Keywords
ALARA - interventional radiology - radiation protection
Introduction
There has been a rapid increase in the number of interventional radiology (IR) procedures
performed in the last decade. As the number and complexity of IR procedures being
performed increase, this leads to increase in radiation exposure to both patients
and staff. This high radiation exposure can lead to the occurrence of deterministic
effects in both patients and staff, and these vary from transient erythema to skin
necrosis.[1]
[2]
[3] Also, all irradiated patients are at risk of an increased incidence of stochastic
injuries. Although IR differs from diagnostic imaging in the sense that IR procedures
are usually therapeutic and, in most cases, the risk associated with radiation exposure
is less than the therapeutic effect.[4] The radiation exposure to the staff and patients should be minimized by using the
ALARA principles—as the radiation protection is optimized when exposure is “as low
as reasonably achievable, economic, and societal factors are being taken into account.[5]”
Deterministic Effect
Deterministic health effects are those in which the severity of the effect is directly
proportional to the dose of radiation above a threshold. The threshold is different
for different individuals and is subject to biological variation. Examples of deterministic
effects include skin injury, hair loss, and cataracts. According to the reports to
U.S. Food and Drug Administration (FDA) and literature, the frequency of injury is
between 1:10,000 to 1:100,000 procedures.[6]
The skin is the tissue of major concern in interventional fluoroscopy procedures as
the skin is the site where the radiation enters the body; thus, it receives the highest
radiation dose out of any body tissue. The Center of Disease Control and Prevention
has classified the deterministic effects of single-delivery radiation dose to the
skin of the neck, torso, pelvis, buttocks, and arms into five bands (A1, A2, B, C,
D) based on skin dose range, national cancer institute skin reaction grade, and approximate
time after the onset of effect.[7]
Stochastic Effect
It is a type of radiation effect in which the severity of the effect is independent
of the total dose, but its probability increases with the dose increase. An example
of this effect is radiation-induced cancer, although the probability of radiation-induced
malignancy caused by an invasive procedure is small compared with the natural frequency
of malignancies.[8] When treating pediatric and young adult patients or performing procedures which
involve substantial absorbed dose to radiosensitive organs, it is crucial to consider
the effects of stochastic effect in the risk–benefit analysis.
Patient Dose
In the 1990s, the FDA reported various radiation-induced skin injuries, which promoted
the development of guidelines to document radiation use.[9] In 2008, the American College of Radiology (ACR) published its recommendations on
patient radiation exposure in medicine, which included diagnostic imaging procedures
and interventional procedures.[10]
Management of radiation dose requires a holistic approach, which includes pre-procedure
planning, intraprocedural management, postprocedural care, and periodic quality assessment.
Complete guidelines are available at https://www.jvir.org/article/S1051-0443(09)00344-3/pdf; however, a summary is present in [Table 1].
Table 1
Guidelines for patient radiation dose reduction
|
Preprocedure planning
|
Individual training: All operators should be trained according to the institutional
requirements for fluoroscopy use
All staff members should receive an initial training course in patient radiation management
before they start working in the IR suite with refresher training courses at least
annually
Equipment: Only rooms with proper radiation measuring equipment should be used for
procedures that have high radiation exposure
Patient consent: Radiation risks associated with IR procedures should be discussed
with the patient while obtaining procedural consent when the risk radiation exposure
associated with a procedure is high, and the patient is in a high-risk category
Procedure planning: Evaluation of patients should be done with non-invasive cross-sectional
imaging modalities that do not require ionizing radiation use whenever possible. If
ionizing radiation producing modalities are used, dose reduction should be made to
decrease total-patient radiation dose
|
|
Procedural planning
|
Procedural radiation monitoring: This should be done throughout the procedure, and
the operator should be notified when the pre-defined radiation dose threshold is crossed
Dose minimization techniques: Pulse fluoroscopy should be used at the lowest pulse
rate, which yields adequate quality image, care should be taken to minimize fluoroscopy
time and fluoroscopic images captured, and appropriate collimation should be used
|
|
Postprocedural care
|
Dose documentation: Radiation dose should be recorded in the medical record according
to SIR guidelines.[11]
Patient follow-up: If the patient receives significant radiation during the procedure,
they should be followed up after the procedure
|
Abbreviation: IR, interventional radiology.
