The CT Technologist's Role in Limiting Radiation Dose

The CT technologist should be aware of the radiation risks associated with CT, and can play a leadership role in implementing tools to limit radiation exposure in patients undergoing CT imaging. Specifically, CT technologists need to understand the parameters that affect radiation dose, practice dose reduction techniques on a regular basis, and be aware of the CT examination types that are the biggest contributors to radiation exposure from CT imaging. The increased use of CT in routine clinical practice has likely resulted in a substantial increase in radiation exposure in the US population. In fact, a report from the National Council on Radiation Protection and Measurements noted as much as 7-fold increase in ionizing radiation exposure from medical procedures between the early 1980s and 2006 (Figure 2). The report estimated that in 2006, 48% of total radiation exposure was from medical procedures, as opposed to just 15% in the early 1980s.¹³ Among the leading contributors to the increase in CT-associated radiation exposure include imaging studies of the head, chest, abdomen/pelvis, and studies of the chest for the diagnosis of pulmonary embolism.

The ongoing desire to limit radiation exposure must be balanced with the need to obtain adequate images during CT examinations. In general, higher radiation doses result in higher-resolution images, whereas lower doses lead to increased image noise and less sharp images. However, increased radiation dosage increases the risk of adverse side effects, most notably the risk of radiation-induced cancer. For instance, a 4-phase abdominal CT gives the same radiation dose as 400 chest X-rays. Fortunately, multiple strategies exist that can reduce the exposure to ionizing radiation during a CT scan.

Computed tomography technologists can employ a variety of dose reduction techniques that adequately balance the need for adequate imaging with adequate patient protection. For instance, technologists can control the z-axis scan length or minimize the number of phases to limit radiation exposure. External bismuth body shields to the breast, gonads, and thyroid are commonly used to protect these sensitive areas during CT imaging. In addition, dose reduction hardware techniques are commonly employed, including noise index and automatic tube current modulation, adjustments for peak kilovoltage (kVp), rotation time, and precise centering on the area to be scanned. In one analysis of the use of bismuth shielding, organ-based tube current modulation, and global tube current reduction as radiation dose reduction strategies using thorax phantoms of different sizes (15, 30, 35, and 40 cm lateral width), radiation dose to the breast region was reduced by approximately 21% and 37% with pediatric (2-ply shield; 15-cm phantom) and adult (4-ply shield; 30-, 35-, and 40-cm phantoms) models, respectively. Organ-based tube current modulation achieved dose decreases of 12% in the pediatric model and 34% to 39% in the adult model, and global lowering of the tube current reduced breast dosage by 23% and 39% in the pediatric and adult models, respectively.