Field verification in radiotherapy with two-dimension ion chamber array

Objective: To research on consistency verification of radiation field size based on 2D ion chamber array matrix. Methods: We have used a 2D ion chamber array detector (IBA MatriXX) to measure the fields of VARIAN 23EX accelerator. The matrix was lied horizontally on the accelerator couch. The centre of matrix coincided with the accelerator isocentre, SAD = 100 cm. The field size was changed from 4.0 cm X 4.0 cm to 16.4 cm x 16.4 cm. Irradiating 6MV-X ray 50 MU per field, the measure data was recorded, and was analysed with the software, OmniPRO I' mRT (1.5). Results: The difference between the length (X,Y) of light and radiation field displays wave mode cyclicity change with the accretion of light field length. The average distance between the border difference wave crest and trough equals (7.6 ± 0.7) mm. The average distance from the trough to the crest in X direction is (3.3 ± 0.6) mm, and the average distance from the trough to the crest in Y direction is (3.3 ± 0.5) mm. Conclusion: Because the distribution of ion chamber in array is discrete and regulative, the difference between the length of light and radiation field displays wave mode cyclicity change with the accretion of light field length. Verifying consistency of radiation field size, the impact of discrete distribution of ion chamber in array over measurement result should be considered sufficiently. (authors)