Measurement of Occupational Exposure
Measurement of Occupational Exposure
Dose limits to workers are expressed in the form of equivalent dose in an organ or
tissue (HT) for exposure of part of the body, and effective dose (E) for exposure
of the whole body, both of them use the SI unit sievert (Sv).
Equivalent dose is measured by multiplying the radiation weighting factor by mean
absorbed dose in a tissue or organ, T, which is measured with the personal help dosimeters,
and effective dose (E) is the weighted sum of all equivalent doses in all specified
tissues and organs of the body.
In the United States, the estimate effective dose is calculated by combining the Hp,[10] which represents the dose equivalent in soft tissues 10 mm below the surface of
the body at the location of the dosimeter, from both the body and collar dosimeters:
E(estimate) = 0.5 Hw + 0.025 HN
HW= Reading from dosimeter at waist or chest under the apron
HN= Reading from dosimeter at the neck outside the apron
Occupational Dosimetry in the Interventional Radiology Suite
The dosimeter has to be used by IR staff during the procedure, and the radiation dose
is monitored monthly, to allow identification of practices leading to high personal
dose and implementation of work habit changes.
The International Commission of Radiological Protection recommends using two dosimeters
by IR staff, one under the apron and one at the collar above the lead apron.[12] In pregnant workers, the fetal dose is estimated by the use of a dosimeter placed
at the mother's abdomen, under the radiation protection garments.
Dose Limits
The dose limits are maximum values of radiation exposure, which ideally should not
be reached. Two types of occupational dose limits have been defined: those that establish
an acceptable risk level for stochastic effects and those intended to protect specific
organs or tissues.[5]
[13] The dose limit recommendations by U.S. National Council on Radiation Protection
and Measurements are given in [Table 2].
Table 2
NCRP recommended dose limits for occupational exposure (adapted from Report No. 116—Limitation
of Exposure to Ionizing Radiation)
|
Dose quantity
|
Effective dose (annual)
|
Effective dose (cumulative)
|
Equivalent dose to lens of the eye
|
Equivalent dose to skin
|
Equivalent dose to extremities
|
|
NCRP maximum permissible dose
|
50 mSv/y
|
10 mSv x age (y)
|
150 mSv/ y
|
500 mSv/y
|
500 mSv/y
|
Abbreviation: NCRP, National Council on Radiation Protection and Measurements.
Evaluation of Personal Dosimetry Data
Evaluation of Personal Dosimetry Data
The personal dose record contains information on effective dose E, equivalent dose
to the lens of the eye from the dosimeter worn at collar level or thyroid shield and
equivalent dose to hand from a ring or bracelet dosimeter; these readings vary based
on the number, type, and location of personal dosimeter used. These personal dose
records should be reviewed by the department's radiation safety section to ensure
that the dose limits are not exceeded. If the monthly exposure reaches 0.5 mSv for
an effective dose, 5 mSv for the dose to the lens of the eye, or 15 mSv to the hands
or extremities a radiation safety officer or a medical physicist should investigate
to determine the cause of unusual dose and should make suggestions to keep the worker's
dose low.
These investigations include checking the validity of the dosimeter reading and evaluating
changes in the operator's work habits if there is a temporary increase. If the increase
is not temporary, the working habits of the individual should be observed over a series
of representative procedures. After the cause(s) of high personal dose levels are
identified, then recommended changes to work practice should be implemented, which
are then checked with a real-time dosimeter, which can provide immediate feedback
about the radiation dose levels.
