Atlas of Pain Medicine Procedures 1st Edition

SECTION I

BASIC APPLICATIONS

CHAPTER 4

Radiation Safety

Vikram B. Patel

INDICATIONS

Fluoroscopy has been a very effective tool in interventional pain management procedures. Not only does the x-ray image help one identify the proper target for the needle placement but also helps to determine the proper spread of the injectate as well as identify inadvertent intravascular placement of a needle and thus the injectate. Portable fluoroscopy units (also called the C-arm) have helped improve the effectiveness as well as safety of interventional pain management procedures. However, at the same time, it has also increased radiation-related injuries to physicians and their staff as well as patients. Whereas proper use of fluoroscopy can help safe placement of the needle and the injectate, excessive and improper use of fluoroscopy can lead to radiation-induced injuries. Physicians who performed radiography and fluoroscopy in the first half of the 20th century had higher rates of cancer-related deaths than any other physicians. The US Food and Drug Administration (FDA) issued an advisory in 1994 suggesting that the key to preventing such unfortunate mishaps may be physician education, training, and credentialing in the safe operation of fluoroscopic equipment. Proper understanding of the radiation dosage, scatter pattern of x-rays while using the fluoroscopy machine, understanding the fluoroscopy machine and using it properly would lead to improved patient care and minimal tissue trauma to the patient, physician, and ancillary staff from radiation.

RELEVANT ANATOMY

Several issues need to be considered when using x-rays on a human body.

• The human body does absorb radiation.
• The human tissue can be damaged by radiation.
• Larger human beings require higher radiation exposure for proper imaging.
• Lateral mass of the human body requires more radiation than anteroposterior mass.
• Larger individuals require longer needles but provide shorter space between the body and the image intensifier, thereby making the placement of the needle more difficult.
• Placement of the image intensifier can influence the amount of radiation scatter around the patient. Usually the scatter is less if the image intensifier is closer to the patient (Figure 4-1).

Figure 4-1. The larger circular part of the C-arm is called the image intensifier (I-I) and the smaller part is the actual x-ray tube. Closer placement of the image intensifier helps reduce the scatter of radiation.

BASIC CONCERNS AND CONTRAINDICATIONS

Some concerns regarding the proper use of fluoroscopy units are inadequately trained radiology technicians, physicians who are untrained in the use of fluoroscopy, improperly maintained machines, and inadequate space.

Use of fluoroscopy is unadvisable during pregnancy as it may lead to fetal injury from radiation, especially during the first trimester.

Effects of radiation on different tissues are variable:

• Radiation is carcinogenic.
• Effects are permanent for the most part.
• Total dosage (absorption) is cumulative over lifetime.
• Any exposed part of the body can be vulnerable.

RELEVANT TERMINOLOGIES

A physician should be familiar with the terms used to describe radiation energy.

• Radiation is defined as “energy that is radiated or transmitted in the form of rays or waves or particles from a central source.”
• Quantity of radiation intensity (exposure) is measured in R or coulomb—C/kg.
• Energy absorbed by a matter from radiation (depends on the matter) is measured as radiation absorbed dose (rad) or gray “Gy”—SI unit (100 rad = 1 Gy).
• Biological effects of radiation are measured as radiation equivalent man (rem) or sievert “Sv”—SI unit (100 rem = 1 Sy).
• For all practical purposes 1 R = 1 rad = 1 rem.
• Milliseivert (mSv) is usually used for measure of the x-ray dosimeters (Figure 4-2).

Figure 4-2. X-ray dosimeters. The circular dosimeter can be worn on the finger and the larger hexagonal dosimeter is usually clipped over the external aspect of the thyroid shield. Some physicians also wear a ring-dosimeter on the fingers and even an eye dosimeter on the side of the eyewear.

MAXIMUM ALLOWABLE DOSE AND EFFECTS OF RADIATION ON HUMAN TISSUE

• The maximum total yearly dosage to a human body should be less than 50 mSv or <4 mSv per month (4mSv ˜100 mrem).
• Maximum permissible radiation dosages (MPD).
• Typical lumbar epidural steroid injection under fluoroscopy from 1 m away—approximately 0.03 mrem (to physician).
• Chest x-ray—15 mrem.
• X-ray of the abdomen—220 mrem.
• X-ray of the L-spine—250 mrem.
• What can happen (single dose)?

Lens—200 rad = cataract

Skin—500 rad = erythema

Skin—700 rad = permanent alopecia

Whole body—200 to 700 rad = hematopoietic failure, death

Whole body—700 to 5000 rad = GI failure, death

Whole body—5000 to 10,000 = cerebral edema, death

Skin—approximately 6 Gy = rash

Skin—approximately 14 Gy = desquamation

FLUOROSCOPIC VIEWS

Various views during the fluoroscopy can influence the amount of radiation.

• An angled view requires higher amount of radiation.
• Lateral views typically require higher radiation.
• Exposure is not limited to the visible areas on the image, but it also engulfs the areas outside the visible image on the monitors (Figure 4-3).
• Continuous exposure is unnecessary for the most part except for certain situations such as:

Figure 4-3. The radiation field extends beyond the borders of visible image on the monitor and would expose a physician’s hands or body even if it is not visible on the monitor image. It is more spherical than conical. The x-rays used on a patient have even a wider field due to scatter caused by the patient’s body.

