Keywords
radiation exposure - radiation safety - operating room - neurointervention - anesthesia
Introduction
With the advent of new modalities of imaging and image-guided interventions, the risk
of radiation exposure (RE) has increased exponentially. Simultaneously, the ambit
of neuroanesthesiologists has expanded from administering anesthesia inside operating
room (OR) to managing patients outside the OR. These also include an increasing number
of procedures that lead to RE ([Table 1]). The exposure in OR can range from single or multiple radiation shots during the
use of mobile image intensifier (C-arm), two-dimensional/three-dimensional (2D/3D)
imaging system (O-arm), and intraoperative computed tomographic (CT) scan. Substantial
risk of RE occurs in neurointerventional radiology suites where live fluoroscopic
imaging is used during a procedure. Gamma knife units pose quite a low risk of RE
to neuroanesthesiologists provided standard prerequisites are followed. Other procedures
such as X-ray and portable bedside CT scans in intensive care unit (ICU) also cause
RE. Hence, a modern-day neuroanesthesiologist has to bear the brunt of the RE both
inside and outside the OR.
Table 1
Sites of RE for neuroanesthesiologist
|
Inside the operating room during
|
Outside the operating room
|
|
Abbreviations: CT, computed tomography; ICU, intensive care unit; RE, radiation exposure.
|
|
|
-
Neurointerventional procedures for head and spine
-
Portable X-ray for patients admitted in neuro-ICU
-
Bedside CT scan for patients admitted in neuro-ICU
-
Gamma-knife procedures
|
Risk and Awareness
It is likely that neuroanesthesiologists, in spite of being remarkably exposed to
radiation, may forego all the necessary measures that ought to be undertaken. Maghsoudi
et al analyzed the amount of radiation received by anesthesiologists posted at various
places over a period of 3 months. On analyzing the badge readings, they found that
anesthesiologists who are posted in high radiation areas such as catheterization laboratory,
interventional radiology (IR) suite, and orthopaedic OR are more exposed to radiation
as compared with those who worked in routine ORs.[1] Similarly, Henderson et al found higher RE to the tune of 180 rem per month in anesthesiologists
working in catheterization laboratory and high-risk areas.[2] Pain physicians are exposed to significant radiation from fluoroscopy because of
their proximity to the patients during procedures.[3] Roguin et al stressed on the fact that the physicians who worked for long hours
in the radiology suite were at high risk of carcinogenesis.[4] A Turkish survey comprising of 491 practicing anesthesiologists showed that the
awareness is very poor among the residents followed by the consultants. The study
observed that professors reported the highest rate (43%) and residents reported the
lowest rate of compliance (5.1%) for adopting protective measures.[5] Hence, less experienced personnel who were exposed to longer working hours in the
catheterization laboratory were more exposed to hazardous radiation due to noncompliance
in wearing lead aprons. Anastasian et al demonstrated that there is up to three times
more facial RE to the anesthesiologists than the interventionalists.[6] This might be because of the typical configuration of fluoroscopy equipment that
directs scatter radiation away from radiologist and toward the anesthesiologist. The
ignorance of neuroanesthesiologists can make them vulnerable to all harmful effects
of ionizing radiation.
Physics of Radiation
Various units are used to measure dose of radiation and exposure. The amount of radiation
travelling through air gives a value of RE measured in roentgen (U.S unit) or coulomb/kg
(SI unit). On the other hand, amount of radiation dose absorbed by matter is known
as radiation absorbed dose or rad (U.S unit). In SI derived units, it is replaced by gray (Gy), where 1 Gy =100 rad.
Both these terms help in measuring the absorbed dose. Effective dose measures the
amount of radiation absorbed by a person, considering biological response of different
tissue and organs to different types of radiation. The roentgen-equivalents-man or rem (U.S unit) is equal to rad multiplied by quality factor (QF), where rad is the amount of energy
deposited per unit weight of human tissue and QF is a number assigned to different
types of ionizing radiation.[7] Sievert is a SI unit for the effective dose of radiation where 1 Sv=100 rem. For
gamma and X-rays, 1 rad=1rem=10 mSv. The power of the radiation beam follows the inverse
square law (1/d2) that means the farther is the subject from the radiation source,
the lesser is the RE.[8]
Dosimetry
The measurement of radiation doses is done by the portable dosimeters or thermoluminescent
dosimeter badge that should be worn by all personnel working in radiation prone areas.
