Calculation of 10 MV x-ray spectra emitted by a medical linear accelerator using the BFGS quasi-Newton method.
To calculate photon spectra for a 10 MV x-ray beam emitted by a medical linear accelerator, we performed numerical analysis using the aluminium transmission data obtained along the central axis of the beam under the narrow beam condition corresponding to a 3x3 cm2 field at a 100 cm distance from the source. We used the BFGS quasi-Newton method based on a general nonlinear optimization technique for the numerical analysis. The attenuation coefficients, aluminium thicknesses and measured transmission data are necessary inputs for the numerical analysis. The calculated x-ray spectrum shape was smooth in the lower to higher energy regions without any angular components. The x-ray spectrum acquired by the employed method was evaluated by comparing the measurements along the central axis percentage depth dose in a water phantom and by a Monte Carlo simulation code, the electron gamma shower code. The values of the calculated percentage depth doses for a 10x10 cm2 field at a 100 cm source-to-surface distance in a water phantom were obtained using the same geometry settings as those of the water phantom measurement. The differences in the measured and calculated values were less than +/-1.0% for a broad region from the shallow part near the surface to deep parts of up to 25 cm in the water phantom.
Shimozato
T
T
Hamamatsu University School of Medicine, University Hospital, 1-20-1 Handayama, Hamamatsu, Shizuoka 431-3192, Japan. shimo-p@umin.ac.jp
Tabushi
K
K
Kitoh
S
S
Shiota
Y
Y
Hirayama
C
C
Suzuki
S
S
D000535:Aluminum / Q000737:chemistry; D006801:Humans; D015233:Models, Statistical; D008962:Models, Theoretical; D009010:Monte Carlo Method; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D017785:Photons; D011874:Radiometry; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D014867:Water / Q000737:chemistry; D014965:X-Rays
D014867:Water; D000535:Aluminum