Monte Carlo based investigations of electron contamination from telecobalt unit head in build up region and its impact on surface dose. (December 2016)

• Record Type: Journal Article
• Authors: Jagtap, A.S.; Palani Selvam, T.; Patil, B.J.; Chavan, S.T.; Pethe, S.N.; Kulkarni, Gauri; Dahiwale, S.S.; Bhoraskar, V.N.; Dhole, S.D.
• Is Part Of: Applied radiation and isotopes. Volume 118(2016:Dec.)
• Page Start: 175
• Page End: 181
• Publication Date: 2016-12
• Subjects: Monte Carlo simulation -- Telecobalt unit -- Gafchromic film -- Secondary electrons -- Surface dose -- Percentage Depth Dose; Radiology -- Periodicals; Radiation -- Industrial applications -- Periodicals; Nuclear chemistry -- Periodicals; Internet resource; Periodical; 660.298
• DOI: 10.1016/j.apradiso.2016.09.012
• Languages: English
• ISSNs: 0969-8043

Abstract

Abstract: A Telecobalt unit has wide range of applications in cancer treatments and is used widely in many countries all around the world. Estimation of surface dose in Cobalt-60 teletherapy machine becomes important since clinically useful photon beam consist of contaminated electrons during the patient treatment. EGSnrc along with the BEAMnrc user code was used to model the Theratron 780E telecobalt unit. Central axis depth dose profiles including surface doses have been estimated for the field sizes of 0×0, 6×6, 10×10, 15×15, 20×20, 25×25, 30×30 cm 2 and at Source-to-surface distance (SSD) of 60 and 80 cm. Surface dose was measured experimentally by the Gafchromic RTQA2 films and are in good agreement with the simulation results. The central axis depth dose data are compared with the data available from the British Journal of Radiology report no. 25. Contribution of contaminated electrons has also been calculated using Monte Carlo simulation by the different parts of the Cobalt-60 head for different field size and SSD's. Moreover, depth dose curve in zero area field size is calculated by extrapolation method and compared with the already published data. They are found in good agreement. Highlights: Electron contamination from various parts of Cobalt-60 unit head has been investigated. Surface dose increases by factor of 2.5 and 2.1 for larger field size at SSD 60 and 80 cm. Depth of maximum dose has shifted towards the surface for larger field size. Build up curve for contamination free 'zero area' field size has been estimated.