The dose limits of exposure are expressed as equivalent dose (HT) for an organ or body part and effective dose for the exposure of total body.[9]
Equivalent dose is calculated by the mean absorbed dose multiplied by the radiation weighing factor
(WR). Effective dose is defined as the weighted average of equivalent doses of all organs and tissues
of the body. The tissue weighing factor is maximum for breast, lung, colon and the
least for skin, brain, salivary glands, and cortical bone. A typical dosimeter provides
two values, the Hp (0.07) and Hp (10), which are the radiation absorption readings
at 0.07 and 10 mm below the skin, respectively.[10] The Hp (10) readings furnished from the collar dosimeter give good readings for
exposure to the lens, neck, and the thyroid. Another dosimeter is recommended to be
worn on the waist to calculate exposure to the trunk and the abdomen. There are several
algorithms for calculation of effective dose from dosimeter readings. When two dosimeters
are worn, the National Council on Radiation Protection and Measurements (NCRP) estimates
the effective dose by combining the Hp (10) dosimeter readings obtained from both
collar and the body.[11]
Effective dose (estimate) = 0.5 HW + 0.025 HN.
where HN = reading obtained from dosimeter worn at neck outside protective apron
HW= reading obtained from dosimeter worn at waist or on chest under protective apron.
The accuracy of the dosimeter readings is, however, a matter of concern owing to the
nonadherence or inappropriate placement of the badges. Badges should not be left at
a place where it is exposed to the radiations; it causes hindrance in correctly measuring
the radiation absorption.
Radiation Hazards and Safe Dose Limits
Radiation Hazards and Safe Dose Limits
There are three types of ionizing RE sources: (1) direct exposure from the primary
X-ray beam; (2) scattered radiation reflected from patient’s body, table, or surrounding
equipment; and (3) leakage from the X-ray tube. Scatter radiations are mainly responsible
for RE.[12] This scatter radiation is of primary concern for neuroanesthesiologists.
Organs such as thyroid, bone marrow, lens of eye, breasts, ovaries, and testicles
are sensitive to radiation. Effects that occur by chance and without a threshold level
of dose, whose probability is proportional to the dose, and whose severity is independent
of the dose is called as stochastic effect, for example, cancer.[13]
Deterministic effect is defined as the effect directly related to the radiation dose that leads to direct
cell injury or death, for example, skin damage and cataract. Exposure to ionizing
radiation can lead to cellular damage via the induction of DNA lesions and the production
of reactive oxygen species. These effects often result in cell death or genomic instability,
leading to various radiation-associated pathologies including an increased risk of
malignancy.[14] The effect of ionizing radiation has probability of causing cancer or genetic damage.
In the recent years, there are reports linked to developmental delay and neurotoxic
effects.[15] Studies on infant mice have shown that exposure to ionizing radiations has led to
lack of habituation, impaired learning, and memory. Extensive research done in determining
the effect of RE on eyes suggested it to be directly proportional to the radiation
dose.[3] The minimum dose that can cause lenticular cataracts has been documented at 0.1
Gy (gray).[16] In cases of pregnant neuroanesthesiologists, one extra dosimeter should be worn
over the abdomen under the apron. This may be considered as surrogate for radiation
absorption to the fetus.[8] However, it may overestimate the exposure as the impedance provided by the maternal
tissues to the radiation absorption will not be taken into account. If pregnancy is
confirmed, the cumulative dose should not exceed 1 millisievert (mSv) for the remaining
period of gestation. The first trimester is the most sensitive time for radiations.
Exposure above 10 mSv is predicted to increase the risk of cancer by 0.1%, in the
fetus.[17] The concern of the neuroanesthesiologist who is continuously exposed to such radiation
prone environment has not been adequately addressed.
The International Commission on Radiation Protection (ICRP) has given the effective
dose limits for various sites of exposure ([Table 2]).[8] The dosimeters should be evaluated by the institutional medical physicist at least
once a year. The report should be sent to the department as well as to the individuals
on yearly basis. There should be a strict surveillance of the occupational doses;
WHO recommends investigation when the effective dose exceeds 0.5 mSv/month.[19] In such cases, the radiation officer should find out the cause of such high RE and
appropriate action is taken.
