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 Table of Contents  
ORIGINAL RESEARCH REPORT
Year : 2016  |  Volume : 13  |  Issue : 4  |  Page : 167-172

Determination of reference dose levels among selected X-ray centers in Lagos State, South-West Nigeria


Department of Radiation Biology, Radiotherapy, Radiodiagnosis and Radiography, College of Medicine, Lagos University Teaching Hospital, Idi-Araba, Lagos, Nigeria

Date of Web Publication14-Oct-2016

Correspondence Address:
Akintayo Daniel Omojola
Department of Radiation Biology, Radiotherapy, Radiodiagnosis and Radiography, College of Medicine, Lagos University Teaching Hospital, Idi-Araba, Lagos
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2468-6859.192275

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  Abstract 

Background: With increasing use of diagnostic X-ray machines across Lagos, South-West Nigeria, relevant international bodies have proposed the use of reference dose levels (RDLs) to help manage radiation dose to patients without compromising image quality. Objectives: The purpose of this study was to determine the entrance surface dose (ESD) at third quartile (75 th percentile) in Lagos metropolis for normal adult radiographic examinations and to compare them with national and international established reference dose guidelines. Materials and Methods: One dedicated X-ray unit in each diagnostic center was used for this study denoted as H1-H10. A noninvasive Unfors ThinX RAD kilovoltage (kVp) meter which served as the phantom (mimicked patient) was used for measurements. The ESDs were determined by placing the Unfors ThinX RAD kVp meter on the patient's table bucky at a source to image distance (SID) of 100 cm and at the erect bucky at a SID of 180 cm. The peak tube kVp was varied at different milliampere seconds (mAs). Results : The mean ESD for adult postero-anterior (PA) chest, antero-posterior (AP) Abdomen and (AP) lumbar spine X-ray examination were 0.603, 2.57, and 2.57 mGy, respectively. While the ESD for the third quartile for adult (PA) chest, (AP) abdomen, and (AP) lumbar spine X-ray examination among the ten X-ray centers were 0.93, 2.74, and 2.47 mGy, respectively. Conclusion: Third quartile ESD which translate to RDL for adult (PA) chest examination for this study was higher compared to other national and international RDLs but adult (AP) abdomen and lumbar spine examinations were within accepted national and international range.

Keywords: Entrance surface dose, milliampere seconds, peak tube kilovoltage, reference dose levels, technical factor, third quartile


How to cite this article:
Akpochafor MO, Omojola AD, Adeneye SO, Aweda MA, Ajayi HB. Determination of reference dose levels among selected X-ray centers in Lagos State, South-West Nigeria. J Clin Sci 2016;13:167-72

How to cite this URL:
Akpochafor MO, Omojola AD, Adeneye SO, Aweda MA, Ajayi HB. Determination of reference dose levels among selected X-ray centers in Lagos State, South-West Nigeria. J Clin Sci [serial online] 2016 [cited 2020 Jul 2];13:167-72. Available from: http://www.jcsjournal.org/text.asp?2016/13/4/167/192275


  Introduction Top


In Nigeria, reports have shown that there are over 4000 X-ray machines in use with <5% of them under any form of regulatory control. [1] Research have shown that adherence to radiation protection practices among radiographers in Lagos metropolis is poor and most X-ray machines in use are quite old with no evidence of quality assurance and quality control test. [2] Of interest to us is the fact that there no standard reference dose levels (RDLs) for normal adult radiographic examinations in Nigeria, indicating that patients are either over exposed or under exposed to the effect of ionizing radiation. [3],[4],[5] A RDL is defined by the International Commission on Radiological Protection (ICRP), as a form of investigation level, applied to an easily measured quantity, usually the absorbed dose in air, or tissue-equivalent material at the surface of a simple phantom or a representative patient. [6] The ICRP has recommended the use of RDLs in diagnostic radiology. [7] It has also proposed that RDLs should be the result of optimization in radiation protection and should be used as an aid to keep doses as low as reasonably achievable principle. [8],[9],[10]

