• Medical exposure to irradiation typically comes from three major sources: Diagnostic radiologic examinations, the use of radiopharmaceuticals in nuclear medicine, and therapeutic applications of radiation. We will focus on radiologic examinations.
• Anesthesia providers are exposed to increasing amounts of radiation as the intraoperative use of fluoroscopy and other radiologic techniques increase.
• Anesthesiology pain practitioners increasingly use fluoroscopy to facilitate proper needle placement for nerve blocks.
• Perspective: Radiation exposure occurs daily in the form of cosmic rays from outer space (higher during airplane travel) and naturally occurring radioactive materials (e.g., radon gas). Persons living at higher altitude or at the north and south poles have higher exposure to cosmic radiation than persons at sea level or nearer the equator.

• Factors affecting the dose of radiation with x-ray include patient size, beam angle, type of fluoroscopy, and acquisitions.
• Patient size:
  • Radiation is attenuated by for every 5 cm of soft tissue. for example, a patient with 10 cm of extra tissue requires four times the dose to maintain the same image quality.
  • Dose increases in a fluoroscopy unit are automatically controlled so the operators do not perceive these differences.
• Beam angle:
  • Directing the beam through the patient at an oblique angle will raise the radiation dose due to increased tissue thickness.
• Type of fluoroscopy:
  • Continuous fluoroscopy allows real time visualization of dynamic activity using low x-ray tube currents.
  • Pulse fluoroscopy acquires frames that are less than real time (e.g., 7.5 or 15 frames per second) thereby reducing patient dose.
  • Pulsed – High (30 f/s) approaches continuous dose rate.
  • Photospot images (e.g., acquisitions) are obtained utilizing the same imaging chain as fluoroscopy but the x-ray tube current increases from 1 to 5 mA to ~300 mA. Photospot images are of diagnostic quality required for most clinical diagnosis.
• Increased magnifications:
  • Dose increased in order to maintain image brightness
  • Not a substantial effect on patient or operator.
• Collimation: The process of restriction and confinement of an x-ray beam to focus only on the area of interest.
  • Decreases area of skin and volume of tissue exposed and makes it easier to distribute the skin dose
  • Less scatter to personnel
  • Improved image quality from less scatter
  • Increases automatic brightness control that increases entrant skin dose

• Tissue weighting factors refer to the different probabilities for the occurrence of stochastic radiation effects. Higher values reflect an increased probability of detrimental effects to that organ system from radiation exposure.

  Organs	Tissue weighting factors
  Gonads	0.2
  Bone marrow	0.12
  Lung	0.12
  Stomach	0.12
  Bladder	0.05
  Chest	0.05
  Liver	0.05
  Thyroid gland	0.05
  Esophagus	0.05
  Skin	0.01
  Bone surface	0.01
  Remainder	0.05

• Additional anatomical considerations:
  • Eyes. Excessive exposure can lead to premature cataracts (left eye most common for c-arm operators due to usual location of beam).
  • Developing fetus during pregnancy can be affected (especially during organogenesis in the first trimester).
  • Patient skin. Varying the entry point of the radiation beam, when practical, will spread the radiation over more skin and reduce the likelihood that any one area will be overexposed. The image intensifier should be lowered as close as practical to the patient's skin to minimize scatter and maximize the gap between the x-ray tube and the skin. Even for a fixed fluoroscopy unit (tube fixed under the unit's table so that the tube to skin distance is fixed) lowering the image Intensifier will lower the skin dose.

• Cells that survive radiation exposure may be subsequently modified. This can occur as carcinogenenesis or hereditary effects, both of which are stochastic effects.
• Stochastic effects (cancer and genetic damage) have an increased risk of occurrence with increased radiation dose; they occur many years after exposure. There is no threshold or certainty that they will occur, only an increased risk (stochastic effects are also known as the "linear-no threshold theory"). Furthermore, the severity of that disease is independent of the dose once the disease is present.
• Nonstochastic effects (deterministic effects). Unlike stochastic effects, they have a clear relationship between the exposure and the effect. Nonstochastic effects often result from very large dosages in a short period of time and manifest within hours or days. Examples include erythema, skin and tissue burns, sterility, and radiation sickness.
• Genetic mutations leading to hereditary effects. Any dose of radiation has the potential to cause a mutation in the DNA that can be passed on genetically. Females are born with all of the eggs that they will have for their lifetime. Proper shielding should occur to minimize the risk.
• Early effects of ionizing radiation. These are dose-dependent stochastic effects of total body radiation that occur in the following sequence:
  • Hematologic (bone marrow syndrome)
  • GI syndrome
  • CNS syndrome (highest doses of exposure).
  • Local tissue damage (skin, gonads, extremities)
  • Hematologic depression
  • Cytogenic damage
• Late effects:
  • Leukemia
  • Malignancies (bone, lung, breast, etc.)
  • Local tissue damage (skin, gonads, eyes)
  • Shortened life span
  • Genetically significant dose
• Effects on fetus:
  • Lethal effects can occur before or immediately after implantation of the fertilized ovum in the uterine wall or at any time during intrauterine development. It can be expressed as prenatal or neonatal death.
  • Congenital malformation is expressed after birth as a result of radiation exposure during organogenesis (multiple organ systems may be affected, but is most commonly seen in the CNS, skeletal, and ocular systems).
  • Childhood malignancies (leukemia)
  • Diminished growth and development (intrauterine or after birth)
  • Atomic bomb survivors exposed in utero most commonly presented with microcephaly and mental retardation defects.

