The research about the output dose rate changed with the size of electron beam fields

Objective: To investigate the relationship between the output dose and the blocked field size of electron beam. Methods: The output dose of different energy and electron beam applicator and blocked fields size of electron beam created were measured with 2D air vented ionization chamber array MatriXX system under a clinic accelerator Primus (Siemens Medical Solution USA, Inc), and the measured data were fitted into a mathematic function with Matlab software and the curves of output dose factor were plotted. Results: If the blocked field sizes were greater than 6 cm x 6 cm, the change of the output dose of it was less than 3% among the different size fields, if the blocked fields were between 2 cm x 2 cm and 5cm x 5 cm, the output doses were changed obviously according to the fields size, the maximum change could nearly reach to 30%. Conclusion: The relationship between output factor of different energy electron beam field and blocked field sizes could be described with the function y= a + k1 · emx + k2·e-mx. (authors)