Penumbra Measurements and Comparison of In-House and Standard Circular Cones by the Gafchoromic Film, Pinpoint Ion Chamber, and MCNPX Monte Carlo Simulation

Document Type : Original Paper


1 Radiotherapy Oncology Research Center, Cancer Institute, Tehran University of Medical Sciences,Tehran, Iran.

2 radiotherapy oncology department, cancer research centre, Tehran university of medical sciences,Tehran,Iran

3 Radiotherapeutic Oncology Department of Cancer Institute, Tehran, Iran

4 Department of Medical Physics, Tehran University of Medical Science, Tehran, Iran

5 Department of Radiotherapy Physics, Cancer Research Centre, cancer Institute, Tehran University of Medical Sciences, Tehran, Iran

6 Tehran University of Medical Sciences

7 Radiotherapy Oncology Research Center, Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran

8 Radiotherapy Oncology Department, Cancer Research Centre, Tehran University of Medical Sciences, Tehran, Iran


Introduction: Penumbra is an important property of the radiation beam to obtain a suitable margin surrounding the target volume. Therefore, the precise penumbra width determination in stereotactic radiotherapy is necessary for treatment planning. This study aimed to compare the obtained results of penumbra width by in-house and standard circular cones by different dosimeters, as well as evaluating the function of EBT3 for dosimetric properties of the small field radiation.
Material and Methods: Different circular cones were mounted on the head of the accelerator to produce 12, 20, and 40 mm field sizes at isocenter. Dosimetric measurements were performed with the EBT3 film, PinPoint ion chamber. Afterwards, MCNPX Monte Carlo simulation was used to evaluate the dosimetric parameters.
Results: According to the obtained results, the penumbra width was increased by larger diameters of circular cones. The obtained measured data by PinPoint ion chamber showed a larger penumbra width compared to those calculated by Monte Carlo at all field sizes. The gamma index analysis revealed  distance-to-agreement and dose-difference of 2 mm /2%/ at all points. The results of this study showed that source to diaphragm distance had a major role in penumbra size determination of small field dosimetry with PinPoint ion chamber, EBT3 film, and Monte Carlo simulation.
Conclusion: As findings of this study reported, EBT3 films are reliable detectors for relative dosimetry due to high spatial resolution for small field sizes. Furthermore, they can be used for measuring beam profile and percentage depth dose curves.


Main Subjects

  1. References


    1. Wilcox EE, Daskalov GM. Accuracy of dose measurements and calculations within and beyond heterogeneous tissues for photon fields smaller than produced by Cyberknife. Medical physics. 2008; 35(6Part1):2259-66.
    2. Betti O, Derechinsky V. Multiple-beam stereotaxic irradiation. Neuro-Chirurgie. 1983;29(4):295-8.
    3. Bortfeld T, Schlegel W, Hoever KH, Schulz-Ertner D. Mini and micro multileaf collimators. Med. Phys. 1999; 26:1094.
    4. Heydarian M, Hoban PW, Beddoe AH. A comparison of dosimetry techniques in stereotactic radiosurgery. Physics in Medicine & Biology. 1996;41(1):93.
    5. Thomas SJ. Factors affecting penumbral shape and 3D dose distributions in stereotactic radiotherapy. Physics in Medicine & Biology. 1994;39(4):761.
    6. Pappas E, Maris TG, Manolopoulos S, Zacharopoulou F, Papadakis A, Green S, et al. Stereotactic radiosurgery photon field profile dosimetry using conventional dosimeters and polymer gel dosimetry. Analysis and inter-comparison. InJournal of Physics: Conference Series. 2009; 164(1) : 012054.
    7. Vatnitsky SM, Schulte RW, Galindo R, Meinass HJ, Miller DW. Radiochromic film dosimetry for verification of dose distributions delivered with proton-beam radiosurgery. Physics in Medicine & Biology. 1997;42(10):1887.
    8. Yin FF, Zhu J, Yan H, Gaun H, Hammoud R, Ryu S, et al. Dosimetric characteristics of Novalis shaped beam surgery unit. Medical physics. 2002;29(8):1729-38.
    9. Serago CF, Houdek PV, Hartmann GH, Saini DS, Serago ME, Kaydee A. Tissue maximum ratios (and other parameters) of small circular 4, 6, 10, 15 and 24 MV x-ray beams for radiosurgery. Physics in Medicine & Biology. 1992;37(10):1943.
    10. Sharma SD, Kumar S, Dagaonkar SS, Bisht G, Dayanand S, Devi R, et al. Dosimetric comparison of linear accelerator-based stereotactic radiosurgery systems. Journal of Medical Physics/Association of Medical Physicists of India. 2007;32(1):18.
    11. Hassani H, Nedaie HA, Zahmatkesh MH, Shirani K. A dosimetric study of small photon fields using polymer gel and Gafchromic EBT films. Medical Dosimetry. 2014;39(1):102-7.
    12. Palmans H, Andreo P, Huq MS, Seuntjens J, Christaki KE, Meghzifene A. Dosimetry of small static fields used in external photon beam radiotherapy: Summary of TRS‐483, the IAEA–AAPM international Code of Practice for reference and relative dose determination. Medical physics. 2018; 45(11):e1123-45.
    13. De Vlamynck K, Palmans H, Verhaegen F, De Wagter C, De Neve W, Thierens H. Dose measurements compared with Monte Carlo simulations of narrow 6 MV multileaf collimator shaped photon beams. Medical physics. 1999;26(9):1874-82.
    14. Sánchez-Doblado F, Andreo P, Capote R, Leal A, Perucha M, Arráns R, et al. Ionization chamber dosimetry of small photon fields: a Monte Carlo study on stopping-power ratios for radiosurgery and IMRT beams. Physics in Medicine & Biology. 2003;48(14):2081.
    15. e Carlo model to predict dosimetric properties of small radiotherapy photon fields. Medical physics. 2008;35(10):4671-84.
    16. Yarahmadi M, Nedaie HA, Allahverdi M, Asnaashari KH, Sauer OA. Small photon field dosimetry using EBT2 Gafchromic film and Monte Carlo simulation. Int J Radiat Res. 2013;11(4):215-24.
    17. Abdullah R, Zakaria A, Mohsin NI, Idris NR, Yusof AL, Mohamed M. Measurement of dosimetric parameters and dose verification in stereotactic radiosurgery (SRS). Jurnal Sains Kesihatan Malaysia (Malaysian Journal of Health Sciences). 2015;13(1).
    18. Gholami S, Nedaie HA, Meigooni AS, Longo F. Grid therapy: impact of radiobiological models on calculation of therapeutic ratio. InWorld Congress on Medical Physics and Biomedical Engineering. Toronto, Canada. 2015;487-9.




Volume 16, Issue 3 - Serial Number 3
May and June 2019
Pages 232-240
  • Receive Date: 24 June 2018
  • Revise Date: 28 October 2018
  • Accept Date: 29 October 2018
  • First Publish Date: 01 May 2019