ESTIMATION OF PATIENT RADIATION DOSES FROM MULTI-DETECTOR COMPUTED TOMOGRAPHY ANGIOGRAPHY PROCEDURES IN TANZANIA.

The aim of the present study was to estimate the volume CT dose index (CTDIvol), dose length product (DLP) and effective dose (ED) to patients from five multi-detector computed tomography angiography (MDCTA) procedures: brain, carotid, coronary, entire aorta and lower limb from four medical institutions in Tanzania; to compare these doses to those reported in the literature, and to compare the data obtained with ICRP 103 and Monte Carlo software. The radiation doses for 217 patients were estimated using patient demographics, patient-related exposure parameters, the geometry of examination and CT-Expo V 2.4 Monte Carlo-based software. The median values of the CTDIvol, DLP and ED for MDCTA procedures of the brain and carotids were 36.8 mGy, 1481.0 mGy∙cm and 5.2 mSv, and 15.9 mGy, 1224.0 mGy∙cm and 7.8 mSv, respectively; while for the coronary, entire aortic, and lower limbs were 49.4 mGy, 1493.0 mGy∙cm and 30.6 mSv; 16.2 mGy, 2287.0 mGy∙cm and 41.1 mSv; and 6.4 mGy, 1406.0 mGy∙cm and 10.5 mSv, respectively. The ratio of the maximum to minimum ED values to individual patients across the four medical centers were 41.4, 11.1, 4.6, 9.5 and 37.4, respectively, for the brain, carotid, coronary, entire aortic and lower limb CT angiography procedures. The mean values of CTDIvol, DLP and ED in the present study were typically higher than the values reported from Kenya, Korea and Saudi Arabia. The 75th percentile values of the DLP were above the preliminary diagnostic references levels proposed by Kenya, Switzerland and Korea. The observed wide range of examination scanning protocols and patient doses for similar MDCTA procedures within and across hospitals; and the observed relatively high patient doses compared to those reported in the literature, call for the need to standardize scanning protocols and optimise patient dose from MDCTA procedures.

Paediatric doses during some common X-ray procedures at selected referral hospitals in Tanzania.

The aim of this study was to determine the radiation doses to paediatric patients of different age groups at three large hospitals for optimisation purposes. The entrance surface air kerma (ESAK) values were determined from the measured X-ray output values using calibrated ionisation chamber, TW 233612 and clinical patient parameters. The air kerma-area product (KAP) values were measured using a calibrated Diamentor E2 system. The volume computed tomography dose index (CTDIvol) and dose length product (DLP) values were obtained from the computed tomography (CT) equipment verified by a calibrated CT chamber, Unifors Xi CT. Irrespective of age groups, the results show that the median ESAK values ranged from 62.6 to 248.1 µGy. The median KAP values ranged from 135.6 to 1612 µGy cm(2), while the median DLP values ranged from 119.1 to 600 mGy cm. Analysis of the results indicates that optimisation can be achieved through good practice awareness and patient dose and image quality evaluations.

Assessment of patient dose and optimization levels in chest and abdomen CR examinations at referral hospitals in Tanzania.

The aim of this study was to evaluate the radiation doses to patient during chest and abdomen CR examinations, and assess the related level of optimization at five referral hospitals in Tanzania. The international code of practice for dosimetry in diagnostic radiology was applied to determine the entrance surface air kerma (ESAK) to patients. The level of optimization was assessed from low-contrast objects scores of phantom images at different exposures. The results show that mean ESAK varied from 0.16 to 0.37 mGy for chest PA and from 2 to 6 mGy for abdomen AP. Assuming similar patient and phantom attenuations, the optimization performed at all facilities was consistent with phantom evaluations in terms of tube potential settings in use. However, all facilities seemed to operate at higher tube load values above 5 mAs for chest examination, which can lead to unnecessary patient doses. Inadequate initial training on CR technology explains in large proportion the inappropriate use of exposure parameters.

A study to establish international diagnostic reference levels for paediatric computed tomography.

