21  Radiation Safety

Authors: Adam P Johnson and Melissa Kirkwood

21.1 Important Terms

Absorbed Dose - energy deposited by ionizing radiation in a medium per unit mass. Dosage measured and communicated most commonly in Gray (Gy) equal to 100 rad.(Reed 2019)

Effective Dose - energy deposited by ionizing radiation in a medium, taking into account the sensitivity of the specific tissue, time and duration of exposure. These factors compose a weighting factor (W) and thus this is calculated by multiplying absorbed dose (Gy) by the weighting factor (W). Dosage measured and communicated most commonly in Sievert (Sv) equal to 100 rem.(Reed 2019)

Reference Air Karma (RAK) - Radiation output at a specific reference point along a fluoroscopic axis.(Kirkwood et al. 2013)

  • Located 15cm along the beam axis toward the focal spot from the isocenter.

  • Best approximation of cumulative patient dose or peak skin dose (PSD).(Kwon, Little, and Miller 2011)

  • Includes dose from fluoroscopy and fluorography acquisitions, however does not account for gantry angulation of changes in height.

Substantial Radiation Dose Level (SRDL) - defined as 5Gy RAK and should trigger specific patient follow up. Of note, 5Gy refers to the RAK that is reported at the end of the procedure, which is an approximation of the peak skin dose (PSD).(Baiter et al. 2011; Hirshfeld et al. 2005; Kirkwood et al. 2015; Stecker et al. 2009)

21.2 Radiation effects

The effects can impact both patients and clinicians. Patients often receive a higher dose during a single procedure, where as clinician doses, even with proper shielding, accumulate over multiple procedures throughout their careers. The effects of radiation are defined as either deterministic or stochastic.

Skin related deterministic effects that can be seen after a single exposure over a certain threshold (Balter et al. 2010; Hirshfeld et al. 2005; Kirkwood et al. 2014; Stecker et al. 2009; Wagner et al. 1999)
Dose Effect
0-2Gy No observable effects
2-5Gy Transient skin erythema and dermatitis, full recovery 6w-1yr(Guesnier-Dopagne et al. 2019; Kirkwood et al. 2014)
5-10Gy Erythema and epilation (hair loss), prolonged erythema up to 1y
10-15Gy Permanent epilation, atrophy or induration up to 1y
>15Gy Dermal Necrosis

The ocular lens is the most radio-sensitive tissue and cataracts is an unfortunately common deterministic effect.(Machan 2018; Brown and Rzucidlo 2011) Annual limits for occupational exposure include 20mSv per year and total threshold of 0.5Gy, which was recently lowered due to risk of cataract development from ocular exposure.(Hamada et al. 2017)

Stochastic effects can occur after exposure of any dose, but are seen more frequently in populations with higher radiation exposure. These are based on population studies and exact dose dependent relationships have not been established. These include:

21.3 Risk factors

Certain patient, procedure and clinician factors put patients at increased risk for radiation exposure.(Killewich et al. 2011; Mitchell and Furey 2011) These should be considered when planing and executing endovascular procedures to ensure that dosages are as low as reasonably achievable (ALARA)

  • Patient Factors

    • Obesity

  • Procedure Factors

    • Case complexity

    • Need for magnification

    • Case orientation and angulation

  • Clinician Factors

    • Use of multiple subtraction runs

21.4 Reduction strategies

The main source of radiation to the clinicians is scatter from the patient. There are a number of techniques that can be used to reduce exposure of clinicians to this radiation.(Heidbuchel et al. 2014; Kirkwood et al. 2013)

  • Reduce the time of exposure, keeping a close eye on fluoroscopy time and dosages as a procedure progresses.

    • Preoperative planning is paramount to efficient use of radiation during a procedure. Recent ESVS guidelines recommend utilization of a 3D pre-operative planning software and image fusion (when available) for complex endovascular procedures.(Modarai et al. 2022)

    • Use last image hold to allow for procedural planning

    • Decrease the frame rate to reduce the frequency of radiation exposure per second.

Take a Look

Check out Dr. Ellozy’s operative planning video where he reviews how to plan for an EVAR procedure utilizing Tera-Recon 3D imaging software.

  • Position the source as far away from the operator as possible to still achieve optimal imaging. Radiation dose changes according to the inverse square of distance. Therefore twice the distance results in one quarter the dose.

    • For example, left anterior oblique (LAO) will bring the source to the patient’s right side, causing higher doses to clinicians on that side of the patient.(Kirkwood et al. 2013; Sailer et al. 2019)

  • Appropriate shielding

    • Recommendations are that clinicians wear lead aprons covering their torso and legs with a thyroid shield and leaded glasses.

    • Collimation can be helpful to reduce patient and operator dose, scatter and improve image quality.(Haqqani et al. 2012)

    • The location with the highest exposure to scatter is below the table.(Gonzales, Moran, and Silberzweig 2014; Miller et al. 2010) Therefore, leaded skirt and extended lower body shields reduce radiation to the operator’s legs.(Kirkwood et al. 2015)

    • Of note: leaded caps DO NOT reduce radiation exposure to the brain because the majority of radiation is received as scatter from the patient up through the face and neck.(Kirkwood et al. 2018)

    • Lead shielding should be regularly inspected and discarded if damaged. Particularly if defect is >15mm2 on a critical organ area, >670mm2 along a seem/overlapping area, >11mm2 on a thyroid shield.(Healthcare Inspections 2014; University, Stanford, and Complaints, n.d.)