Radiation Protection
Three basic principles are at play, time, distance, and shielding are at play to achieve
radiation protection. In fluoroscopy-guided interventions, the time spent checking
the C-arm fluoroscopy is directly related to radiation exposure. Time exposure of
the staff should be ALARA as generally less exposure time correlates to less radiation
dose.[14] The fluoroscopy time is often used as an indicator of procedural dose, but the actual
correlation is very poor, and therefore fluoroscopy time individually should not be
used as the dose indicator.[15] Total fluoroscopy time during an IR procedure can be reduced by optimizing the number
of fluoroscopic images captured, the number of x-pulses generated per image, number
of runs, and their duration and frame rate.
A greater distance from the source of radiation can also reduce radiation exposure,
as the amount of radiation exposure is inversely proportional to the square of the
distance.[16]
Radiation Protection Tools
Radiation Protection Tools
The primary source of radiation exposure to the operator and staff is the scatter
from the patient undergoing the procedure; this can usually be reduced by controlling
the patient dose. Nevertheless, to prevent complications from chronic radiation exposure,
protective tools should be used to limit the occupational radiation dose to an acceptable
level.
Radiation Shields
Architectural Shields
Architectural shielding primarily denotes the lead shield, which is built into the
walls of IR suites. Rolling and stationary shields rest on the floor of the suite;
they are constructed by using transparent-leaded plastic and are useful for providing
additional shielding to both operators and staff. These shields are particularly very
useful for nurses and anesthesia personnel working in the IR room.[17]
Mobile and Fixed Shielding
Mobile and Fixed Shielding
A variety of shields are available in a fluoroscopy suite for radiation protection.
These include table skirts, ceiling-suspended shielding, and mobile shields on wheels.
The shields work by decreasing the scatter radiation from the patient to the operator
and the staff, which is the main mechanism of radiation exposure. Equipment-mounted
shielding includes the protective drapes that are suspended from the tables and the
ceilings. Protective lead curtains are detachable devices that can be placed on either
side of the table where the operator is working; they help prevent the radiation exposure
to lower extremities of the operator, which are otherwise not protected with the help
of a lead apron.[18] In a study published by Shortt et al, the use of protective lead curtains under
the table showed statistically significant dose reduction in lower extremities as
compared with control (Siemens Angioskop C-Arm undercouch fluoroscopy systems [Siemens
Medical Solutions, Forchheim, Germany]).[19]
Ceiling suspended shields are generally made out of transparent leaded plastic and
should always be used in lengthy procedures. They are most useful when they are positioned
close to the patient's skin; they work by reducing the scatter radiation to the operator.
When placed at an appropriate location and angle, they can reduce the radiation exposure
to the lens of the eye significantly.[20]
[21] The reduction in the radiation can be as much as 90 to 98% depending on the location
of the X-ray source and the shield.[22]
Radiation Shielding Placed on Patients
Radiation Shielding Placed on Patients
Disposable protective drapes or shields, which can be placed directly on patients,
drastically decrease the scatter radiation. RADPAD (Worldwide innovations & technologies,
Inc., Kansas City, Kansas) is one such shield; it is available as a sterile surgical
drape and contains bismuth and barium as radiation protection materials. It should
be placed appropriately on the patient between the image intensifier and the operator
to reduce scatter radiation. Proper positioning of RADPAD is critical; if it is placed
in the path of the primary beam, it can increase the radiation to the patient drastically.
Various types of RADPAD are available in the market based on the procedure being performed,
and these include RADPAD peripheral shield with absorbent, RADPAD biopsy shield with
absorbent, RADPAD Jugular Access/TIPS shield with absorbent, RADPAD biliary shield
with absorbent, RADPAD fenestrated radial entry shield with absorbent, and RADPAD
infant collimation shield.
In IR suites instead of standard surgical drapes, sterile lead-free disposable drapes
can be used, which are made of lightweight disposable cloth with a 0.1mm lead equivalency.
These drapes are simple to position and do lead to a significant reduction in radiation
exposure, varying from 14% up to 94%.[23]
[24]
[25]
Personal Radiation Protection Garments
Personal Radiation Protection Garments
Leaded Aprons and Thyroid Shields
Lead aprons and thyroid shields are the principal radiation protection tool for interventional
radiologists, and they should be worn at all times during the procedure. The radiation
protection provided by these lead aprons is similar to a 0.25 to 1 mm thick lead.