In a multinational prospective study conducted in 2008 in 12 countries involving three continents (Africa, Asia, and Eastern Europe), the mean entrance surface doses (ESDs) which translate to the country's RDL in Democratic Republic of Congo for a normal adult chest postero-anterior (PA), abdomen antero-posterior (AP), and lumbar spine (AP) X-ray examination were 0.3, 0.3, and 0.4 mGy, respectively; the respective mean ESDs in Ghana were 0.1, 10.3, and 8.3 mGy; the respective mean ESDs in Madagascar were 0.29, 3.92, and 3.92 mGy; the respective mean ESDs in Sudan were 0.21, 1.5, and 1.63 mGy; the respective mean ESDs in Tanzania were 0.3, 0.9, and 2.1 mGy; and the respective mean ESDs in Zimbabwe were 0.2, 0.6, and 0.7 mGy. In Asia, the respective mean ESDs in Iran were 0.45, 4.1, and 4.43 mGy; the respective mean ESDs in the United Arab Emirates were 0.2, 3.8, and 4.1 mGy; the respective mean ESDs in Saudi Arabia were 0.4, 8.8, and 0.8 mGy; the respective mean ESDs in Thailand were 0.18, 3.9, and 5.19 mGy. In Eastern Europe, the respective mean ESDs in Federation of Bosnia and Herzegovina were 0.07, 1.53, and 3.7 mGy; the respective mean ESDs in Serbia were 0.94, 5.8, and 10.05 mGy. [11] Other national established mean ESDs for a normal adult chest (PA), abdomen (AP), and lumbar spine (AP) X-ray in the United States were 0.25, 4.5, and 3.7 mGy (without backscatter radiation); [12],[13] the respective mean ESDs in the United Kingdom (UK) were 0.15, 4.7, and 5.0 mGy; [4] the respective mean ESDs in Australia were 0.12, 4.2, and 6.1 mGy; the respective mean ESDs in Canada were 0.11, 2.35, and 3.34; the respective mean ESDs in Finland were 0.24, 7.1, and 8.8 mGy; the respective mean ESDs in New Zealand were 0.22, 20.4, and 22.8 mGy; [14] the respective mean ESDs in Korea were 0.21, 2.33, and 2.8 mGy; [15] and finally the respective mean ESDs in Taiwan were 0.52, 4.77, and 5.91 mGy [16] . In an international proceeding held in Malaga in 2001, the International Atomic Energy Agency (IAEA) RDL for 400 − film screen for normal adult chest (PA), abdomen (AP) and lumbar spine (AP) X-ray was 0.2, 5.0 and 5.0 mGy and 200 − film screen was 0.4, 10, and 10 mGy, respectively. [17]

In the United Kingdom, the Health Protection Agency (formerly the National Radiological Protection Board) reported a 55% reduction in the third quartile (75 th percentile) of radiation dose to patients following 20 years of use of and education about Diagnostic Reference Levels (DRLs). [18]

This study was therefore carried out to determine the third quartile (75 th percentile) ESD which translate to RDL for normal adult radiographic examinations in selected X-ray centers in Lagos metropolis, South-West Nigeria and to compare these measured RDLs with national and international established reference dose guidelines.


