Survey of computed tomography scanners in Taiwan: Dose descriptors, dose guidance levels, and effective doses

Patient effective dose and radiation biological risk in the chest and abdominopelvic computed tomography

The incidence and mortality (per 100,000) rates in chest CT are highest for the lungs and breasts (incidence: lung = 116, breast = 98.64; mortality: lung = 113.43, breast = 49.72). Abdominopelvic CT scans showed the highest incidence for stomach (79.57), colon (62.86), bladder (48.69), and liver (28.63), respectively. Mortality is highest for the bladder (80.44), stomach (72.43), colon (69.02), and liver (63.78), respectively. This study helps to better understand the concept of radiation dose and the numbers reported as organ dose and effective dose and identify the probability of the stochastic effect.

Evaluation of the dual vascular supply patterns in ground-glass nodules with a dynamic volume computed tomography

BACKGROUND

In recent years, the detection rate of ground-glass nodules (GGNs) has been improved dramatically due to the popularization of low-dose computed tomography (CT) screening with high-resolution CT technique. This presents challenges for the characterization and management of the GGNs, which depends on a thorough investigation and sufficient diagnostic knowledge of the GGNs. In most diagnostic studies of the GGNs, morphological manifestations are used to differentiate benignancy and malignancy. In contrast, few studies are dedicated to the assessment of the hemodynamics, i.e., perfusion parameters of the GGNs.

AIM

To assess the dual vascular supply patterns of GGNs on different histopathology and opacities.

METHODS

Forty-seven GGNs from 47 patients were prospectively included and underwent the dynamic volume CT. Histopathologic diagnoses were obtained within two weeks after the CT examination. Blood flow from the bronchial artery [bronchial flow (BF)] and pulmonary artery [pulmonary flow (PF)] as well as the perfusion index (PI) = [PF/(PF + BF)] were obtained using first-pass dual-input CT perfusion analysis and compared respectively between different histopathology and lesion types (pure or mixed GGNs) and correlated with the attenuation values of the lesions using one-way ANOVA, student’s t test and Pearson correlation analysis.

RESULTS

Of the 47 GGNs (mean diameter, 8.17 mm; range, 5.3-12.7 mm), 30 (64%) were carcinoma, 6 (13%) were atypical adenomatous hyperplasia and 11 (23%) were organizing pneumonia. All perfusion parameters (BF, PF and PI) demonstrated no significant difference among the three conditions (all P > 0.05). The PFs were higher than the BFs in all the three conditions (all P < 0.001). Of the 30 GGN carcinomas, 14 showed mixed GGNs and 16 pure GGNs with a higher PI in the latter (P < 0.01). Of the 17 benign GGNs, 4 showed mixed GGNs and 13 pure GGNs with no significant difference of the PI between the GGN types (P = 0.21). A negative correlation (r = -0.76, P < 0.001) was demonstrated between the CT attenuation values and the PIs in the 30 GGN carcinomas.

CONCLUSION

The GGNs are perfused dominantly by the PF regardless of its histopathology while the weight of the BF in the GGN carcinomas increases gradually during the progress of its opacification.

Differences in clinical and imaging presentation of maxillary sinus fungus ball with and without intralesional hyperdensity

Maxillary sinus fungal balls (MSFBs) mostly occur in older individuals and demonstrate female predominance. Early diagnosis is important to avoid treatment delays. Intralesional hyperdensity (IH) indicates the presence of heavy metal deposition within fungal hyphae and has been the most specific characteristic of MSFB on computed tomography (CT). For those without IH on CT, the diagnosis of MSFB remains challenging. This study aimed to characterize clinical presentation of MSFB with and without IH and to study factors contributing to MSFB with no IH formation. We retrospectively identified 588 patients with MSFB. The clinical characteristics and CT findings were reviewed. Patients with unilateral MSFB had a mean age of 57.4 years and demonstrated female predominance (64.63%). The female-to-male ratio was highest at 51–60 years (2.02) and rose to 2.60 in MSFB with IH only. Compared to those with IH, MSFB without IH was significantly more common in males (OR = 2.49), in those with diabetes mellitus (DM) (OR = 1.87), adjacent maxillary odontogenic pathology (OR = 1.75). Complete opacification on CT was less common in MSFB without IH (OR = 0.60). Patients with MSFB without IH were more likely to have DM, no female predominance, adjacent maxillary odontogenic pathology, and partial opacification of the sinus, compared to those with IH. These may be helpful in better understanding of the formation of MSFBs without IH, early identification of them and prevention of post-operative recurrence.