Ninety percent or more reduction of scatter radiation is observed when lead aprons
with 0.5 mm thickness are used.
The selection of aprons and thyroid shields from a wide variety of styles, sizes,
and materials depends on radiation protection efficacy, fit, comfort, weight, durability,
and ease of maintenance. Different designs of lead aprons are available in the market.
These include aprons with only front covers, aprons that wrap around the body, and
two-piece garments with vest and kilt. Styles with front closures provide a double
barrier of thickness to the chest, abdomen, and pelvis in the front as the fabric
overlaps her;, this may be desirable to operators of reproductive age. The aprons
that cover the back are heavier than others, but they protect the back when the operators
turn away from the patient during fluoroscopy. Any of these designs can be used, but
the apron that is selected must fit properly and give adequate coverage at the neckline
and armholes.[26]
Thyroid shields are also available in various styles, but all of them wrap around
the neck. They are especially recommended for personnel who receive monthly collar
radiation monitor readings over 4 mSv and are below 40 years of age due to the risk
of radiation-induced thyroid cancer.[27]
[28]
Ceiling-Suspended Personal Protective Garments
Ceiling suspected personal protection apron (Zero Gravity, CFI Medical Solutions)
has been developed to reduce fatigue and prevent orthopaedic injuries in operators,
which occur from wearing heavy protective apparel.[29] They utilize a suspended 1.0 mm lead body shield, which engages magnetically to
a vest worn by the operator, which allows it to move in sync with the operator; also,
it employs a 0.5 mm lead equivalent acrylic face shield that protects the head, eyes,
and neck of the operator. These ceiling-suspended aprons provide superior operator
protection as compared with conventional lead aprons with under table shield or ceiling
mount shields. They have an added advantage of being more flexible, which allows clinicians
freedom of movement during challenging procedures.
Eye Protection
Radiation exposure to the eye lens can lead to the formation of cataracts until recently
maximum permissible dose for the lens is 150 mSv per year, but now new data has shown
that the threshold might be significantly lower or even zero.[30]
[31] Operators can minimize radiation dose to the lens by paying attention to imaging-chain
geometry, beam projection, position and head orientation of the operator, leaded eyewear,
and ceiling-suspended shields. Lead glasses with different styles and fit provide
different lens protection, although glasses with lead equivalences of 0.35 and 0.5 mm
and higher provide similar protection.[32]
[33] Large-sized lens glasses (at least 27 cm2 per glass) and those with large side panels are preferred.[34]
[35] There are various types of eyeglasses; these include fit-over glasses, wraparound,
rectangular with a side shield, sports wrap, and newer lightweight models.
Typically, during fluoroscopy, the operator's head is placed at an angle to the scatter
volume because of which the operator's eyes are exposed to radiation from the side;
therefore, they should use glasses designed to block side exposure. All eyewear styles
are found to be less effective as the exposure is changed from the front so side,
but the sportswear model has the lowest profile side panel and therefore offers the
least protection. The newer lightweight models are comfortable to wear on a regular
basis as they are not heavy, they also provide equal frontal and lateral protection
due to the wide area of the frame, but the overall protection is inferior to the classic
models. Finally, to attain proper radiation protection, lead glasses should have a
good fit.
Radiation Protection for the Head and Hands
Radiation Protection for the Head and Hands
For cranial protection disposable, lightweight, surgical caps containing two layers
of barium sulfate-bismuth oxide composite can be used.[36] Hands are the closest body part of the operator to the patient and the primary beam,
so they can potentially be exposed to a very high radiation dose. Most operators believe
that instead of using hand radiation shielding, using collimation, oblique views,
and intermittent fluoroscopy to avoid hand placement in the beam results in more radiation
protection to the patient and operator.
A variety of hand protective products are still available in the market for operators
to choose from. Some products that are most commonly used include attenuation gloves,
and radiation protection creams containing bismuth oxide.
