Dosimetric properties of photon beams from a flattening filter free clinical accelerator.
Basic dosimetric properties of 6 MV and 18 MV photon beams from a Varian Clinac 21EX accelerator operating without the flattening filter have been measured. These include dose rate data, depth dose dependencies and lateral profiles in a water phantom, total scatter factors and transmission factors of a multileaf collimator. The data are reviewed and compared with measurements for the flattened beams. The unflattened beams have the following: a higher dose rate by factors of 2.3 (6 MV) and 5.5 (18 MV) on the central axis; lower out-of-field dose due to reduced head scatter and softer spectra; less variation of the total scatter factor with field size; and less variation of the shape of lateral dose profiles with depth. The findings suggest that with a flattening filter free accelerator better radiation treatments can be developed, with shorter delivery times and lower doses to normal tissues and organs.
The University of Texas M D Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030, USA. onvassil@mdanderson.org
Oleg N
ON
Vassiliev
Uwe
U
Titt
Falk
F
Pönisch
Stephen F
SF
Kry
Radhe
R
Mohan
Michael T
MT
Gillin
D010315:Particle Accelerators; D019047:Phantoms, Imaging; D017785:Photons; D011829:Radiation Dosage; D012542:Scattering, Radiation