Planning and preparation in advance for radiological emergencies can help to minimise potential public health and environmental threats if and when an actual emergency occurs. During the planning process, emergency response organisations think through how they would respond to each type of incident and the resources that will be needed. In Malaysia, planning, preparation for and response to radiological emergencies involve many parties. In the event of a radiological emergency and if it is considered a disaster, the National Security Council, the Atomic Energy Licensing Board and the Malaysian Nuclear Agency (Nuclear Malaysia) will work together with other federal agencies, state and local governments, first responders and international organisations to monitor the situation, contain the release, and clean up the contaminated site. Throughout the response, these agencies use their protective action guidelines. This paper discusses Malaysian preparedness for, and response to, any potential radiological emergency.
Uranium, thorium and potassium are the most abundant naturally occurring radioactive materials (NORMs) found in soils and other environmental media including foodstuffs. Since the human exposures to NORMs is an unavoidable phenomenon, in such a way that they can easily find their way to human being via food chain, detailed knowledge on their presence in foodstuffs is necessary to assess the radiation dose to the population. Thus, the present study concerns the assessment of natural radioactivity in maize, a staple foodstuff for Nigerian, via HPGe gamma-ray spectrometry. Activity concentrations (Bq/kg) in the maize samples were found to be in the range of 6.1 ± 0.6-8.2 ± 1.3, 2.2 ± 0.4-5.1 ± 0.7 and 288 ± 16-401 ± 24 for 226Ra, 232Th and 40K, respectively. Measured data for 226Ra and 232Th show below the world average values of 67 Bq/kg and 82 Bq/kg, respectively, while the activity of 40K exceeds the global average of 310 Bq/kg. The annual effective dose via the maize consumption was found to be far below the UNSCEAR recommended ingestion dose limit of 290 μSv/y, and the estimated lifetime cancer risk show lower than the ICRP (1991) cancer risk factor of 2.5 × 10-3 based on the additional annual dose limit of 1 mSv for general public, thus pose no adverse health risk to the Nigerian populace.
This study characterises and evaluates an Al2O3:C-based optically stimulated luminescent dosemeter (OSLD) system, commercially known as the nanoDot™ dosemeter and the InLight® microStar reader, for personal and in vivo dose measurements in diagnostic radiology. The system characteristics, such as dose linearity, reader accuracy, reproducibility, batch homogeneity, energy dependence and signal stability, were explored. The suitability of the nanoDot™ dosemeters was evaluated by measuring the depth dose curve, in vivo dose measurement and image perturbation. The nanoDot™ dosemeters were observed to produce a linear dose with ±2.8% coefficient variation. Significant batch inhomogeneity (8.3%) was observed. A slight energy dependence (±6.1%) was observed between 60 and 140 kVp. The InLight® microStar reader demonstrated good accuracy and a reproducibility of ±2%. The depth dose curve measured using nanoDot™ dosemeters showed slightly lower responses than Monte Carlo simulation results. The total uncertainty for a single dose measurement using this system was 11%, but it could be reduced to 9.2% when energy dependence correction was applied.
The radioluminescent (RL) dosemeter is excellent for real-time radiation measurement and can be used in various applications. A plastic scintillator is often the choice sensor because of its size and tissue equivalency. This study aims to characterise a novel plastic scintillator irradiated with high-energy photon beams. An RL dosimetry system was developed using the plastic scintillator. The RL dosimetry system was irradiated using a linear accelerator to characterise the dose linearity, dose rate, energy dependency and depth dose. The developed system showed a linear response toward the dose and dose rate. An energy dependency factor of 1.06 was observed. Depth dose measurement showed a mean deviation of 1.21% from the treatment planning system. The response and characteristics of the plastic scintillator show that it may be used as an alternative in an RL dosimetry system.