Quality Control
It is an essential part of radiation protection in any IR department. Qualified personnel
with medical physicists help perform acceptance tests like image quality, radiation
output, and visual inspection of protective devices on all image systems and personal
protective devices. These quality control tests have to be performed annually under
the medical physicist.
Good Radiation Safety Practices
Good Radiation Safety Practices
The Society of Interventional Radiology and Cardiovascular and Interventional Radiology
Society of Europe published occupational radiation protection in IR guidelines in
2010. These guidelines provide some techniques that can be implemented by all IR departments
to decrease the patient dose, scatter dose, and occupational dose. Key points are
mentioned below[37]:
-
Minimize fluoroscopy time
-
Minimize the number of fluoroscopic images
-
Use available patient dose reduction technologies
-
Use good image chain geometry
-
Use collimation
-
Use all available information to plan the interventional procedure
-
Position yourself in a low-scatter area
-
Use protective shielding
-
Use appropriate fluoroscopic imaging equipment
-
Obtain appropriate training
-
Wear your dosimeters and know your own dose
Radiation Protection during Pregnancy
Radiation Protection during Pregnancy
The risk of adverse health effects to the embryo or fetus is extremely low or possibly
nonexistent when the radiation exposure is lower than 100 mGy. Radiation exposure
can lead to two types of adverse health effects to the conceptus—tissue reactions
(i.e., deterministic effects—congenital disabilities, pregnancy loss, mental retardation,
growth retardation) and stochastic effects (damage to a single cell that is enough
to cause a mutation which increases the risk of cancer as the dose increases). The
risk of these adverse health effects depends on the gestational age during which the
exposure occurred (maximum risk during the preimplantation and organogenesis, second-trimester
exposure, and the least risk in the third trimester).[38]
In the United States, the National Council on Radiation Protection and Measurements
(NRCP) recommends limiting exposure to a monthly equivalent dose of 0.5 mSV once the
pregnancy is identified.[39] The Nuclear Regulatory Commission has declared a regulatory limit of 5 mSV for the
entire duration of pregnancy.[38] The dose of exposure to the conceptus can be approximated as one half of the personal
equivalent dose at 1 cm, Hp (10), for the dosimeter placed on the waist/abdomen.[40] The employer must evaluate and ensure that the conceptus dose is kept below the
recommended threshold throughout the gestation period.
For monitoring radiation exposure, the use of a single personal dosimeter worn under
any protective apron at the level of the waist is recommended. An additional dosimeter
can also be placed on the mother's abdomen. These readings should be monitored monthly.
Any worker contemplating pregnancy can also request a waist/abdominal badge.
Workplace Injury Illness Prevention Programs are mandatory in 15 states in the United
States to provide hazard awareness training to the employees upon initial hire and
subsequently annually. Counseling on the potential risks of radiation exposure to
pregnant workers and their partners, if possible, is an integral part of radiation
protection programs.[38]
Following work modifications are recommended whenever possible:
-
Minimizing fluoroscopy time (prohibiting less-experienced workers from operating the
fluoroscopy controls).
-
Substituting ultrasound for fluoroscopy guidance if it does not affect patient outcome.
-
Carefully planning the intervention may reduce unnecessary fluoroscopy.
-
Stepping into the control room during imaging runs.
-
Standing behind a full-length leaded shield.[41]
-
Increase the distance between the operator and the radiation source.
-
Placing movable lead shields between the operator and the X-ray beam when one cannot
step away from the table.[42]
-
Redelineation of roles with the redistribution of responsibilities where possible.[41]
Conclusion
With the exponential rise in the use of IR procedures, it is essential to follow a
holistic approach to limit radiation exposure to the operators and staff and to ensure
improved patient safety. To ensure maximum radiation protection, it is paramount to
understand the basics of radiation physics, understand its detrimental effects—deterministic
and stochastic effects, learn to evaluate personal dosimetry data, and adhere to dose-limiting
thresholds. Knowledge about various radiation protection equipment and good radiation
safety practice is of utmost importance.