Table 2
Comparative dose limits of radiation exposure from two different regulatory bodies
|
Dose quantity
|
Occupational dose limit (ICRP)
|
Dose limit (BARC)
|
|
a1 mSv=100 mRem.
Adapted from International Commission on Radiological Practice (ICRP) and Bhabha Atomic
Research Centre (BARC) newsletter.8,18
|
|
Effective dose
|
20 mSva/year averaged over 5 consecutive years (100 mSv in 5 years)
|
100 mSv in consecutive 5 years
20 mSv annual average
30 mSv in any year
|
|
Pregnant worker
|
Cumulative exposure less than 0.1mSv/month
|
|
|
Equivalent dose in:
|
|
|
|
Ocular lens
|
20 mSv/year
|
150 mSv/year
|
|
Skin
|
500 mSv/year
|
500 mSv/year
|
|
Hands and feet
|
500 mSv/year
|
500 mSv/year
|
|
Lifetime effective dose
|
|
1 mSv/year
|
Existing Guidelines
The ICRP suggests the goal of RE to be “as low as reasonably allowable (ALARA)” and
a dose limit of 10 mSv/year for 5 years.[20] There are two basic tenets of the ALARA principle:
The consensus guidelines of Joint Commission of Cardiology and Interventional Radiology
Society of Europe (CIRSE) and the Society of Interventional Radiology (SIR) acknowledge
that during interventional procedures the concern for radiation safety has been neglected,
especially in developing countries.[21] The anesthesiologist, who most of the time remains inside the radiology suite and
hence, is equally exposed to radiations as the primary physician.[22] As the neuroanesthesiologist is unable to control the duration of exposure, protective
measures should be strictly adopted and adequate distance should be maintained to
minimize the harmful effects of radiation. It also requires care of the ergonomics
and equipment standards.
Specific Modalities of Radiation
Specific Modalities of Radiation
Portable X-Ray
Portable X-ray used for routine imaging in the ICU (Mobility HP, Siemens, California,
United States) operates in a wide range of power starting from 30Kw to 450 mA and
provides a rapid image acquisition with improved clarity ([Fig. 1]). The RE is calculated from the dose area product (DAP). A standard X-ray exposure
ranges from 2100 to 3400 mRad for anteroposterior and lateral images.[23] A study showed that the exposure is minimum at a distance of 6 feet or 36 inches
from the source of X-ray.[24]
Fig. 1 Portable X-ray machine in neurointensive care unit.
Conventional Fluoroscopy, C-Arm and O-Arm
With the advent of C-arm and O-arm, complex spine surgeries can be now performed meticulously.
In the C-arm, the X-ray tube and image intensifier are both aligned by means of a
c-shaped element that enables image retrieval at almost any angle ([Fig. 2A]). In case of standard C-arm, the RE is ~0.2 ± 1.8 mSv for imaging of thoracolumbar
spine procedures.[25] The newer 3D isocentric C-arm offers advanced features such as image reconstruction
and CT-like images unlike conventional fluoroscopy. The O-arm has a 360-degree circular
arc capable of acquiring 2D/3D images along with the possibility of carrying out image-guided
spine surgeries ([Fig. 2B]). It has the capacity for acquiring 750 images in a single scan. In a single shot,
RE ranges from 30 ± 4 μGy to 20.0 ± 3.0 mGy for spine procedures. For a single 3D
acquisition, the maximum ambient equivalent dose at 2 m from the isocenter was 11
± 1 μSv.[26] The amount of RE can be decreased by allowing the surgical staff to leave the room.
Fig. 2 (A) C-arm assembly. (B) O-arm unit.
Computed Tomography Scan
Patients are often subjected to CT scan of head or spine during perioperative period.
Bedside CT scans have been made feasible with the availability of portable machines
([Fig. 3A]), which obviates the need for shifting the patient to a radiology facility. A CT
operative suite with an integrated image guidance system facilitates high-quality
CT imaging that helps in carrying out surgery more accurately ([Fig. 3B]). It also allows revision of instrumentation, before final surgical closure. The
accuracy of intraoperative CT has been observed to be comparable to O-arm for spinal
instrumentation.[27]
Fig. 3 (A) Portable computed tomography (CT) scan machine in neurointensive care unit. (B)
CT machine for intraoperative use. (Courtesy: Max Hospital, Saket, New Delhi).
