Study On Small Field Dosimetry Based On Monte Carlo

The Objective of this paper is that based on the Monte Carlo method,the accuracy of the three detectors for the measurement of small field dosimetry was evaluated,and the maximum error detector was corrected.The PDD curves and Dose Profile(at the depth of 1.5cm,5cm,10 cm,20cm)of the 2cm×2cm,3 cm×3cm,4 cm×4cm field were measured using CC13 ionization chamber,SFD,and PFD under the 6MV X ray of the Trilogy Accelerator(Varian Company).After that,the above data was simulated with EGS4 code,the structure of the accelerator head was simulated with BEAMnrc,the three-dimensional water tank was simulated with DOSXYZnrc.Finally,the date from the 3ddose file was analyzed by the MATLAB software.Compared with the measured date and simulation,the better detector for small fields was decided.Besides,the worse detector could be corrected through the simulation.The result is that the surface dose and the built-up area dose of the SFD detector measurement were close to those of the Monte Carlo simulation.However,the other two detectors were far from the simulation.After the maximum dose point,the difference between the three detectors was less.For the Dose Profile curve,the curve of the SFD measurement was close to that of the Monte Carlo simulation,and the measurement curve of the PFD and CC13 was quite different from the simulated value in the penumbra.For CC13,the correction factor near central axis was close to 1,while far from 1 in the penumbra area,and there was no obvious value rule.So,the conclusion is that SFD detector could be used to measure dose curve of small fields,and clinical reference was also achieved with CC13 through correction factor.