X-ray tube operators can be exposed to equal or higher scattered radiation doses to the hand as cassette holders during diagnostic radiographic procedures of the equine vertebral column and limbs

Alexandra F. Belotta Department of Small Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada

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Monique N. Mayer Department of Small Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada

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Cheryl L. Waldner Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada

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Narinder P. Sidhu British Columbia Cancer, Prince George, BC, Canada

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Kate A. Robinson Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada

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James L. Carmalt Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada

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Fernando P. Freitas Department of Small Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, Canada

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Niels K. Koehncke Department of Medicine, College of Medicine, University of Saskatchewan, Saskatoon, SK, Canada

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Abstract

OBJECTIVE

The objectives of this study were to investigate scattered radiation doses to the hands of equine workers holding the cassette and the x-ray tube by hand, for both limb and vertebral column studies, and to compare the scattered radiation attenuation of lead with radiation protection lead-free gloves. Radiation doses to the hands of the cassette holder in the primary beam were also investigated.

SAMPLE

A whole-body horse cadaver.

PROCEDURES

A portable x-ray unit was used to simulate 6 radiographic study types in the horse cadaver. Doses were measured with no shielding and, for cassette holders, with the ion chamber enclosed in a lead glove and a lead-free glove. Thirty exposures were performed for each study view and condition (n = 1,920).

RESULTS

Mean scattered doses to x-ray unit operators were higher than doses to cassette holders for ungula (hoof), thoracic vertebrae, and lumbar vertebrae studies, whereas doses to cassette holders were higher than doses to x-ray tube operators for studies of the metacarpophalangeal joint (fetlock) and tarsus (hock). Doses did not differ for the stifle joint. Mean percentage decrease in scattered radiation dose was 99.58% with lead gloves and 98.9% with lead-free gloves.

CLINICAL RELEVANCE

X-ray tube operators can be exposed to equal or higher scattered radiation doses to the hand as cassette holders. Lead-free hand shielding should only be considered as an alternative to lead gloves if their lighter weight increases frequency of use by workers.

Abstract

OBJECTIVE

The objectives of this study were to investigate scattered radiation doses to the hands of equine workers holding the cassette and the x-ray tube by hand, for both limb and vertebral column studies, and to compare the scattered radiation attenuation of lead with radiation protection lead-free gloves. Radiation doses to the hands of the cassette holder in the primary beam were also investigated.

SAMPLE

A whole-body horse cadaver.

PROCEDURES

A portable x-ray unit was used to simulate 6 radiographic study types in the horse cadaver. Doses were measured with no shielding and, for cassette holders, with the ion chamber enclosed in a lead glove and a lead-free glove. Thirty exposures were performed for each study view and condition (n = 1,920).

RESULTS

Mean scattered doses to x-ray unit operators were higher than doses to cassette holders for ungula (hoof), thoracic vertebrae, and lumbar vertebrae studies, whereas doses to cassette holders were higher than doses to x-ray tube operators for studies of the metacarpophalangeal joint (fetlock) and tarsus (hock). Doses did not differ for the stifle joint. Mean percentage decrease in scattered radiation dose was 99.58% with lead gloves and 98.9% with lead-free gloves.

CLINICAL RELEVANCE

X-ray tube operators can be exposed to equal or higher scattered radiation doses to the hand as cassette holders. Lead-free hand shielding should only be considered as an alternative to lead gloves if their lighter weight increases frequency of use by workers.

Introduction

Equine workers such as veterinarians, technicians or technologists, assistants, students, and staff involved in diagnostic radiographic procedures may be exposed to high levels of scattered radiation due to factors inherent to the nature of the radiographic examination of the horse, such as close proximity to their patients.1 Animal owners and members of the general public may also be involved in procedures.2 Exposure to scattered radiation can substantially increase with heavy caseloads and prepurchase examinations because these lead to a high number of radiographic exposures or radiographic acquisitions.

In general, during the radiographic examination, hands are the closest body part of workers to the main source of scattered radiation, which is the horse. The National Council on Radiation Protection and Measurements (NCRP) provides guidelines to keep radiation doses to the hands as low as reasonably achievable. Limitation of exposure to ionizing radiation is achieved by increasing the distance of the worker to the source of radiation, maximizing the distance between the worker and the source, and using appropriate shielding.2,3 During the use of portable x-ray equipment, the NCRP recommends the use of mechanical devices to hold the x-ray tube and the cassette to increase workers’ distance from the source of scattered radiation, thus reducing their exposure. Additionally, the use of 0.5-mm lead-equivalent gloves is recommended, and the guidelines state that hands should never be within the primary beam.2

