The physical characteristics of the 15 MV Varian Clinac 2100C unflattened beam

• Published in: Radiation physics and chemistry (Oxford, England : 1993) Vol. 95; pp. 205 - 209
• Main Authors: Najem, MA, Spyrou, N M, PodolyA!k, Z, Abolaban, F A
• Format: Journal Article
• Language: English
• Published: 01-02-2014
• Subjects: Beams (radiation); Computer simulation; Dosage; Flattening; Mathematical analysis; Monte Carlo methods; Photon beams; Photons
• ISSN: 0969-806X
• DOI: 10.1016/j.radphyschem.2013.04.035

A 15 MV photon beam of a Varian Clinac 2100C medical linear accelerator operating with and without a flattening filter was simulated using the Monte Carlo code aFLUKAa in order to calculate differences in their dosimetric properties. These include: the dose rate, the percentage depth dose on the central axis, the beam profile, the out-of-field dose, the surface dose on a 40A40A40 cm3 water phantom and the neutron contamination. The results obtained showed that the unflattened beam has a dose rate 4.86 times higher than the flattened one. The average out-of-field dose from the edge of the field to the edge of the phantom was reduced by 44%, the neutron fluence at the isocentre was reduced by 77% and the surface neutron dose-equivalent was reduced from 2.11A-0.05 to 0.40A-0.01 mSv(n) Gya1(X) after normalising both beams to give the same dose at dmax (the depth of maximum dose). However, the photon surface dose of the unflattened beam increased by 13%. From this information, it can be concluded that the unflattened beam can lead to better treatment outcome and may reduce the beam-on time which may be required for specific cases.