  Materials and methods Top


In this prospective cross-sectional study carried out between June 2 nd , 2015 and October 30 th , 2015, convenience sampling technique was used to select 10 X-ray centers in Lagos metropolis. No human subject was used but rather, the Unfors ThinX RAD kilovoltage (kVp) meter served as the patient. Only X-ray centers with at least one functional X-ray machine were selected. Eight out of the ten selected centers were diagnostic based; the remaining two were hospitals that had Radiology Departments. The X-ray machine type, manufacturer and installation dates were noted [Table 1]. Furthermore, only radiographers with at least 2 years job experience were recruited. Recruited radiographers were all registered and licensed to practice in the country by radiographers' registration board of Nigeria and they all gave verbal consent to take part in the study before being recruited. A certified medical physicist carried out dose assessment in each center using the kVp Thinx RAD detector (serial number - 30001232 manufactured by Unfor). The kVp meter (Thinx RAD detector) which served as the patient/phantom was positioned at the image receptor stand (erect bucky) of source to image distance (SID) of approximately 180 cm for both PA chest and AP abdomen examinations. In similar method, the kVp meter was positioned on the patient couch (table bucky) with SID of 100 cm for AP lumbar spine X-ray [Figure 1]. The range of technical factors used for each examination was 50 − 90 kVp/11.4 − 48 mAs for PA adult chest projection, 78 − 120 kVp/16 − 75 mAs for AP adult abdomen projection and 70 − 120 kVp/16 − 75 mAs for AP adult lumbar spine projection. The above examinations were selected for this study because they were the most common requested procedure by physicians according to radiographers in each X-ray center. One international and three national guidelines were used. The results obtained were compared with IAEA; basic safety standards 1996, [19] American Association of Physicists in Medicine (AAPM) 1999, [20] UK 2002 [21] and joint effort by the American College of Radiology (ACR) and the AAPM 2014. [22] Data were analyzed using descriptive statistics by determining mean, maximum/minimum, and third quartile (75 th percentile) ESD which translate to this study RDL.
Table 1: X-ray machine product name, manufacture and installation dates

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Figure 1: Experimental setup of Unfors ThinX RAD kVp meter at 100 cm source to image distance

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  Results Top


Technical factors, national and international RDLs, and measured ESD for adult PA chest examination [Table 2] were compared to (IAEA) 1996 (with reference dose of 0.4 mGy), (AAPM) 1999 (with reference dose of 0.25 mGy), (UK) 2002 (with reference dose of 0.2 mGy) and (ACR/AAPM) 2014 (with reference dose of 0.15 mGy). X-ray center H1 (0.4 mGy), H2 (0.4 mGy), H4 (0.38 mGy), H5 (0.4 mGy), H7 (0.36 mGy) and H9 (0.24 mGy) had doses ≤ 0.4 mGy. X-ray center H6 had a dose of 0.71 mGy and H10 had a dose of 1.0 mGy. Highest doses were recorded in X-ray center H3 and H8 (1.07 mGy), respectively.
Table 2: Technical factors, national and international reference dose level and measured entrance surface dose for adult postero-anterior chest examination

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In a similar way, the technical factors, national and international RDLs, and measured ESD for normal adult AP abdomen [Table 3] were compared to (IAEA) 1996 (with reference dose of 10.0 mGy), (AAPM) 1999 (with reference dose of 4.5 mGy), (UK) 2002 (with reference dose of 6.0 mGy) and (ACR/AAPM) 2014 (with reference dose of 3.4 mGy). X-ray center H4 had the highest dose (6.26 mGy). The least dose was recorded in X-ray center H1 (0.7 mGy).
Table 3: Technical factors, national and international reference dose level and measured entrance surface dose for adult antero-posterior abdomen examination

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In addition, technical factors, national and international RDLs, and measured ESD for normal adult AP lumbar spine [Table 4] were compared to (IAEA) 1996 (with reference dose of 10.0 mGy), (AAPM) 1999 (with reference dose of 5.0 mGy), (UK) 2002 (with reference dose of 6.0 mGy) and (ACR/AAPM) 2014 (with reference dose of 4.2 mGy). Measured ESDs from H1 to H10 were 0.56 mGy, 1.61 mGy, 2.38 mGy, 8.39 mGy, 2.5 mGy, 2.71 mGy, 0.86 mGy, 2.26 mGy, 1.32 mGy, and 2.12 mGy, respectively.
Table 4: Technical factors, national and international reference dose level and measured entrance surface dose for adult antero-posterior lumbar spine examination

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The mean ESD among the ten X-ray centers for adult PA chest examination was 0.603 mGy. Adult AP abdomen and lumbar spine examination was 2.57 mGy. The ratio of maximum to minimum dose for PA chest was 4.46 mGy. AP abdomen and lumbar spine were 8.94 and 14.98 mGy, respectively [Table 5].

