A comparative analysis of head computed tomography scans protocols and thyroid dosimetry

Computed Tomography (CT) is currently one of the most widely used imaging modalities for disease identification, benefiting numerous patients with its advanced technology. However, there is a concern regarding its inappropriate use, which can lead to higher radiation doses in patients and consequently increase the potential risks of developing stochastic effects. Therefore, it is crucial to explore methodologies for optimizing patient doses, particularly in organs with higher radiosensitivity. Within this context, the aim of the proposed study is to compare absorbed dose and noise among different head CT scans using a polymethylmethacrylate (PMMA) phantom, proposing a better relationship between image quality and dose reduction for protocol and thyroid in head CT scans. The tests were conducted using head acquisition protocols on two CT scanners: a GE LightSpeed VCT with 64 channels and a Toshiba CT with 4 channels. The PMMA head-neck phantom consisted of two cylinders, one with a diameter of 16 cm and another with a diameter of 11 cm was used in this work. Radiochromic films and an ionization chamber were also utilized. The study evaluated discrepancies in CT scans, including Noise Power Spectrum (NPS), dose profiles, and punctual doses in thyroid. Protocols P_1A and P_2B had the lowest and highest CTDI_vol values, respectively. Radiochromic films facilitated precise dose analysis, identifying position 12 with the highest dose. NPS analysis revealed variations in noise distribution between the protocols.