The article reports results from the largest international dose survey in paediatric computed tomography (CT) in 32 countries and proposes international diagnostic reference levels (DRLs) in terms of computed tomography dose index (CTDI vol) and dose length product (DLP). It also assesses whether mean or median values of individual facilities should be used. A total of 6115 individual patient data were recorded among four age groups: <1 y, >1-5 y, >5-10 y and >10-15 y. CTDIw, CTDI vol and DLP from the CT console were recorded in dedicated forms together with patient data and technical parameters. Statistical analysis was performed, and international DRLs were established at rounded 75th percentile values of distribution of median values from all CT facilities. The study presents evidence in favour of using median rather than mean of patient dose indices as the representative of typical local dose in a facility, and for establishing DRLs as third quartile of median values. International DRLs were established for paediatric CT examinations for routine head, chest and abdomen in the four age groups. DRLs for CTDI vol are similar to the reference values from other published reports, with some differences for chest and abdomen CT. Higher variations were observed between DLP values, based on a survey of whole multi-phase exams. It may be noted that other studies in literature were based on single phase only. DRLs reported in this article can be used in countries without sufficient medical physics support to identify non-optimised practice. Recommendations to improve the accuracy and importance of future surveys are provided.

Occupational radiation exposure in Tanzania (1996-2010): status and trends.

Data on occupational radiation exposure using the thermoluminescence dosimetry methodology in Tanzania for the years 1996-2010 are analysed and discussed. The results of the analysis indicate that over 80 % of the total collective dose was from diagnostic radiology. In addition, <1 % of workers received annual individual doses above 5 mSv, and there were no doses that exceeded the recommended limit of 20 mSv y(-1), except for one incidence in non-destructive testing. Furthermore, the trends in occupational exposure remained approximately constant and largely within the ranges of average doses in the literature. The status and trends in occupational exposure demonstrate that radiation protection conditions at the majority of workplace were adequate. Despite that, further optimisation is necessary due to large variations observed in the maximum individual doses over three 5-y sub-periods.

Paediatric CT examinations in 19 developing countries: frequency and radiation dose.

The aims of this study were to investigate the frequency of computed tomography (CT) examinations for paediatric patients below 15 y of age in 128 CT facilities in 28 developing countries of Africa, Asia and Eastern Europe and to assess the magnitude of CT doses. Radiation dose data were available from 101 CT facilities in 19 countries. The dose assessment was performed in terms of weighted CT dose index (CTDI(w)), volume CT index and dose length product (DLP) for chest, chest (high resolution), lumbar spine, abdomen and pelvis CT examinations using standard methods. The results show that on average the frequency of paediatric CT examinations was 20, 16 and 5 % of all CT examinations in participating centres in Africa, Asia and Eastern Europe, respectively. Eleven CT facilities in six countries were found to use adult CT exposure parameters for paediatric patients, thus indicating limited awareness and the need for optimisation. CT images were of adequate quality for diagnosis. The CTDI(w) variations ranged up to a factor of 55 (Africa), 16.3 (Asia) and 6.6 (Eastern Europe). The corresponding DLP variations ranged by a factor of 10, 20 and 8, respectively. Generally, the CTDI(w) and DLP values in Japan are lower than the corresponding values in the three regions in this study. The study has indicated a stronger need in many developing countries to justify CT examinations in children and their optimisation. Awareness, training and monitoring of radiation doses is needed as a way forwards.

Patient doses in CT examinations in 18 countries: initial results from International Atomic Energy Agency projects.

The purpose of this prospective study at 73 facilities in 18 countries in Africa, Asia and Eastern Europe was to investigate if the CT doses to adult patients in developing countries are higher than international standards. The dose assessment was performed in terms of weighted computed tomography dose index (CTDIw) and dose length product (DLP) for chest, chest (high resolution), lumbar spine, abdomen and pelvis CT examinations using standard methods. Except in one case, the mean CTDIw values were below diagnostic reference level (DRL) while for DLP, 17 % of situations were above DRLs. The resulting CT images were of adequate quality for diagnosis. The CTDIw and DLP data presented herein are largely similar to those from two recent national surveys. The study has shown a stronger need to create awareness and training of radiology personnel as well as monitoring of radiation doses in many developing countries so as to conform to the ALARA principle.

Application of European protocol in the evaluation of contrast-to-noise ratio and mean glandular dose for two digital mammography systems.

