Optimization of Head CT Protocol to Reduce the Absorbed Dose in Eye Lenses and Thyroid: A Phantom Study

Introduction: This study was conducted to measure the gamma emitters (e.g., uranium-238 [238U], thorium-232 [232Th], and potassium-40[40K]) and alpha emitters (e.g., radon-222 [222Rn] and radium), and also to evaluate the radiation hazard indices of radionuclides in parenteral nutrition samples utilized in the hospitals of Iraq. Material and Methods: An anthropomorphic phantom was examined with head protocols in both helical and sectional modes using two 16-slice CT scanners. The entrance surface dose of eye lenses and thyroid was measured with standard protocols and after reducing the mAS and kilo-voltage using thermo-luminescence dosimeters (TLDs). Results: In sectional mode with standard protocol, the highest surface dose was 2.3 mSv1 for eye lens and 0.021 mSv for thyroid in hospital A. Moreover, in helical mode with standard protocol, the highest surface dose was 0.964 and 0.02 mSv for eye lens and thyroid in hospital B, respectively. Reducing tube current and kilovoltage decreased the dose up to 35% for eye lens and 45% for thyroid in hospital A. By the mentioned reductions a dose decrease of up to 40% was achieved for both eye lens and thyroid in hospital B. There were no considerable differences in image quality between scans with standard protocol and the protocols of reduced parameters. Conclusion: Head CT scans with standard factors conduce to images with the best quality. It may be possible to diminish the absorbed dose up to 40% without losing information, especially in follow up head scans