Journal of Radiation and Cancer Research

ORIGINAL ARTICLE
Year
: 2019  |  Volume : 10  |  Issue : 2  |  Page : 117--123

Radiographic assessment of protective aprons and dose simulation to personnel


Akintayo Daniel Omojola1, Michael Onoriode Akpochafor2, Samuel Olaolu Adeneye2, Ukeme Pius Aniekop1,  
1 Department of Radiology, Medical Physics Unit, Federal Medical Centre, Asaba, Nigeria
2 Department of Radiation Biology, Radiotherapy and Radiodiagnosis, College of Medicine, University of Lagos, Lagos, Nigeria

Correspondence Address:
Mr. Akintayo Daniel Omojola
Department of Radiology, Medical Physics Unit, Federal Medical Centre, Asaba
Nigeria

Abstract

Background: Studies have shown that protective aprons are carelessly handled after working hours. This, in turn, leads to crack, tear, hole, and creases on the apron, which may lead to distortion in the attenuating property and hence reduction in efficiency. Aim and Objective: The aim of the study was to carry out the radiographic assessment of four protective aprons (denoted A–D), to check for tear, crack, or pressure marks and to simulate what the equivalent dose rate, dose/procedure, percentage absorbance, and transmission factor (TF) would be if a physician is to perform hysterosalpingogram (HSG), for which he/she will be averagely exposed twice/procedure. Materials and Methods: This study used a functional mobile X-ray unit, four protective aprons, a measuring tape, an electronic dosimeter and a locally designed phantom as materials. The first phase involved the radiographic exposure of the protective aprons. The second phase involved the use of a plastic phantom to produce scatter, a wooden T-stand to hold the apron, which was positioned 1.6 m diagonally from the X-ray collimator. This position was assumed to be where a physician would stand during the procedure. Results: Two out of the four aprons were defective (50%). One out of the four aprons was rejected because it exceeded the 670 mm[2] criteria for acceptance. The mean estimated dose/procedure was 65.69–347.56 μSv, and the estimated mean dose per year for 0.25, 0.35, and 0.50 mm protective aprons was 35,592, 9689, and 7900 μSv/year, respectively. TF for 0.25, 0.35, and 0.50 mm protective aprons was 20.4–23.2, 5.3–6.9, and 3.7%–6.3%, respectively. Absorbance for 0.35 and 0.50 mm protective aprons was ≥94%. There was no statistically significant difference in mean percentage absorbance for 0.25 mm protective aprons, compared to other studies (P = 0.981). Conclusion: Estimated equivalent skin dose per year to a physician with 0.25, 0.35, and 0.50 mm protective aprons was below 500 mSv/year, and the mean percentage absorbance for 0.25 mm protective aprons was seen to be below 90%.



How to cite this article:
Omojola AD, Akpochafor MO, Adeneye SO, Aniekop UP. Radiographic assessment of protective aprons and dose simulation to personnel.J Radiat Cancer Res 2019;10:117-123


How to cite this URL:
Omojola AD, Akpochafor MO, Adeneye SO, Aniekop UP. Radiographic assessment of protective aprons and dose simulation to personnel. J Radiat Cancer Res [serial online] 2019 [cited 2019 Sep 15 ];10:117-123
Available from: http://www.journalrcr.org/text.asp?2019/10/2/117/266117


Full Text



 Introduction



The use of X-ray and other forms of ionizing radiation (gamma-rays and alpha- and beta-particles) has progressively increased over the years for radiological investigation.[1],[2],[3] Shielding of radiosensitive organs that may be at risk has been well-documented, and the reduction of scatter radiation to personnel has been much dealt with. The aim of shielding is to reduce dose to vital organs, arising from either primary or secondary radiation.[4],[5]

Two major reasons for using protective aprons are because of its effectiveness in shielding vital organs arising from primary radiation to the patient and the effect of scatter radiation that is produced from the patient which reaches the personnel.[6],[7],[8] In many occasions, in interventional studies, the radiologist/physician is proximal to the patient. Usually, the scattering effect of X-ray is mostly dependent on the volume of the tissue, kilovoltage (kV), density of matter, and X-ray field size. Most of the interventional X-ray procedures require the use of lead/lead-free protective apron to shield radiation worker from the harmful effect of secondary (scatter) radiation. In most of the intervention studies, the eye lens, thyroid, and gonads are shielded because of their radiosensitivity nature. Studies have shown that interventional examinations are associated with higher radiation dose compared to routine conventional imaging.[9],[10]

