Variation In Effective Dose Research Articles

The estimation of effective radiation dose following computed tomography urography at Aminu Kano Teaching Hospital, Kano Nigeria

Background: Computed tomography urography (CTU) is an efficient radiological examination for the evaluation of urinary system disorders. However, the procedure exposes patients to a substantial amount of radiation dose associated with increased cancer risks. Objectives: To determine computed tomography (CT) dose index following CTU and to evaluate organs equivalent doses and cancer-induced risks. Materials and Method: A prospective cohort study was carried out at a tertiary health facility in Kano, Northwestern Nigeria. Ethical approval was sought and obtained. Patients Demographics scan parameters and CT radiation dose data were obtained from patients that had CTU procedure. Effective dose (ED), organ equivalent doses, and cancer risks were estimated using SPSS statistical software version 16 and CT dose calculator software. Results: A total of 56 consented patients were included in the study, consisting of 29 males and 27 females. Radiation dose data for CTU was estimated as follows: dose length product (2,320 mGy*cm), computed tomography dose index (9.67 mGy), and ED (34.5 mSv). The probability of cancer risks was also estimated to be 600 per a million CTU examinations. Conclusion: The study revealed that the radiation dose for CTU is considerably high with increase in cancer risks probability. Variations in ED between studies suggest that optimization is not fulfilled. Patient radiation dose estimate should be taken into consideration when imaging protocols are planned for CTU.

Using Age and Weight Specific CT Protocol to Estimate Reference Effective Dose to Patients Undergoing CT Examination

In x-ray computed tomography (CT), the most common parameters used to estimate and minimize patient dose is the CT dose index (CTDI) and DLP. The aim of the study is to serve as a reference values during QC for the purposes of QA in other to reduce doses to patients undergoing CT scan using the age and weight specific CT protocol set out by various manufacturers and other international organizations. This was done by recording CTDI and DLP values to patients within a specific age and weight bracket during scanning on the scanning console and on image data. The effective dose values represents an averaged dose to patients, hence the measurements are only an approximation of the dose to patient, these doses may be overestimated or underestimated by a factor of two or more with CTDI and DLP values in comparison with point dose values. CTDI and DLP were used to evaluate CT scanner output and estimating patient regional effective dose in this study. The estimated head CTDI scans base on the various protocol from all the hospitals increase from approximately 2.8mGy in newborns to approximately 8.7mGy in adults. Resulting with a variation of effective dose from 0.67mSv in new born to approximately 1.03mSv in oversize adults. Neonates head CT effective doses are higher than those for the normal adults except oversize adults as shown in Table 4.4. The chest, abdominal and pelvis CTDI values increases from 2.8, 2.5 and 2.7 mGy in neonates of approximately 3.4kg of weight to 19.84, 7.78 and 11.33mGy in adults of approximately 72.5kg of weight respectively. The estimated effective doses for neonates undergoing chest, abdomen and pelvis of the body CT were 0.83, 6.7, 4.87 and 5.52mSv, whereas those for normal-sized adults are 13.31, 4.61 and 5.34mSv respectively. Chest oversize patients’ examinations exceeded the recommended dose levels of 19.84mSv whiles the head, abdomen and pelvis were: 1.03, 7.16 and 5.98mSv respectively. It was concluded that patient body doses could be substantially minimized through careful selection of scanning parameters based on clinical indications of study, patient age, body size, and body region being examined. Additional dose reduction to superficial body regions would require the use of shielding materials.

Nuclear cardiology practice and associated radiation doses in Europe: results of the IAEA Nuclear Cardiology Protocols Study (INCAPS) for the 27 European countries.

