I am a Radiologic Technologist based out of the United States, and have been following many articles and publications by the Radiography community regarding lead shielding and its importance in modern practice. Recently, there has been much scrutiny regarding the efficiency and realistic protection that lead shielding provides both patient and operator. I will be discussing this topic, while referencing information from the American Journal of Roentgenology. I'd like to hear from this community as to what your take is on this topic, and if your practices have changed regarding lead shielding.
The publication is titled "Patient Shielding in Diagnostic Imaging: Discontinuing a Legacy Practice", by Rebecca M. Marsh and Michael Silosky, found at https://www.ajronline.org/doi/full/10.2214/AJR.18.20508.
As an introduction to the background of patient shielding: Lead placed inside of aprons and wrap-around waist bands has been the common material used to protect patients from scatter radiation. To quote Paul Frame, PhD, CHP from the Health Physics Society, "For gamma rays and x rays, lead is a particularly effective shield because lead has a high atomic number (Z) of 82. The atomic number is the number of protons in an atom. Since the number of protons per atom of lead is large, the number of electrons is also large, and it is the electrons that stop gamma rays and x rays. " (2006)
To understand the next portion of the publication by the American Journal of Roentgenology, I will be explaining the function of an Ionization Chamber, which is an integral part of image acquisition for many radiographic examinations. Inside of (most) image receptors used in modern radiography exists a device called the Ionization Chamber. This chamber acts as a photo-timer for a common technique called "AEC". or Automatic Exposure Control. A radiographer can select this technique when acquiring particular images in order to acquire images while allowing a predetermined histogram of what the resultant image is expected to appear like. In order for this process to work, a gas exists inside of the ionization chamber, which is energized by x-ray photons liberating electrons from the gas when ionized. Once the predetermined amount of energization occurs within the ionization chamber, the image acquisition and radiation exposure ceases. This function must be selected by the radiographer, and is not typically used in mobile radiography. It is also not suggested for many radiographs, therefore having a niche usage. Radiographers are always able to manually select the radiographic techniques for image acquisition in lieu of AEC.
The American Journal of Roentgenology suggests that the usage of Automatic Exposure Control (AEC) and therefore the usage of Ionization Chambers, in association with lead shielding, is detrimental to patient safety. By placing lead into the field of view (FOV) of the radiograph, the histogram that determines when the adequate amount of radiation has been utilized to acquire the selected radiograph will not function properly. Instead, increased radiation exposure will occur, as the lead will block the radiation in the area that it is placed, causing the AEC to continually generate radiation until a predetermined amount of radiation has been generated, ceasing x-ray production as a safety feature. Additionally, lead shielding cannot protect patients from internal radiation scatter, and is not designed for use protecting patients when the primary beam of the x-ray tube is directed to the placement of the lead.
However, the American Journal of Roentgenology DOES suggest that lead shielding can be effective at preventing radiation exposure, but shielding patients leads to the possibility of lead being inadvertently placed within the area of interest, necessitating a repeat radiograph, which leads to increased radiation exposure. To quote the AJR: " One must also consider the amount of protection that shielding provides to a patient. This varies based on whether anatomy is located outside the imaging FOV (i.e., not in the path of the primary x-ray beam) or inside the imaging FOV. For anatomy outside the imaging FOV, radiation exposure results almost entirely from internal scatter generated within a patient <21>. Because contact shielding cannot protect against internal scatter, shielding anatomy outside the imaging FOV provides negligible protection to the patient. This holds true for all examinations, including those of pediatric and pregnant patients <13, 15, 22–25>. For anatomy that is within the imaging FOV, the use of patient shielding may reduce patient dose, but this potential dose savings comes at the risk of inadvertently increasing patient dose or adversely affecting the diagnostic efficacy of the examination." (2019)
In conclusion: Lead shielding CAN be detrimental to patient safety when placed inappropriately on a patient during radiographic exams, especially in the case of AEC usage. Additionally, internal scatter cannot be prevented by lead shields. However, lead shielding DOES provide absorption of x-ray photons when placed correctly, but creates a possibility of improper usage, therefore necessitating a repeat radiograph and subsequently increasing radiation dose.
Is this simply an issue of Radiographers requiring additional training and education regarding lead shield placement, should the possibility of necessitating additional radiographs abolish the traditional shielding methods, or do we require more specially designed lead shielding for individual body parts (thyroid, genitalia, etc.)?
Marsh, Rebecca M., and Michael Silosky. “Patient Shielding in Diagnostic Imaging: Discontinuing a Legacy Practice.” American Journal of Roentgenology, vol. 212, no. 4, Apr. 2019, pp. 755–757., doi:10.2214/ajr.18.20508. Retrieved from: https://www.ajronline.org/doi/full/10.2214/AJR.18.20508
Frame, Paul. “Answer to Question #44 Submitted to ‘Ask the Experts.’” Can Lead Protect Us from Radiation Because of Its Density?, Health Physics Society, 18 Feb. 2006, https://web.archive.org/web/20060218053005/http://www.hps.org/publicinformation/ate/q44.html. Retrieved from: https://web.archive.org/web/20060218053005/http://www.hps.org/publicinformation/ate/q44.html
Wong, Monica, and Henry Knipe. “Ionization Chamber: Radiology Reference Article.” Radiopaedia Blog RSS, https://radiopaedia.org/articles/ionisation-chamber?lang=us. Retrieved from: https://radiopaedia.org/articles/ionisation-chamber?lang=us
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