A lead/lead-free protective apron is a material made of lead-impregnated vinyl or rubber[11],[12] that is capable of attenuating incident (primary) or scatter radiation (secondary) striking it. They are generally made of different thicknesses depending on their purpose. Most of the protective aprons generally have shielding equivalence between 0.25 and 0.5 mm with attenuating property of 90%–95% of scatter radiation reaching them and may be having a front protection side only or may be wrapped around (front and back protection).[13]

Aprons must cover the full width of the front of the body from the throat to within 10 cm of the knees, as well as the sides of the body. Wrap-around types of aprons have front and back protection and must cover from the shoulder blades to below the buttocks. Fastenings must be provided to keep aprons closed. Where aprons have two overlapping front panels, the total of the two panels when correctly worn must not be <0.3 mm in lead equivalence at 100 kVp.[14] The Australian Radiation Protection and Nuclear Safety Agency guideline has stated that aprons should be tested for integrity on initial receipt and then every 12–18 months.[15] The time frame for testing protective aprons may vary depending on usage. A study by Cohen who investigated the use of protective aprons from three hospitals showed that maintenance protocol greatly varies. In his study, one of the hospital barley carryout the maintenance test on protective aprons.[16]

Several articles have investigated radiation dose to personnel during intervention studies. An increase in the number of medical specialists in other areas of medicine using fluoroscopy is emerging, and there has been poor compliance to radiation protection and safety in this aspect. Procedures such as endovascular aneurysm repair, renal angioplasty, iliac angioplasty, ureteral stent placement, therapeutic endoscopic retrograde cholangiopancreatography, and bile duct stenting and drainage have the potential to impart skin, thyroid, eye lens, and gonadal dose.[17],[18],[19]

Testing for defects in an apron can be achieved using fluoroscopy or radiography. The purpose is to spot tear, cracks, holes, or pressure marks (creases). International best practices recommend that those areas with a defect should be marked and recorded, and further evaluation test should be performed before a protective apron is replaced. To reduce costs, a protective apron may only have to be replaced if the defect is ≥15 mm2 in areas close to critical organs, and for areas at the back or along the seams, a replacement can be made if the defect is ≥670 mm2.[20]

To ensure that protective aprons and thyroid shields provide the best protection possible, it is important that they are stored properly. Improper storage can lead to creases and eventually cracks in the lead, which diminishes its ability to absorb radiation. X-ray racks and hangers are used to safely hold the protective aprons; similarly, the apron can be placed on a flat material that can bear weight, and the aim of this is to avoid the folding of sensitive areas that cover the chest, abdomen, and pelvic regions.

In reality, most of the fluoroscopy units in Nigeria have more downtime due to poor management and lack of maintenance engineers and hence the use of conventional imaging in lieu of fluoroscopy unit. Some articles have investigated the use of conventional X-ray in determining both patient and staff dose in hysterosalpingogram (HSG) procedure. Likewise, phantom studies have been conducted to estimate patient and personnel dose using thermoluminescent dosimeters.[21],[22],[23] Protective apron maintenance protocol is still a major problem, and appropriate proper handling of protective apron before and after use has been seen to reduce their life expectancy.[16]

The aim of this study is to check the integrity of the front/back protective area of four protective aprons using conventional means (radiography) and to estimate radiologist/physician dose/procedure and dose rate from HSG investigation using a plastic phantom to simulate the patient and to create scatter radiation. This investigation also intends to compare its result with related studies.

 Materials and Methods



The study was prospective in nature. It involved the use of an X-ray mobile unit [Table 1] with a floating table bucky. Professionals who were involved in this study were a clinical medical physicist and a qualified radiographer. In the first stage, each of the protective apron was positioned at a Focus to Image Distance (FID) of 1 m (100 cm) on the table bucky, and the dimensions of the radiation field were opened to cover a 17 by 14 cassette. Two out of the four protective aprons were wrapped around, and only one of the aprons had a front/back protection of 0.35/0.25 mm [Table 2]. Two exposures were made to cover the chest and abdomen-pelvic region in other not to miss out defects. Appropriate technical factor for radiographic assessment was 80 kVp on 21 mAs, and determination of transmission factor (TF) was 100 kVp on 20 mAs. The average time per exposure was 0.32 s. Images were processed using a DX-M Agfa digital system to process the latent image formed.{Table 1}{Table 2}