A recent survey study4 of 154 members of the American Association of Equine Veterinary Technicians and Assistants found that the NCRP guidelines are not followed. In that study, 56% (73/130) of x-ray tube operators and 61% (90/148) of cassette holders always held the equipment by hand. Despite this practice, 58% (73/125) of x-ray tube operators and 25% (35/140) of cassette holders reported that they never wore hand shielding. The most important reason that workers identified for not wearing gloves when holding the x-ray tube and cassette by hand was that gloves interfere with the workers’ ability to perform their task. In an observational study5 of equine workers at an academic institution and 2 private equine practices in Canada, the x-ray tube was held by hand for 100% (1,293/1,293) of radiographic acquisitions, and the cassette was held by hand for 97% (1,078/1,114) of radiographic acquisitions. In that study, gloves were used by x-ray tube operators for < 1% (5/1,293) of radiographic acquisitions and by cassette holders for 54% (606/1,114) of radiographic acquisitions. Finally, an Australian survey study6 also found a lack of compliance of equine veterinary clinics with radiation safety regulations, including use of lead gloves by employees in only 8% (6/77) of the participating clinics.

Previous studies have investigated scattered radiation doses to the hands of x-ray tube operators79 and cassette holders7,8 during equine radiographic procedures; however, these studies were limited to radiography of the limb, with 2 studies7,9 using only the distal limb. The scattered dose to the x-ray tube operator may be higher during radiography of body regions other than the limb, such as the vertebral column, due to the thicker body regions generating more scatter, and the higher kilovolt and milliampere settings that may be used. As well, one of these studies7 measured scattered radiation dose to workers using an x-ray tube positioned on a tripod and a device to hold the cassette, and these methods do not represent the clinical practices of most workers in North America.4,5

Lead-free personal protective equipment has been reported to provide similar10 or superior11 scattered radiation attenuation in comparison with lead personal protective equipment while being lighter in weight and more flexible. Because interference with positioning equipment was identified as the most important reason for not wearing lead gloves by equine technicians,4 availability of more flexible radiation protection lead-free gloves could potentially increase the frequency of glove use by workers.

The first objective of this study was to investigate scattered radiation doses to the hands of equine workers holding the cassette and the x-ray tube by hand, for both limb and vertebral column studies. In the authors’ experience, shielded and unshielded body parts are at times visible on radiographs, and therefore we also measured the radiation dose in the primary beam. Our second objective was to compare the scattered radiation attenuation of lead gloves with radiation protection lead-free gloves containing barium sulfate–bismuth oxide composite.

Materials and Methods

Animal

This study was conducted in the Western College of Veterinary Medicine Large Animal Clinic. A whole-body horse cadaver weighing 545 kg was placed in a standing position with the use of an Anderson sling support system (CDA Products), which did not contain metal frame on its components. The head was supported with ropes and with an equine dental head stand. The horse cadaver used in this study was donated to this institution and euthanized due to reasons unrelated to this study. Therefore, this study was considered to be exempt from review by the Behavioral Research Ethics Board, University of Saskatchewan, according to Article 2.5 of the Tri-Council Policy Statement: Ethical Conduct for Research Involving Humans (BEH ID 668).12

Radiographic studies

Radiographic studies of the metacarpophalangeal joint (fetlock), tarsus (hock), and ungula (hoof) were selected as the most frequent studies of the study institution whereas studies of the stifle joint, thoracic vertebrae, and lumbar vertebrae were selected as the ones associated with the highest technical settings, based on a previous study performed by the authors of this study.5

An experienced equine veterinarian (KAR) positioned a portable x-ray unit and a digital radiographic cassette (MinXray Inc) to obtain each radiographic image. The portable x-ray unit was designed for veterinary use and had a total filtration of 2.7-mm aluminum equivalent, measured 18.8 X 15.7 X 31.2 cm, and weighed 6.4 kg. Lateromedial (LM) and dorsoplantar views were acquired of the right hind hoof; LM, LM flexed, dorsopalmar, dorsolateral-palmaromedial oblique, and dorsomedial-palmarolateral oblique views were acquired of the right front fetlock; LM, dorsoplantar, dorsolateral-plantaromedial oblique, and dorsomedial-plantarolateral oblique views were acquired of the right hock; LM, caudocranial, and caudolateral-craniomedial oblique views were acquired of the right stifle joint; and 1 left lateral view was acquired of each of the thoracic and lumbar portions of the vertebral column. Radiographic settings used were 80 kVp, 1 mA, and 60-cm focal distance for studies of the hoof, fetlock, hock, and LM view of the stifle joint; 80 kVp, 2 mA, and 60-cm focal distance for caudocranial and caudolateral-craniomedial oblique views of the stifle joint and left lateral views of thoracic vertebrae; and 90 kVp, 2.04 mA, and 60-cm focal distance for the left lateral views of lumbar vertebrae. While more than 2 views are commonly acquired for hoof studies, the LM and dorsopalmar views are the only views for which the cassette is held by hand at the Western College of Veterinary Medicine; a radiograph cassette tunnel is used for other views. For this reason, and to limit the number of exposures so that dose measurements could be made within 2 days, only these 2 views were included for the hoof study. Dose for each radiographic view was measured 30 times to capture measurement error and tube output variation.

