CHARACTERIZATION OF A MEGAVOLTAGE LINEAR ACCELERATOR BREMSSTRAHLUNG BY MEANS OF MONTE CARLO SIMULATIONS

M. VALENTE, N. CASTRO, F. CARRASCO

Cabo Frio (Rio de Janeiro) Brasil

Congreso; XI Latin American Seminar of Analysis by X-ray techniques; 2008

Universidade Federalñ do Rio de Janeiro

Nowadays, megavoltage linear accelerator (Linac) is the most employed worldwide feature for treatment radiation production. Typical Linacs are capable of dual modalities, i.e. high energy electrons and X-rays by means of Bremsstrahlung. Both radiation types are useful for radiotherapy, however each one having specific characteristics and advantages. Radiation damage depends strongly on the radiation type and quality, therefore incident beam characterization becomes mandatory for accurate dosimetric calculations and treatment planning. Due to the extremely high fluence, direct measurements of Linac spectra are extremely hard to perform, however Monte Carlo simulations have shown to be a suitable method to this aim. This work presents a method for megavoltage X-ray Bremsstrahlung assessment by means of Monte Carlo (PENELOPE) simulations. The proposed method provides suitable spectra characterization by means of a few parameters, namely the acceleration potential and electron range. The obtained spectra have been used as incident beam for in-depth dose distribution determination with the aim of performing further comparisons with experimental data. This comparison procedure has been employed for Bremsstrahlung assessment optimization. Once, the Linac Bremsstrahlung is well-established, it may be used as incident beam for further dosimetric purposes, like spatial dose distribution calculations. The whole process has been applied for the characterization of the megavoltage Bremsstrahlung from a typical Linac, namely the 10MV Varian clinac 18. The obtained results for in-depth dose distributions, when compared with experimental measurements, show an overall good agreement, which may suggest the feasibility of the method.