The second phase made use of the same X-ray unit to estimate % absorbance for each protective apron. A Perspex locally designed phantom was positioned 1 m (100 cm) away from the X-ray source. The reason for using a phantom was to create scatter radiation. Each protective apron was positioned on a T-shaped hanger, which assumed the position of the radiologist during HSG procedure. The distance from the X-ray source to the phantom was 1 m, while from the focus/X-ray source to the apron, it was 1.56 m diagonally. Using Pythagoras' theorem, the distance from the reflected light beam on the table bucky to the apron was 1.2 m. A SEI inspector USB/digital radiation detector was used. The inspector is a health and safety instrument that is operated to detect low levels of radiation between the ranges of 40 KeV to 10 MeV. It is designed to measure alpha (α)- and beta-particles (β), gamma-rays (γ), and X-ray radiation (ionizing radiation only). It has the capacity to work in milliroentgens per hour and count per minute or SI units' microsievert per hour and count per se conds. It was positioned just before the apron and in-between to determine unshielded air kerma and shielded air kerma for front and back protection, respectively. The mathematical expression for percentage absorbance is given by:

[INLINE:1]

Instantaneous dose rate (IDR) was obtained by positioning the detector at the surface of the apron to determine the unshielded air kerma and placing it few centimeters in-between the apron to determine the shielded air kerma. In the studied facility, HSGs were usually performed twice a week with one radiologist per each day. An average of ten patients was done in a week.

 Results



Images of the four aprons were achieved using conventional means (radiography). Only front areas were presented. Two out of the four protective aprons were defective. Apron D was the most defective lead apron [Figure 1], [Figure 2], [Figure 3], [Figure 4].{Figure 1}{Figure 2}{Figure 3}{Figure 4}

The dose per procedure and total annual dose rate (ADR) of the front side of apron A (0.50 mm) were 65.69 μSv/procedure and 6832 μSv/year and the back side (0.25 mm) were 347.56 μSv/procedure and 36146 μSv/year; the front side of apron B (0.35 mm) were 86.76 μSv/procedure and 9023 μSv/year and the back side (0.25 mm) were 336.89 μSv/procedure and 35037 μSv/year; apron C (0.50 mm) were 86.22 μSv/procedure and 8967 μSv/year; and apron D (0.35 mm) were 99.56 μSv/procedure and 10354 μSv/year, respectively. There was a statistically significant difference in dose rate for the aprons using a one-sample Student's t-test (P = 0.026). IDR for aprons A–D ranged from 0.739 to 3.910 μSv/h, and the ADR for a total of 104 procedures per year ranged from 6832 to 36146 μSv/year [Table 3].{Table 3}

An independent samples t-test shows that there was a statistically significant difference between the mean shielded air kerma of aprons A and C for 0.50 mm (P = 0.035). Furthermore, there was no difference between the mean shielded air kerma for aprons B and D of 0.35 mm (P = 0.679), and for 0.25 mm protective apron, there was no difference between shielded air kerma for protective aprons A and B (P = 0.407).

Apron A with lead thickness of 0.50 and 0.25 mm had an absorbance of 95.4% and 77.5%, apron B with 0.35 and 0.25 mm thickness had an absorbance of 94.4% and 78.2%, apron C with 0.5 mm thickness had an absorbance of 94%, and apron D with 0.35 mm thickness had an absorbance of 93.07% [Table 4].{Table 4}

 Discussion



The average number of years of the aprons in this study was 9.3 years. In a study by Finnerty and Brennan, protective aprons were seen to be above 2 years.[24] Similarly, the average age of 19 aprons from a study by Cohen in Johannesburg, South Africa, was 4.26 years (standard deviation = 1.12 years), with the newest being 1.5 years old and the oldest being 7.65 years old.[16] Comparison of average age shows that our study was higher. Although aprons may wear as they get older, this does not really affect their durability/effectiveness. Most of the times poor handling of this aprons tends to reduce their life span and hence their attenuating properties.

From this study, protective aprons A and C appeared to be nondefective from their radiographs, and white stains of contrast (barium sulfate) were noticed, indicating that the apron was not cleaned after use. The defect was also noticed in protective apron B at the upper part of the chest. Similarly, the arrow in [Figure 2] shows a slight defective area. Based on the investigation by Lambert and McKeon,[20] it is suggested that a protective apron be replaced if defect is seen to be ≥15 mm2, where critical organ lie and if defect is clearly not over critical organ, then the use of the apron may continue. It is imperative that the size, location and the date of the defect be documented. It is also necessary to inform wearers about the condition of any apron under further investigation or scrutiny. Apart from the above mentioned criteria, it is also recommended that defect to other parts (along stitched areas, in overlapped areas, or on the back of the protective apron) should not exceed 670 mm2. In line with our study, defective areas in apron B were not located in the pelvic region, and the defective areas were <670 mm2. Apron D showed large defective areas from the radiographs [Figure 4]a and b] at the upper and lower parts and was marked for replacement. Although before this study, visual investigation had suggested, it should be immediately replaced. The radiograph was an indication and confirmation of the extent of defects observed.