• Radiation reduction can be accomplished by
  • Reducing the gap between the patient and the image intensifier (less scatter)
  • Minimizing beam time
  • Collimating (with fluoro OFF)
  • Using the lowest possible fluoro pulse rate (high-dose settings deliver 10 times the dose).
  • Minimizing acquisition (use last image hold and cine hold).
  • Using lowest frame rate acquisition as needed (and variable frame rate).
  • Changing beam angle to vary skin dose to avoid patient skin burns (collimation helps).
  • Using the least magnification possible.
  • Positioning the C arm fluoroscopy field of view on the opposite side of the practitioner (reduces the exposure of the upper body).
  • During cross table x-rays, if the image intensifier side is positioned over the patient, dosing can be reduced by 1/5^th (scatter occurs as the beam contacts the patient).
• Reducing provider dose:
  • Lead apron. During fluoroscopy, a 0.5 mm lead equivalent apron can attenuate 95% of the scattered radiation to the shielded torso; a 0.25 mm apron attenuates 80%. Wear a wrap-around apron if the back will be to the source.
  • Thyroid shield
  • Custom lead protective glasses: A 5 mm thick lens will block 92% of the radiation and a 10 mm thick lens will block 99%. Regular glass lenses of 5 and 10 mm thickness block 30% and 50% of radiation, respectively.
  • Table skirt
  • Overhead shield
  • Lead gloves provide minimal protection and may cause a false sense of security – Holding hands with lead-lined gloves in x-ray beam causes fluoroscopy unit to adjust to increase the dose delivered (don't place hands in primary beam).
  • Stand at least 6 feet from beam if possible.
• Monitoring provider radiation dose:
  • Over apron dosimeter is placed at the thyroid collar to monitor exposure to eyes, thyroid, and head.
  • Under apron dosimeter to monitor exposure to the rest of the body.
  • for practitioners near the beam, a finger ring dosimeter to monitor exposure to hands.
  • Pregnant providers should be provided an additional dosimeter to be worn under the lead apron at waist level to monitor fetal exposure and should strongly consider a wrap around lead apron that provides coverage from exposure from behind. Usual precautions should be utilized as well.
• Recommended dose limits. The International Commission on Radiological Protection recommends an effective dose limit of 20 mSv/year (mSv = millisievert) averaged over 5 years to limit the probability of stochastic effects. In addition, the effective dose should not exceed 50 mSv in any given year. Pregnant females should have a supplementary equivalent dose limit of 2 mSv applied to the surface of the abdomen to reduce the risk of fetal effects.

• Equivalent doses = sum of the weighted absorbed doses; does not take into account the differing susceptibilities of radiation to different organs.
• Effective dose = sum of the weighted equivalent doses in all tissues and organs of the body. Accounts for the "tissue weighting factor" that represents the relative contribution of that organ to the total detriment due to those effects resulting from uniform radiation of the whole body.
• Rule of thumb – One step back from tableside: Cuts exposure by a factor of 4.

Radiation units – There are a number of units to measure radiation dose and exposure:

• rad: Radiation absorbed dose
• rem: Roentgen-equivalent-man
• Roentgen (R, r) (rent-gen, rent-chen).
• sievert (Sv) (see-vert). The most pertinent unit for measuring ionizing radiation effective dose, which accounts for relative sensitivities of different tissues and organs exposed to radiation. The radiation quantity measured by the sievert is called the effective dose. A mSv is one-thousandth of a sievert.
• Comparative patient radiation doses of different studies:
  • Dental x-ray – 0.005 mSv
  • Chest x-ray – 0.1 mSv
  • Mammogram – 0.4 mSv
  • CT abdomen/pelvis – 15 mSv
  • CT abdomen/pelvis with and without contrast – 30 mSv
  • Fluoroscopic-guided procedures – Difficult to measure due to operator variability and fluoroscopy time differences.

• Infectious Disease Exposure in the Health Care Worker

990 Effects of radiation, unspecified

• T66.XXXA Radiation sickness, unspecified, initial encounter
• T66.XXXD Radiation sickness, unspecified, subsequent encounter
• T66.XXXS Radiation sickness, unspecified, sequela

Russell K. McAllister , MD

Bradley T. Dollar , MD