Measured RDLs for this study were compared well with other reference guidelines [Table 6]. Third quartile (75 th percentile) RDL for adult PA chest examination with reference dose of 0.93 mGy was compared with four established reference dose guidelines in a bar chart [Figure 2]. Similar comparison was made with a bar chart for AP abdomen examination with reference dose of 2.74 mGy [Figure 3] and AP lumbar spine examination with reference dose of 2.47 mGy [Figure 4].
Table 6: Comparison of this study reference dose level with national and international reference dose level for adult postero-anterior chest, antero-posterior abdomen and antero-posterior lumbar spine examinations

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Figure 2: Comparison of this study third quartile entrance surface dose (reference dose level) with other guidelines for adult postero-anterior chest examination

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Figure 3: Comparison of this study third quartile entrance surface dose (reference dose level) with other guidelines for adult antero-posterior abdomen examination

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Figure 4: Comparison of this study third quartile entrance surface dose (reference dose level) with other guidelines for adult antero-posterior lumbar spine examination

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Table 5: Mean, maximum/minimum and ratio of maximum to minimum entrance surface dose for adult postero-anterior chest, antero-posterior abdomen and antero-posterior lumbar spine examinations

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  Discussion Top


This study revealed that normal adult PA chest examination in X-ray center H1, H2, H4, H5, H7, and H9 [Table 2] passed IAEA 1996 guideline (60%). X-ray center H9 was the only center that passed AAPM 1999 guideline (10%). None of the centers in this study met UK 2000 and ACR/AAPM 2014 for PA chest examination. The mean ESDs in X-ray center H3, H6, H8 and H10 were the above established reference dose guidelines of (IAEA) 1996, (AAPM) 1999, (UK) 2002 and (ACR/AAPM) 2014, indicating that 40% of the total chest examinations did not meet national and international reference dose guidelines. For PA chest examination, 60% met the international guidelines and only 10% met national guidelines. The reason why 60% met international guideline was because of the flexibility that exists in IAEA 1996 guideline. Only 10% met national guideline as was seen in X-ray center H9 with technical factor of 100 kVp on 12.8 mAs, which was close to the WHO-recommended factors for adult PA chest examination. [23]

The mAs range for adult PA chest examination for this study was between 35.2 and 48, which was higher than Johnston and Brennan with range of 0.99 − 20 mAs, Ng et al. with range of 2 − 30 mAs and Paydar et al., whose mAs range for 3 hospitals were 5 − 8 mAs, 8 − 13 mAs and 1 − 2.1 mAs, respectively. [24],[25],[26] The primary reason why two-fifth (40%) of the total adult PA chest examination in this study was higher than recommended guidelines was attributed to higher mAs technique used by most radiographer in these centers which in turn increased the mean ESDs. [27] Although the kVp values for this study ranged from 50 to 100 showing more consistency on the lower boundary with those of Johnston and Brennan and Ng et al., whose kVps ranged from 52-150 to 55-125, respectively. [24],[25] The kVp for this study was consistent with Paydar et al. whose kVp range among the three hospital was 60 − 110. [26]

Johnston and Brennan and Ng et al. third quartile RDLs for chest were 0.3 mGy, respectively, compared to 0.93 mGy for this study for chest examination. [24],[25] Mean ESD for adult PA chest examinations in three hospitals (Osogbo, Ibadan, and Ijebu-Ode) in South-Western Nigeria in a related study by Olowookere were (1.37 ± 0.85) mGy, (0.32 ± 0.01) mGy and (0.61 ± 0.41) mGy. This study mean ESD range (0.24 − 1.07 mGy) was consistent with two out of three of the hospitals used. Mean ESD for PA chest in Osogbo was higher than that obtained in this study. [28]