A systematic review on the current status of adult diagnostic reference levels in head, chest and abdominopelvic Computed Tomography

Computed tomography (CT) is a routinely employed diagnostic tool for the detection and diagnosis of disease processes. Despite the primary focus of radiation dose reduction and improvements in CT scanners, radiation dose exposure remains an ever-increasing concern. Scanning protocol optimisation relative to body weight and scanner manufacturer still lags behind the diagnostic reference levels (DRLs) that are set on an international scale. The aim of this systematic review is to evaluate the current status of adult DRLs in head, chest and abdominopelvic CT over time on a global scale. A search was carried out in early 2019 using the Medline, PubMed, EMBASE, SCOPUS and manual databases. The reference lists of published articles were also assessed to identify further articles. The preferred reporting items for systematic reviews and meta-analyses (PRISMA) methodology was employed to evaluate articles for relevance. Articles were included if they assessed the DRL in head, chest and abdominopelvic scans. The search resulted in 6079 articles, of which 67 were included after a thorough screening process. The literature demonstrates a wide dose variation in reported head, chest and abdominopelvic dose length product (DLP) DRL, ranging from 700-1359, 330-707 and 550-1486 mGy·cm, respectively. Where reported, the volumed CT dose index (CTDI_vol) DRL in the head, chest and abdominopelvic studies ranged from 30.4-85.5, 9-15 and 12.3-31 mGy·cm, respectively. The global means were shown to be slightly lower and significantly lower than the reported values of DLP and CTDI_vol values for the American College of Radiology and European Commission, respectively. This review emphasises the need for an international standardisation for head and body DRL establishment methods, to provide a more comparable global measurement of dose variations across CT sites as well as regular monitoring of delivered radiation dose to patients.

Radiation doses with various body weights of phantoms in brain 128-slice MDCT examination

The effective dose (HE) and organ or tissue equivalent dose (HT) for use in brain computed tomography (CT) examinations with various body weights were evaluated. Thermoluminescent dosimeters (TLD-100H) were inserted into Rando and five anthropomorphic phantoms. These phantoms were made of polymethylmethacrylate (PMMA), according to the specifications of ICRU 48, with masses from 10 to 90 kg. Brain CT examinations were conducted, scanning the maxillae from the external auditory meatus to the parietal bone using a 128-slice multi-detector CT (MDCT) scanner. To reduce errors, three independent trials were conducted. Calculated HE,TLD, based on the weighting factor recommended by ICRP 103, was 1.72 ± 0.28 mSv, which slightly exceeds the HE,DLP of 1.70 mSv, that was calculated from the dose-length product (DLP) of the Rando phantom. This experiment yielded HE,TLD values of ICRP 103 from the highest 1.85 ± 0.28 (90 kg) to the lowest 1.47 ± 0.22 (10 kg) mSv. HE,TLD (mSv) = 5.45×10-3 W(kg) + 1.361, with an R2 of 0.87667. Using the DLP protocol, HE,DLP was estimated from CTDIvol that was recorded directly from the console display of the CT unit and multiplied by the conversion coefficient (k) recommended by the ICRP 103. Finally, the experimental results obtained herein are compared with those in the literature. Physicians should choose and adjust protocols to prevent the exposure of patients to unnecessary radiation, satisfying the as low as reasonably achievable (ALARA) principle. These findings will be valuable to patients, physicians, radiologists and the public.

Multisection computed tomography: Results from a Chinese survey on radiation dose metrics

BACKGROUND

As multisection spiral computed tomography (MSCT) have been extensively used, it is important to consider the amounts of doses the patients are exposed during a computed tomography (CT) examination. The aim of the current study was to summarize MSCT doses in Chinese patients to establish the diagnostic reference levels (DRLs).

METHODS

Radiation dose metrics were retrospectively collected from 164,073 CT examinations via the Radimetrics Enterprise Platform. Radiation dose metrics (volume CT dose index [CTDIvol], dose-length product [DLP], effective dose [ED], and organ dose) and size-specific dose estimate (SSDE) were calculated for adults and children based on anatomic area and scanner type.

RESULTS

The median CTDIvol and DLP values were highest in the head at 51.7 mGy (interquartile range [IQR], 33.2-51.7 mGy) and 906.5 mGy·cm (IQR, 582.4-1068.2 mGy·cm) and lowest in the chest at 7.9 mGy (IQR, 7.9-10.3 mGy) and 284.8 mGy·cm (IQR, 249.0-412.6 mGy·cm), respectively. The median SSDE values of chest and pelvis were 12.1 mGy (IQR, 10.8-14.1 mGy) and 36.3 mGy (IQR, 34.0-38.9 mGy), respectively. EDs for children were similar to adults except for an increased 1.5-, 0.77-, and 1.7-fold in the chest, neck, and pelvis, respectively (p < 0.001). Furthermore, radiation doses tended to increase with increasing slice number and decrease when exposure reduction techniques were used.

