DOSE MEASUREMENT OF COBALT-60 RADIOTHERAPY BEAMS IN TREATMENT FIELDS
AbstractBackground: Radiation therapy is a complex process with multiple steps, each of which has an impact on the quality of treatment. Accurate dosimetry is a critical step during the radiotherapy of cancer patients.The aim of the present study was to measure and evaluate the doses of two cobalt-60 (60Co) teletherapy units GWXJ80 of NPIC China and Theratron 780 of AECL Canada at various points within fields for different field sizes. Methods: This cross-sectional descriptive study was done to measure the 60Co doses in the treatment fields.The dose measurements were done in air and 30×30×30 cm3 Phantom at 80 cm SSD by using calibrated NE 2570 Farmer Electrometer & NE 2571 Farmer Ionization Chamber and percentage of doses were calculated. Results: The results showed that 60% central area of all fields ranging from 100–98.79% and 100–96.12% for GWXJ80 in the air and phantom, whereas for Theratron 780, they were ranging from 100–98.50% and 100–96.45% in air and phantom respectively. The percentages of doses at the edges for GWXJ80 and Theratron 780 in the air were 75.39–38.66% & 85.65–46.47% respectively and they were 82.22–40.39% & 49.05–24.55% respectively in phantom. Conclusions: The doses within 60% central area of fields in air were higher than phantom for both teletherapy units. The doses at field edges in air were lower in GWXJ80 than Theratron 780 whereas in phantom they were vice versa. But all were in the acceptable range as recommended by International Commission on Radiation Units and Measurements.Keywords:Cobalt-60 ( 60Co), Quality Assurance, Dosimetry, Exposure, Central Area, Edge
Dyk JV. Megavoltage radiation therapy: Meeting the technological needs, standard and codes of practice in medical radiation dosimetry proceedings of an international symposium; 2002 November 25–28; Vienna: IAEA; 2002.
Praveenkumar RD, Santhosh KP, Augustine A. Estimation of inhomogenity correction factors for a Co-60 beam using Monte Carlo simulation. J Canc Res Ther 2011;7:308–13.
Parker W, Patrocinio H. Clinical treatment planning in external photon beam radiotherapy. In: Podgorsak EB, editor. Radiation oncology physics: A handbook for teachers and students. Vienna: IAEA; 2005.p. 219.
Reda MS, Massoud E, Hanafy MS, Bashter II, Amin EA. Monte Carlo dose calculations for breast radiotherapy using Co-60 gamma rays. J Nuclear Radiat Phys 2006;1:61–72.
International Atomic Energy Agency. Technical Reports Series No. 277, Absorbed dose determination in photon and electron beams. 2nd ed. Vienna: IAEA; 1997.
International Atomic Energy Agency. TRS-398, Absorbed dose determination in external beam radiotherapy: an international code of practice for dosimetry based on standards of absorbed dose to water. Vienna: IAEA; 2000.
International Commission on Radiation Units and Measurements. Prescribing, recording and reporting photon beam therapy. Report 50, USA: ICRU; 1993.
Nordic Association of Clinical Physicist. Specification of dose delivery in radiation therapy. NACP; 1994.
International Atomic Energy Agency. Commissioning and quality assurance of computerized planning systems for radiation treatment of cancer. Technical report series 430. Vienna: IAEA; 2004.
International Atomic Energy Agency. Design and implementation of a radiotherapy programme: Clinical, medical physics, radiation protection and safety aspects. TECDOC-1040. Vienna: IAEA; 1996.
International Atomic Energy Agency. Quality assurance in radiotherapy. TECDOC-989. Vienna: IAEA; 1997.
Novotny J. In: Accidents in radiotherapy: lack of quality assurance, ‘Quality assurance in radiotherapy’, TECDOC-989, Vienna, IAEA; 1997.p. 19–34.
Samat SB, Evans CJ, Kadni T, Dolah MT. Accurate measurement of exposure rate from a 60Co teletherapy source: deviations from the inverse-square law. Brit J Radiol 2000;73:867–77.
Radiation dose in radiotherapy from prescription to delivery. TECDOC-896, Vienna: IAEA; 1996.p. 281.
Podgorsak EB. External photon beams, Physical aspects. In: Radiation Oncology Physics: A handbook for teachers and students’. Vienna: IAEA; 2005.p. 169.
Podgorsak EB. External photon beams: Physical aspects. In: Radiation Oncology Physics: A handbook for teachers and students’. Vienna: IAEA; 2005.p. 195.
Khan FM, editor. The physics of radiation therapy 4th Edition, USA: Lippincott Williams & Wilkins; 2010.p. 176–8.
Dyk JV, Battista JJ. Cobalt-60: An Old modality, a renewed challenge. UK: Physics Department London. Available at: http://www.theratronics.ca/press/VanDyk.pdf
Glasgow GL, Kurup RG, Leybovich L, Wang S, Fatyga M. Dosimetry and use of Co-60 100cm source-to-axis distance teletherapy units. Curr Oncol 1996;3:17–25.
Laughlin J, Mohan R, Kutcher GJ. Choice of optimum megavoltage energy for accelerators for photon beam treatment, Int J Radiat Oncol Biol Phys 1986;12:1551–7.
Rawlinson JA. The choice of equipment for external beam radiotherapy. Proceedings of the IAEA Seminar on Organization and Training of Radiotherapy; Cairo, Africa; 1989 Dec; IAEA;.p. 11–5.
Sasane JB, Iyer PS. Relevance of radiation penumbra in high-energy photon beam therapy. Strahlentherapie 1981;157:658–61.
Podgorsak EB. External photon beams: Physical aspects. In: Radiation Oncology Physics: A handbook for teachers and students. Vienna: IAEA; 2005.p. 199.
Buzdar SA, Rao MA, Nazir A. An analysis of depth dose characteristics of phtons in water. J Ayub Med Coll 2009;21(4):4,41–5.
Starkschall G, Ph.D. Presentation on dose distribution. Department of Radiation Physics, U.T. M.D. Anderson Cancer Center, Texas, Available at: www.uthgsbsmedphys.org/RadOncRes/13b-IsodoseDistributions.pdf.