**8. Measuring severity of radiation dose**

to each individual [1]. Substantial exposure of emergency responders and clinicians caring for potentially heavily contaminated patients may occur. Emergency medical services and clinicians must use caution and adhere to strict precautions for managing hazardous materials to prevent inadvertent contamination of themselves and others [27]. Personnel should wear radiation dosimeters, sealed in clear, airtight plastic bags, and worn outside the clothing to allow rapid assessment and early detection of contamination. Workers and work areas should undergo repeated surveillance with radiation detectors at appropriate

In cases of more significant exposure, ARaS manifests initially through the hematopoietic system as blood marrow tissues are highly radiosensitive [27]. Of all the components of hematopoiesis, circulating lymphocytes have the most radiosensitive cell lines and provides a useful laboratory tool to screen for the severity of the radiation sickness early in observation (**Figure 2**) [56]. After whole body exposure above 0.5 Gy, the rapid fall in lymphocyte number starts within hours, and the lymphocyte depletion is proportional to the dose between 1 and 10 Gy [56]. GM-CSF may be helpful for the recovery of the bone marrow function after clinically significant radiation exposure [57]. Lymphocyte depletion kinetics serves as the single best estimator of radiation exposure and clinical outcome [27]. A decrease in absolute lymphocyte levels may be observed at whole-body doses as low as 100 mSv, but clinically significant response may not be seen below 1–2 Sv. Depending on the absorbed dose, such changes can begin within hours of exposure, so it is recommended that an immediate complete blood count with differential is performed as a baseline and then every 6–12 hours thereafter for 2–3 days [27]. An elevated serum amylase provides a supplementary piece of information that may also be an early sign of serious radiation exposure involving the head and neck. The results of this test are nonspecific; however, and they may also reflect alcohol intake, a stress response, trauma

**Figure 2.** Time-dependent lymphocyte depletion kinetics following either severe or moderate radiation exposures. As

early as 6–12 hours following exposure, there may be some indication of the severity of the exposure [35].

**7. Laboratory evaluation of acute radiation injury**

intervals [1, 27].

64 Vignettes in Patient Safety - Volume 4

Similar to other toxicological phenomena, determining the potential harm of radiation exposure mandates consideration of three factors: dose of radiation exposure, tissue or surface area exposed, and duration of exposure. Whole body radiation exposure to 4 or 5 Sv (or Gy) imparts potentially lethal effects, while an extremity can tolerate several times that exposure [27]. General measures of radiation exposure (e.g., fluoroscopy time) have low utility and accuracy [28]. At this juncture, it is important to introduce the concept of KERMA, or "Kinetic Energy Released in Matter", which is a measure of energy delivered (or dose) [28]. Air-KERMA is the KERMA measured in air (e.g., low scatter environment) [28]. More useful methods of determining radiation administered include: (a) total air-KERMA (exposure) at pre-specified reference point, (b) air-KERMA area product, and (c) peak skin dose or the maximum dose received by any local area of patient skin [28, 59]. See **Figures 3–5** for further information.

**Figure 3.** Timeline for post exposure injury for dosage of 2–5 Gy.