PurposeNuclear cardiology is widely used to diagnose coronary artery disease and to guide patient management, but data on current practices, radiation dose-related best practices, and radiation doses are scarce. To address these issues, the IAEA conducted a worldwide study of nuclear cardiology practice. We present the European subanalysis.MethodsIn March 2013, the IAEA invited laboratories across the world to document all SPECT and PET studies performed in one week. The data included age, gender, weight, radiopharmaceuticals, injected activities, camera type, positioning, hardware and software. Radiation effective dose was calculated for each patient. A quality score was defined for each laboratory as the number followed of eight predefined best practices with a bearing on radiation exposure (range of quality score 0 – 8). The participating European countries were assigned to regions (North, East, South, and West). Comparisons were performed between the four European regions and between Europe and the rest-of-the-world (RoW).ResultsData on 2,381 European patients undergoing nuclear cardiology procedures in 102 laboratories in 27 countries were collected. A cardiac SPECT study was performed in 97.9 % of the patients, and a PET study in 2.1 %. The average effective dose of SPECT was 8.0 ± 3.4 mSv (RoW 11.4 ± 4.3 mSv; P < 0.001) and of PET was 2.6 ± 1.5 mSv (RoW 3.8 ± 2.5 mSv; P < 0.001). The mean effective doses of SPECT and PET differed between European regions (P < 0.001 and P = 0.002, respectively). The mean quality score was 6.2 ± 1.2, which was higher than the RoW score (5.0 ± 1.1; P < 0.001). Adherence to best practices did not differ significantly among the European regions (range 6 to 6.4; P = 0.73). Of the best practices, stress-only imaging and weight-adjusted dosing were the least commonly used.ConclusionIn Europe, the mean effective dose from nuclear cardiology is lower and the average quality score is higher than in the RoW. There is regional variation in effective dose in relation to the best practice quality score. A possible reason for the differences between Europe and the RoW could be the safety culture fostered by actions under the Euratom directives and the implementation of diagnostic reference levels. Stress-only imaging and weight-adjusted activity might be targets for optimization of European nuclear cardiology practice.

Organ and effective dose estimates for patients undergoing hepatic arterial embolization for treatment of liver malignancy

Effective dose (E) is useful as a dose index for patient exposures in interventional radiology; therefore, the authors estimated E from the kerma-area product (P(KA)) utilized during hepatic embolization interventional radiology cases performed at a cancer center and determined the variation of such doses over a representative patient population. A single-center, IRB-approved retrospective study was performed to estimate doses from consecutive hepatic embolization procedures performed during 2006. Organ doses E and E/P(KA) were determined from patient height, weight, P(KA), procedure geometry factors, beam quality, the PCXMC Monte Carlo model, and the International Commission on Radiological Protection organ weighting factors. One hundred thirteen patients were included in the study population, 72 males and 41 females, with a median age of 63 yr (29-89 yr), weight of 79 kg (42-111 kg), height of 170 cm (147-188 cm), and P(KA) of 233 Gy cm2 (9-1020 Gy cm2). E was directly correlated with P(KA) r2 = 0.8 (p < 0.01), with a median E/P(KA) of 0.18 mSv Gy(-1) cm(-2) (0.12-0.33 mSv Gy(-1) cm(-2)). The E/P(KA) ratio was inversely and exponentially correlated with weight r2 = 0.9 (p < 0.001). The median E (mSv) for the study patient population was 44 mSv (2.0-255 mSv). Values of E can be estimated utilizing patient-specific and procedure-specific parameters. The strong inverse correlation of E/P(KA) with patient weight allows simple estimation of E from P(KA) and patient weight. There is a wide variation in effective dose in oncologic hepatic embolizations with doses up to an order of magnitude higher than diagnostic imaging of the abdomen by CT radiology. Variation is likely due to patient geometry, clinical technique factors, and procedure complexity.

Radiation Exposure from CT Examinations in Japan

BackgroundComputed tomography (CT) is the largest source of medical radiation exposure to the general population, and is considered a potential source of increased cancer risk. The aim of this study was to assess the current situation of CT use in Japan, and to investigate variations in radiation exposure in CT studies among institutions and scanners.MethodsData-sheets were sent to all 126 hospitals and randomly selected 14 (15%) of 94 clinics in Gunma prefecture which had CT scanner(s). Data for patients undergoing CT during a single month (June 2008) were obtained, along with CT scan protocols for each institution surveyed. Age and sex specific patterns of CT examination, the variation in radiation exposure from CT examinations, and factors which were responsible for the variation in radiation exposure were determined.ResultsAn estimated 235.4 patients per 1,000 population undergo CT examinations each year, and 50% of the patients were scanned in two or more anatomical locations in one CT session. There was a large variation in effective dose among hospitals surveyed, particularly in lower abdominal CT (range, 2.6-19.0 mSv). CT examinations of the chest and upper abdomen contributed to approximately 73.2% of the collective dose from all CT examinations. It was estimated that in Japan, approximately 29.9 million patients undergo CT annually, and the estimated annual collective effective dose in Japan was 277.4 *103 Sv person. The annual effective dose per capita for Japan was estimated to be 2.20 mSv.ConclusionsThere was a very large variation in radiation exposure from CT among institutions surveyed. CT examinations of the chest and upper abdomen were the predominant contributors to the collective dose.

SU-GG-I-61: Variation of Effective Dose with Projection Angle during Cardiac-Catheterization Imaging

Purpose:Cardiac catheterization is a high‐dose x‐ray imaging procedure that includes several radiosensitive organs in the beam. This work demonstrates the variation of effective dose with projection angle for this procedure. Methods and Materials: ICRP 103 effective doses were calculated using PCXMC 2.0 for the geometry of simulated cardiac procedures with the Toshiba Infinix C‐Arm unit equipped with a 20 × 20 cm flat‐panel detector (FPD). With the heart at isocenter, effective dose was calculated per mAs for cranial/caudal (CRA/CAU) angles from 50° CRA to 50° CAU and left‐anterior oblique / right‐anterior oblique (LAO/RAO) projection angles from 90° LAO to 90° RAO from the posterior‐anterior (PA) direction. An estimate of view effective dose was made using technique parameters that were recorded for cardiacimaging of a Rando torso phantom at various projection angles with the unit operating under automatic brightness control. Results: Effective dose per mAs values are seen to peak at an LAO/RAO angle of about 30 degrees and drop rapidly as the beam moves more laterally, with a reduction of about 60% at 90 degrees. A decrease of about 20% is seen as the CRA/CAU angle is increased. With the phantom, there was an increase in technique parameters with increasing projection angle that tends to offset the effective dose per mAs decrease, so that the view effective dose generally increases with angle. Conclusion: The stochastic risk increment to the patient as reflected in the effective dose varies with the projection view used during the cardiac‐catheterization procedure. In general, the more that larger CRA/CAU and RAO/LAO angles are used, the greater will be the cumulative effective dose. (Support: Toshiba Medical Systems Corporation)

Diagnostic CT radiation and cancer induction

Background radiation makes up most of an individual’s exposure; however, medical sources are the largest manmade component and have been rising rapidly [1–3]. Whilst in the UK general radiology doses have decreased dramatically [4], it is only interventional and CT doses that have increased. CT use in particular has increased, and in 7 years one US Level 1 Trauma Centre increased the use of chest CT from 2.7 to 28.7% of blunt trauma cases [5]. The deterministic effects of radiation occur after a predictable threshold dose, e.g. opacification in the lens of the eye is followed by cataracts, or skin irradiation progressively produces transient erythema, temporary epilation, skin erythema, and telangiectasia to desquamation at increasing threshold doses. Random stochastic effects, which are not dependent on the threshold, include genetic mutations and carcinogenesis. The effect of radiation from CT scans depends on the field of view scanned and the sensitivity of the organs within the area. Highly radiosensitive organs include bone marrow, lung, stomach mucosa, thyroid and breast glandular tissue. Thyroid irradiation may cause hypothyroidism and thyroid cancers, particularly at a younger age [6]. Atomic bomb survivors, exposed to up to 4 Gy, have shown a linear and statistically highly significant radiation dose response, causing breast cancers [7]. The Computed Tomography Dose Index (CTDI) works out concentration units, expressed in mGy, for a procedure, depending on the total energy deposited in the patient divided by the mass of that section. Using Monte Carlo dosimetry [8], the CTDI value can be used to derive mean organ doses in a CT section in millisieverts (mSv). The effective dose (E) is the sum of the dose to individual organs, each organ dose being weighted according to the radiosensitivity, and can be converted numerically to estimate excess radiation risk. It has been recommended [9] that effective dose values be treated with caution as additional uncertainty is introduced by applying organ weighting factors, but nevertheless the effective dose quantity is a useful measure when received as an indication of relative total stochastic risk, that is, the random risk. The International Commission on Radiation Protection (ICRP) has set the nominal risk coefficient for cancer induction at 5.5% per sievert for adults [9]. Some feel that this relationship between dose and cancer risk is controversial [4]. There is a large variation in the calculated effective dose between X-ray units and CT scanners [10–12]. For example, in a recent UK national survey, the chest, abdomen and pelvis examination mean effective dose was 12 millisieverts (mSv) with a coefficient of variation of 34% for multislice scanners [10]. Variations in effective dose have also been reported for the same model of scanner because of protocol variations [13]. Modern multislice scanners are so fast that there is an inevitable tendency to scan a larger field of view (the length of the patient) than is absolutely necessary [3] and increased scanning of the whole cervical spine rather than level-specific examinations [14]. Estimation of life time cancer risks also varies widely P. J. Richards (*) X-ray Department, University Hospital of North Staffordshire NHS Trust, Princes Road, Hartshill, Stoke-on-Trent ST4 7LN Staffordshire, UK e-mail: paula.richards@uhns.nhs.uk

SU‐FF‐I‐27: CT Urography Radiation Dose Using Automatic Exposure Control

Purpose: To measure and compare patient radiation doses during CT urography with automatic exposure control (both angular and z‐axis tube current modulation) to patient radiation doses without automatic exposure control (tube current modulation alone), and to correlate these doses with corresponding image noise measurements. Method and Materials: Skin doses were measured by exposing thermoluminescent dosimeters placed on the abdomen (AP) and side (lateral position) of 18 patients examined with CT urography consisting of automatic exposure control (CARE Dose 4D group), and 20 different patients examined with angular tube current modulation only (CARE Dose group). Mean and standard deviation of patient skin doses were calculated. The CT urography protocol included three volumetric acquisitions of the abdomen and pelvis. Effective doses were calculated and used to compare radiation risk between the two patient groups. The variation in effective dose with patient size was also evaluated. Image noise was evaluated by calculating the standard deviation of pixel values from a region of interest in patient liver images. Results: The mean skin dose for CARE Dose 4D patients (63.4 ± 16.4 mGy) was 14.2% higher than that of CARE Dose patients (54.4 ± 7.39 mGy). The mean effective dose for CARE Dose 4D patients (10.6 ± 2.3 mSv) was 17.1% higher than that of CARE Dose patients (8.8 ± 1.8 mSv). Image noise increased with increasing patient size, however the increase was less for patients exposed with automatic exposure control. Conclusion: Patient effective dose, and thus radiation risk was 17.1% higher for CT urography patients examined with automatic exposure control compared to those examined with tube current modulation alone. Using automatic exposure control techniques in CT may be useful in reducing dose in small patients, however, for large patients the dose may actually increase to compensate for the increase in image noise.

Calculation of the effective dose and its variation from environmental gamma ray sources.

