(11):1943.   
  7. Das IJ, Cao M, Cheng C-W, Misic V, Scheuring K, Schule E, et al. A quality assurance phantom for electronic portal imaging devices. Journal of Applied Clinical Medical Physics. 2011;12(2).    
  8. Midgley S, Millar R, Dudson J. A feasibility study for megavoltage cone beam CT using a commercial EPID. Physics in medicine and biology. 1998;43(1):155.
  9. Bissonnette J-P, editor Quality assurance of image-guidance technologies. Seminars in radiation oncology; 2007: Elsevier.
  10. Tournel K, De Ridder M, Engels B, Bijdekerke P, Fierens Y, Duchateau M, et al. Assessment of intrafractional movement and internal motion in radiotherapy of rectal cancer using megavoltage computed tomography. International Journal of Radiation Oncology* Biology* Physics. 2008;71(3):934-9.
  11. Gopal A, Samant SS. Use of a line‐pair resolution phantom for comprehensive quality assurance of electronic portal imaging devices based on fundamental imaging metrics. Medical physics. 2009;36(6):2006-15.
  12. Klein EE, Hanley J, Bayouth J, Yin FF, Simon W, Dresser S, et al. Task Group 142 report: quality assurance of medical accelerators. Medical physics. 2009;36(9):4197-212.
  13. Bissonnette JP, Balter PA, Dong L, Langen KM, Lovelock DM, Miften M, et al. Quality assurance for image‐guided radiation therapy utilizing CT‐based technologies: A report of the AAPM TG‐179. Medical physics. 2012;39(4):1946-63.
  14. Kanakavelu N, Samuel EJ. Assessment and evaluation of MV image guidance system performance in radiotherapy. Reports of Practical Oncology & Radiotherapy. 2015 May 1;20(3):188-97.
  15. Low DA, Klein EE, Maag DK, Umfleet WE, Purdy JA. Commissioning and periodic quality assurance of a clinical electronic portal imaging device. International Journal of Radiation Oncology• Biology• Physics. 1996 Jan 1;34(1):117-23.             
  16. Herman MG, Balter JM, Jaffray DA, McGee KP, Munro P, Shalev S, et al. Clinical use of electronic portal imaging: report of AAPM Radiation Therapy Committee Task Group 58. Medical Physics. 2001;28(5):712-37.
  17. Smith PL. New technique for estimating the MTF of an imaging system from its edge response. Applied Optics. 1972 Jun 1;11(6):1424-5.
  18. Rout BK, Shekar MC, Kumar A, Ramesh KK. Quality control test for electronic portal imaging device using QC-3 phantom with PIPSpro. International Journal of Cancer Therapy and Oncology. 2014 Sep 29;2(4).
  19. Cunningham IA, Reid BK. Signal and noise in modulation transfer function determinations using the slit, wire, and edge techniques. Medical physics. 1992 Jul 1;19(4):1037-44.
  20. E. Samei, M. Flynn and D. Reimann, A method for measuring the presampled MTF of digital radiographic systems usingan edge test device. Medical Physics. 1998;25: 102–13.
  21. Gustafsson H, Vial P, Kuncic Z, Baldock C, Greer PB. EPID dosimetry: Effect of different layers of materials on absorbed dose response. Medical physics. 2009 Dec 1;36(12):5665-74.
  22. Winkler P, Hefner A, Georg D. Dose‐response characteristics of an amorphous silicon EPID. Medical physics. 2005 Oct 1;32(10):3095-105.
  23. Van der Sypt, Jan, Carlos De Wagter, and Luc Van Hoorebeke. EPID based quality assurance of Total Body Irradiation. Master [dissertation]. Belgium: Ghent university. 2016.
  24. Sukumar P, Padmanaban S, Jeevanandam P, Kumar SS, Nagarajan V. A study on dosimetric properties of electronic portal imaging device and its use as a quality assurance tool in Volumetric Modulated Arc Therapy. Reports of Practical Oncology & Radiotherapy. 2011;16(6):248-55.
  25. Balter JM, Antonuk LE. Quality Assurance for kV and MV In-room Imaging and Localization for Off- and Online Setup Error Correction. International journal of radiation oncology, biology, physics. 2008;71(1 Suppl): 48-52.
