Suitability of Chambers in Relative Dose Measurement of Small Fields for Accelerated Photon Delivered by a Medical Linear Accelerator

Document Type : Original Paper


1 Department of Physics, University of Chittagong, Bangladesh

2 Department of Radiology, North East Cancer Hospital, Sylhet., Bangladesh

3 SSDL, Bangladesh Atomic Energy Commission, Savar, Bangladesh

4 Department of Physics, Comilla University, Cumilla


Introduction: Using the small field in modern radiotherapy, the present study aimed at measuring the relative dosimetry (scattering factor, percentage depth dose (PDD), and profile of penumbra) with ionization (FC65-G, CC13, CC01) and diode (razor) chambers.
 Material and Methods: Applying TRS-398 in Varian Clinac™ IX-5982 for 6 MV photon beams, the conditions (pressure, temperature, direction, polarity) were kept the same for a set of field sizes (1 × 1, 2 × 2, 3 × 3, 4 × 4, 5 × 5, 7 × 7, and 10 × 10 cm2), and relative dosimetry was performed at the North-East Cancer Hospital, Sylhet, Bangladesh.
Results: During the output factor measurement in small fields, the razor showed better results than CC13. Taking CC01 as a standard in small fields, the data obtained from the study showed a good agreement with those of the previously published works.
Conclusion: Razor, with extremely small active volume, was very much suited for small field dosimetry, except for PDDs.


Main Subjects


    1. Paskalev KA, Seuntjens JP, Patrocinio HJ, Podgorsak EB. Physical aspects of dynamic stereotactic radiosurgery with very small photon beams (1.5 and 3 mm in diameter). Med Phys. 2003;30(2):111–8.
    2. Rikner G. Silicon diodes as detectors in relative dosimetry photon, electron and proton fields. Sweden: Uppasala University; 1983.
    3. Scott AJD, Nahum AE, Fenwick JD. Using a Monte Carlo model to predict dosimetric properties of small radiotherapy photon fields. Am Assoc Phys Med.  2008;35(10):4671-84.
    4. Heydarian M, Hoban PW, Beddoe AH. A comparison of dosimetry techniques in stereotactic radiosurgery. Phys Med Biol. 1996;41(1):93–110.
    5. Cheng CW, Cho SH, Taylor M, Das IJ. Determination of zero-field size percent depth doses and tissue maximum ratios for stereotactic radiosurgery and imrt dosimetry: Comparison between experimental measurements and Monte Carlo simulation. Med Phys. 2007;34(8):3149–57.
    6. Francescon P, Cora S, Cavedon C. Total scatter factors of small beams: A multidetector and Monte Carlo study. Med Phys. 2008;35(2):504–13.
    7. Alfonso R, Andreo P, Capote R, Huq MS, Klby W, Mackie, TR et al. A new formalism for reference dosimetry of small and nonstandard fields. Med Phys. 2008;35(11):5179-86.
    8. International Atomic Energy Agency. Technical Report Series (TRS) No.398. Absorbed Dose Determination In External Beam Radiotherapy: An International Code of Practice for Dosimetry based on Standards of Absorbed Dose to Water. Vienna. 2001.
    9. Podgorsak EB. Radiation Oncology Physics: A Handbook for Teachers and Students. IAEA. 2005; STI/PUB/1196.
    10. IBA Dosimetry Group. Independent & Integrated Quality Assurance for Radiation Therapy. 2020.
    11. Holt JG, Laughlin JS, Moroney JP. The extension of the concept of tissue-air-ratio (TAR) to high energy X-ray beams. Radiol. 1970;96(2): 437- 46.
    12. Netherlands Commission on Radiation Dosimetry Recommendations for the determination and use of scatter correction factors of mega voltage photon beams. NCS Report No. 12. Netherlands; 1998.
    13. Dutreix A, Bjarngard BE, Bridier A, Garibaldi C, Torzsok K, Venselaar J. Monitor unit calculations of high energy photon beams. Estro booklet No.3. Belgium;1997.
    14. Storchi P, Gasteren JJMV. A table of phantom scatter factors of photon beams as a function of quality index and field size. Phys Med Biol. 1996;41(3):563-71.
    15. Verhaegen F, Das IJ, Palmans H. Monte Carlo dosimetry study of a 6 MV stereotactic radiosurgery unit. Phys Med Biol. 1998;43(10):2755–68.
    16. Agarwal A, Rastogi N, Das KJM, Yoganathan SA, Udayakumar D, Kumar S. Investigating the Electronic Portal Imaging Device for Small Radiation Field Measurements. J Med Phys. 2017;42(2):59-64.
    17. Chen Li, Chen LX, Sun HQ, Huang SM, Sun WZ, Gao XW, et al. Measurements and comparisons for data of small beams of linear accelerators. Chinese Journal of Cancer. 2009;28(3):272-6.
    18. Laub WU, Wong T. The volume effect of detectors in dosimetry of small fields used in IMRT. Am Assoc Phys Med. 2003;30(3):341-7.
    19. Dosimetry of Small Static Fields used in External Beam Radiotherapy: An International Code of Practice for Reference and Relative Dose Determination. IAEA and AAPM, Technical Report Series No.483. Vienna. 2017.
    20. Dawson DJ, Harper JM, Akinradewo AC. Analysis of physical parameters associated with the measurement of high energy x-ray penumbra. Med Phys. 1984;11(4):491-7.
    21. Beddar AS, Mason DJ, O’Brien PF. Absorbed dose perturbation caused by diodes for small field photon dosimetry. Med Phys. 1994;21(7):1075-9.
    22. Das IJ, Cheng CW, Ronald JW, 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. Med Phys. 2008;35(9):4186-215.