Fluoroscopic radiation is a carcinogen that can also cause severe injury (“radiation burns”) in patients and practitioners. Figures 11-1,11-2,11-3,11-4 illustrate the severe effects of radiation. All effects pictured were caused by radiation associated with fluoroscopy. Note the characteristic demarcation of injuries with sharp borders, a feature usually but not always associated with severe radiation effects from fluoroscopy.
FIGURE 11-2
Deep skin wound following 2 ablation procedures separated by 4 months and having occurred 6 and 10 months previously. Wound progressed into deep tissue necrosis and osteoradionecrosis of the ribs, shown approximately 4 years after procedures. (Copyright retained by patient and figure reproduced with permission.)
FIGURE 11-3
Injury following percutaneous transluminal coronary angioplasty (PTCA) and stent placement involving 63 minutes of fluoroscopy and nearly 5000 frames of cine. This left anterior oblique (LAO) view with cranial tilt resulted in a large entrance dose build-up in the lower right back. The injury required grafting. (Adapted with permission from Wagner LK. Radiation dose management in interventional radiology. In: Balter S, Chan R, Shope T, eds. Interventional Brachytherapy—Fluoroscopically Guided Interventions (American Association of Physicists in Medicine Monograph #28). Madison, WI: Medical Physics Publishing; 2002;195-218.)
FIGURE 11-4
Severe prolonged erythema and central area of induration and necrosis about 14 months following coronary intervention. (Reproduced with permission from Balter S, Hopewell JW, Miller DL, Wagner LK, Zelefsky MJ. Fluoroscopically guided interventional procedures: a review of radiation effects on patients’ skin and hair. Radiology. 2010;254:326-341, © RSNA.)
Figure 11-11 is a breast cancer caused by fluoroscopically guided interventional procedures performed to cure pulmonary tuberculosis in the mid-20th century. Chronic radiation dermatitis is also readily apparent in this picture, taken in the 1960s approximately 10 to 15 years after exposure to the radiation.
Figure 11-2 shows a deep necrotic wound following 2 ablation procedures 6 and 10 months previously. The ribs underlying the wound necrosed at about 4 years after the procedure. Advances in cardiac mapping during electrophysiologic procedures have mitigated the need for long-duration fluoroscopy and have reduced the likelihood of such effects in these patients.
Figures 11-32 and 11-4 are skin injuries in patients who underwent fluoroscopically guided invasive cardiologic procedures. The patient in Figure 11-3 underwent coronary angioplasty and stent placement involving 63 minutes of fluoroscopy and about 5000 frames of cine fluorography. The affected skin area required a full-thickness graft. The patient in Figure 11-4 underwent a prolonged procedure for coronary artery intervention. Both cases involved x-ray irradiation with the x-ray beams oriented in a fixed trajectory for long periods of time, resulting in very high doses to the affected areas.
The first radiation injury related to interventional cardiology occurred in 1990.3 By September 1994, the US Food and Drug Administration (FDA) had issued a warning to physicians and healthcare providers about occasional but severe radiation injuries in patients undergoing certain fluoroscopically guided interventional procedures.4 The warning described the nature of these injuries and provided numerous recommendations on how to avoid them. Many, but not all, of those recommendations are addressed in this chapter.
The FDA has since retired this warning, but their recommendations to physicians and facilities regarding the need to pursue a high level of quality radiation management for medical procedures remains and is available on their website (http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/MedicalImaging/MedicalX-Rays/ucm115354.htm#imagingteam). In the years since the FDA warning, hundreds of serious radiation-induced injuries have occurred. Many have been reported in the medical literature.2,3,5-15
Many medical practitioners of the 20th century accumulated considerable radiation doses during their medical practice and developed radiation-induced cancer, cataracts, or skin injury.16-19 The modern interventional radiation environment creates conditions conducive to the accumulation of high doses in personnel. Attention to rigorous radiation abatement measures is therefore warranted and required.20
When fluoroscopy is well managed, the likelihood that these severe effects could occur is extremely low. However, when it is not well managed, the carcinogenic risk to both personnel and patient is higher than necessary, and the risk for injury to the patient increases.7,9 The goal of this chapter is to discuss factors involved in the careful management of fluoroscopic and fluorographic radiation.
