Research Article

Inter-Observer Variability of a Commercial Patient Positioning and Verification System in Proton Therapy

Yuanshui Zheng* and Xiaoning Ding

Published: 06 February, 2017 | Volume 1 - Issue 1 | Pages: 031-038

Purpose:Accurate patient positioning is crucial in radiation therapy. To fully benefit from the preciseness of proton therapy, image guided patient positioning and verification system is typically utilized in proton therapy. The purpose of this study is to evaluate the inter-observer variability of image alignment using a commercially available patient positioning and verification system in proton therapy.

Methods:The VeriSuite patient positioning and verification system (MedCom GmbH, Darmstadt, Germany) provides a six degrees of freedom correction vector by registering two orthogonal x-ray images to digitally reconstructed radiograph (DRR) images that are rendered in real time from the planning computed tomography (CT) images. Six cases of various disease sites, including brain, head & neck, lung, prostate, pelvis, and bladder, were used in this study. For each case, the planning CT images and a daily orthogonal x-ray portal image pair were loaded into the VeriSuite system. The same set of x-ray images and CT images for each case were reviewed and aligned separately by each of the 10 radiation therapist, following the clinical procedure for the corresponding disease site. The resulting correction vectors were then recorded and analyzed.

Results:Our study shows that the inter-observer variation (One standard deviation) in image alignment using the VeriSuite system ranged from 1.2 to 2.0 mm for translational correction and from 0.6 to 1.3 degrees for rotational correction for the six cases. The use of fiducial markers for prostate patient alignment achieved the least inter-observer variation while the bladder case produced the largest.

Conclusions:Inter-observer variation in image alignment could be relatively large, depending on the complexity of patient anatomy, image alignment approach, and user experience and software limitations. Automatic registration and fiducial markers could potentially be used to align patient more accurately and consistently. To ensure adequate tumor coverage in proton therapy, inter-observer variability in patient alignment should be carefully evaluated and accounted for in patient setup uncertainty analysis and treatment planning margin determination.

Read Full Article HTML DOI: 10.29328/journal.jro.1001004 Cite this Article Read Full Article PDF