The performance of two digital mammography systems, Agfa CR75 and CRMM3 computed radiography (CR) and IMS Giotto MD direct digital radiography (DR), was assessed by applying a method recommended in the European protocol for quality control in mammography screening. The contrast-to-noise ratio (CNR) and mean glandular dose (MGD) values were measured and contrast detail (CD) analysis was performed. The CNRs for system CR were 21.9, 12.9, 9.5, 8.8, 7.4, 5.5 and 4.4 for 2, 3, 4, 4.5, 5, 6 and 7-cm polymenthylmethacrylate (PMMA) thickness, respectively. The respective CNRs for system DR were 10.4, 8.8, 6.3, 7.3, 7.2, 6.4 and 6.54. For the same phantom thickness sequence, the MGDs were 0.7, 1.1, 1.3, 1.6, 1.9, 2.5 and 3.4 mGy for system CR, whereas they were 0.7, 1.2, 1.1, 1.3, 1.8, 3.5 and 3.9 mGy for system DR. The CNR and MGD results satisfactorily correlate with CD analysis results. The MGD values compare well with the values recommended in the European protocol. Despite being simple, CNR and MGD can provide an effective system for performance assessment and constancy checks for related optimisations.

Radiation doses to patients during selected CT procedures at four hospitals in Tanzania.

The dose characteristics of CT scanners from local scanning protocols were investigated on the basis of questionnaire information provided by four hospitals conducting CT procedures in Tanzania. The information included scanner model, scanner manufacturer, number of most frequent CT examinations and the employed scanning parameters to previously diagnosed patients. For each scan technique, patient doses were estimated in terms of computerized tomography dose index, dose length product and effective dose using the software developed by the ImPACT scan group in conjunction with the NRPB conversion coefficients data. The results show that the mean CTDI_w,100, DLP and effective dose ranged from 8.5 +/- 2.8 to 79.3 +/- 23.7mGy, 145 +/- 5 to 1400 +/- 812.5 mGy cm and 3 +/- 2.3 to 15.7 +/- 10.4 mSv, respectively. On average, the observed CT doses are however roughly higher than the reported literature data such as 30 to 60 mGy, 570 to 1050 mGy cm and 2.4 to 11.7 mSv recommended by European Commission for similar CT examinations. The higher dose levels, which are possibly associated with significant risks, justify extensive similar studies at the national level in order to unify different approaches towards optimisation of CT examinations. In pursue of this noble objective, the need to train the radiology personnel, establish and using protocols and continuously monitor the performance of CT equipment to control patient CT doses is of utmost importance.

Comparison of four methods used in determination of secondary shielding requirements for a teletherapy facility: a case study of 137Cs room in Tanzania.

The performance of four methods often used to calculate the secondary barrier requirements is evaluated for a typical 137Cs-therapy room as a case study. The first two methods are provided by the NCRP49 and IAEA and both consider the influence of the primary, leakage and scattered radiation at a point as corrected for the workload, use and occupancy factors. A different shielding model encompasses the third method, which determines the doses as corrected for build-up effects assuming the narrow beam geometry. The fourth method is based on the calculation of the dose rates from the source activity with a relevant gamma constant. In all four methods, an appropriate transmission factor for the protective barrier in question is applied. The results show that for controlled area, the similarity in the calculated thicknesses using all four methods was nearly within 50%. For uncontrolled areas, a significant difference of magnitude up to a factor of 2.4 was found, which is mainly attributed to the non-consideration of occupancy factors in the latter two methods. Nevertheless, the non-agreement is useful to validate the specific assumptions taken for the employed shielding method. Despite being slightly high, it is concluded that the current shielding methods based on NCRP fundamentals are satisfactorily optimal in planning new therapy facilities. However for existing facilities, such as those undesigned according to the standard requirements, the combination of the four different methods with the dose rate measurements tend to offer a better cost effective shielding option. Retrospectively, additional 41-cm thick concrete is recommended for the unshielded southern barrier of the 137Cs room. Interestingly, the recommended thickness agrees to within +/-5% with that estimated by using the recently recommended method by IAEA.

Performance characteristics of LiF thermoluminescent dosemeters employed in the National Personnel Radiation Dose Services in Tanzania.