No discussion of radiation management is meaningful without a clear understanding of the quantities used to measure or describe radiation levels. In particular, a well-honed understanding and use of the concepts of air kerma, absorbed dose, equivalent dose, effective dose, and dose area product are essential. Table 11-1 summarizes the relevant quantities.21
| Quantity | Units of Measurement | What It Is | What It Measures | Why It Is Useful | Conversion Between Old and New Units |
|---|---|---|---|---|---|
| Absorbed dose | Gray (Gy) or milligray (mGy) (rad or millirad [mrad]) | The amount of energy locally deposited in tissue per unit mass of tissue | Measures concentration of energy deposition in tissue | Assesses the potential biologic risk to that specific tissue | 100 mrad = 1 mGy 1 rad = 10 mGy |
| Effective dose | Sievert (Sv) or millisievert (mSv) (rem or millirem [mrem]) | An attributed whole-body dose that produces the same whole-person stochastic risk as an absorbed dose to a limited portion of the body | Converts any localized absorbed or equivalent dose to a whole-body risk factor | Permits comparison of risks among several exposed individuals, even though the doses might be delivered to different sets of organs in these individuals | 100 mrem = 1 mSv 1 rem = 10 mSv |
| Air kermaa | Gray (Gy) or milligray (mGy) (rad or millirad [mrad]) | The sum of initial kinetic energies of all charged particles liberated by the x-rays per mass of air | Measures the amount of radiation at a point in space | Assesses the level of hazard at the specified locationb | 100 mrad = 1 mGy 1 rad = 10 mGy |
| Equivalent dosec | Sievert (Sv) or millisievert (mSv) (rem or millirem [mrem]) | A dose quantity that factors in the relative biologic damage caused by different types of radiations | Provides a relative dose that accounts for increased biologic damage from some types of radiations | The most common unit used to measure radiation risk to specific tissues for radiation protection of personnelc | 100 mrem = 1 mSv 1 rem = 10 mSv |
Air kerma relates to how much radiation is present at a specific location. The presence of x-rays at any location can be measured by analyzing the ionization they produce in air at that location. Because energy must be transferred to create ions in air, air kerma is defined as the concentration of energy released by the x-rays in air. The special unit of air kerma is the gray (Gy) or milligray (mGy). One gray of air kerma is the same as 1 joule of energy released in 1 kilogram of air. One manufacturer sometimes reports air kerma in units of microgray (μGy). Air kerma is used to monitor and manage radiation delivery to patients, as discussed later.
Instantaneous air kerma and cumulative air kerma differ only in the temporal interval or sequence over which all air kerma is delivered. When air kerma is measured at some reference position in space, the air kerma is said to be instantaneous if it is measured over a short interval of time, usually on the order of seconds or less. When multiple short radiation exposures occur or when several long exposures occur, the cumulative air kerma is the summation of all air kerma measurements over the entire procedure time.
Absorbed dose is used to assess the potential risk for stochastic and deterministic effects in specific tissues. Absorbed dose is the concentration of radiation energy transferred to and absorbed by a particular tissue. Specifically, as x-rays pass through tissues, they interact with the biologic matter, and this transfers energy that causes molecular changes. These changes can potentially lead to biologic effects. Assessing the concentration of energy deposited in the specific tissue provides a measure of the amount of biochemical disruption, and thus a measure of risk for biologic effects. The special unit of absorbed dose is the gray, and 1 Gy is the same as 1 J of energy concentrated in 1 kg of tissue.
Absorbed dose and air kerma are measured in the same units of gray, but they are not the same thing. There is no fixed relationship between the two, but there are some rules of thumb. For instance, the absorbed dose to the skin of a patient is about 40% greater than the air kerma at the location of the skin when the air kerma is measured under the same radiation output conditions but without the patient present.
Equivalent dose is an estimate of the biologic potency that a particular radiation might have for an absorbed radiation dose delivered by that radiation. Equivalent dose is the quantity usually quoted in radiation safety reports for doses to the hands or to the eyes of personnel. For radiations other than x-rays, equivalent dose can be quantitatively greater than the absorbed dose and is specified in units of sievert (Sv) or millisievert (mSv). Because cardiologists do not apply other types of radiation during interventional work, this quantity is used solely to communicate radiation safety doses. For our purposes in interventional cardiology, 1 Sv of equivalent dose is the same as 1 Gy of absorbed dose. (It should be remembered that this is not true for other specialties, like radiation therapy, where neutron radiation might be used.) Thus, equivalent dose is a radiation safety term that, for our purposes, carries the same risk as the absorbed dose in gray.
Many radiation safety reports for personnel exposures still use outdated units of millirem. To convert the dosimetry to units of millisievert, just divide the value in millirem by 100. That is, 100 millirem are equal to 1 millisievert.
