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 Table of Contents 
ORIGINAL ARTICLE
Year : 2016  |  Volume : 39  |  Issue : 1  |  Page : 7-12  

Radiological safety survey of medical radiographic equipment


Regulatory Control Division, Radiation Protection Institute, Ghana Atomic Energy Commission, Legon, Accra, Ghana

Date of Web Publication1-Jul-2016

Correspondence Address:
Kofi Ofori
Radiation Protection Institute, Ghana Atomic Energy Commission, P. O. Box LG 80, Legon, Accra
Ghana
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-0464.185151

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  Abstract 

The areas of concern in a medical X-ray equipment are the focal spot, filtration, collimation, kVp calibration, timer accuracy, and exposure linearity, alignment of tube and image receptor, all of which impact exposure. This paper presents an analysis of historical data on 284 X-ray equipment over a 5-year period based on field measurements using well-defined protocols prepared by the National Regulatory Authority responsible for regulating the activities of users of ionizing radiation nationwide. All the data were collected and recorded for posterior analysis and subsequent preparation of quality control reports to be submitted to clients. The safety parameters assessed were the kVp accuracy, mA linearity, half-value layer, collimation accuracy, X-ray/light beam perpendicularity, and the timer accuracy. An electronic parameter such as the kVp which is important not only for radiation protection, but also for image quality showed significant improvements. Again, only 57% of conventional X-ray systems showed kVp conformity in 2010, a percentage that improved to 89% in 2014. Mobile X-ray systems showed an increase in this conformity index from 50% in 2010 to 84% in 2014. All these improvements were attributed to the continuous and extensive enforcement of the provisions of the legislation (Legislative Instrument 1559, Ghana, 1993).

Keywords: Compliance, medical X-ray, quality control, radiological safety


How to cite this article:
Ofori K, Darko EO, Owusu I. Radiological safety survey of medical radiographic equipment. Radiat Prot Environ 2016;39:7-12

How to cite this URL:
Ofori K, Darko EO, Owusu I. Radiological safety survey of medical radiographic equipment. Radiat Prot Environ [serial online] 2016 [cited 2020 Oct 30];39:7-12. Available from: https://www.rpe.org.in/text.asp?2016/39/1/7/185151


  Introduction Top


X-ray machines used primarily for diagnostic purposes in private and public medical facilities have proven to be the largest contributor of exposure of the public to ionizing radiation sources. It is estimated that 80% of the dose to the population is caused by medical diagnostic X-ray examinations. The average annual doses from diagnostic medical X-ray to the population are estimated to range from 0.3 to 2.2 mSv. [1]

According to the International Commission on Radiological Protection, all medical exposures should be guided by the radiation safety principles of justification and optimization. [2] The International Basic Safety Standards for Protection against ionizing radiation and for the safety of radiation sources, Safety Series No. GSR Part 3 [3] identifies various technical, scientific, and administrative requirements for ensuring the protection of people from exposure to ionizing radiation and the safety of radiation sources. The requirements, inter alia, include the establishment and continued maintenance of a safety culture, quality assurance program, monitoring and verification of compliance with safety requirements, safety assessment and verification of safety records, inspections, and enforcement of appropriate actions in case of noncompliances.

In the establishment of quality control (QC) program, it is required that a set of procedures for the regular and periodic testing of medical equipment and the evaluation of image quality are implemented to ensure that the radio-diagnostic imaging process is in conformity with regulations. [4],[5] In order for facilities to continuously improve to reduce costs and enhance the efficiency and quality of their services, it is recommended that they use a variety of quality systems and models, including continuous quality improvement. [6]

The Ghana Radiation Protection Board (GRPB) is the competent authority for enforcing regulatory provisions for radiation protection in the country. The body authorizes only those practices involving medical exposures that have been generically justified and ensure that the regulatory requirements are consistent with existing health care. The GRPB conducts compliance monitoring to determine whether sources are being used in accordance with the requirements of the regulations and the conditions of the authorization. The key elements of compliance monitoring include on-site inspections, radiological safety appraisals, incident notifications, and periodic feedback from users about key operational safety parameters. [7]

The GRPB has established and published an enforcement policy [8] both to encourage compliance and to correct noncompliance. This is a part of the general regulatory infrastructure established to meet the principal requirements of the Basic Safety Standards (BSS). The Safety Guide GRPB-G7 includes specific examples related to noncompliance in relation to medical exposures and the resulting enforcement action by the GRPB.