Exposure during Different Procedures
Exposure during Different Procedures
Microscopic Pituitary Surgery
Conventional fluoroscopy provides radiological guidance to identify sella and guides
the surgical trajectory to approach the tumor. This helps in improving the resection
quality and approach during pituitary surgeries. CT-based neuronavigation offers more
detailed 3D anatomy during pituitary surgeries but is associated with higher RE to
patients.[28] However, in recent times endoscopic surgery with stereotactic navigation has obviated
the need for RE.
Spine Surgeries
The imaging modalities such as portable X-ray, C-arm fluoroscopy, and O-arm are important
for the localization of level of spine as well as facilitating spinal instrumentation.
However, the RE can be significant depending upon the duration of exposure and complexity
of the procedure. Yu and Khan carried a systematic review and found that there is
more RE in noninvasive or minimally invasive spine surgeries as compared with open
spine surgeries. This can possibly be due to more reliance on imaging modalities during
these procdeures.[29] The newer imaging modalities and spinal navigation systems have been developed in
an effort to replace conventional fluoroscopy and reduce RE.[30] Typically, an imaging mechanism is used to collect radiographic images that are
then imported into a computer workstation that creates a 3D reconstruction of the
anatomy of interest. The various types of imaging devices integrated with navigation
are isocentric C-arm, O-arm, and CT-guided navigation. Various anthropometric and
phantom-based models have been used by researchers who found that the CT-guided navigation
systems resulted in low RE as compared with standard fluoroscopic techniques.[31]
[32] The time needed for procedures has also been found to be less in C-arm-guided navigation
systems as compared with standard fluoroscopy. The isocentric C-arm use has been found
to be associated with lower total mean RE to the surgeon’s torso (0.33 vs. 4.33 mREM)
as compared with standard fluoroscopy.[33] Similarly, the O-arm is programmed with preset modes that optimize kilovoltage and
milliampere settings for various patient sizes and anatomical regions. Nelson et al
designed an experimental model to determine the amount of RE to patients and OR staff
during spine surgery.[23] The anesthesiologist received highest RE during O-arm followed by portable X-ray
and the C-arm acquisitions. On the other hand, radiology technologist and surgeon
receive most RE during portable X-ray, followed by the O-arm and C-arm image acquisitions.
This difference can possibly be owed to the respective standing position of staff
in the OR. In a recent systematic review, RE by different imaging technology was assessed
during thoracolumbar spinal fusion.[34] The authors found that intraoperative CT imaging offered the lowest surgeon and
OR staff RE, while increasing intraoperative patient RE relative to both conventional
fluoroscopy and fluoroscopy with preoperative CT-based navigation. The least RE during
intraoperative CT imaging can be explained by surgeon and staff stepping outside the
OR when scan is run. Overall patient RE remains well below safety levels for both
intraoperative CT and fluoroscopy-based techniques and it also eliminates need for
preoperative and postoperative CT scans.
Neurointerventional Suite
Patients having neurovascular conditions such as cerebral aneurysms, acute ischemic
stroke, arteriovenous malformations, or fistula are often subjected to diagnostic
and therapeutic procedures in neurointerventional suite. Amount of RE depends upon
the length and complexity (diagnostic or therapeutic) of the procedure. Digital subtraction
angiography (DSA) is a commonly performed fluoroscopic procedure used for real-time
visualization of blood vessels.[35] The net exposure during DSA will depend on the fluoroscopy time and the number of
runs taken. On an average, the range of exposure is around 17.4 (SD ±0.5) mGy in posteroanterior
plane and 13.2 (SD ±0.2) mGy in lateral planes.[36] The conventional four- or six-vessel DSA contributes to a radiation dose of 21.5
± 0.5 mGy. To reduce the exposure, one such technique is the use of fluoroscopy in
pulsed and low-dose mode. Pulsed mode refers to a method where power to the radiation
source is applied intermittently producing short pulses of radiation, while low-dose
mode reduces the peak kilovolts and mA necessary to create the radiation beam. Other
dose reduction techniques include intermittent fluoroscopy and last image hold. Intermittent
fluoroscopy refers to applying fluoroscopy only for short time periods, while last
image hold displays the last collected image even when fluoroscopy is not being applied.