Estimated IDR to defective part from protective apron D was the highest (13.02 μSv/h), compared to other aprons. A relative dose difference of 168% was seen between affected and nonaffected areas of the same apron. The maximum ADR from a 0.25 mm protective apron was 36.15 mSv/year, which was above the international recommended value of 20 mSv/year for a radiation worker.[25] The above statement of result can only be valid if a person is to work throughout the year. In real sense, we have five radiologists which will amount to 7.23 mSv per personnel in a year. Estimation of dose per year to staff by Canevaro et al.[26] using TLDs shows that the average dose to the forehead for radiologists was 48 μSv/year; this value was 74 times lower, compared to our mean simulated phantom value (3545 μSv/year), considering if a radiologist will work 20.8 times. Differences may be as a result of the location where the detector/TLD was placed from point of scatter. Furthermore, it has been shown that for an under-table fluoroscopy unit, dose to the gonad is high, and for an over-table unit, dose to the head is high.[27] Typical dose rate levels at chest level of a surgeon by Athwal et al.[28] ranged from 4 to 20 μGy/h with mini C-arm. Our study was below their range (0.739–3.91 μSv/h). Similarly, the mean exposure from a phantom to determine shielded air kerma by Lichliter et al. was estimated at 1.48 μSv/h to the phantom which represents the personnel; this value was close to our study, where the mean value for 0.5 mm Pb was 0.855 μSv/h.[29] Based on Lichliter et al. study, exposure for all garments ranged from 0.52 to 13.8 μSv/h; our study was seen to be within their range (0.739–3.91 μSv/h). Personnel entrance surface dose from Sulieman et al. reported 180 μSv/procedure with a slight increase when an HSG is performed on conventional X-ray film (210 μSv/procedure) compared to digital imaging (140 μSv/procedure). Their study also reported staff eye lens, thyroid, and hand dose as 220, 150, and 190 μSv/procedure and with negligible dose to staff when a 0.35 and 0.50 mm Pb is worn.[30] The above results were lower than our maximum simulated value which was 347.56 μSv/procedure.

TF at 100 kVp for apron A for 0.25 mm and 0.5 mm was 22.1%–23.2% and 3.7%–4.8% and that of apron B for 0.25 mm and 0.35 mm was 20.4%–21.9% and 5.3%–6%, respectively. In the same vein, aprons C and D (0.5 and 0.35 mm thickness) were 5.6%–6.3% and 6%–6.9%, respectively. The result for 0.25 mm thickness was comparable and within the range of Lyra et al. and McGuire et al. whose values were within 20%–35%,[31],[32] but TF for this study (20%–23%) was higher than Christodoulou et al. whose range for 0.25 mm protective apron was 12%–21%.[33] TF investigation for 0.5 mm Pb in this study was 3.7%–6.3%, and this range was in line with Christodoulou et al. whose range was 3.5%–6.7% but was not in agreement with Hyun et al. (0.4%–2.2%).[34] TF of apron A with a thickness of 0.5 mm had a range of 3.7%–4.8%; Stam and Pillay result for 0.5 mm thickness was within our study (3.8%).[35] Transmission through the defective area in apron D was 80.6%, showing the extent of deterioration.

The mean radiation absorbance in a study conducted by Livingstone and Varghese[36] in India using 0.25 and 0.50 mm thickness was 90% and 97%, respectively; the value for the 0.5 mm protective apron was 2% more accurate than our result (95%). Similarly, our study was less accurate (0.5 mm: percentage absorbance ≡ 95%) compared to Bushberg et al.[37] who quoted for 0.50 mm as having an attenuation of 99%; this difference may be due to the difference in detector used (thermoluminescent dosimeter and electronic dosimeter). A good comparison was seen for 0.35 mm percentage attenuation which was >90% for this study and Bushberg. The % absorbance of the defective area was 19.44 [Figure 4]b. Lead thickness from our study had a significant impact on percentage absorbance (P < 0.001). This was similar to a related study by Daniel et al.[38] The relative difference (RD) in percentage absorbance (0.25 mm thickness) between this study and Kicken and Bos[39] and Aldridge et al.,[40] Oyar and Kışlalıoǧlu,[41] and Livingstone and Varghese[36] was ≤21%. An independent t-test shows that there was no difference in mean percentage absorbance for 0.25 mm thickness between our study and other international studies (P = 0.981). Lesser RD was observed for percentage absorbance (0.5mm of protective apron) between our study and other relevant investigations.

 Conclusion



This study has investigated the integrity of protective aprons using radiographic means, and it has also done some simulation to estimate dose to a physician performing HSG. The finding from radiographic assessment shows that individual clinical center must fashion consistent protocol to check if a protective apron is faulty or not. Similarly, the use of appropriate protective apron should be encouraged during special procedures to limit scatter dose to personnel.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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