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International Journal of Engineering & Technology IJET-IJENS Vol: 12 No: 06 109 An Attempt to Establish National Dose Reference Levels for Head CT-Scan Examinations in Indonesia: Preliminary Results from Malang Hospitals Johan Andoyo Effendi Noor and Indrastuti Normahayu Abstract— CT-scanners are becoming more and more popular imaging modality amongst medical practitioners as their tools for diagnostic practices. Yet, since CT-scanners employ ionizing x-ray beam as the source of imaging light, protection against its damaging effects must be observed closely to ensure that the harmful effects to patients are minimum. Our study involved three Departments of Radiology in three major hospitals in the city of Malang, East Java, Indonesia. We took at least 100 (50 males and 50 females) patients who were sent to the department CT facility to have non-contrast head CT examination in each hospital. The effective dose of each patient was calculated using the CTDosimetry version 1.0.4 dose calculator software. Our results reveal that the effective doses received by patients were in range 1.25 – 2.51 mS v for male patients and 1.14 – 2.39 mS v for female patients. In general, male patients received more doses than the female counterparts as predicted. Index Term— CT-scanner, ionizing x-ray beam, radiodiagnostic, medical imaging I. INT RODUCT ION X–RAYS are invisible rays at a frequency band between 3 × 1016 Hz to 3 × 1019 Hz and an energy band between 100 eV to 100 keV in the spectrum of electromagnetic waves. With such energy x-rays are capable of penetrating objects and ionized the objects in its path. X-rays have been used in many fields, including the military, security, indus trial, and health. In medical world x-rays are used in the field of diagnostics (radiodiagnostic) and therapy (radiotherapy). In the field of diagnostic x-rays are used to image internal organs of human body (medical imaging) and in the field of therapy x-rays are used to kill cancer cells (such as with a linear accelerator machine). Overall, x-rays share over 70% of ionizing radiation J.A.E. Noor is with the Department of Physics, Faculty of Mathematics and Natural Sciences, Brawijaya University, Jl. Veteran 2, Malang 65145, Indonesia (corresponding author, phone:+62 -341575833; fax:+62-341-575834; e-mail: jnoor@ ub.ac.id). I. Normahayu is with the Department of Radiology, Faculty of Medicine, Brawijaya University, Jl. Veteran 2, Malang 65145 and the Department of Radiology, Dr Saiful Anwar Public Hospital, Malang 65122, Indonesia (e-mail: [email protected]). used in medical field globally. In further developments, along with the development in computer technology and programming algorithms, in the 1970s, Sir Godfrey N. Hounsfield, a British engineer invented a computed tomography (CT) scanner to make a tomographic image of the human body interior transversely using x-ray. The first image was generated from the CT scan of brain on 1October 1971 and presented to the public on 20 April 1972 at the 32nd Congress of the British Institute of Radiology [1] and later published in 1973 [2-4]. At the same time Allen McLeod Cormack, a South African American, wrote an algorithm for CT image reconstruction [5]. The advent of computed tomography (CT) has revolutionized diagnostic radiology. Since its inception in the 1970s, CT has been used intensively and demand for this imaging modality has increas ed rapidly. It is estimated that more than 62 million CT scans per year currently take place in the United States, including at least 4 million in pediatric [6]. By its nature, CT involves larger radiation doses from the more common x-ray conventional imaging procedures (Table I). Thus the risk of cancer in patients as a consequence of the use of ionizing radiation is also elevating. Although the risk for everyone is small and not uniform, the increased radiation exposure to public becomes health concern, now and in the future. The radiation dose received by the patient depends on the magnitude of the x-ray intensity and duration of exposure. Typical radiation dose for adult posterior-anterior (PA) chest radiography is about 0.02 mSv (2 mrem) and 0.04 mSv (4 mrem) for lateral imaging, with dose received by the lung is given in Table II. While in CT scanning, the effective dose received by patients undergoing chest examination is about 7 mSv [7], which is about 175-350 times higher than the conventional xray radiography. Low-dose radiation carries cancer risk to patients receiving it [7-13] and the possibility of deterministic effects, such as skin injury [14], temporary bandage-shaped hair loss [15], as well as leukemia and brain tumors [16]. 127606-1515 IJET-IJENS © December 2012 IJENS IJENS International Journal of Engineering & Technology IJET-IJENS Vol: 12 No: 06 T ABLE I T YP ICAL ORGAN RADIATION DOSES FROM VARIOUS RADIOLOGICAL STUDIES. T ype of Study Relevant Organ Relevant Organ Dose* (mGy or mSv) 0.005 0.01 Dental Radiography Brain Posterior-anterior chest Lung radiography Lateral chest radiography Lung 0.15 Mammography screening Breast 3 Adult abdominal CT Stomach 10 Barium enema Colon 15 Neonatal abdominal CT Stomach 20 * Radiation dose, a measure of the ionizing energy absorbed per unit of mass, expressed in gray (Gy) or milligray (mGy), 1 Gy = 1 joule per kilogram. T he radiation dose is often expressed as an equivalent dose in unit of sievert (Sv) or millisievert (mSv). For x-ray radiation, which is the type of radiation used in CT scanners, 1 mSv = 1 mGy.. From the technology side, CT-scanner has experienced rapid development, both in the aspect of hardware and software. All the developments are intended to minimize the dose received by the patient while accelerating the process of data acquisition and image reconstruction. In addition, in radiation protection the principle of ALARA (As Low As Reasonably Acceptable), the principle of minimizing the radiation dose while maintaining the produced image quality, must always be observed [17]. The first CT scanner was capable of producing a single slice image with 2 minutes scan time and 20 minutes image reconstruction. Improvements were made to reduce gantry rotation time of only 2 seconds for a complete rotation (360º). In the latest development CT-scanner has employed a MSMD (multi-slice multi-detector) technique [18] and AEC (Automatic Exposure Control) that is able to work under 2 minutes to produce an image up to 128 slices and reducing the dose by 10-60% [19-21]. The difference between the doses received by patients undergoing conventional scanning (fixed tube current) and scanning using AEC is illustrated in Fig. 1. Fig. 1. Illustration of dose profiles generated by a fixed current machine compared to dose generated by a scanner with an automatic exposure control (taken from reference [20]). In total, the dose of AEC scanner is smaller than the dose of a conventional scanner. The use of CT scan procedure is to obtain the internal image of the object of interest for diagnostic and treatment purposes. Reconstructed image quality depends on a number of factors 110 that will determine the level of dose received by the patient. Thus, in the end there is a need to optimize the dose level while keeping the image quality acceptable [22-24]. Many studies have been conducted to determine the safe doses for both local and national standards [25-36]. Effective dose (ED) is a measure to express and compare the radiation dose given to patients of various CT-scanner machines introduced by the ICRP in 1977 [37] and is defined as the sum of weighted dose to the tissue known to be sensitive to radiation as (1) H E wT HT with wT is the specific tissue or organ weighting coefficient (T), HT is the equivalent dose to tissue T, and HE is the sum of the product wT • HT. In the publication number 102, ICRP provides an estimate for the effective dose using the relationship [37, 38], (2) DE k DLP –1 –1 with k (mSv.mGy .cm ) is an empirical weighting factor, which is independ on the type of machine and specific to a particular area of the body. This formulation is also used in the dose calculation software CTDosimetry version 1.0.4 created by the imPACTscan group [39] which was used in this study. The software calculates the dose using Monte Carlo simulation techniques [40-42]. This paper discusses the results of our study in estimating the doses received by patients undergoing CT imaging examination procedures at three major hospitals in Malang that operate single slice CT-scanners with fixed current mode and automatic mode as well as a multi slice scanner, to see if the doses received by patients were below the recommended value of the ICRP (International Commission on Radiological Protection) published in its Publication No. 103 [12] and the Indonesian Government Regulation No. 63 year 