Effective dose, an indicator of the stochastic effect of radiation, has been widely used in dose evaluation in the environment. Though conversion factors have been used to obtain E from the air kerma or air absorbed dose, the variation of the conversion factors due to the change of exposure conditions has not been sufficiently investigated. This report documents an investigation of the variation of the effective dose per air kerma for environmental gamma rays depending on the exposure conditions using anthropomorphic phantoms and Monte Carlo calculations, taking into account the precise angular and energy distributions of the environmental gamma rays incident on the human body. As causes of the variation, posture of human bodies, biases of environmental source distributions, and body size were considered. The variation of effective dose in a prone position compared with that in a standing position was found to be within 30%. The bias of environmental sources causes the effective dose per air kerma to vary by 20% at maximum, but in some cases for low-energy gamma rays the variation was found to be up to 40% due to the change in the energy spectrum. The effective dose for a new born infant was estimated to be higher than that for an adult by a maximum of 80-90% for low-energy gamma rays from anthropogenic sources because of a lower shielding effect of the smaller body. The variation of the effective dose equivalent shows a similar tendency to the effective dose. Consequently, this study made it possible to estimate the uncertainties of effective dose and effective dose equivalent evaluated from air kerma or absorbed dose in air using the standard available conversion factors.

Indicators of matrix dependent variation in effective dose for chromium and nickel aerosol exposures

Inhaled particulates containing Cr and Ni are partially cleared or dissolved thus contributing to short-term internal exposures and partial retention in airways and airspaces. The retained fraction may continuously contribute to internal exposure after external exposure has ceased, through intra- and extracellular chemical processes which continuously liberate various metallic species; i.e. via an active deposit. Recent experiments with Ni and Cr compounds, and freshly produced welding fumes, which contain Ni and Cr, demonstrate a strong dependence of the distribution of these metals on oxidation state, solubility, bioavailability and toxicity as measured by in-vitro bioassay, depending on the collection, storage and analytical technique. It is suggested that exposure limits must consider the wide variation in short- and long-term delivered dose of toxic metals to target tissue with matrix, and that current protocols may be inadequate to protect workers in different industries involving exposures to widely different types of aerosols having only the same chemical element in common.

Effect of climatic factors on the potency of ioxynil and bromoxynil

AbstractOutdoor pot experiments, carried out between 1967 and 1971, mainly with Polygonum lapathifolium L. and Stellaria media (L.) Vill., showed that herbicidal potency of ioxynil and bromoxynil salts and esters was affected by climatic conditions, particularly solar radiation and relative humidity. Multiple regression equations were frequently obtained which accounted for 80% or more of the observed variation in effective dose (ED90). By contrast, experiments in growth cabinets suggested that air temperature was the most important climatic variable; the reasons for this disagreement are discussed. It is concluded that climatic factors affect the potency of ioxynil and bromoxynil via their influence on leaf uptake; ester formulations (emulsions) were much less affected than aqueous salt solutions.

The meaning and importance of drug potency in medicine.

The term “potency” is ambiguous, because it may refer to the quantity of drug necessary to produce a given effect, or it may refer to the maximum response which can be achieved with the drug. In the first sense, cyclopenthiazide is more potent than frusemide, and in the second sense the reverse is true. Potency cannot be measured in precise and absolute terms without detailed specification of the method of measurement, and then it becomes an excessively arbitrary measurement. Relative potency is more easily determined, but it also is variable according to the circumstances in which it is assessed. An approximate estimate of potency is afforded by the dose ordinarily used therapeutically. For some groups of drugs, variation in effective dose is enormous and for others, quite small. The causes of such variations are not well known, but probably involve the cumulation of several separate factors. Differences in maximal effect generally indicate a different mode of action and raise doubts about the strict comparability of the drugs concerned. Such differences have definite therapeutic utility. Otherwise high potency (in the sense of small effective dosage) has some advantages and some disadvantages to a therapist and is, at best, a minor merit in most circumstances.

Consideration of dose-weight relationships.

SummaryThe toxicity of alpha-naphthyl thiourea for both wild pigmented and laboratory albino rats, when expressed as a dose per animal, appears to be constant over a wide age and weight range. The use of the customary mg/kg correction for body weight introduces marked systemic variation. The requirements for a proper correction factor of dose for weight of animal are considered and it is suggested that this factor should minimize variation in effective dose between groups of animals of different weights and make corrected dose independent of body weight.