The main objective of this work is to present the summary of the data and analysis of results contained in the safety assessment reports of X-ray equipment evaluated at diagnostic facilities throughout Ghana over a 5-year-period protocols established by the GRPB. This will help in assessing the safety status and improvements achieved in regulating the medical X-ray facilities over the stipulated period.


  Materials and methods Top


The X-ray machines included for the study were those from the hospitals and diagnostic centers. The survey was conducted in conformity with the powers conferred on the GRPB. [9] Overall, 284 X-ray machines were tested for six different parameters, three of which were electrical (kVp, mA linearity, and timer accuracy) and the other three were mechanical (half-value layer [HVL], beam alignment, and collimation accuracy).

For the purpose of estimating the HVL, a Radcheck plus ionization chamber, Nuclear Associates Div. of Victoreen, Inc., USA, with serial number 0000107690 and model 06-526 and five aluminum (Al) filters (sheets) of thickness 1, 2, 3, 4 and 5 mm, respectively, were used. The ion chamber was kept at 100 cm from the X-ray target and the radiation field was collimated to ion chamber size. Without the interposition of any filter, the first exposure was made at frequently used kVp and about 15 mAs. An Al filter of 1 mm was then placed over the Radcheck plus ion chamber and the exposure was measured. The thickness of the Al filter was subsequently increased in steps from 1 to 5 mm. Each time, three exposure measurements were taken. A curve was then plotted with the mGy/mAs reading on the vertical axis and the Al filter thickness in mm on the horizontal axis after the measurements were completed. The HVL of the X-ray beam at the given kVp was evaluated in terms of Al thickness in mm from the graph. As per the available nomograms showing the relation between HVL and total filtration of the X-ray beam, the total tube filtration was determined. The acceptable limit (maximum deviation) for total filtration assessment is ≥2.3 mm Al at 80 kVp (for a total filtration of at least 2.5 mm of Al) for medical diagnostic X-ray machines. [10],[11],[12]

In assessing the kVp and timer accuracy, multi-function meter with serial number 800391-2674 and model RMI 240 A was used. The tube voltage and timer accuracies were examined for each machine. Three different exposures were taken for kV and timer accuracy, and a mean for each set of readings was recorded. The accuracy of Rx was calculated using the Equation 1: [13]



Where, Rx is the voltage or timer accuracy, Xm is the measured value of time (ms) or voltage (kV), and Xn is the nominal value of time (ms) or voltage (kV). The kVp ranges verified included kVp values from 60 to 110 kVp in steps of 10 kVp. The deviation between the kVp and time set on the control panel and measured by kVp meter was determined for ensuring the acceptance criteria of ± 5% kVp and ≤ ±10% ms, respectively. [10],[11]

The mA linearity was assessed using Radcheck plus ionization chamber, Nuclear Associates Div. of Victoreen, Inc., USA, with serial number 0000107690 and model 06-526 with focus to detector distance of 100 cm, kilovoltage from 60 to 80 kVp, and exposure time of 0.1 s. The air kerma was measured at different mAs values, and the ratio of air kerma to mAs was obtained to determine the coefficient of linearity to verify the compliance with the acceptance criteria of 0.1 [10],[11] using Equation 2: [13]



Where, X1 and X2 are the maximum and minimum values of air kerma/mAs recorded for each successive reading, respectively.

The X-ray/light beam alignment and the collimation test were verified using beam alignment and collimator test tools manufactured by Radiation Measurement Inc. Middleton, WI 53562, US, Patent D259, 406 with serial numbers 161B-5242 and 162A-4271, respectively; and a cassette with a photographic film of 10 inches ×12 inches and a speed of 200. Other equipment used included spirit level and a meter rule. The main purpose of this test was to check the coincidence of the radiation field with the light field of the light beam diaphragm (LBD) and to check that the central ray, as defined by the cross wires of the light LBD is perpendicular to the table top. The spirit level is used to ensure that the X-ray tube is parallel to table top. The collimator test tool and beam alignment test tool is placed on the top of cassette. The LBD is collimated to the inner rectangle of collimator test and must ensure that the center of the light beam coincides with steel ball bearings of beam alignment. At a focus-to-film distance (FFD) of 100 cm, the film was exposed for exposure settings of 5-10 mAs at 60 kVp, processed, and evaluated. The maximum permitted collimation error in radiation to light registration is 1 cm (within ± 1%) in any one direction at 100 cm FFD, [11] and the beam alignment errors should not exceed 2% of SID (3°). [14],[11 ]


  Results and discussions Top


Out of a total of 284 X-ray equipment verified for safety within the period, 75% of them were fixed conventional and the remaining 25% were portable. Currently, there are more than 800 diagnostic X-ray equipment functioning all over in the country. Those X-ray equipment included for the study were from all the ten regions of the country and it is suggested that this reflects the country-wide scenario.