Take a Look

Check out our episode with Dr. Jasmine Bhinder, discussing a recently published quality improvement project for institutional level changes that lead to reductions in radiation exposure for trainees.

21.4.1 Pregnancy considerations

Pregnancy of both patients and clinicians need to be considered in relation to radiation exposure and safety.(Chandra et al. 2013; Mitchell and Furey 2011; Shaw et al. 2011) This is a highly tested subject on vascular surgery examinations. Some important take aways include:

  • CDC has released guidance for potential prenatal effects on radiation exposure(CDC 2011) The majority of effects on fetuses is extrapolated from studies of the fall out from Hiroshima, Nagasaki and Chernobyl.

    • <0.05Gy represents no measurable risk to embryo or fetus at any gestational age.

    • 0.05-0.5Gy can be dangerous in the first trimester, but has not been associated with defects later in pregnancy.(Shaw et al. 2011)

    • >0.5Gy can be dangerous at any point during pregnancy.

  • Dose limit recommendations during the 9 months of pregnancy is 5 mSv (500mrem) or 0.5 mSv (50mrem) per month.(Dauer et al. 2015; Chandra et al. 2013)

Strategies to reduce exposure include:

  • Avoid direct fluoroscopy to the fetus, high-gantry angulation, and femoral access

    • Use collimation to ensure fetus is excluded from imaging field.

  • Use adjuncts of intravascular ultrasound and lead shielding when able.

  • Limit fluoro time.

  • Some recommendations state that operators who intend to get pregnant should start wearing maternity aprons (lead equivalent to 1mm) even prior to knowing they are pregnant.(Shaw et al. 2011)

    • Original studies demonstrated reduction in fetal exposure by 80% and is currently common practice.(Witrak and Sprawls 1984)

    • However, a recent multi-institutional review showed that fetal exposure is minimal even in regular lead, therefore the additional weight of maternal lead may be unnecessary.(Chandra et al. 2013)

21.4.2 Regulation

Joint Commission Oversight - sentinel radiation reporting is aimed to promote awareness of preventable events perform root cause analyses to understand the reasons for events.(Commission 2019) It is important to escalate events early, as effects may not occur until much later.(Arbique, n.d.) Sentinel events include:

  1. The patient has a permanent cutaneous injury and the proper dose saving techniques were not used during the procedure

  2. Cumulative dose of 15 Gy for a single field over 6mo - 1yr.

  3. Delivery of radiotherapy to the wrong body region.

  4. Actual dose more than 25% above planned radiotherapy dose.(Jones and Pasciak 2011)

Institutional Oversight - many institutions develop their own guidelines for employee exposure and mitigation strategies. Some common policies regarding dose limits include:

  • Monthly limit for dosimeter reading of 0.1 mSv (100mrem) per month.

  • Recommendations for annual occupational dose is <20mSv per year averaged over 5y and no more than 50mSv in any one year. Occupational dose <100mSv per year is not thought to increase cancer risk

    • Recent reduction of occupational dose limit to 50mSv is due to increasing data connecting cataracts to radiation exposure.(Hamada et al. 2017)

21.5 Contrast Reduction

The most common complications related to iodinated contrast during endovascular procedures are hypersensitivities and acute kidney injury. There are a number of mitigation strategies to limit the effect of contrast on patients undergoing endovascular procedures.

In general patients with food allergies do have an increased incidence of contrast media allergies, however no specific common allergen has been identified. A new seafood allergy should not postpone or require pre-medication if a patient has previously tolerated IV contrast.(Schabelman and Witting 2010)

21.5.1 CO2 Angiography

CO2 angiography is often utilized in place of iodinated contrast during fluoroscopy. A bolus of CO2 is injected, which then absorbs less ionizing radiation than surrounding tissue and provides a map of the arterial tree. CO2 can be used in a wide range of endovascular procedures, even a ruptured AAA.(Knipp et al. 2010) However, there are specific limitations and complications that should be understood.

21.5.1.1 Limitations

21.5.1.2 Complications

  • Vapor lock - can occur with high volume, serial injections where contaminated air accumulates. Strategies to reduce incidence include waiting 1-3min between angiography runs. Operators should use a one way valve to reduce risk of air contamination.(Kyung J. Cho and Hawkins 2011; Kyung Jae Cho 2015)

    • Cardiac/pulmonary vapor lock can occur with venography. Mimics a PE with hypoxia and hypotension. Initial management is to place patient in the left lateral decubitus/trendelenberg position.(Caridi and Hawkins 1997; Sharafuddin and Marjan 2017)

    • Mesenteric vapor lock presents with significant unrelenting abdominal pain. Fluoroscopy can confirm a retained bubble. Initial management includes ongoing heparinization to prevent down stream thrombosis and maneuvers to break up the bubble by rotating the patient side-to-side or deep abdominal massage. Catheter aspiration may be needed.(Caridi and Hawkins 1997; Sharafuddin and Marjan 2017)

Take a Listen

Check out our previous episode with a panel with Drs. Kirkwood, Wohlauer, and Chandra discussing occupation hazards for the vascular surgeon, of which an important hazard includes radiation safety.