Reducing Patient Dose
There are seven common practices to reduce patient dose during radiographic procedures. They include the following:
• Minimize repeat radiographs: A primary cause of repeat radiographs is poor communication between the technologist and the patient. The technologist must clearly explain the procedure to the patient. Carelessness in positioning and selection of erroneous technique factors are common causes of repeats and should be avoided.
• Correct filtration: Filtration of the primary x-ray beam reduces exposure to the patient by preferentially absorbing low-energy “unusable” x-rays, which mainly expose the patient’s skin and superficial tissue without contributing to image formation.
• Accurate collimation: The practice of close collimation to only the area of interest reduces patient dose by reducing the volume of tissue directly irradiated, and the amount of accompanying scattered radiation is decreased.
• Specific area shielding (gonadal and female breast shielding): Specific area shielding is essential when radiosensitive organs such as the thyroid gland, breasts, and gonads are in or near the useful beam and the use of such shielding do not interfere with the objectives of the examination. The most common and most important area shielding is gonadal shielding, which significantly lowers the dose to the reproductive organs. Gonadal shields, if placed correctly, reduce the gonadal dose by 50% to 90% if the gonads are in the primary x-ray field.
• Protection of the fetus: All women of childbearing age should be screened for the possibility of pregnancy before an x-ray examination.
• Optimum imaging system speed: The highest-speed analog (film-screen combination) that results in diagnostically acceptable radiographs is desirable to manage patient dose. Digital imaging systems have essentially replaced film-screen for most radiographic applications. These digital receptors are more sensitive than film-screen and thus have the potential to reduce patient dose.
• Select projections and exposure factors appropriate for the examination: Perform projections (pending department approval) that minimize dose to radiosensitive tissues such as the breast and eye. A PA projection will greatly reduce dose to these tissues as compared to an AP projection. Select exposure factors that use highest allowable kV and lowest mAs to further reduce patient dose.
Ethical Practice in Digital Imaging: The wide dynamic range of digital imaging enables an acceptable image to be obtained with a broad range of exposure factors. During the evaluation of the quality of an image, the technologist must ensure that the exposure indicator is within the recommended range. Any attempt to process an image with a different algorithm to correct overexposure is not acceptable; it is vital that patient dose be minimized at the outset and that the ALARA principle be upheld.
To maintain dose at a reasonable, consistent dose level, the following practices are recommended: