Dosimetric properties of a flattening filter-free 6-MV photon beam: a Monte Carlo study.
OBJECTIVE
The dosimetric features of an unflattened 6-MV photon beam of an Elekta SL-25 linac was calculated by the Monte Carlo (MC) method.


METHODS
The head of the Elekta SL-25 linac was simulated using the MCNP4C MC code. The accuracy of the model was evaluated using measured dosimetric features, including depth dose values and dose profiles in a water phantom. The flattening filter was then removed, and beam dosimetric properties were calculated by the MC method and compared with those of the flattened photon beam.


RESULTS
Our results showed a significant (twofold) increase in the dose rate for all field sizes. Also, the photon beam spectra for an unflattened beam were softer, which led to a steeper reduction in depth doses. The decrease in the out-of-field dose and increase in the contamination electrons and a buildup region dose were the other consequences of removing the flattening filter.


CONCLUSIONS
Our study revealed that, for recent radiotherapy techniques, the use of multileaf collimators for beam shaping removing the flattening filter could offer some advantages, including an increased dose rate and decreased out-of-field dose.
Mesbahi
Asghar
A
Medical Physics Department, Medical School, Tabriz University of Medical Sciences, Attare Nishabouri Street, Tabriz, Iran. asgharmesbahi@yahoo.com
Mehnati
Parinaz
P
Keshtkar
Ahmad
A
Farajollahi
Alireza
A
D009010:Monte Carlo Method; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D017785:Photons; D011829:Radiation Dosage; D012542:Scattering, Radiation
Med Phys. 2006 Jun;33(6):1738-46
16872081
Med Phys. 2006 Jun;33(6):1595-602
16872067
Med Phys. 2004 Feb;31(2):396-404
15000626
Appl Radiat Isot. 2005 Mar;62(3):469-77
15607926
Med Phys. 1997 Sep;24(9):1485-9
9304577
Med Phys. 2002 Mar;29(3):379-90
11930913
Phys Med Biol. 2006 Apr 7;51(7):1907-17
16552113
Phys Med Biol. 2004 Apr 21;49(8):1535-47
15152690
Appl Radiat Isot. 2006 Jun;64(6):656-62
16455264
Med Phys. 1991 May-Jun;18(3):519-21
1908047
Med Phys. 2006 Apr;33(4):820-7
16696457
Med Phys. 1993 Sep-Oct;20(5):1491-5
8289733