Effective dose is used to relate the potential for stochastic risk to an individual from an exposure to radiation, regardless of the spatial nonuniformities of the exposure. For example, interventionalists wear lead aprons to protect themselves. When an interventionalist is exposed in the laboratory, the arms, legs, and head are not as well protected from radiation as are the internal organs under the apron. Therefore, the spatial distribution of the radiation throughout the interventionalist’s body is very nonuniform. This is permitted because the exposed limbs and head are not as radiosensitive as thoracic and abdominal organs. The risk associated with such an exposure is not well specified by absorbed dose because low-sensitivity limbs receive a much higher dose than sensitive organs in the thorax and abdomen.
Effective dose attempts to remove this complexity in risk assessment. Effective dose is a hypothetical dose that would have to be delivered uniformly to an interventionalist’s entire body to yield the same numerical risk for stochastic effects as the nonuniform dose actually delivered. Thus, as a hypothetical uniform whole-body dose, effective dose is a risk descriptor that permits us to compare the risk associated with any type of nonuniform exposure to that of any other nonuniform exposure.
Derivation of effective dose from the nonuniform exposure is complex and not within the scope of this chapter. (For a more complete description, see the International Commission on Radiological Protection Report No. 103 entitled “The 2007 Recommendations of the International Commission on Radiological Protection.”22) The important thing to know is that effective dose allows assessment of stochastic risks from nonuniform dose deliveries. The special unit of effective dose is the sievert or millisievert. In cardiology, any effective dose measured in units of millisievert may be considered to be the same as a hypothetical uniform whole-body absorbed dose of x-rays assigned the same numerical value but quoted in units of milligray. That is, an effective dose of 1 mSv in cardiology is the same as a uniform whole-body absorbed dose of 1 mGy.
Air kerma area product (KAP) and dose area product (DAP) are the same thing because air kerma from cardiologic-type x-rays and the absorbed dose to air (as opposed to the absorbed dose to tissue) are the same thing. This quantity is used to assess the total stochastic risk to patients from x-rays. It is the multiplicative product of the beam area at entrance to the patient and the free-in-air air kerma located at the entrance surface of the patient. “Free-in-air” means the measurement is made as if the patient were not present. This means that the measurement is not enhanced by radiation scattered back into the area by the presence of a patient. KAP, therefore, is an indirect measure of the total number of x-rays that entered the patient. This makes it an indicator of stochastic risk to the patient.
DAP has no relevance for radiation exposure to personnel.
All of the previous dose and kerma descriptors can be assessed as an instantaneously delivered amount or as an amount accumulated over time. The rate at which radiation is delivered can also be of importance, as, for example, air kerma rate, which is measured in units of milligray per minute (mGy/min). These concepts should be clear in the context of any discussion on dose or air kerma.
Dose delivery is monitored for both patients and personnel.
Personal radiation monitors are used to assess the cumulative amount of radiation to which an individual is exposed during the course of their work. Measurements of cumulative radiation exposure are made over intervals of months. Typically, the primary personal radiation monitor should be worn at the collar outside the lead apron. Some states might require that 2 monitors be worn, one outside and the other under the lead apron. All personal radiation exposures are reported in terms of equivalent dose or effective dose. The unit primarily used in the United States is the millirem, where 1 mrem is the same as 0.01 mSv.
Personal radiation monitoring is a serious business. It is an essential tool in assuring healthy working habits around radiation. A rule of guidance is that the annual effective dose to interventionalists from exposure to stray fluoroscopic or angiographic radiation should not exceed 20 mSv and, by regulation, must not exceed 50 mSv. If your monitor suggests you are exceeding the 20-mSv effective dose per year, then remedial action should be taken to try to reduce this dose accumulation.
Doses to extremities can also be monitored using extremity monitors that come in a variety of forms. Monitors attached to rings can be worn on a finger. These ring monitors can be sterilized using a hydrogen peroxide vapor technique. Ring badges are an important monitoring device if the hands get close to the radiation field. This might be the case, for example, for physicians assisting in transcatheter aortic valve replacement procedures.
All modern cardioangiographic units have built-in monitors to help assess dose delivered to the patient. Since 2006, the air kerma and air kerma rate at a reference point must be displayed for the physician to see.
Monitoring radiation delivery to patients has many advantages. It provides useful information about radiation risks to your patients; it provides highly effective quality improvement data; and it can be applicable during a prolonged procedure, when dose buildup can be substantial and dose abatement steps may be necessary.
There are several types of monitors, including monitors that measure cumulative air kerma at a standard point located at a fixed distance from the x-ray source, cumulative KAP monitors (also known as DAP meters), and dose mapping monitors.