The x-ray unit was positioned in place with the use of 22 X 22 X 2-inch Styrofoam sheets. Layers of Styrofoam were added according to the height needed for each radiographic study (maximum elevation of 1.5 m for lumbar and thoracic vertebrae studies), except for the hoof study when the x-ray tube was positioned on the floor. For studies of the hoof and fetlock, the cassette was positioned on the floor and kept in place by the use of a Styrofoam sheet with its back portion pressing against the limb and a wood block supporting the limb. For studies of the hock, stifle joint, thoracic vertebrae, and lumbar vertebrae, a mobile cassette holder was used, allowing the desired adjustment of the height and angulation of the cassette. The x-ray hand switch was used at its maximum distance (approx 2 m) and placed behind 2 mobile radiation shielding screens where the investigator (AFB) responsible for taking the radiographic acquisitions was located.

Radiation dose measurements

Following calibration by a certified medical physicist (NPS), a 180-cm pancake flat ion chamber with a cross-sectional area of 100 cm2 (Radcal Corp) was placed in the same orientation as the worker’s hands with the use of a wooden mechanical device adjustable for multiple heights and angulations. The ion chamber measurements were triggered with a multisensor solid state probe placed in the primary beam to avoid measurement of background radiation and instrument leakage (Radcal Corp). This ensured the measurement of dose by the ion chamber during the period when the x-ray beam was on.

Measurements of scatter radiation dose to the hand region of the tube operator and cassette holder were performed with no shielding, with the ion chamber enclosed in a 0.5-mm lead-equivalent glove, and with the ion chamber enclosed in a radiation protection lead-free mitt containing barium sulfate–bismuth oxide composite (BLOXR Solutions; Figure 1). The lead-free mitt had a slit in the palm region to allow fingers to slide out, increasing dexterity. This slit was sealed using tape and oriented away from the source of the scatter. Scatter dose was measured for 30 radiographic acquisitions for each study view and each glove condition (n = 1,920). Dose was also measured in the primary beam for each view using the multisensor solid-state probe. The positioning and scenario were kept the same during the 30 radiographic acquisitions.

Figure 1
Figure 1
Figure 1
Figure 1
Figure 1

Positioning of a portable x-ray unit, digital radiographic cassette, 545-kg horse cadaver, and ion chamber (arrows) to measure scattered radiation doses detected where the hands of an individual would be when holding the cassette without gloves for a lateromedial view of the right front ungula (hoof; A) and with lead-free gloves (B) or lead gloves (C) for a dorsopalmar view of the same hoof or when operating the x-ray unit without gloves (D).

Citation: American Journal of Veterinary Research 83, 5; 10.2460/ajvr.21.08.0134

Statistical analysis

Descriptive statistics (mean and SD) were calculated for scattered radiation dose measurements. Mean doses were assessed across study types by worker types with mixed linear regression accounting for repeated measures within study, view, and measurement with random effects after log transforming values for hand dose. As well, mean doses were assessed across glove types for the cassette holder with mixed linear regression accounting for repeated measures within study, view, and measurement with random effects after log transforming values for hand dose. The log values for resulting means and absolute differences in log values were back transformed, and relative differences were reported with 95% CIs. Percentage decreases in dose relative to no shielding gloves were also compared between lead-free and lead gloves for the cassette holder using mixed linear regression accounting for study type, radiographic view, and measurement. Statistical analysis was performed using a commercial statistical software program (Stata SE version 16; StataCorp LP). P values ≤ 0.05 were considered statistically significant.

Results

Mean scattered radiation doses per radiographic acquisition for each radiographic view for the 6 studies to the hands of workers involved as cassette holders and as x-ray tube operators were summarized (Table 1). Mean scatter radiation doses per radiographic acquisition measured for each study at the position of the workers’ hands including comparisons between the cassette holder and the x-ray tube operator were summarized (Table 2). Mean doses for cassette holders and for x-ray tube operators ranged from 0.26 to 2.64 μGy/study and from 0.84 to 12.09 μGy/study, respectively.

Table 1

Mean ± SD scattered radiation dose (μGy) detected with the use of an ion chamber placed where the hands of an individual would be when holding either a portable x-ray unit or digital radiographic cassette when radiographing 6 areas of interest (right front hoof and fetlock, right hock, right stifle joint, and left lateral views of thoracic and lumbar vertebrae) on a horse cadaver that was suspended to simulate positioning for standing radiographic examinations.