Active injection of contrast during a transforaminal injection to identify vascular spread

Injection of cement during a vertebroplasty

Guiding a spinal cord stimulator lead

Using an epidural adhesiolysis catheter

Minimally invasive lumbar decompression (MILD) procedure

How to minimize the amount of radiation during interventional procedures:

• Time

Least amount of exposure time—use single shots rather than continuous exposure

• Reduce the amount of x-rays delivered from the x-ray tube (Figure 4-4)

Figure 4-4. Example of fluoroscopic images using collimation during fluoroscopy. The middle image is without collimation. This is the best way to minimize the exposure while maintaining a superior image quality compared to pulsed and low-dose modes. It may even enhance an image (such as in thoracic spine with lung fields on both sides, or the cervical spine with air within the fields) by eliminating the surrounding fields from the image.

Use of collimation (metal plates within the tube that reduce the amount of x-rays emitted by the tube). The collimation can be linear or circular (Figures 4-5 and 4-6).

Figure 4-5. Inside view of the x-ray tube. The open circular collimation plates are visible at the top and the linear plates are underneath. These plates prevent x-rays from being emitted from the source.

Figure 4-6. Inside view of the x-ray tube showing open and collimated circular plates. They function similar to a camera shutter iris.

• Distance

Stay as far away from the x-ray tube as possible.

If you can touch the C-arm you are probably too close.

Radiation decays exponentially with increased distance (1 m = 0.1% of entrance skin exposure).

The x-ray tube should be as far from the patient as possible (same as the image intensifier being as close to the patient as possible).

• Barriers and lead-based protection

Cover the patient’s body parts not subject to treatment.

Physicians should use lead aprons (preferably wrap around), thyroid shields, leaded eyewear, leaded gloves.

Everyone including the staff in the procedure room should wear radiation protection aprons and thyroid shields.

Equipment

Several companies make portable C-arm fluoroscopy machines. Various extras are now almost standard in most machines such as options for data storage (built-in hard disc, CD or DVD burners, USB key storage, network storage capabilities, etc).

• Newer fluoroscopy units use digital enhancement of the image that helps reduce radiation and also provides better image quality.
• Flat panel monitors provide better image quality.
• Some units have low-dose exposure as well as pulsed modes (delivery of x-rays as 3-10 pulses per second rather than continuous delivery while the button is pressed). These parameters may provide a slightly degraded quality of the image but it is more than sufficient for identifying the osseous structures and thus the target areas for most interventions (Figure 4-7).
• Digital subtraction angiography (DSA) is now used by many physicians to identify inadvertent intravascular injection. This type of imaging is considered the gold standard for vascular imaging and can help avoid intravascular injection that may lead to severe morbidity and even mortality. However, it also requires continuous exposure while the radiologic contrast is being injected and would lead to higher amount of radiation to the patient as well as the physicians. Fluoroscopy units equipped with DSA capability are much costlier.

Figure 4-7. This image shows the amount of dosage reduction (as measured in mA) when a low-dose and pulsed mode are activated (in the right image). The reduction is nearly 1/3 compared to normal exposure without collimation.

Technique

Proper knowledge of the fluoroscopy machine is essential for an interventional pain physician. One should try to use the least amount of time for exposure, maintain as much distance between the x-ray tube and one self, minimize the use of continuous fluoroscopic exposure except in certain situations mentioned above, and measure the exposure by properly wearing the dosimeters outside the lead aprons—preferably outside the thyroid shield (Figure 4-8).

Figure 4-8. Proper protection and distance while using a fluoroscopy machine. Note the eyewear with side protection, the radiation attenuation gloves and the thyroid shield. The wrap around apron is worn underneath the gown. The minimal distance between the physician and the C-arm should be at least the arm’s length (˜1 m), which would reduce the exposure to about 0.1% of the amount emitted by the x-ray tube.

Potential complications and pitfalls include:

• Potential complications of overexposure are listed above, but any body tissue can be affected.
• Exposure to the patient cannot be ignored.
• Exposure to the procedure room staff also should be considered and proper protection should be provided.
• It is very tempting to use the fluoroscopy with continuous exposure for easier guidance of the needle or to identify the entry point, but should be avoided as much as possible.
• Always remember that the effects of radiation are cumulative over the life time and cannot be reversed.

Suggested Reading

Botwin KP, Thomas S, Gruber RD, Torres FM, Bouchlas CC, Rittenberg JJ, et al. Radiation exposure of the spinal interventionalist performing fluoroscopically guided lumbar transforaminal epidural steroid injections. Arch Phys Med Rehabil. 2002 May.

Botwin K, et al. Radiation exposure to the spinal interventionalist performing lumbar discography. Pain Phys J. 2003 Jul.

www.epa.gov/radiation/

www.iaea.org/Publications/Booklets/Radiation/radsafe.html

www.michigan.gov/lara/0,4601,7-154-35299_63294_35791—,00.html