These methods allow for both reduced total fluoroscopy time and the ability to better
plan surgical approaches through image review. Anastasian et al measured the amount
of radiation to the face and the eyes of the anesthesiologist, and found that there
is a six fold increase in the RE during neurointerventional procedures.[6] The exposure was more than three times the exposure to the radiologist possibly
due to the configuration of the horizontal fluoroscopy that subjects the anesthesiologist
to more scatter radiation. It was concluded that the RE was higher than permissible
limits, and anesthesiologist should wear protective eye gear during such procedures.
Injections of drugs or alterations in pump settings would normally draw the anesthesiologist
toward the intravenous tubing and, thus, toward the patient’s head, closer to the
source of scatter radiation. Similarly, switching the anesthesia ventilator off to
provide an apneic patient during imaging would do the same. Thus, it is recommended
to constantly stay behind the 6 feet long, 0.5 mm lead drape, to place all the tubings,
injection ports, and infusion devices behind the protective lead curtain, and to maintain
a distance from the fluoroscopic beam. Modern interventional neuroradiology suites
generally use biplanar equipment with one C-arm in the anteroposterior plane and one
C-arm aimed laterally ([Fig. 4]). The neuroanesthesiologist receives comparatively less scatter radiation by standing
on the side of the image intensifier rather than standing on the same side as radiograph
tube.[6] Whenever feasible, one should emerge from behind the shield only when the fluoroscopy
is off.
Fig. 4 A biplanar digital subtraction angiography unit.
Pain Procedures
During pain ablation procedures of head and spine, fluoroscopy is used to identify
the anatomic bony landmarks as well as to direct the needle trajectory toward the
area of interest. This exposes the neuroanesthesiologist to significant radiations
because of the repetitive exposure and proximity to the patient especially during
procedures for facial pain. Telischak et al have developed a novel technique using
C-arm and CT guidance to form a 3D image-based technique that decreases the procedural
time and improves the patient comfort.[37] However, whether the amount of RE is more or less than the conventional technique
is not yet known. Pain procedures carried under fluoroscopy guidance need to follow
same precautions to reduce RE as any other fluoroscopic-guided procedure.[38]
Radiation Exposure in Neuro-ICU
Portable X-ray and bedside head CT scanner are used in ICU for imaging and point-of-care
testing. Fan Chiang et al found that the average exposure from bedside X-ray machines
in ICU is around 0.24 ± 0.04 mSv at a distance of 4 m from the scanner.[39] The average is 1.04 mSv/year in ICU staff. The portable CT scan has 4000 times more
RE than a simple chest X-ray and on an average effective dose for a routine head CT
examination is around 1.7 mSv.[30] The dose may range from 1 to 2 mSv for a routine noncontrast CT scan head. Owing
to several times these CT scans are repeated especially in the postoperative setting,
the cumulative exposure to neurointensivist may be alarmingly high if precautions
are not taken. During CT scan of head, the continuous RE is around 2.5 µsv/sec at
a distance of 5 m.[40]
[Table 3] shows the effective dose limit for various radiological procedures.
Table 3
Effective dose limit for various radiological examinations
|
Procedure
|
Effective dose (mSv)
|
|
Abbreviation: CT, computed tomography.
|
|
Chest X-ray
|
0.02–0.05
|
|
X-ray skull or neck
|
0.1–0.2
|
|
X-ray abdomen
|
0.5–1.5
|
|
CT head
|
5–10
|
|
Abdomen CT
|
15–20
|
Gamma Knife Radiotherapy
The role of gamma knife radiotherapy (GKRT) is evolving at a rapid pace for the treatment
of craniopharyngiomas, pituitary tumors, arteriovenous malformations, metastatic tumors,
acoustic neuromas, and skull base tumors.[41] During certain circumstances that require sedation or general anesthesia, the neuroanesthesiologist
is involved in taking care of the patient. At the time when gamma therapy is being
delivered, neuroanesthesiologist leaves the room and monitors the patient through
a camera mounted outside the gamma knife room. The room is usually triple lead insulated
([Fig. 5]) and personnel enters only when required, wearing protective gear and badges. The
procedure time may vary from 2 to 4 hours and the dose to the patient ranges from
10 to 100 Gy depending on the location and size of the tumor.[42]
Fig. 5 Gamma knife unit.