Cassette holder X-ray tube operator
Radiographic study View Mean (μGy) SD (μGy) Mean (μGy) SD (μGy)
Metacarpo-phalangeal joint Lateromedial flexed 4.10 0.03 1.07 0.01
Lateromedial 2.39 0.01 1.15 0.01
Dorsolateral-palmaromedial oblique 2.52 0.01 1.17 0.01
Dorsopalmar 2.03 0.03 0.98 0.09
Dorsomedial-palmarolateral oblique 2.55 0.01 0.94 0.01
Tarsus Lateromedial 2.10 0.01 0.97 0.01
Dorsolateral-plantaromedial oblique 1.73 0.02 0.93 0.01
Dorsoplantar 1.87 0.01 0.72 0.01
Dorsomedial-plantarolateral oblique 1.58 0.01 0.78 0.01
Stifle joint Lateromedial 5.02 0.01 2.69 0.01
Caudolateral-craniomedial oblique 0.73 0.17 5.21 0.04
Caudocranial 4.74 0.01 1.46 0.01
Thoracic vertebrae Lateral 1.20 0.01 12.09 0.03
Lumbar vertebrae Lateral 0.26 0 10.23 0.02
Ungula Lateromedial 0.84 0 1.37 0
Dorsoplantar 1.76 0 1.46 0.01
Table 2

Comparisons of the predicted mean (95% CI) scattered radiation dose (μGy) per simulated hand exposure detected with the construct described in Table 1 simulating radiation exposure to the hands of workers with no hand shielding when holding the digital radiographic cassette versus operating x-ray unit for 30 radiographic acquisitions/imaging plane (view) for each of the 6 anatomic areas of interest.

Radiographic study Cassette holder mean dose in μGy (95% CI) X-ray tube operator mean dose in μGy (95% CI) Relative mean difference (95% CI) P value
Metacarpophalangeal joint (n = 150 acquisitions) 2.64 (1.80–3.86) 1.06 (0.86–1.30) 0.40 (0.37–0.43) < 0.001*
Tarsus (n = 120 acquisitions) 1.81 (1.18–2.78) 0.84 (0.67–1.07) 0.47 (0.43–0.50) < 0.001*
Stifle joint (n = 90 acquisitions) 2.58 (1.58–4.22) 2.73 (2.09–3.58) 1.06 (0.97–1.16) 0.20
Thoracic vertebrae (n = 30 acquisitions) 1.20 (0.51–2.83) 12.09 (7.57–19.31) 10.04 (8.55–11.78) < 0.001*
Lumbar vertebrae (n = 30 acquisitions) 0.26 (0.11–0.60) 10.23 (6.41–16.34) 39.78 (33.88–46.69) < 0.001*
Ungula (n = 60 acquisitions) 1.22 (0.67–2.23) 1.41 (1.02–1.97) 1.16 (1.04–1.30) 0.01*

The mean scatter radiation dose per radiographic acquisition to the hands was higher for the cassette holder (mean of 2.64 μGy for the fetlock and 1.81 μGy for the hock) than for the x-ray tube operator (mean of 1.06 μGy for the fetlock and 0.84 μGy for the hock) for the fetlock study (P < 0.001) and the hock study (P < 0.001). The mean scatter radiation dose per radiographic acquisition to the hands was lower for the cassette holder (mean of 1.2 μGy for the thoracic vertebrae, of 0.26 μGy for the lumbar vertebrae, and of 1.22 μGy for the hoof) than for the x-ray tube operator (mean of 12.09 μGy for the thoracic vertebrae, of 10.23 μGy for the lumbar vertebrae, and of 1.41 μGy for the hoof) for the thoracic vertebrae study (P < 0.001), the lumbar vertebrae study (P < 0.001), and the hoof study (P = 0.01). There was no difference in the mean scatter radiation dose per radiographic acquisition to the hands between the cassette holder (2.58 μGy) and the x-ray tube operator (2.73 μGy) for the stifle joint study (P = 0.2).

When comparing mean scattered radiation doses across all studies for both worker tasks, dose to the hands of the x-ray tube operator for studies of the thoracic vertebrae (P < 0.01) and the lumbar vertebrae (P < 0.01) were the highest (12.09 and 10.23 μGy, respectively), whereas dose to the hands of the cassette holder for the lumbar vertebrae (0.26 μGy) study was the lowest (P < 0.01).

When comparing the effect of hand shielding for the cassette holder across all studies, the mean scatter radiation dose per radiographic acquisition was 1.429 μGy (95% CI, 0.783 to 2.608 μGy) when no glove was used, 0.012 μGy (95% CI, 0.007 to 0.023 μGy) when the radiation protection lead-free glove was used, and 0.004 μGy (95% CI, 0.002 to 0.008 μGy) when the lead glove was used. The mean scatter radiation dose was lower when a lead glove was used than when a lead-free glove was used (P < 0.001). The mean scatter radiation dose was lower when either type of glove was used than when no glove was used (P < 0.001).

The mean percentage decrease in scatter radiation dose for a lead glove, compared with no glove, was 99.58% (95% CI, 99.25% to 99.91%), and the mean percentage decrease in dose for a lead-free glove, compared with no glove, was 98.90% (95% CI, 98.58% to 99.23%). The mean percentage decrease in dose was higher when a lead glove was used than when a lead-free glove was used (P < 0.001).

