1. Scatter radiation is the main source of exposure to the operator (1). Anything that reduces the patient’s radiation dose will reduce scatter and therefore reduce operator dose as well.

2. Remember TIDS: Time, Intensity, Distance, Shielding

a. Time: Limit the amount of fluoroscopy time. Use fluoroscopy only to observe objects in motion. Use last-image-hold images or stored fluoroscopy loops as much as possible.

b. Intensity: Use the lowest fluoroscopic dose rate that yields adequate image quality. Know what the dose rate is. Use the lowest digital acquisition rate that provides the necessary information. Remain aware of the patient dose throughout the procedure.

c. Distance: Stay as far away from the primary beam and from the x-ray tube as possible.

d. Shielding: Wear appropriate personal protective equipment (aprons and eyewear).

3. Treat radiation like you treat iodine. Use radiation the same way that you use iodinated contrast material—give as much as necessary, but no more; do not give it without a good reason. As the dose increases, be more aggressive in managing its use. In particularly sensitive patients, try to limit radiation dose as much as possible.

a. Indirect: interaction of a photon with an atom or molecule; formation of a reactive free radical that then interacts with DNA. The most common interaction is with water to form a hydroxyl radical.

b. Direct: physical interaction of a photon with DNA (less common)

c. DNA damage is usually repaired within 24 hours (2). As opposed to singlestrand DNA breaks, double-strand DNA breaks are more often repaired incorrectly. Incorrect repair can result in point mutations, chromosome translocations, or gene fusions.

d. Repopulation of cells that are damaged beyond repair and die can take several months (2).

a. Stochastic: The result of unrepaired or incorrectly repaired DNA damage in a single cell. With time, descendants of this cell may result in a cancer. The current model used for stochastic risk is the “linear no threshold” (LNT) model, a conservative model designed for radiation protection purposes. This states that stochastic risk increases linearly as dose increases, and injury severity is independent of dose. The actual risk is unknown for effective doses <100 mSv (3,4). (Effective dose is defined in the following text, under “Radiation Dose Measurement” section.) An analogy for the LNT model is a lottery with only one “prize” (cancer); you could win if you buy only one ticket (small amount of radiation), but you are more likely to win if you buy lots of tickets. In the end, you either win the entire prize (develop cancer) or lose. Unlike a lottery, the chance of getting the “prize” increases the longer you hold your “ticket.” For patients exposed at a very young age, lifetime risk is increased, both because their lifetimes are longer and because the risk of induction of certain cancers (leukemia and thyroid, skin, breast, and brain cancer) is greater for young patients (5).

b. Tissue reactions (deterministic effects): Large numbers of cells are damaged beyond repair and die, resulting in injury (typically to skin and subcutaneous tissues in interventional radiology procedures). Patients who undergo interventional procedures may be at risk for injuries ranging from transient mild erythema to skin necrosis and bone necrosis. Radiation-induced tissue reactions are unlikely below an absorbed dose to the skin (threshold) of 2 Gy; serious skin effects are unlikely below a skin dose of 5 Gy (2). The threshold dose demonstrates biologic variability. The most severe injuries are typically seen only after very high skin doses (>10 Gy). Sunburn is an exact analogy with regard to threshold and severity; you can stay out in the sun for a period of time with no ill effects, but after that time (the threshold), you are certain to develop a sunburn. How long you can stay out in the sun safely varies from person to person. The severity of the sunburn will increase the longer you are exposed to the sun.

All measurements of patient dose contain some degree of uncertainty related to variations in instrument response with changes in beam energy, dose rate, and collimator size. To accommodate these uncertainties, displayed cumulative air kerma values, for example, are permitted to deviate from the actual value by ±35% (6).

1. Skin dose: Ideally should be estimated and mapped during procedures with the potential for high-radiation dose, but at present, this capability is not generally available on most fluoroscopes. The highest dose to any point on the skin surface, or peak skin dose (PSD) measured in Gy, determines the severity of a radiation-induced skin injury.

2. Cumulative air kerma (synonyms: reference dose, reference point dose, reference point air kerma, reference air kerma, RPDose, K_a,r, cumulative dose, CD): Indicated in mGy or Gy and displayed automatically on all fluoroscopic equipment sold in the United States since mid-2006. It is the dose at the patient entrance reference point (PERP). For C-arm units, the PERP is located along the
central ray of the x-ray beam, 15 cm back from the isocenter (the central point about which the C-arm rotates) toward the x-ray tube. Cumulative air kerma is not the same as the skin dose; reference air kerma is usually greater than PSD. When PSD estimates are not available, cumulative air kerma may be used as a guide to indicate when patient follow-up is necessary to detect possible tissue reactions (7,8).

3. Kerma-area product (synonyms: KAP, P_KA, air kerma-area product, dose-area product, DAP

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