  26. Buhr E, Günther‐Kohfahl S, Neitzel U. Accuracy of a simple method for deriving the presampled modulation transfer function of a digital radiographic system from an edge image. Medical physics. 2003;30(9):2323-31.
  27. Fujita H, Tsai D-Y, Itoh T, Doi K, Morishita J, Ueda K, et al. A simple method for determining the modulation transfer function in digital radiography. IEEE Transactions on medical imaging. 1992;11(1):34.
  28. Greer PB, Van Doorn T. Evaluation of an algorithm for the assessment of the MTF using an edge method. Medical Physics. 2000;27(9):2048-59.              
  29. Marshall N. Early experience in the use of quantitative image quality measurements for the quality assurance of full field digital mammography x-ray systems. Physics in medicine and biology. 2007;52(18):5545.
  30. Hassanein AS, Mohammad S, Sameer M, Ragab ME. A survey on Hough transform, theory, techniques and applications. arXiv preprint arXiv:1502.02160. 2015 Feb 7.
  31. Carton AK, Vandenbroucke D, Struye L, Maidment AD, Kao YH, Albert M, et al. Validation of MTF measurement for digital mammography quality control. Medical Physics. 2005 Jun 1;32(6Part1):1684-95.
  32. Saunders RS, Samei E. A method for modifying the image quality parameters of digital radiographic images. Medical physics. 2003 Nov 1;30(11):3006-17.
  33. B. Hasegawa, The Physics of Medical X-Ray Imaging, Madison, Wisconsin: Medical Physics Publishing Company. 1990.
  34. Donovan M, Zhang D, Liu H. Step by step analysis toward optimal MTF algorithm using an edge test device. Journal of X-ray science and technology. 2009 Jan 1;17(1):1-5.
  35. Rowshanfarzad P, McGarry CK, Barnes MP, Sabet M, Ebert MA. An EPID-based method for comprehensive verification of gantry, EPID and the MLC carriage positional accuracy in Varian linacs during arc treatments. Radiation Oncology. 2014;9(1):249.
  36. Bailey DW, Kumaraswamy L, Bakhtiari M, Malhotra HK, Podgorsak MB. EPID dosimetry for pretreatment quality assurance with two commercial systems. Journal of applied clinical medical physics. 2012 Jul 1;13(4):82-99.
  37. Sun B, Goddu SM, Yaddanapudi S, Noel C, Li H, Cai B, Kavanaugh J, Mutic S. Daily QA of linear accelerators using only EPID and OBI. Medical physics. 2015 Oct 1;42(10):5584-94.
  38. Elekta Customer Acceptance tests for iViewGT. Document number: 45133701945 04. Elekta company; 2008.
  39. Bissonnette JP, Jaffray DA, Fenster A, Munro P. Optimal radiographic magnification for portal imaging. Medical physics. 1994 Sep 1; 21(9):1435-45.
  40. Levitt SH, Purdy JA, Perez CA, Vijayakumar S. Technical basis of radiation therapy.4th ed. Minnesota: Springer. 2012; 104.
  41. Kavuma A. Transit dosimetry based on water equivalent path length measured with an amorphous silicon electronic portal imaging device: University of Glasgow; 2011.
  42. Jomehzadeh A, Shokrani P, Mohammadi M, Amouheidari A. A quality assurance program for an amorphous silicon electronic portal imaging device using in-house developed phantoms: A method development for dosimetry purposes. Int J Radiat Res. 2014 Jul 1; 12: 257-64.
  43. Clements R, Luchka K, Pouliot J, Sage J, Shalev S. Initial comparison of three Am-Si EPIDs using the QC-3V Phantom. The 7th international workshop on electronic Portal Imaging–EPI2K2; 2002.
  44. Doi K. Basic imaging properties of radiographic systems and their measurement. In: Orton C. Progress in medical radiation physics. 2th ed. Chicago (IL): Springer US. 1985: 181-248.
  45. JJ. Sonke. In-room imaging techniques. In: KK. Brock. Image Processing in Radiation Therapy [e-book]. Michigan: CRC Press; 2013 [cited 2015 February 3]. Available from : Wiley Online Library.
  46. Rowshanfarzad P, Riis H, Zimmermann S, Ebert M. A comprehensive study of the mechanical performance of gantry, EPID and the MLC assembly in Elekta linacs during gantry rotation. The British journal of radiology. 2015;88(1051):20140581.