Radiation Safety Measures
Radiation Safety Measures
There is inverse square relationship between RE and distance that implies that if
the person doubles the distance from the point source, the RE should be reduced to
one fourth. Therefore, it is suggested to keep a far distance from the source during
imaging to reduce RE. ALARA principle is the utmost thing to follow for reducing the
RE. Every institution should formulate its radiation protection institutional protocol
and spread awareness among the concerned personnel. There are several factors that
are responsible for determining the scatter such as patient size, duration of fluoroscopy,
gantry angulation, intensity of the beam, the metallic surfaces of different equipment,
and cracks in the apron.[32] The best way is to use appropriate shielding including the use of protective gear.
[Table 4] enumerates the important protective measures that need to be adopted to minimize
radiation risk.
Table 4
Measures to be adopted to reduce radiation exposure
|
Parameter
|
Adoptive measures
|
|
Distance
|
-
Maximize distance from the radiation beam
-
To stand on the side of the image intensifier
-
Position the image intensifier closer to the patient to achieve maximum magnification
|
|
Shielding
|
|
|
Imaging
|
-
Correct orientation of the beam to reduce repeated exposure
-
Collimation
-
Using pulsed mode
-
Intermittent needle advancement
-
Last image hold
-
Using low dose protocols
-
Ergonomic design of intervention laboratories
|
|
Regular measurement
|
|
|
Education
|
|
Protective Shielding
There are three types of shielding available: architectural, equipment mounted, and
personal protective devices. The architectural shielding hangs from the walls and
includes drapes and transparent lead barriers. Combination of both wall hanging and
trolley mounted lead should be used to screen radiation from the cathode ray beam
([Fig. 6A]). Shielding with lead barriers may reduce the exposure to scatter radiations by
more than 50%.[43] The equipment-mounted devices are the lead drapes, mounted on either side of the
table that separates the X-ray collimator placed under the table from the operator
([Fig. 6B]). Trolleys of transparent leaded plastic are used as they significantly reduce radiation
to the eyes. A radiation protection drape placed over the patient’s body confers protection
from scattered radiation and has been suggested as a reasonable alternative when standard
lead shielding is unavailable or impractical to use.[44]
[45] These drapes contain bismuth and tungsten-antimony and can be used as lead alternatives.
They are a bit costly, but provide good protection to the operator. In the wake of
the new era on dynamic radiation protective gear, it has been long debated that the
0.5 mm lead equivalent aprons may have flaws in design. Thus, a team of researchers
headed by Marichal et al designed the “ZeroGravity” (Zgrav) radiation protection system.[46] It is a suspended lead suit (Interventco, Dallas, Texas, United States), which provides
radiation shielding from the top of the head to the calves (except the right arm and
left forearm) via a complex overhead motion system to eliminate weight on the operator
while maintaining freedom of motion in all three spatial axes and range of arm motion
during procedures.
Fig. 6 Different types of radiation protective shielding. (A) The arrangement of architectural shielding during neurointervention procedures with
arrows depicting (a) mobile lead screen and (b) ceiling-mounted lead screen. (B)Equipment (table)-mounted lead screen. (C) Arrows showing (a) front coverage lead apron, (b) thyroid shield, and (C) lead cap.