The mean primary beam radiation dose per radiographic acquisition was 156.66 μGy (95% CI, 176.41 to 166.12 μGy) for the fetlock study, 188.36 μGy (95% CI, 113.35 to 201.13 μGy) for the hock study, and 146.34 μGy (95% CI, 133.38 to 160.55 μGy) for the hoof study. The primary beam dose rate exceeded the upper limit of the solid-state dosimeter (5.7 mGy/s) for the stifle joint and the thoracic and lumbar vertebrae studies, with the exception of the lateral medial view of the stifle joint, and no mean radiation doses were reported for those studies.

Discussion

This study reported mean scattered radiation extremity doses for workers holding the x-ray unit or cassette by hand during radiographic studies of the equine limbs and vertebral column, and measured dose reduction with lead and radiation protection lead-free shielding. We found that the scattered radiation doses to the hands of x-ray tube operators for thoracic vertebrae and lumbar vertebrae studies were the highest across all radiographic studies and both worker tasks. Lead gloves provided higher attenuation of scattered radiation than the lead-free gloves; however, the lead-free gloves attenuated almost 99% of x-rays, compared with using no hand shielding.

The finding in 2 previous studies4,5 of lower frequency of hand shielding use by x-ray tube operators in comparison with cassette holders may have been due to workers assuming that they were exposed to higher scattered radiation doses when holding the cassette than when operating the x-ray tube. Indeed, a previous study8 showed that doses to the unshielded hands of cassette holders were significantly higher than doses to the hands of x-ray tube operators for lateral views of the pes (foot), fetlock, and hock as well as for all 3 views of the stifle joint study. In our study, we found that mean doses to the hands of x-ray tube operators were higher than for cassette holders in 3 of the 6 radiographic studies investigated (hoof, lumbar, and thoracic vertebrae). In addition, mean doses to the hands of x-ray tube operators were higher for the thoracic vertebrae and the lumbar vertebrae studies than for all other studies considering both worker tasks. This finding was likely due to increased scattered radiation toward the x-ray tube operator from the thicker bony and soft tissue structures in the vertebral column region. The mean dose to the hands of the cassette holder for the lumbar vertebrae study was the lowest, in comparison with all other studies and accounting for both worker tasks. This was likely because, for that study, the body of the horse was located between the cassette holder’s hands and the x-ray tube, and the scattered radiation would have been absorbed by the horse, decreasing the scattered radiation dose. Based on these findings, we strongly suggest that protective gloves be worn or mechanical devices to increase distance be used not only by cassette holders but also by x-ray tube operators.

Although comparison across studies is limited due to different methods, including x-ray tube settings and film focus distance, the mean dose of 1.37 μGy to the hands of the x-ray tube operator obtained in our study for the LM view of the foot was comparable to the operator dose of 0.394 mR reported in a previous study.9 Another study7 reported a dose of only 0.0625 μSv to the operator for the same study and view. This was likely due to the use of a tripod and x-ray acquisition cord in that study, allowing the operator to increase their distance from the horse and the x-ray tube, whereas in the current study we measured the hand dose for an operator holding the tube by hand. In our study, radiation doses were expressed in grays, which are the international unit for absorbed dose. Absorbed dose is defined as the amount of energy absorbed by a unit of a mass of any material and is dependent on the type of radiation and on the atomic number of the mass. For radiation safety purposes, equivalent dose, expressed as rems (1 rem = 0.01 Sv) or sieverts, was used and is based on the absorbed dose to a specific organ, adjusted by a quality factor to account for the effectiveness of the type of radiation. Because 1 is the quality factor for x-rays, 1 unit of gray is equal to 1 unit of sievert.

In equine practice, unshielded hand exposure to primary beam radiation is possible given that workers hold the cassette by hand without shielding.4,5 In the authors’ experience, lead gloves or unshielded human body parts such as the phalanges of the hand can occasionally be identified on radiographic images. We found mean radiation doses approximately 100 times that of scattered radiation dose in the primary beam for the fetlock, hock, and hoof studies. The dose exceeded the detectable limit of the solid-state dosimeter for the stifle joint, thoracic, and lumbar vertebrae studies. Therefore, in no instance should hands be placed in the primary beam. Hand shielding is designed to attenuate lower-energy scattered x-rays, not higher-energy primary beam x-rays, and so hands should be kept out of the beam even when shielding is worn.

