| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 1882437 | Radiation Physics and Chemistry | 2014 | 5 Pages |
•We made a Monte Carlo simulation to study the dosimetric properties of the unflattened beam of the 15 MV Varian Clinac 2100C.•Removing the flattening filter increase the dose rate of the beam.•Removing the flattening filter decrease the out-of-field dose.•Removing the flattening filter decrease the photoneutron production.•The surface dose to the patient is increased by removing the flattening filter.
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 ‘FLUKA’ 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 40×40×40 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 2.11±0.05 to 0.40±0.01 mSv(n) Gy−1(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.
