Measurement of axial dose profile for wide detector CT using radiochromic films

To investigate the application of radiochromic film LD-V1 for measuring the dose profile of wide detector CT and comparing the measurements with the console-displayed CTDI_vol, with the aim of obtaining correction factors. Calibration curves in CTDI phantoms were first obtained with various tube currents at 120 kV. Then, at the selected wide beam collimations (80, 100, 120, 140, 160 mm), the film was placed in the extended phantom holes to obtain the dose profile. CTDI was calculated for different integration intervals, which allowed obtaining the CTDI₁₀₀ measurement efficiency. Finally, the CTDI_vol,300 measured was compared to the console-displayed CTDI_vol, and corresponding correction factors were derived. The discrepancy between the CTDI₁₀₀ obtained by the calibration curve and ionization chamber was essentially in the range of -8-4%. The CTDI₁₀₀ measurement efficiency was found to decrease with increasing beam widths. Furthermore, under selected wide beam collimations (80, 100, 120, 140, 160 mm), the correction factors in the head phantom were 1.299, 1.284, 1.157, 1.151, 1.099; 1.566, 1.585, 1.512, 1.365, 1.327 in the body phantom, respectively. Radiochromic film LD-V1 is feasible for measuring the dose profile of a wide detector CT scanner. The console-displayed CTDI_vol doesn't provide a full assessment of the radiation dose. It is recommended that the correction factors obtained in this study be used to improve the accuracy for evaluating the radiation dose to the subject.