Inter-observer variability; Image alignment; Proton therapy


  1. Engelsman M, Schwarz M, Dong L. Physics controversies in proton therapy. Semin Radiat Oncol. 2013; 23: 88-96. Ref.: https://goo.gl/4gbQgV  
  2. Rosen L. Everything is changing in oncology and proton therapy. J Proton Ther. 2015; 1: 111. Ref.: https://goo.gl/zwd392
  3. Yin F, Wong J, Balter J, Benedict S, Craig J, et al. The role of in-room kV X-ray imaging for patient setup and target localization. Report of AAPM Task Group. 2009; 104. Ref.: https://goo.gl/rYpMVS
  4. De Los Santos J, Popple R, Agazaryan N, Bayouth JE, Bissonnette JP, et al. Image guided radiation therapy (IGRT) technologies for radiation therapy localization and delivery. Int J Radiat Oncol Biol Phys. 2013; 87: 33-45.Ref.: https://goo.gl/7QP8CU  
  5. Fuss M, Salter BJ, Cavanaugh SX, Fuss C, Sadeghi A, et al. Daily ultrasound-based image-guided targeting for radiotherapy of upper abdominal malignancies. Int J Radiat Oncol Biol Phys. 2004; 59: 1245-1256. Ref.: https://goo.gl/iHRfcE
  6. Molloy JA, Chan G, Markovic A, McNeeley S, Pfeiffer D, et al. Quality assurance of U.S.-guided external beam radiotherapy for prostate cancer: report of AAPM Task Group 154. Med Phys. 2011; 38: 857-871. Ref.: https://goo.gl/1gjnSQ
  7. Wooten HO, Rodriguez V, Green O, Kashani R, Santanam L, et al. Benchmark IMRT evaluation of a Co-60 MRI-guided radiation therapy system. Radiother Oncol. 2015; 114: 402-405. Ref.: https://goo.gl/eFrX0L
  8. Oelfke U, Tucking T, Nill S, Seeber A, Hesse B, et al. Linac-integrated kV-cone beam CT: technical features and first applications. Med Dosim. 2006; 3: 62-70. Ref.: https://goo.gl/XHfpFn
  9. Morin O, Gillis A, Chen J, Aubin M, Bucci MK 3rd, et al. Megavoltage cone-beam CT: system description and clinical applications. Med Dosim. 2006; 31: 51-61. Ref.: https://goo.gl/WqIuHI  
  10. Bert C, Metheany KG, Doppke KP, Taghian AG, Powell SN, et al. Clinical experience with a 3D surface patient setup system for alignment of partial-breast irradiation patients. Int J Radiat Oncol Biol Phys. 2006; 64: 1265-1274. Ref.: https://goo.gl/RAah6i
  11. Fattori G, Riboldi M, Pella A, Peroni M, Cerveri P, et al. Image guided particle therapy in CNAO room 2: implementation and clinical validation. Phys Med. 2015; 31: 9-15. Ref.: https://goo.gl/jxDrtO
  12. Depauw N, Batin E, Daartz J, Rosenfeld A, Adams J, et al. A novel approach to postmastectomy radiation therapy using scanned proton beams. Int J Radiat Oncol Biol Phys. 2015; 91: 427-434. Ref.: https://goo.gl/ffCgk0
  13. Enke C, Ayyangar KM, Saw CB, Zhen W, Thompson RB, et al. Inter-observer variation in prostate localization utilizing BAT. Int J Radiat Oncol Biol Phys. 2002; 54: 269. Ref.: https://goo.gl/ahKfKs  
  14. Aubin M, Liu Y, Langen K, Shinohara K, Anezinos C, et al. Set-up verification using portal images of implanted prostate markers: an inter-observer study. Int J Radiat Oncol Biol Phys. 2002; 54: 269-270. Ref.: https://goo.gl/xSUqNI
  15. Ullman KL, Ning H, Susil RC, Ayele A, Jocelyn L, et al. Intra- and inter-radiation therapist reproducibility of daily isocenter verification using prostatic fiducial markers. Radiat Oncol. 2006; 1: 2. Ref.: https://goo.gl/FLxAde
  16. Court LE, Dong L, Taylor N, Ballo M, Kitamura K, et al. Evaluation of a contour-alignment technique for CT-guided prostate radiotherapy: an intra- and interobserver study. Int J Radiat Oncol Biol Phys. 2004; 59: 412-418. Ref.: https://goo.gl/VSUDZv
  17. Court LE, Allen A, Tishler R. Evaluation of the precision of portal-image-guided head-and-neck localization: an intra- and interobserver study. Med Phys. 2007; 34: 2704-2707. Ref.: https://goo.gl/tIx8VX
  18. Guckenberger M, Sweeney RA, Wilbert J, Krieger T, Richter A, et al. Image-guided radiotherapy for liver cancer using respiratory-correlated computed tomography and cone-beam computed tomography. Int J Radiat Oncol Biol Phys. 2008; 71: 297-304. Ref.: https://goo.gl/3buPTa
  19. Commission IE. IEC 61217 radiotherapy equipment-co-ordinates, movements and scales. International Electrotechnical Commission. 2011. Ref.: https://goo.gl/q0LxHM
  20. Pella A, Riboldi M, Tagaste B, Bianculli D, Desplanques M, et al. Commissioning and quality assurance of an integrated system for patient positioning and setup verification in particle therapy. Technol Cancer Res T. 2014; 13: 303-314. Ref.: https://goo.gl/Ece8Ao  
  21. Walter S. Automatic patient alignment in six degrees of freedom for particle beam treatment. PTCOG; 2007 May 18-23; Wanjie, Shandong, China.
  22. Sejpal SV, Amos RA, Bluett JB, Levy LB, Kudchadker RJ, et al. Dosimetric changes resulting from patient rotational setup errors in proton therapy prostate plans. Int J Radiat Oncol Biol Phys. 2009; 75: 40-48. Ref.: https://goo.gl/w6Z32h
  23. Rana S, Zhang Y, Larson G, Vargas C, Dunn M, et al. Investigating dosimetric effect of rotational setup errors in IMPT planning of synchronous bilateral lung cancer. Int J Cancer Ther Oncol. 2015; 3. Ref.: https://goo.gl/99xLw5
  24. Fuss M, Cavanaugh SX, Fuss C, Cheek DA, Salter BJ. Daily stereotactic ultrasound prostate targeting: inter-user variability. Technol Cancer Res Treat. 2003; 2: 161-170. Ref.: https://goo.gl/QmxFHr


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