As a reference photon field, several radionuclides have been used frequently, such as 241Am,137Cs and60 Co for calibration. These nuclides provide mono-energy photons for dosemeters covering few tens of keV-MeV. The main energy around 200 keV is important for both environmental and medical fields since the former should consider scattering photons and the later should measure photons from X-ray generator. In our previous work, a backscattered layout can provide a uniform photon field spectra and dose rate with an energy of 190 keV by using an affordable intensity 137 Cs gamma source. Several other quasi-monoenergetic photon fields in the range of 100-200 keV could be obtained by using several available gamma sources. Two calibrated environmental CsI(Tl) survey meters, Horiba PA-1000 and Mr. Gamma A2700, had been measured with the developed backscattered photon field to understand energy-dependent features in order to confirm dosemeter readings. Consequently, both scintillator instruments are sensitive for measurements of the relatively low dose rates at 190 keV.
The objective of this study is to estimate the annual effective dose for cardiologists and nurses by measuring Hp(10) and Hp(0.07) during cardiac catheterization procedures. A total of 16 staffs members were working in interventional cardiology during 1 year at a tertiary hospital. The occupational dose was measured using calibrated thermo-luminescent dosemeters (TLD-100, LiF:Mg,Ti). The overall mean and range of the annual Hp(10) and Hp(0.07) (mSv) for cardiologists were 3.7 (0.13-14.5) and 3.2 (0.21-14.7), respectively. Cardiologists were frequently exposed to higher doses compared with nurses and technologists. The exposure showed wide variations, which depend on occupation and workload. Staff is adhered to radiation protection guidelines regarding shielding the trunk, thyroid shield, thus appropriately protected. Lens dose measurement is recommended to ensure that dose limit is not exceeded.
The mass attenuation coefficients (mu/rho) of Rhizophora spp. were determined for photons in the energy range of 15.77-25.27 keV. This was carried out by studying the attenuation of X-ray fluorescent photons from zirconium, molybdenum, palladium, silver, indium and tin targets. The results were compared with theoretical values for average breast tissues in young-age, middle-age and old-age groups calculated using photon cross section database (XCOM), the well-known code for calculating attenuation coefficients and interaction cross-sections. The measured mass attenuation coefficients were found to be very close to the calculated XCOM values in breasts of young-age group.
During the years 1985-2008, the Secondary Standards Dosimetry Laboratory of Malaysia (SSDL Malaysia) has participated 37 times in the IAEA/WHO intercomparison programmes. This paper reports an analysis of the intercomparison data and demonstrates that the quality of the SSDL calibration service is well within the limits required by IAEA.
For the specific absorbed dose constant for 60Co photons, three values quoted directly in the literature and two derived indirectly from published information are reported. The three publications giving the direct values mentioned no medium of absorption, whereas the other two specify tissue. A database of the specific absorbed dose constant is generated for each of 14 media namely air, water, bone and 11 types of soft tissue. These values are consistent with the three directly quoted values plus one of the indirectly obtained values. Air is found to be unlikely as the medium for the first three; and appropriate media for these are suggested. For the other two values, the generated database suggests that one is too small to be accurate; while the other is correct for tissue (as stated in the publication). An apparent error of 10(3) is identified in one of the values directly quoted.
A femur phantom made of wax and a real human bone was used to study the dose during radiographical procedures. The depth dose inside the phantom was determined using DOSXYZnrc, a Monte Carlo simulation software. The results were verified with measurements using TLD-100H. It was found that for 2.5 mm aluminium filtered 84-kVp X-rays, the radiation dose in the bone reached 57 % higher than the surface dose, i.e. 3.23 mGy as opposed to 2.06 mGy at the surface. The use of real bone introduces variations in the bone density in the DOSXYZnrc model, resulting in a lower attenuation effect than expected from solid bone tissues.
An extensive survey was carried out for gamma dose rates (GDRs) in the Mersing district, Johor, Malaysia. The average value of GDR measured in the district was found to be 140 nGy h(-1), in the range of 40-355 nGy h(-1). The mean weighted dose rate to the population, annual effective dose equivalent, collective effective dose equivalent, lifetime cancer risk were 0.836 mSv y(-1), 0.171 mSv, 1.18 × 10(1) man Sv y(-1) and 6.98 × 10(-4) Sv y, respectively. An isodose map was produced for the district. One way analysis of variance was used to test for differences due to different geological formations present in the Mersing District.
This study has sought to evaluate patient exposures during the course of particular diagnostic positron emission tomography and computed tomography (PET/CT) techniques. A total of 73 patients were examined using two types of radiopharmaceutical: 18F-fluorocholine (FCH, 48 patients) and 68Ga-prostate-specific membrane antigen (PSMA, 25 patients). The mean and range of administered activity (AA) in MBq, and effective dose (mSv) for FCH were 314.4 ± 61.6 (462.5-216.8) and 5.9 ± 1.2 (8.8-4.11), respectively. Quoted in the same set of units, the mean and range of AA and effective dose for 68Ga-PSMA were 179.3 ± 92.3 (603.1-115.1) and 17.9 ± 9.2 (60.3-11.5). Patient effective doses from 18F-FCH being a factor of two greater than the dose resulting from 68Ga-PSMA PET/CT procedures. CT accounts for some 84 and 23% for 18F-FCH and 68Ga-PSMA procedures, accordingly CT acquisition parameter optimization is recommended. Patient doses have been found to be slightly greater than previous studies.
A study on the radiation dose associated with cerebral CT angiography (CTA) and CT perfusion (CTP) was conducted on an anthropomorphic phantom with the aim of estimating the effective dose (E) and entrance skin dose (ESD) in the eyes and thyroid gland during different CTA and CTP protocols. The E was calculated to be 0.61 and 0.28 mSv in CTA with 100 and 80 kV(p), respectively. In contrast, CTP resulted in an estimated E of 2.74 and 2.07 mSv corresponding to 40 and 30 s protocols, respectively. The eyes received a higher ESD than the thyroid gland in all of these protocols. The results of this study indicate that combining both CTA and CTP procedures are not recommended in the stroke evaluation due to high radiation dose. Application of modified techniques in CTA (80 kV(p)) and CTP (30 s) is highly recommended in clinical practice for further radiation dose reduction.
A retrospective analysis was performed in patients undergoing prospective ECG-triggered coronary computed tomography (CT) angiography (CCTA) with the single-source 64-slice CT (SSCT), dual-source 64-slice CT (DSCT), dual-source 128-slice CT and 320-slice CT with the aim of comparing the radiation dose associated with different CT generations. A total of 164 patients undergoing prospective ECG-triggered CCTA with different types of CT scanners were studied with the mean effective doses estimated at 6.8 ± 3.2, 4.2 ± 1.9, 4.1±0.6 and 3.8 ± 1.4 mSv corresponding to the 128-slice DSCT, 64-slice DSCT, 64-slice SSCT and 320-slice CT scanners. In this study a positive relationship was found between the effective dose and the body mass index (BMI). A low radiation dose is achieved in prospective ECG-triggered CCTA, regardless of the CT scanner generation. BMI is identified as the major factor that has a direct impact on the effective dose associated with prospective ECG-triggered CCTA.
This study was conducted to investigate the effectiveness of dose-saving protocols in dual-source computed tomography (CT) coronary angiography compared with invasive coronary angiography (ICA). On 50 patients who underwent coronary CT angiography was performed dual-source CT (DSCT) and compared with ICA procedures. Entrance skin dose (ESD), which was measured at the thyroid gland, and effective dose (E) were assessed for both imaging modalities. The mean ESD measured at the thyroid gland was the highest at 120 kVp, followed by the 100 kVp DSCT and the ICA protocols with 4.0±1.8, 2.7±1.0 and 1.1±1.2 mGy, respectively. The mean E was estimated to be 10.3±2.1, 6.2±2.3 and 5.3±3.4 mSv corresponding to the 120-kVp, 100-kVp DSCT and ICA protocols, respectively. The application of 100 kVp in DSCT coronary angiography is feasible only in patients with a low body mass index of <25 kg m(-2), which leads to a significant dose reduction with the radiation dose being equivalent to that of ICA.
This paper presents the results of the evaluation of the uncertainty in measurement of the personal dose equivalent, Hp(10), at nine individual monitoring services (IMSs) in Asia and the Pacific region. Different types of passive dosemeters were type-tested according to the International Electrotechnical Commission 62387 requirements. The uncertainty in measurement was calculated using the Guide to the Expression of Uncertainty in Measurement approach. Expanded uncertainties ranged between 24 and 86% (average = 38%) for Hp(10) values around 1 mSv and between 14 and 40% (average = 27%) for doses around the annual dose limit, Hp(10) = 20 mSv. The expanded uncertainties were lower than the 1.5 factor in either direction proposed by the International Commission on Radiological Protection for doses near the relevant dose limits. This indicates an acceptable level of uncertainty for all participating IMSs. Uncertainty evaluation will help the IMSs to acknowledge the accuracy of their measurements.
An intercomparison exercise (IC) on whole body dosemeters to determine the quantity personal dose equivalent Hp (10) in photon radiation fields was jointly organised and conducted by the International Atomic Energy Agency (IAEA) and the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) for individual monitoring services (IMS) in Asia and the Pacific region. This was arranged to help the IMS in the region to achieve a more accurate dosimetry service and to improve their performance. Twenty-four IMS participated in this IC. Four sets of dosemeters were irradiated using X-ray and gamma radiation qualities at 0° and 20° angle of incidence, respectively. All the IMS provided results that were within the acceptable limits defined by the IAEA. However, only a minority of participants reported confidence intervals that included the reference dose, for each exposure scenario. For few systems, the overall performance could be significantly improved by reviewing calibration procedures.
The aim of this study was to propose local diagnostic reference levels (LDRLs) for the most common computed tomography (CT) examinations (including contrast and non-contrast scan phase) performed at Advanced Medical and Dental Institute (AMDI), Universiti Sains Malaysia (USM), Malaysia. A retrospective CT dose survey of 1488 subjects from January 2015 until December 2018 was performed at AMDI USM, Malaysia. The proposed DRLs were established at 50th and 75th percentile of dose distribution for all dose metrics (CT dose index [CTDI]; CTDIvol, CTDIw and dose-length product). The proposed LDRLs were compared with national DRLs and other established DRLs. The 10 most common CT examinations at AMDI were thorax-abdomen-pelvis (TAP) CT (46%), followed by pelvis CT (17%), abdomen-pelvis CT (10%), brain/head CT (9%) and other CT protocols. The local DRLs were established using the third quartile values of dose distribution and were categorized based on CT region protocols. Most of the proposed DRLs were exceeded the national DRLs (63%) and other international DRLs (67%). From the dose auditing, almost half of the recent dose data (for year 2018) exceeded the proposed local DRLs and the unusual dose were observed in TAP, brain/head and pelvis CT examinations. The unusual higher dose could be due to higher mAs settings, higher number of scan phase for contrast study and higher pitch factor. The local DRLs should be established for dose optimization and reduction of the occurrence of excessive radiation exposure to the patients. The establishment of the Ads and LDRLs should also consider all the factors that affect the variation in DRLs such as CT technology, scanning protocols and population characteristics. The local dose distribution should always be revised for improvement of the current local practice.
Measurements of external radiation level, radon/thoron daughters concentrations in air and uranium/thorium concentrations in airborne mineral dust at 16 amang plants in Malaysia were carried out for three consecutive months to assess radiation dose to workers. Estimated occupational dose was within the range of 1.7-10.9 mSv y(-1). The mean total dose at the amang plants was 4.1 mSv y(-1). Overall, it was found that the major dose contribution of 80% came from external radiation. Radon/thoron daughters and airborne mineral dust contributed to only 11 and 9% of the total dose, respectively.