Journal of Medical Physics
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Year : 1996  |  Volume : 21  |  Issue : 4  |  Page : 189-195

Surface Region Electron Beam Dosimetry In The Presence Of Cerrobend Cutouts

Correspondence Address:
K.M Ayyangar

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Source of Support: None, Conflict of Interest: None

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The dosimetry of electron beams from four different linear accelerators (Varian Clinac 1800, Siemens Mevatron MD, Mitsubishi EXL-14 and Mitsubishi EXL-17 DP) was studied as a function of beam energy, applicator size, and cutout size. The cutout factors (COF) were calculated as the ratio of the blocked field to open field ionizations at the surface, the reference depth (dmax) and an intermediate depth. Polystyrene phantom material was used as the scattering medium and the two electron energies (6 and 12 MeV) common to all accelerators were selected. From these studies, it is apparent that a COF greater than unity is possible when the blocking is approximately more than 50%. The COF was found to be different for different accelerators and generally, the variation was more pronounced for the 12 MeV compared with the 6 MeV electron beam. For the small diameter cutouts, the COF decreases with increasing depth of measurement. The surface dose showed about 6% increase for the 12 MeV and about 3% increase for the 6 MeV beams in the Siemens unit. These measurements implicate that the COF is significantly affected by the accelerator and applicator design, angular distribution of the electron beam, and the air gap between the applicator and skin surface.

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