Thermoluminescent dosemeters (TLDs) have been used to estimate the personal dose equivalent for external occupationally exposed workers in Tanzania. The reliability and precision of dose measurements and the accuracy of dose evaluation are important factors for the improvement and achievement of individual monitoring objectives. In this piece of work we describe a study of the major characteristics of TLDs (linearity of response, photon energy response, batch homogeneity and uniformity, calibration of TLDs and TLD systems in terms of operational quantities, fading, etc) in order to initiate a routine performance testing and quality assurance programme to be undertaken by central personal dosimetry services. The energy response of the dosemeters relative to that measured using 137Cs gamma rays was found to vary between 1.0 and 1.3 over the range of 33-1250 keV (60Co). The linearity of the response for the TL dose dependence in the dose range of 0.1-30 mGy for 48 keV and 137Cs (662 keV) radiation protection qualities varied from 15% to 7% respectively, for both energies. The minimum detectable dose, the batch homogeneity and uniformity, and the batch reproducibility were found to be 0.1 mGy, 16%, and 9% respectively while the fading characteristic of doped LiF after a received dose of 3 mGy was found to be 6.3% over a one-month period. These results are discussed in order to demonstrate the degree of accuracy achieved and the need for its improvement where necessary.

Energy response of LiF:Mg, Ti dosemeters to ISO 4037 and typical diagnostic x-ray beams in Tanzania.

The energy response of three types of LiF:Mg, Ti dosemeter to standard x-ray calibration qualities and diagnostic x-rays has been studied. The aim of this study was to investigate whether the inherent mismatch between these qualities compromises the accuracy of the evaluated occupational doses in diagnostic x-ray facilities. A sample of 10 dosemeters of each type was exposed to air kerma of 5 mGy from each of six ISO 4037 (series 407) x-ray radiation protection calibration qualities (2.7 mm Al to 2.45 mm Cu HVL (half-value layer)) and 11 diagnostic x-ray qualities (1.45-4.9 mm Al HVL). The results show that the TLD energy response to ISO 4037 and diagnostic x-rays as normalised to 137Cs ranged from 1.1 to 1.44 and 0.57 to 1.54 respectively. This implies an energy response range from -52 to +7% for diagnostic x-rays relative to ISO 4037 x-rays, hence a maximum over-response of 52%. Despite this discrepancy, the results show that the mismatch between calibration and diagnostic x-ray beams does not significantly compromise the accuracy of individual doses in diagnostic x-ray facilities.

Experiences with the European guidelines on quality criteria for radiographic images in Tanzania.

Objective assessment of the quality of radiographic images is practically a difficult task and protocols that address this problem are few. In 1996, the European union published nearly objective image quality criteria to unify the practices in Europe. However, experience with these criteria in countries of lower health care levels is little documented. As a case study in Tanzania, we present the general performance of European guidelines in some Tanzanian hospitals to a total of 200 radiographs obtained from some common x-ray examinations. The results show that more than 70% of chest (PA), lumbar spine (AP), and pelvis AP radiographs passed the quality criteria, while the performance of lumbar spine LAT x-ray examinations was about 50% and therefore less satisfactory. The corresponding mean entrance dose to the patient for specified x-ray techniques was of range 0.08-0.56 mGy, 3.1-7.7 mGy, 2.53-5.4 mGy, and 4.0-16.78 mGy for chest PA, lumbar spine AP, pelvis AP, and lumbar spine LAT x-ray examinations, respectively. Although a good number of observers were not well familiar to the guidelines, the quality criteria have been found useful and their adoption in the country recommended. The need to provide relevant education and training to staff in the radiology departments is of utmost importance.

The potential for reduction of radiation doses to patients undergoing some common X ray examinations in Tanzania.

The potential for patient dose reduction in diagnostic radiology was investigated in five major Tanzanian hospitals. The aim of this study was to follow up previously reported suggestions for improved practices to achieve dose reductions. The suggestions were implemented and entrance surface dose measurement repeated by using well-calibrated LiF thermoluminescence dosemeters. The results show that dose reductions in chest PA X ray examinations ranged from 15% to 50%. For abdomen AP and pelvis AP X ray examinations, the dose reductions ranged from 24% to 73% and from 25% to 72%, respectively. The respective dose reductions for lumbar spine AP and LAT projections ranged from 4% to 58% and from 16% to 77%. Interestingly, the majority of radiographs obtained after the implementation of dose reduction measures were useful for intended diagnosis according to the opinion of radiologists. It is concluded that significant dose reductions can be achieved in the country without loss of diagnostic information. Such dose reductions also predict reductions of radiation risk to patients.