The International Commission on Radiological Protection recommends an annual equivalent dose limit to the hands of 500 mSv.13 However, equivalent dose limits do not identify a safe dose, but rather are intended as a reference above which workers are subjected to unacceptable risks. Use of occupational equivalent dose limits recommended by the International Commission on Radiological Protection should be associated with optimization of protection, in particular for stochastic effects that have no threshold dose limit for occurrence.14 In addition, reference levels should be used in conjunction with dose constraints, defined as a level of dose above which it is unlikely that protection is optimized and above which action must almost always be taken to reduce dose.15 For example, Health Canada recommends that where radiation doses exceed 20% of the permissible dose equivalent limits, investigation of the nature and cause be performed and actions be taken to reduce dose.16 Dose constraints are used in radiation safety planning to ensure optimization of protection.2

Based on the doses measured in this study and the number of radiographs acquired by workers in 2 recent studies,4,5 it is unlikely that workers with a caseload similar to those 2 studies would reach 20% of the permissible dose equivalent limit to the hand in a year. However, workers regularly performing prepurchase examinations may have much higher exposure to radiation. As well, workers regularly performing studies of the thoracic vertebrae and lumbar vertebrae without protective gloves would need a relatively modest number of radiographic acquisitions (112 radiographic acquisitions/d and 24 radiographic acquisitions/d, respectively) to reach the Health Canada dose constraint. Finally, equine workers who regularly position their hands without gloves within the primary beam would easily reach 20% of the permissible limit and higher. Although this study is focused on dose assessment and radiation protection of hands, other body parts, such as the lens of the eyes, may be more sensitive to ionizing radiation and have much lower equivalent dose limits.13 At times, a worker’s head may also be in close proximity to the source of scattered radiation, and the worker may approach dose constraints for the lens of the eye well before those for the hands. Adverse effects of chronic low-dose exposure to the hands include cancer, while radiation exposure of the lens of the eye increases the risk of cataracts.14 Exposure of workers to increased doses, such as prepurchase examinations at large horse auctions, which may include thousands of horses,9 must be justified by economic benefit or benefit to the animals.2

The reduction in dose with lead was consistent with previous reports.9 Higher scattered radiation attenuation was observed with lead gloves in comparison with radiation protection lead-free gloves. However, if the lighter weight of the lead-free gloves increases the frequency of use by workers, they may result in lower doses to the hands of workers overall, despite their slightly lower x-ray attenuation. To the authors’ knowledge, there is only 1 manufacturer offering a radiation protection lead-free glove option. There are 2 designs available for purchase, an open mitt that protects only the back of the hand, and a closed mitt with a small slit that allows the worker to extend their fingers outside the glove if desired. If lead-free hand shielding is used, we recommend that the closed mitt be used and that fingers not be extended outside the shielding during the exposure.

Limitations of the present study included use of only 1 set of positioning and technical settings, selected by 1 equine veterinarian, for each exposure; this study was unable to represent the full range of clinical practices that contribute to workers’ hand doses. Dose measurements for each radiographic view were repeated 30 times to capture measurement error and variation in tube output. Additional measurements for each radiographic view made after repeated positioning by additional veterinarians would have allowed assessment of dose variation due to repositioning. However, use of a whole equine cadaver suspended in a standing position limited data collection to 2 days to minimize impact on client access to the clinic and to ensure availability of a portable x-ray tube and an equine veterinarian. The number of exposures in this study design (n = 1,920) required the full 2 days to acquire. While the slit in the radiation protection lead-free mitt was positioned on the side of the detector away from the source of scattered radiation, and was sealed, it is possible that this may have contributed to the lower x-ray attenuation measured for the lead-free shielding. The measurements made with the veterinary x-ray tube used in this study, designed to be lightweight to increase portability, would not apply to other portable x-ray units with different specifications, including different amounts of inner shielding. The measurements made for the operator included both scattered radiation and tube leakage, which was not measured separately in this study. In a previous study9 using a comparable portable x-ray tube, a mean tube leakage exposure of 0.158 mR (1.39 μGy) was reported at the top of the machine. Because it contributes to operator hand dose, tube leakage should be measured regularly.

In conclusion, for the stifle joint, thoracic vertebrae, lumbar vertebrae, and hoof studies, hands of workers involved as x-ray tube operators can be exposed to equal or higher scattered radiation doses in comparison with hands of workers involved as cassette holders. Therefore, the same principles applied to optimize radiation protection to the hands of cassette holders should also be applied to x-ray tube operators, including use of protective gloves and use of mechanical devices to keep their hands at an adequate distance. Radiation protection lead-free hand shielding may be considered as an alternative to lead gloves, but only if their lighter weight increases frequency of use by workers.

Acknowledgments

This study was supported by a College of Medicine Research Award, College of Medicine, University of Saskatchewan, Saskatoon, SK, Canada. The stipend for Dr. Belotta’s postdoctoral fellowship was provided by the Saskatchewan Health Research Foundation.

The authors declare that there were no conflicts of interest.

References

  • 1.

    Hupe O, Ankerhold U. Dose to persons assisting voluntarily during x-ray examinations of large animals. Radiat Prot Dosimetry. 2008;128(3):274278. doi:10.1093/rpd/ncm422

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 2.