The interventional reference point (IRP) is located 15 cm from isocenter along a line between the x-ray source and the isocenter of the C-arm (Fig. 11-5). (The isocenter is the point in space about which the imaging system rotates, and an object at that point remains in the center of the image regardless of beam rotation.) The IRP roughly approximates the position of the skin where the beam enters the patient. Figure 11-5 demonstrates the location of this reference point. The measure of cumulated air kerma at this position in space is highly useful as a quality control device and as a guide to manage procedures. Almost all modern machines measure and record this quantity.
FIGURE 11-5
Location of the interventional reference point (IRP; indicated by the dark rectangle marked IRP). This point is located along a line from the x-ray source to the image receptor and 15 cm from the isocenter (dot in figure) of the C-arm in a direction toward the x-ray tube. As the C-arm is rotated, the IRP rotates with it. Although the IRP is representative of the entrance skin site, for some beam orientations and patient positions, it is located a distance from the actual skin site. Thus, the cumulative dose at the IRP might over- or underestimate the true cumulative skin dose. This dose reference must therefore be used only as a guide for patient care and not as an absolute measure of risk to the skin. (Adapted with permission from Hirshfeld JW, Balter S, Brinker JA, et al. ACCF/AHA/HRS/SCAI clinical competence statement on optimizing patient safety and image quality in fluoroscopically guided invasive cardiovascular procedures: a report of the American College of Cardiology/American Heart Association/American College of Physicians Task Force on Clinical Competence [ACCF/AHA/HRS/SCAI Writing Committee to Develop a Clinical Competence Statement on Fluoroscopy]. J Am Coll Cardiol. 2004;44:2259.)
Because the cumulative air kerma is measured at a point fixed relative to the source, 3 things must be kept in mind when using it. First, as an accumulation monitor, it adds up all the radiation produced by the source, regardless of beam orientation. This fact means that radiation dose to a single skin site might be overestimated. Second, at any one skin site, the actual skin dose is about 40% greater than the cumulated entrance air kerma; thus, the cumulated air kerma might render an underestimated impression of the true skin dose. Third, the reference point is only an approximation of the position of the skin, and the true entry site might be closer to or further away from the x-ray tube, rendering an over- or underestimation of the true skin dose. Thus, the cumulative air kerma is not an exact measure of skin-absorbed dose and can only be used as a rough guide to assess the risk to skin when procedures are prolonged and doses are high. Regardless of these difficulties, dose at the IRP is a highly useful tool to assist the physician in management of the patient’s skin dose.
For example, guidelines might be established to assist the physician during a procedure. It might be useful, for example, to establish a 2-4-6-8 rule for management. If the reference accumulation air kerma reaches 2 Gy, then the physician is advised that dose is building and that this is an “FYI” so that the physician knows the pace of radiation buildup. The threshold for transient erythema (Table 11-2) may have been breached, but transient erythema is not a significant health concern. At 4-Gy air kerma, the physician is advised again and now knows that the threshold of skin erythema (as opposed to transient erythema; see Table 11-2) might have been reached if the beam was not reoriented and if the IRP is inside the skin surface. At 6-Gy air kerma, the potential for skin erythema is higher, and actions to abate the risk might be an important consideration. At 8-Gy air kerma, the risk of skin injury is an important possibility, especially if there was no beam reorientation earlier and the same skin site is being dosed. The purpose of this is to assist the physician in making the appropriate benefit-risk decisions for the patient and in managing the patient after the procedure. Other recommendations by national organizations are available.23
| Band | Single-Site Acute Skin-Dose Range (Gy)* | NCI Skin Reaction Grade† | Approximate Time of Onset of Effects | |||
|---|---|---|---|---|---|---|
| Prompt | Early | Midterm | Long Term | |||
| A1 | 0–2 | NA | No observable effects expected | No observable effects expected | No observable effects expected | No observable effects expected |
| A2 | 2–5 | 1 | Transient erythema | Epilation | Recovery from hair loss | No observable effects expected |
| B | 5–10 | 1–2 | Transient erythema | Erythema, epilation | Recovery; at higher doses, prolonged erythema, permanent partial epilation | Recovery; at higher doses, dermal atrophy or induration |
| C | 10–15 | 2–3 | Transient erythema | Erythema, epilation; possible dry or moist desquamation; recovery from desquamation | Prolonged erythema; permanent epilation | Telangiectasia‡; dermal atrophy or induration; skin likely to be weak |
| D | >15 | 3–4 | Transient erythema; after very high doses, edema and acute ulceration; long-term surgical intervention likely to be required | Erythema, epilation; moist desquamation | Dermal atrophy; secondary ulceration due to failure of moist desquamation to heal; surgical intervention likely to be required; at higher doses, dermal necrosis, surgical intervention likely to be required | Telangiectasia‡; dermal atrophy or induration; possible late skin breakdown; wound might be persistent and progress into a deeper lesion; surgical intervention likely to be required |
