Performance of Radiation Dosimeters in Gradient Regions at Different Dose Rates of Linear Accelerators

Document Type : Original Paper


1 Radiotherapy Department, Children’s Cancer Hospital, Egypt Department of Physics, Faculty of Science, Helwan University, Egypt

2 Radiotherapy Department, Saudi German Hospital Cairo, Egypt

3 Department of Physics, Faculty of Science, Helwan University, Egypt

4 Radiotherapy Department, Children’s Cancer Hospital, Egypt Department of Clinical Oncology, Faculty of Medicine, Aswan University, Egypt


Introduction: This work aimed to evaluate the accuracy of using parallel plane against thimble chambers in beam data commissioning of the high dose gradients region for versa HD linear accelerator performing clinical advanced modulated radiation treatment techniques.
Material and Methods: All clinical commissioning data were collected from Elekta Versa HD for energies of 6 MV, 10 MV, 6 MV FFF, and 10 MV FFF for different field sizes using thimble ionization chamber CC13, some from the pool of the measured data were rescanned using parallel plate chamber PPC05 and Gafchromic films and compared to those collected using the thimble ionization chamber.
Results: The skin doses differences measured by thimble chamber against reference films were (0.8%, 0.5%, 1.2% 4.7%) and for the parallel plane chamber against films were (8.4%, 9.7%, 9%, 12%) for 6 MV, 10 MV, 6 MV FFF, 10 MV FFF, respectively. The parried test-test showed a highly significant difference (p> 0.001) between the two chambers in measurements of penumbra regions taking over all the investigated field sizes and depths in both inline and crossline datasets. The parallel plate showed a wider and broader penumbra than the thimble chamber and films.
Conclusion: Robust and consistent scans were obtained for the thimble chamber compared to the parallel plane chamber in the highest dose gradient of buildup and penumbra regions. Using a parallel plane chamber might bring dosimetric clinical uncertainties affecting the modeling of the gradient regions in the treatment planning system.


Main Subjects

  1. Das IJ, Cheng CW, Watts RJ, Ahnesjö A, Gibbons J, Li XA, et al. Accelerator beam data commissioning equipment and procedures: report of the TG‐106 of the Therapy Physics Committee of the AAPM. Medical physics. 2008 Sep;35(9):4186-215.
  2. Podgorsak EB. Radiation oncology physics. Vienna: IAEA. 2005 Jul; 123-271.
  3. Khan FM, Gibbons JP. Khan's the physics of radiation therapy. Lippincott Williams & Wilkins; 2014.
  4. Gersh JA, Best RC, Watts RJ. The clinical impact of detector choice for beam scanning. Journal of applied clinical medical physics. 2014 Jul;15(4):174-93.
  5. Mahmoudi A, Geraily G, Shirazi A. Penumbra reduction technique and factors affecting it in radiotherapy machines–Review study. Radiation Physics and Chemistry. 2019 Apr 1;157:22-7.
  6. Yan G, Fox C, Liu C, Li JG. The extraction of true profiles for TPS commissioning and its impact on IMRT patient‐specific QA. Medical physics. 2008 Aug;35(8):3661-70.
  7. Farrukh S, Ilyas N, Naveed M, Haseeb A, Bilal M, Iqbal J. Penumbral dose characteristics of physical and virtual wedge profiles. International Journal of Medical Physics, Clinical Engineering and Radiation Oncology. 2017;6(02):216.
  8. Narayanasamy G, Saenz D, Cruz W, Ha CS, Papanikolaou N, Stathakis S. Commissioning an Elekta Versa HD linear accelerator. Journal of applied clinical medical physics. 2016 Jan;17(1):179-91.
  9. Shende R, Gupta G, Patel G, Kumar S. Commissioning of TrueBeam TM medical linear accelerator: quantitative and qualitative dosimetric analysis and comparison of flattening filter (FF) and FLATTENING FILTER FRee (FFF) beam. International Journal of Medical Physics, Clinical Engineering and Radiation Oncology. 2016;5(01):51.
  10. Yarahmadi M, Allahverdi M, Nedaie HA, Asnaashari K, Vaezzadeh SA, Sauer OA. Improvement of the penumbra for small radiosurgical fields using flattening filter free low megavoltage beams. Zeitschrift für Medizinische Physik. 2013 Dec 1;23(4):291-9.
  11. Xiao Y, Kry SF, Popple R, Yorke E, Papanikolaou N, Stathakis S, et al. Flattening filter‐free accelerators: a report from the AAPM Therapy Emerging Technology Assessment Work Group. Journal of applied clinical medical physics. 2015 May;16(3):12-29.
  12. Sharma SD. Unflattened photon beams from the standard flattening filter free accelerators for radiotherapy: advantages, limitations and challenges. Journal of Medical Physics/Association of Medical Physicists of India. 2011 Jul;36(3):123.
  13. Ding GX, Duggan DM, Coffey CW. Commissioning stereotactic radiosurgery beams using both experimental and theoretical methods. Physics in Medicine & Biology. 2006 May 4;51(10):2549.
  14. Hentihu FK, Ryangga D, Pawiro SA. The impact of flattening filter free (FFF) photon beams to ion recombination correction factor. InJournal of Physics: Conference Series 2019 Jun 1 (Vol. 1248, No. 1, p. 012062). IOP Publishing.
  15. Khalil MS. Evaluation of the Characteristics of Ionization Chambers Used for Commissioning in High Dose Rate Linacs. ARCHIVOS DE MEDICINA. 2019;4(1):1.
  16. Pönisch F, Titt U, Vassiliev ON, Kry SF, Mohan R. Properties of unflattened photon beams shaped by a multileaf collimator. Medical physics. 2006 Jun;33(6Part1):1738-46.
  17. Manavalan M, Duraisamy M, Subramani V, Godson HF, Krishnan G, Venkataraman M, et al. Analysis of various dosimetric parameters using multiple detectors in the cyberknife® robotic radiosurgery system. International Journal of Radiation Research. 2020 Jul 1;18(3):437-47.
  18. Singh A, Saini A, Pahwa S, Kumar A, Dora T, Chhabra A, et al. Surface dose variations in 6 and 10 MV flattened and flattening filter-free photon beams. Journal of Medical Physics. 2017;42(suppl. 1):198-9.
  19. Apipunyasopon L, Srisatit S, Phaisangittisakul N. An investigation of the depth dose in the build-up region, and surface dose for a 6-MV therapeutic photon beam: Monte Carlo simulation and measurements. Journal of radiation research. 2013 Mar 1;54(2):374-82.
  20. Imae T, Takenaka S, Watanabe Y, Aoki A, Matsuda K, Sasaki K, et al. Surface and build‐up dose comparison between Elekta 6 MV flattening filter and flattening‐filter‐free beams using an advanced Markus ionization chamber and a solid water‐equivalent phantom. Journal of Applied Clinical Medical Physics. 2020 Dec;21(12):334-9.
  21. Patatoukas GD, Kalavrezos P, Seimenis I, Dilvoi M, Kouloulias V, Efstathopoulos E, et al. Determination of beam profile characteristics in radiation therapy using different dosimetric set ups. JBUON. 2018 Sep 1;23(5):1448-59.





Volume 19, Issue 2
March and April 2022
Pages 66-73
  • Receive Date: 31 October 2020
  • Revise Date: 19 April 2021
  • Accept Date: 20 April 2021
  • First Publish Date: 20 April 2021