    International Atomic Energy Agency. Radiation Protection and Safety in Veterinary Medicine. Safety Reports Series 104. International Atomic Energy Agency; 2021:696.

    • Search Google Scholar
    • Export Citation
  • 3.

    National Council on Radiation Protection and Measurements. Radiation Protection in Veterinary Medicine. National Council on Radiation Protection and Measurements; 2004: Report No. 148.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 4.

    Belotta AF, Mayer MN, Koehncke NK, Carmalt J, Freitas FP, Waldner CL. Survey of self-reported radiation safety practices among North American veterinary technicians involved in equine radiography using portable x-ray equipment. J Am Vet Med Assoc. 2021;259(8):919926. doi:10.2460/javma.259.8.919

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 5.

    Belotta AF, Mayer MN, Waldner CL, et al. Radiation safety practices among Canadian equine veterinary workers during diagnostic procedures with portable x-ray equipment. Can Vet J. 2021;62(4):349356.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 6.

    Surjan Y, Ostwald P, Milross C, Warren-Forward H. Radiation safety considerations and compliance within equine veterinary clinics: results of an Australian survey. Radiography. 2015;21(1):224230. doi:10.1016/j.radi.2014.11.007

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7.

    Šterc J, Lepková R. Personnel exposure to scattered radiation during radiography of the distal interphalangeal joint in the horse using a portable x-ray machine. Acta Vet Brno. 2007;76(1):105111. doi:10.2754/avb200776010105

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 8.

    Ellis KL, Morton AJ, Hernandez JA, Winter MD. Radiation exposure to personnel obtaining equine appendicular radiographs using a handheld generator. J Equine Vet Sci. 2019;73:7074. doi:10.1016/j.jevs.2018.11.013

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 9.

    Tyson R, Smiley DC, Pleasant RS, Daniel GB. Estimated operator exposure for hand holding portable x-ray units during imaging of the equine distal extremity. Vet Radiol Ultrasound. 2011;52(2):121124. doi:10.1111/j.1740-8261.2010.01754.x

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 10.

    Uthoff H, Benenati JF, Katzen BT, et al. Lightweight bilayer barium sulfate-bismuth oxide composite thyroid collars for superior radiation protection in fluoroscopy-guided interventions: a prospective randomized controlled trial. Radiology. 2014;270(2):601606. doi:10.1148/radiol.13122834

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11.

    Uthoff H, Pena C, West J, Contreras F, Benenati JF, Katzen BT. Evaluation of novel disposable, light-weight radiation protection devices in an interventional radiology setting: a randomized controlled trial. AJR Am J Roentgenol. 2013;200(4):915920. doi:10.2214/AJR.12.8830

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 12.

    Panel on Research Ethics, Government of Canada. Scope and approach. In: Tri-Council Policy Statement: Ethical Conduct for Research Involving Humans—TCPS 2. Canadian Institute of Health Research; 2018. Accessed December 13, 2021.https://ethics.gc.ca/eng/tcps2-eptc2_2018_chapter2-chapitre2.html#a

    • Search Google Scholar
    • Export Citation
  • 13.

    Stewart FA, Akleyev AV, Hauer-Jensen M, et al. ICRP publication 118: ICRP statement on tissue reactions and early and late effects of radiation in normal tissues and organs—threshold doses for tissue reactions in a radiation protection context. Ann ICRP. 2012;41(1-2):1322. doi:10.1016/j.icrp.2012.02.001

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 14.

    Widmer WR, Shaw SM, Thrall DE. Effects of low-level exposure to ionizing radiation: current concepts and concerns for veterinary workers. Vet Radiol Ultrasound. 1996;37(3):227239. doi:10.1111/j.1740–8261.1996.tb01225.x

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15.

    The 2007 Recommendations of the International Commission on Radiological Protection. ICRP Publication 103. Ann ICRP. 2007;37(2-4):1332. doi:10.1016/j.icrp.2007.10.003

    • Search Google Scholar
    • Export Citation
  • 16.

    Environmental Health Directorate Health Protection Branch. Radiation protection in veterinary medicine—recommended safety procedures for installation and use of veterinary x-ray equipment—Safety Code 28. 1991. Accessed December 12, 2021.https://www.canada.ca/en/health-canada/services/environmental-workplace-health/reports-publications/radiation/radiation-protection-veterinary-medicine-recommended-safety-procedures-installation-use-veterinary-equipment-safety-code-28.html

    • Search Google Scholar
    • Export Citation

Contributor Notes

Corresponding author: Dr. Belotta (alexandra.belotta.vet@gmail.com)
  • Figure 1

    Positioning of a portable x-ray unit, digital radiographic cassette, 545-kg horse cadaver, and ion chamber (arrows) to measure scattered radiation doses detected where the hands of an individual would be when holding the cassette without gloves for a lateromedial view of the right front ungula (hoof; A) and with lead-free gloves (B) or lead gloves (C) for a dorsopalmar view of the same hoof or when operating the x-ray unit without gloves (D).