A full discussion of use of a KAP meter to monitor patient absorbed skin dose is beyond the scope of this chapter. Recall that KAP is the product of the air kerma at a position in space and the area of the beam at that position. With distance from the source, beam area naturally increases and air kerma naturally decreases in identically compensating manners. The product of these two entities is, therefore, theoretically the same at all positions along the unobstructed accessible beam. It is primarily a quality control tool and is not a very useful monitor of dose to the skin of a patient, although that task is possible. A medical physicist is usually employed in any attempts to use such a device for management of skin doses to patients. The National Council on Radiation Protection and Measurements also provides recommendations on how to use KAP as a skin dose monitor.23
Skin dose mapping (Fig. 11-6) provides explicit diagrams showing the accumulation of dose to specific skin sites of a patient. This dose monitor takes the guesswork out of accumulation of skin dose during procedures. It accounts for a wide variety of factors that are not accounted for by the previously discussed dose monitors. These factors include beam orientation, scattered radiation, location of the entrance skin site from the x-ray source, table attenuation of radiation, and other factors. It is the preferred method for monitoring dose to a patient because it is the best assessment of skin dose in real time. This monitoring is visually enhanced by a patient contour map showing how dose is distributed around the patient as the beam is rotated (see Fig. 11-6).
Health effects of radiation are commonly separated into 2 categories: stochastic and deterministic.
Stochastic effects involve alterations in single cells that render them adversely functional. Alterations of important macromolecules can conceivably result from a single interaction with radiation. Therefore, these effects probably occur at any radiation dose level, although they are extremely unlikely to occur at very minimal levels. The two prominent stochastic effects are radiation-induced neoplasm and heritable changes in reproductive cells. The likelihood of their occurring increases as dose increases, and induced cancer becomes measurable in exposed adult populations at doses in excess of about 100 mSv.24 In children and in the fetus, lower doses have been implicated as carcinogenic.25 Although genetic effects heritable by progeny have been observed at high doses in animal studies, bona fide genetically heritable effects have never been observed in humans.
Deterministic effects are the result of damage to many cells. Examples are skin erythema, depilation, and vision-impairing cataract. Because the effect results from changes in multiple cells, a certain minimal level of radiation damage is necessary before the effect can occur. This is referred to as the threshold dose. As dose increases beyond the threshold, the severity of the effect increases. The most familiar examples of this are effects in the skin. Table 11-226 lists various effects of large doses to the skin. Note how the severity increases as dose increases. Variations on sensitivities occur for different skin sites, and there are also variations among individuals due to differences in health of the skin, medications that the patient is taking, and other factors.23,26
The threshold for radiation-induced cataract is now known to be lower than previously believed.27 Radiation may have subtle or progressively worsening effects on vision, and only careful attention to radiation management can avoid them or reduce their severity.
For both stochastic effects and deterministic effects, there is a delay between irradiation and the detection of a change. For neoplasms, delays may be as short as two years or as long as many decades. For deterministic effects in the skin, the delay is typically many days to weeks before erythema develops and is likely to be weeks to months before inflammation or necrosis develops. The delays provided in Table 11-2 are relevant to effects occurring following acute threshold doses. Delays vary depending on skin sensitivity, dose level, and rate of accumulation of dose. The transient form of erythema can occur within 24 hours, but this does not always occur and usually goes unnoticed. It may sometimes be confused with erythema resulting from electrosurgical pads.
An important fact is that a fluoroscopy-related “burn” is markedly unlike that of a thermal burn. Thermal insults are readily recognized by conscious individuals, and immediate measures can be taken by them to defend against further injury. With medical radiation, there is no sensation that forewarns of an injury; the first signs that an injury has been induced usually do not occur until the procedure has been long over. Therefore, physicians cannot rely on any signal from the patient that a burn is occurring. In contrast to an injury from fluoroscopy, the progression of a thermal burn occurs within a short time after the injury (days), and the extent of medical care necessary for treatment can be readily determined soon afterward. For a fluoroscopic radiation injury, the progression of the injury is slow (months), and early interventions often fail because of residual injury that has yet to manifest itself. Prevention of these painful and slowly developing injuries is clearly an important goal. Proper radiation management with fluoroscopic equipment requires a knowledgeable application of the effective and careful use of radiation to keep risk of skin injury at bay. The strategic use of radiation monitoring devices is a valuable resource in achieving this goal.