[Table 1] shows the type of X-ray equipment assessed and the year of analysis.
Table 1: Distribution of X - ray equipment by type and year of analysis

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[Table 2] gives the acceptance criteria for the QC tests that were performed on various X-ray machines. [10],[11],[12]
Table 2: The major parameters and acceptance criteria for medical X - ray diagnostic machines

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Electronic parameters: kVp, mA, and exposure time

The electroninc parameters (kVp, mA and exposure time) are shown in [Figure 1],[Figure 2] and [Figure 3]. Considering kVp conformity in comparison with nominal and measured, in both conventional and portable X-ray systems, significant improvements were recorded for the years under review. Whereas the level of compliance for conventional machines increased from 57% in 2010 to 62% in 2011, 77% in 2012, 85% in 2013, and 89% in 2014, that of the portable systems increased from 50% in 2010 to 58% in 2011, 69% in 2012, 81% in 2013, and 84% in 2014. These improvements in conformity appeared to indicate a drastic reduction in repetition of examinations on patients thereby minimizing the risk of ionizing radiation, especially to children of younger age to whom the risk is greater.
Figure 1: kVp compliance

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Figure 2: Exposure time compliance

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Figure 3: Dose/mAs compliance

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The mAs consistency shows the linear relationship of dose values as a function of selected time and tube current. In this regard, the highlight of the outcome is on exposure time. Mobile X-ray systems often have only one current station per chosen kVp value; therefore, exposure adjustments are made based on selected irradiation time. There was improvement in the precision of exposure times in this equipment category which showed 68% in 2010 to 94% in 2014. For the fixed conventional X-ray, compliance in the accuracy of exposure time was 62% in 2010 increasing markedly to 91% in 2014.

Mechanical parameters: Half-value layer, beam alignment, and light field congruence

The mechanincal parameters (Half-value layer, beam alignment and light field congurence) are shown in [Figure 4],[Figure 5] and [Figure 6]. The HVL which is important for both radiation protection purposes and image quality showed remarked improvements. In 2010, 83% of the conventional X-ray equipment had HVL values above the recommended value of 2.3 mm Al at 80 kVp which improved to 99% in 2014. Mobile X-ray systems showed an increase in compliance from 78% in 2010 to 98% in 2014.
Figure 4: Half-value layer compliance

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Figure 5: X-ray/light beam alignment

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Figure 6: Collimation accuracy

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With regard to X-ray/light beam conformity, there was a dramatic increase from 53% in 2010 to 88% in 2014 for fixed conventional X-ray systems whereas that of portable machines increased from 58% in 2010 to 94% in 2014.

The compliance for fixed X-ray equipment in the area of beam congruence increased remarkably from 51% in 2010 to 96% in 2014 while that of the mobile systems increased from 57% to 93% in 2014.

The analysis based on the safety assessment report clearly showed that the compliance index increased over the period. This indicates that most of the parameters analyzed conform to the current standards of QC measurements and quality assurance programs as required by the regulations and the conditions of the authorization. [7] A great concern was that older equipment were still used in majority of radiological examinations and there was poor maintenance culture on the part of the operators of the facilities. Mobile equipment are used extensively in most of the hospital's Intensive Care Units, surgery rooms, and neonatal centers, where the environment frequently lacked protective barriers for workers, other patients in the same room, and the general public, which is a cause for concern. In quite a number of cases, the workers who performed the examinations in patient rooms, Intensive Care Units, and surgical centers did not have personal radiation dosimeters for future analysis of radiation exposure records.

The compilation unmistakably shows that the introduction and subsequent enforcement of regulations imposing radio-diagnostic imaging quality analysis parameters has, from 2010 to 2014, led to significant improvements in the compliance of X-ray equipment QC parameters.