X-ray center H1, H2, H3, H5, H7, H8, H9 and H10 were ≤3.4 mGy, indicating that 80% of these centers were within established reference dose guidelines for AP abdomen examination. X-ray center H6 met all established reference dose guidelines except (ACR/AAPM) 2014, which was a more recent study. X-ray center H4 was only able to meet up with (IAEA) 1996. It was observed that the kVp for this study ranged from 78 to 120 which was higher than those of Johnston and Brennan and Ng et al. whose kVps ranged from 64-90 to 60-85, respectively. [24],[25] More difference was seen in mAs values in this study (16 − 75 mAs) against those obtained by Johnston and Brennan (7.08 − 288 mAs) and Ng et al. (13 − 100 mAs). [24],[25] The reason for this success achieved for adult AP abdomen (with 80% pass) was attributed to the choice of technical factors used by radiographer, since organs within the abdominal region have similar densities. [23]

Nine centers out of ten for AP lumbar spine examination met both national and international guidelines [Table 4] except X-ray center H4 which only met (IAEA) 1996 reference dose guidelines. This indicated that 90% of the center passed the established reference dose guidelines. The kVp values ranged from 70 to 120; these values were higher compared to kVp values of 64 − 84 and 60 − 90 from other related studies. [24],[25] Similar to what was obtained for AP abdomen, the mAs for AP lumbar spine was as relatively high (16 − 75) against higher mAs of (7.08 − 288) and (13 − 100) in related studies. [24],[25] This 90% fit was achieved due to proper choice of technical factors used by radiographers in this region of the body where higher kVp is needed for deep penetration of the lumbar spine with relatively high mAs for good contrast.

The mean ESD for this study for PA chest examination was 0.603 mGy; this value was much higher than Johnston and Brennan, Ng et al. and Škrk et al., whose mean doses were 0.219, 0.28, and 0.29 mGy, respectively. [24],[25],[29] Although mean AP abdomen examination for this study was 2.57 mGy which was quite lower than Johnston and Brennan, Ng et al. and Škrk et al. whose mean doses were 4.7, 10.0, and 4.43 mGy, respectively. [24],[25],[29] In a similar manner, AP lumbar spine examination had a mean dose 2.57 mGy which was quite lower when compared with Johnston and Brennan, Ng et al. and Škrk et al. whose mean doses were 6.42, 10.56, and 6.06 mGy, respectively. [24],[25],[29] The above results indicated that the mean dose for AP abdomen and lumbar spine showed good correlation with already established reference dose guidelines. The maximum/minimum ratio for this study ranged between factors of 4.46 and 14.98. This range was seen to be consistent with Johnston and Brennan whose maximum/minimum ratio ranged between factors of 3 and 23. [24]

The third quartile (75 th percentile) for adult PA chest examination was higher compared to other established guidelines [Figure 2], indicating that dose optimization in most of the centers where compromised since chest examination is one of the most common examination performed in most of the X-ray centers. The third quartile (75 th percentile) for adult AP abdomen and lumbar spine examinations were below national and international guidelines, showing that technical factors were properly optimized.


  Conclusion Top


This study has been able to determine ESDs which translate to local RDLs for common radiographic examinations in selected X-ray centers in Lagos metropolis, South-West Nigeria, and it has also compared them with established guidelines. The study found out that most adult PA chest examinations were higher when compared to the established guidelines. This indicated that most mAs technical factors for adult PA chest examination used by radiographers need to be reviewed in most of the centers for better optimization. However, AP abdomen and lumbar spine examination were within accepted range, indicating that the technical factors used should be sustained and improved on.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]



 

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