2000 on Occupational Safety and Health in Utilization of Ionizing Radiation, article 5, paragraph 1 that states: "If there are multiple nuclear energy facilities in a single location, the employers must observe lower dose level for each installation, so the cumulative dose does not exceed the threshold dose". II. SUBJECT S AND M ET HODS Patients Routine head CT scans are common examinations performed in hospitals. We have collected CT data of three groups of 100 patients (50 males and 50 females) sent to the Departments of Radiology in three major hospitals in Malang. The data used in this study were obtained from patients having head CT procedures from April up to October 2011 in the participating hospitals. The age of the patients ranged from 17 to 87 years of age. Imaging Techniques The CT examinations were performed with a General Electric (GE) HiSpeed DX/i system in Hospital A, a Siemens Somatom Spirit in Hospital B, and a Siemens Somatom Emotion6 in 127606-1515 IJET-IJENS © December 2012 IJENS IJENS International Journal of Engineering & Technology IJET-IJENS Vol: 12 No: 06 Hospital C. Dosimetry Data Dosimetry data were obtained from image headers of the image series. The information extracted included: acquisition date and time, manufacturer and model name, study description, patient age and sex, tube voltage (kVp), protocol name, series information, slice thickness (mm), tube current (mA), exposure time (s), scan length (cm), CTDIvol (mGy), and DLP (mGy.cm). CT organ doses were obtained using the ImPACT CTDosimetry software package ver. 1.0.4 (27/05/2011) [39] that calculates dose for irradiation of a mathematical head phantom as depicted in Fig. 2 which uses CT dosimetry data generated by the National Radiological Protection Board [40-42]. See Fig. 2 for the phantom model used in the ImPACT calculation. 111 currents also vary. The CTDI values were averaged from the MSAD (Multiple Scan Average Dose). The MSAD is an average dose parameter in CT examination. The BAPETEN (The Indonesia Nuclear Energy Regulatory Agency) set the threshold of an adult MSAD to 50 mGy. The average CTDI for male patients were 43.35 mGy and 40.48 mGy for female patients. Therefore the CTDI values in Hospital A Malang are below the threshold. Fig. 3. Chart relating patients’ age to CT DIvol (mGy) for Hospital A. The effective dose for each age group is charted in Fig. 4. The effective dose is the radiation exposure received by the patient during the CT examination procedure. The effective dose was calculated using the CTDosimetry spreadsheet and referred to the ICRP (International Commission on Radiological Protection) publication No. 103. The average effective dose was 1.32 mSv and 1.21 mSv for male and female patients, respectively. Fig. 2. T he ImpACT scan CT Dosimetry software showing the phantom set up used in this study. T he scan was made to the head, started at 80 cm and ended at 94 cm (within the pink shaded area). T he effective dose calculation can be selected using the organ weighting scheme of ICRP -60 or ICRP-103. III. RESULT S AND DISCUSSION Analyses were conducted over a 100-patient group having head scans between April 2011 and October 2011 in each participating hospital. The results from each hospital are discussed below. Hospital A The GE CT scanner installed in Hospital A utilizes an adaptive tube current technique. The current supplied to the xray tube and the CTDIvol calculations for the patient age group are presented in Fig. 3. The CTDIvol ranged from 38.93 mGy to 45.54 mGy. It is shown that the CTDI values vary since the tube Fig. 4. T he bar chart of the average effective dose (mSv) received by the patients in the age group in Hospital A. Hospital B The CT-scanner employed in Hospital B is a Siemens Somatom Spirit. Unlike the machine in Hospital A that utilizes an adaptive current supply, the Siemens used a fixed current mode. In this mode, the magnitude of the current supplied to the scanner is constant throughout the examination, which is 240 mA. Therefore the CTDIvol also is constant, 47.5 mGy. The effective dose calculation used the similar software and ICRP 127606-1515 IJET-IJENS © December 2012 IJENS IJENS International Journal of Engineering & Technology IJET-IJENS Vol: 12 No: 06 112 recommendation. The results are graphed in Fig. 5. The average effective doses are 1.38 mSv and 1.32 mSv for male and female patients, respectively. Fig. 6. T he bar chart of the average effective dose (mSv) received by the patients in the age group in Hospital C. Fig. 5. T he bar chart of the average effective dose (mSv) received by the patients in the age group in Hospital B. T ABLE II COMP ARISON OF THE AVERAGE EFFECTIVE DOSE FOR MALE P ATIENTS IN THE THREE P ARTICIP ATING HOSP ITALS VALCULATED ACCORDING TO THE ICRP RECOMMENDATION NO . 