Radiation Protection Gear
Personal protection devices include the armamentarium of lead apron, thyroid shield,
gloves, lead cap and eye gear ([Fig. 6C]). The different types of apron designs available are aprons with front coverage,
wrap around, and a vest and kilt/skirt combination. The wrap around and vest/skirt
configuration provide better protection where back is exposed to RE. These aprons
should be at least 0.5 mm thickness in lead equivalent to provide 90% of protection
from scatter radiation. It is important for these to have a proper fit for providing
adequate coverage. For additional upper arm and lateral thorax protection, humeral
arm shields may also be worn. These aprons need to be hanged properly and stored when
not in use. Visual and tactile inspection should be done regularly in addition to
the fluoroscopic inspection once yearly for cracks or damages as a quality control
policy.[47] A standard lead apron should protect 82% of the bone marrow, which still leaves
a substantial amount exposed for radiation hazard.[7] Lead dust produced from these aprons may cause environmental contamination. Depending
upon their size, these can be quite heavy and may cause significant shoulder and back
ache when worn for long period of time. The vest/skirt is more comfortable to wear
than the front coverage aprons. A newer version of the light weight lead apron is
available (weightless aprons) that are good alternatives to the old heavy lead variants.[48] The shielding materials have changed from heavy lead impregnated vinyl rubber attires
to the new lighter, composite lead along with high atomic number elements such as
tungsten, bismuth, antimony, titanium, and magnesium. Protection ensured by 0.5 mm
lead equivalence or lead-free aprons have been found to be around 0.6 to 6.8% of transmission.[8] The choice of the apron should depend upon the working conditions, imaging protocols,
use of other radiation protective shields, and personal health conditions (spine problems).
In-house validation of aprons for radiation safety should be done as different aprons
provide varied radiation protection even if labeled as having equal lead equivalence.[49]
Eyes are very sensitive to harmful effects of radiation, so, protective eye goggles
with large lenses are recommended for lenticular protection. The amount of radiation
protection with lead gloves is debatable.[50] It is better to avoid placement of hands in the direct projection beam because in
that case gloves will provide limited hand protection. It may be of use in those cases
where operator’s hand is near the beam for long periods of time.
RE to the head leading to the possible development of tumors is a concern. Karadagz
et al studied the efficacy of the lead cap in radiation protection of the head and
compare it with that of a ceiling mounted lead glass screen in a real life setting.[51] They found that a 0.5 mm lead equivalence was more effective than the mounted lead
shields during routine interventional procedures. Even most of the users said that
the lead cap was ergonomic in design and comfortable in wearing for long periods ([Fig. 6C]).
Design of the Catheterization Laboratory
The design of the neuroradiology suite should be robust and should allow adequate
radiation protective amenities. A large display monitor reduces the need for magnification
and RE. An X-ray-shielded control window allows observation of the patient from the
console room. Real-time projection monitors outside the main neuroradiology suite
and in the console room allows the anesthesiologist to monitor the patient outside
the suite. Proper radiation shielding of the laboratory is also necessary to prevent
RE to adjacent occupancies.
Imaging Techniques
A technological upgradation from continuous fluoroscopy projection to use short taps
of fluoroscopy beam is called “pulsed fluoroscopy.” It is better as it cuts out the unnecessary continuous exposure in a case.[35] Alarm bells to remind the operator regarding the approximate exposure timing (e.g.,
5 minutes) or live readouts help to warn the operator regarding the exposure.[52] Other ways to reduce exposure are by low-dose fluoroscopy settings, spectral beam
filtration, and use of antiscatter grid. Adjusting collimator settings to focus on
the area of interest helps to reduce image intensity and exposure. Use of appropriate
fluoroscopy instruments that comply with the International Electro Technical Commission
Standards (IEC) is advocated.
Radiation Safety Education
Awareness and training should be organized for the neuroanesthesia personnel as most
of the time, users are not aware of the risk. The misconception that “one which is
not visible, is not harmful” needs to be erased from the minds. The MARTIR project
(Multimedia and Audiovisual Radiation Protection Training in Interventional Radiology)
developed a free training program and is a good self-evaluation tool.[53] Training in awareness regarding radiation hazards has been imparted by the International
Atomic Energy Agency (IAEA).[54] In India, Bhabha Atomic Research Centre (BARC) is the monitoring agency for potential
RE. From time to time, BARC publishes the safe recommended doses for different organs
and effective doses of various modalities.
Conclusion
Overall, the neuroanesthesiologist is quite prone to the deterministic and stochastic
effects of radiation, the extent of which is still largely unknown. The effects are
dependent on many modifiable factors that should be taken into consideration during
our day-to-day clinical practice. Ergonomic design, appropriate shielding, and personal
radiation protective devices, all contribute to minimize RE. Constant monitoring of
such RE must be done using appropriate adherence to dosimetry badge guidelines. Still
a lot of ignorance and nonadherence remains in the field of radiation safety. Awareness
programs and training curriculum should be our goal for better health of the neuroanesthesiologist
working in the radiation zones.
