- Author: Vinod K Panchbhavi, MD, FACS; Chief Editor: Gowthaman Gunabushanam, MD, FRCR more...
Reduction of risks due to ionizing radiation can be achieved by various measures, which involve the design and usage of equipment, use of targeting devices and certain measures that can be taken by the personnel involved.
In vertical positioning, the x-ray source is under the table and the image intensifier is above (see the images below). This positioning is preferable because it reduces scatter radiation, because even the scattered x-rays must pass through the patient before they reach medical personnel in the patient's vicinity. Therefore, exposure due to scatter x-rays is less. The patient should be positioned as far from the x-ray source as practicable to minimize patient skin entrance dose. The image intensifier should be positioned as close to the patient as practicable. This results in a lower patient dose and sharper image.
Scatter is great in horizontal positioning for cross-table fluoroscopy and in vertical positioning in which the tube is above the table and the part to be screened closer to the image intensifier (see image below). Such positioning should be avoided if possible.
Protection of the patient and other personnel in the vicinity during the conduct of fluoroscopy is an important safety requirement. Lead aprons, lead gloves, lead neck or thyroid shields, lead eyeglasses, lead drapes, and lead glass barriers help reduce the radiation exposure to the personnel. A lead barrier of 0.25-mm lead equivalent thickness typically stops 90% of the x- rays, and a 0.5-mm lead equivalent apron typically absorbs 97% of x-rays.
Safety regulations require that all persons, including staff or other patients, within 2 meters of the tube head, direct beam, or exposed area of the patient’s body be protected by lead shielding of a thickness equivalent to 0.25 mm of lead (Pb). Furthermore, gonadal lead shielding of at least 0.5 mm Pb-equivalent shielding must be used for patients who have not passed reproductive age for radiographic procedures. Since staff aprons are frequently used for this function, current recommendations state that all lead or lead-equivalent aprons be of 0.5 mm Pb-equivalence.
Radiation dose rate varies inversely to the square of the distance from the source. The main source of radiation exposure to medical personnel is from scattered radiation from the patient, not from the x-ray tube. In the interest of radiation safety, all persons, including staff or other patients, must be as far as possible (at least 2 meters) from the tube head, direct beam, or exposed area of the patient’s body unless protected by lead barriers.
The use of a laser-aiming device to help position during fluoroscopy is recommended in an effort to reduce radiation exposure.
Panchbhavi et al reported a prospective study on whether the use of a laser-aiming device attached to the C-arm improves the accuracy of intraoperative fluoroscopy, in order to reduce, by implication, radiation exposure in the operating room. From March to October 2004, they had 92 consecutive cases requiring use of fluoroscopy for foot and ankle surgery. The number of accurate and inaccurate images with or without the presence of a radiology technician and a laser-aiming device were compared. They found that the accuracy of imaging with the laser-aiming device was higher than the imaging without the device (P < .001). The accuracy of the images obtained by the surgeon was higher than the technicians’ images when laser guidance was used (P = .027). There was no significant difference between the images obtained by the surgeon or the technicians when the aiming device was not used (P = .09).
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