  • 1.

    Hupe O, Ankerhold U. Dose to persons assisting voluntarily during x-ray examinations of large animals. Radiat Prot Dosimetry. 2008;128(3):274278. doi:10.1093/rpd/ncm422

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 2.

    International Atomic Energy Agency. Radiation Protection and Safety in Veterinary Medicine. Safety Reports Series 104. International Atomic Energy Agency; 2021:696.

    • Search Google Scholar
    • Export Citation
  • 3.

    National Council on Radiation Protection and Measurements. Radiation Protection in Veterinary Medicine. National Council on Radiation Protection and Measurements; 2004: Report No. 148.

    • Search Google Scholar
    • Export Citation
  • 4.

    Belotta AF, Mayer MN, Koehncke NK, Carmalt J, Freitas FP, Waldner CL. Survey of self-reported radiation safety practices among North American veterinary technicians involved in equine radiography using portable x-ray equipment. J Am Vet Med Assoc. 2021;259(8):919926. doi:10.2460/javma.259.8.919

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 5.

    Belotta AF, Mayer MN, Waldner CL, et al. Radiation safety practices among Canadian equine veterinary workers during diagnostic procedures with portable x-ray equipment. Can Vet J. 2021;62(4):349356.

    • Search Google Scholar
    • Export Citation
  • 6.

    Surjan Y, Ostwald P, Milross C, Warren-Forward H. Radiation safety considerations and compliance within equine veterinary clinics: results of an Australian survey. Radiography. 2015;21(1):224230. doi:10.1016/j.radi.2014.11.007

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7.

    Šterc J, Lepková R. Personnel exposure to scattered radiation during radiography of the distal interphalangeal joint in the horse using a portable x-ray machine. Acta Vet Brno. 2007;76(1):105111. doi:10.2754/avb200776010105

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 8.

    Ellis KL, Morton AJ, Hernandez JA, Winter MD. Radiation exposure to personnel obtaining equine appendicular radiographs using a handheld generator. J Equine Vet Sci. 2019;73:7074. doi:10.1016/j.jevs.2018.11.013

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 9.

    Tyson R, Smiley DC, Pleasant RS, Daniel GB. Estimated operator exposure for hand holding portable x-ray units during imaging of the equine distal extremity. Vet Radiol Ultrasound. 2011;52(2):121124. doi:10.1111/j.1740-8261.2010.01754.x

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 10.

    Uthoff H, Benenati JF, Katzen BT, et al. Lightweight bilayer barium sulfate-bismuth oxide composite thyroid collars for superior radiation protection in fluoroscopy-guided interventions: a prospective randomized controlled trial. Radiology. 2014;270(2):601606. doi:10.1148/radiol.13122834

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 11.

    Uthoff H, Pena C, West J, Contreras F, Benenati JF, Katzen BT. Evaluation of novel disposable, light-weight radiation protection devices in an interventional radiology setting: a randomized controlled trial. AJR Am J Roentgenol. 2013;200(4):915920. doi:10.2214/AJR.12.8830

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 12.

    Panel on Research Ethics, Government of Canada. Scope and approach. In: Tri-Council Policy Statement: Ethical Conduct for Research Involving Humans—TCPS 2. Canadian Institute of Health Research; 2018. Accessed December 13, 2021.https://ethics.gc.ca/eng/tcps2-eptc2_2018_chapter2-chapitre2.html#a

    • Search Google Scholar
    • Export Citation
  • 13.

    Stewart FA, Akleyev AV, Hauer-Jensen M, et al. ICRP publication 118: ICRP statement on tissue reactions and early and late effects of radiation in normal tissues and organs—threshold doses for tissue reactions in a radiation protection context. Ann ICRP. 2012;41(1-2):1322. doi:10.1016/j.icrp.2012.02.001

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 14.

    Widmer WR, Shaw SM, Thrall DE. Effects of low-level exposure to ionizing radiation: current concepts and concerns for veterinary workers. Vet Radiol Ultrasound. 1996;37(3):227239. doi:10.1111/j.1740–8261.1996.tb01225.x

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15.

    The 2007 Recommendations of the International Commission on Radiological Protection. ICRP Publication 103. Ann ICRP. 2007;37(2-4):1332. doi:10.1016/j.icrp.2007.10.003

    • Search Google Scholar
    • Export Citation
  • 16.

    Environmental Health Directorate Health Protection Branch. Radiation protection in veterinary medicine—recommended safety procedures for installation and use of veterinary x-ray equipment—Safety Code 28. 1991. Accessed December 12, 2021.https://www.canada.ca/en/health-canada/services/environmental-workplace-health/reports-publications/radiation/radiation-protection-veterinary-medicine-recommended-safety-procedures-installation-use-veterinary-equipment-safety-code-28.html

    • Search Google Scholar
    • Export Citation

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