The greater awareness by the diagnostic centers and hospitals for the need to adopt safety culture, societies' demand for quality processes as well as the continuing practice of the enforcement of the regulations led to significant improvements.

The current situation in the country could be improved by observing the following recommendations:

Each facility may appoint a quality manager who will be responsible for ensuring that quality checks are undertaken at specified times. The designated quality manager should also review noncompliance issues and provide strategies for corrective and preventative action in a timely manner and formulate quality improvement strategies within the department. The designated quality manager must be also responsible for the organization, dissemination, and document control of all incoming quality guidelines, policies, and directives from accrediting or regulatory bodies, local health service, and state departments of health.

There is a need to review QC results immediately and action must be taken if they are found to be out of tolerance. The service engineer may be contacted, if necessary. The urgency of remedial action by the service engineer should be determined by personal judgment. For instance, a minor failure in X-ray to light-beam alignment could be fixed at the next service visit, but anything that may affect patient dose or image quality should be addressed immediately.

The other safety and image quality tests which include the measurement of X-ray tube focal spot, grid alignment, automatic exposure control, screen-film contact, measurement of low- and high-contrast resolution, tube output (air kerma-beam area product), tube leakage, and area survey among others will be focused on in a later study.


  Conclusions Top


The establishment of regulatory infrastructure by the GRPB to meet the principal requirements of the BSS has been fundamental in ensuring the improvements of quality standards and good working conditions of the X-ray equipment and image processing conditions at the hospitals and diagnostic centers. The nonconformity issues observed at the facilities led to recommendations for corrective actions to be undertaken which improved the equipment QC standards over the years. The overall effect was that diagnostic quality improved, as well as reduction in repetitions in examinations has led to reduction in patients' exposure to radiation. Compliance with the regulations became a natural outcome of the routine at diagnostic centers when quality assurance procedures became a part of the working culture.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Bennett BG. Exposures from medical radiation world-wide. Radiat Prot Dosimetry 1991;36:237-42.  Back to cited text no. 1
    
2.
International Commission on Radiological Protection. Recommendations of the Commission on Radiological Protection ICRP Publication 60, Ann. of the ICRP 21. Oxford: Pergamon; 1990.  Back to cited text no. 2
    
3.
International Atomic Energy Agency. International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources. Safety Series, No. GSR Part 3. Vienna: IAEA; 2014.  Back to cited text no. 3
    
4.
Gray L, Dowling A, Gallagher A, Gorman D, O′Connor U, Devine M, et al. Acceptance testing and routine quality control in general radiography: Mobile units and film/screen fixed systems. Radiat Prot Dosimetry 2008;129:276-8.  Back to cited text no. 4
    
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Ertuk SM, Ondategui-Parra S, Ros PR. Quality management in radiology: Historical aspects and basic definitions. J Am Coll Radiol 2005;2:985-91.  Back to cited text no. 6
    
7.
Ghana Radiation Protection Board. Radiation Protection and Safety Guide No 9. Accra: GRPB; 2003.  Back to cited text no. 7
    
8.
Ghana Radiation Protection Board. Radiation Protection and Safety Guide No 9. Accra: GRPB; 2000.  Back to cited text no. 8
    
9.
Ghana Radiation Protection Board. Legislative Instrument 1559. Guide No 9. Accra: GRPB; 1993.  Back to cited text no. 9
    
10.
American Association of Physicists in Medicine. Quality Control in Diagnostic Radiology, Report of Task Group #12, AAPM Report No. 74; 2002.  Back to cited text no. 10
    
11.
Environment Protection Authority. Radiation Guideline 6: Registration Requirements & Industry Best Practice for Ionizing Radiation Apparatus Used in Diagnostic Imaging, Australia; 2004.  Back to cited text no. 11
    
12.
International Atomic Energy Agency. Optimization of the Radiological Protection of Patients Undergoing Radiography, Fluoroscopy and Computed Tomography. Vienna: IAEA-TECDOC-1423; 2004.  Back to cited text no. 12
    
13.
Taha TM. Study the quality assurance of conventional X-ray machines using non-invasive KV meter. Int J Sci Res 2015;4:372-5.  Back to cited text no. 13
    
14.
Moores BM, Henshaw ET, Watkinson SA, Pearcy BJ. Practical Guide to Quality Assurance in Medical Imaging. London: Wiley & Sons; 1987.  Back to cited text no. 14
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
 
 
    Tables

  [Table 1], [Table 2]



 

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