103 Hospital C The CT-scanner in Hospital C is of the same manufacturer as the Hospital B, only the type is different. The scanner in Hospital C is Siemens Somatom Emotion6 that capable of reconstructing six slices of image in one single rotation. The tube current used in the head examination is 140 mA and 2 s rotation time. This makes the mAs parameter of the scanner 280 mAs and gives a constant CTDIvol of 47 mGy. The calculation of the effective dose also used the ICRP recommendation 103. The results are provided in Fig. 6. The average effective doses are 2.06 mSv and 1.93 mSv for male and female patients, respectively. Effective Dose Comparison The scanners employed in the three participating hospitals are categorized into two groups: fixed current, that is represented by the scanners of Siemens Healthcare and adaptive current that is represented by the scanners of General Electric (GE) Healthcare. The fixed current system uses a constant current to the x-ray generator tube, whilst the adaptive current system adjusts the current supplied to the tube according to the thickness of the object being imaged. The latter system is aimed to reduce the radiation exposed to the patients, thus reducing the radiation effects. The effective doses from the three scanners investigated in the research are tabulated in Tables II and III for male and female patients, respectively. Age (y.o.) Hosp A 1.34 1.41 1.25 1.34 1.25 1.25 ≤30 31-40 41-50 51-60 61-70 >71 Effective Dose (mSv) Hosp B 1.40 1.36 1.39 1.38 1.38 1.34 Hosp C 2.21 2.31 2.39 2.51 2.23 2.14 T ABLE III COMP ARISON OF THE AVERAGE EFFECTIVE DOSE FOR FEMALE P ATIENTS IN THE THREE P ARTICIP ATING HOSP ITALS VALCULATED ACCORDING TO THE ICRP RECOMMENDATION NO . 103 Age (y.o.) ≤30 31-40 41-50 51-60 61-70 >71 Hosp A 1.25 1.14 1.15 1.17 1.24 1.20 Effective Dose (mSv) Hosp B 1.28 1.32 1.34 1.32 1.33 1.33 Hosp C 1.92 2.39 2.38 2.36 2.28 2.31 It is revealed that the GE scanner produced a lower dose compared to the Siemens scanners. It shows that the adaptive current scanner is safer that its counterparts that utilize fixed current technique. IV. CONCLUSION Our study reveals that, as predicted, the multislice machine (i.e. of Hospital C) produces higher dose to patients (2.06 mSv and 1.93 mSV for male and female patients, respectively) than that of single slice (i.e. 1.32 mSv and 1.21 mSV for male and female patients, respectively in Hospital A and 1.38 mSv and 1.32 mSV for male and female patients, respectively in Hospital B); and the fixed current machine (i.e. of Hospital B) emits higher radiation than that of adaptive current machine (i.e. of Hospital A). We also found that, in general, female patients received lower dose than male patients. The recommendation we would like to propose is the use of 2.0 127606-1515 IJET-IJENS © December 2012 IJENS IJENS International Journal of Engineering & Technology IJET-IJENS Vol: 12 No: 06 mSv threshold as the local dose reference for CT head examinations in hospitals in Greater Malang district. Further research is required to extend the area coverage in order to establish a national reference. A CKNOWLEDGMENT This research was funded by the Directorate General of Higher Education (DGHE), Ministry of Education and Culture through the DIPA of Brawijaya University Rev. 1 No: 0636/02304.2.16/15/2011 R, dated 30 March 2011 and the letter of DP2M DGHE No: 121/D3/PL/2011 dated 7 February 2011. The authors would like to thank radiographers at the participating hospitals for the supply of the image data. [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [16] [17] [18] REFERENCES [1] [15] E. C. Beckmann, "CT scanning the early days," British Journal of Radiology, vol. 79, pp. 5-8, 2006. J. Ambrose, "Comput erized transverse axial scanning (tomography): Part 2. Clinical application," British Journal of Radiology, vol. 46, pp. 1023-1047, 1973. J. Ambrose and G. N. Hounsfield, "Computerized transverse axial tomography," British Journal of Radiology, vol. 46, pp. 148-149, Feb 1973. 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