CONCLUSION

Our findings provide a basis for the evaluation of CT radiation doses and evidence for establishment of DRLs in China.

Topogram-based tube current modulation of head computed tomography for optimizing image quality while protecting the eye lens with shielding

BACKGROUND

Multiple rounds of head computed tomography (CT) scans increase the risk of radiation-induced lens opacification.

PURPOSE

To investigate the effects of CT eye shielding and topogram-based tube current modulation (TCM) on the radiation dose received by the lens and the image quality of nasal and periorbital imaging.

MATERIAL AND METHODS

An anthropomorphic phantom was CT-scanned using either automatic tube current modulation or a fixed tube current. The lens radiation dose was estimated using cropped Gafchromic films irradiated with or without a shield over the orbit. Image quality, assessed using regions of interest drawn on the bilateral extraorbital areas and the nasal bone with a water-based marker, was evaluated using both a signal-to-noise ratio (SNR) and contrast-noise ratio (CNR). Two CT specialists independently assessed image artifacts using a three-point Likert scale.

RESULTS

The estimated radiation dose received by the lens was significantly lower when barium sulfate or bismuth-antimony shields were used in conjunction with a fixed tube current (22.0% and 35.6% reduction, respectively). Topogram-based TCM mitigated the beam hardening-associated artifacts of bismuth-antimony and barium sulfate shields. This increased the SNR by 21.6% in the extraorbital region and the CNR by 7.2% between the nasal bones and extraorbital regions. The combination of topogram-based TCM and barium sulfate or bismuth-antimony shields reduced lens doses by 12.2% and 27.2%, respectively.

CONCLUSION

Image artifacts induced by the bismuth-antimony shield at a fixed tube current for lenticular radioprotection were significantly reduced by topogram-based TCM, which increased the SNR of the anthropomorphic nasal bones and periorbital tissues.

Dose Comparison Using Thermoluminescent Dosimeters During Multislice Computed Tomography With Different Parameters for Simulated Spine Tumor Examination

This study aims to compare the effect of Philips' Brilliance 64-slice and 256-slice (multislice) computed tomography on effective doses when changing the operating parameters for simulated examinations of patients' spine tumors, including changes in pitch, tube voltage (kV), and effective tube current-time product (mA s). This study considers the possibility of using other probable operating conditions to reduce patients' effective doses. The absorbed doses to organs and skin are measured by taking data from thermoluminescent dosimeters (GR-200 and GR-200F) in relevant positions on the anthropomorphic Rando phantom. We also used an American College of Radiology computed tomography accreditation phantom to experiment with image spatial resolution under various scan conditions in order to achieve results over 5 line pairs per cm, the analytical capability required to meet diagnostic needs. The results show that, in general, when we change the pitch, effective tube current-time product, and tube voltage, the effective doses from 256-slice computed tomography exceed those from 64-slice computed tomography.

ESTIMATION OF FEMALE RADIATION DOSES AND BREAST CANCER RISK FROM CHEST CT EXAMINATIONS

Breast organ doses, effective doses and lifetime attributable risk (LAR) of breast cancer from chest CT scans are presented for 200 female patients surveyed from 10 hospitals in the West Bank and Gaza Strip, Palestine. Patient data were collected and organized in a database from May to November 2016. Data include age (15-80 years), weight, height, and calculated body mass index. Exposure data were also recorded for every examination. Exposure data includes milliampere-second (mAs), X-ray tube kilovoltage (kVp), computed tomography dose index, dose length product, manufacturer, name and type of operated CT scanner. Organ and effective doses were evaluated using a web-based commercially available Monte Carlo software: VirtualDose™CT, a product of Virtual Phantoms, Inc. The software utilizes male and female tissue equivalent phantoms of all ages and sizes including pregnant patients. The corresponding phantom was selected for every patient according to patient's tomographic parameters. Calculated organ doses were used to estimate the LAR of breast cancer according to BEIR VII Phase 2 report. It was found that radiation doses resulting from the same exam vary widely between different hospitals, depending on the parameters used and the type of scanner. For all patients, the breast organ dose ranged from 6.5 to 28 mGy per examination, with an average breast organ dose of 15 mGy. The effective dose from chest CT scan per examination ranged from 3 to 14.7 mSv with an average of 7 mSv. For younger females (15-29 years), the LAR of breast cancer risk was estimated to be around 0.05%. For older female patients (60-79 years), the risk was ~0.001%. It was found that LAR decreases remarkably with patient's age. Values obtained in this study vary between hospitals, they are generally low and consistent with other studies reported worldwide.

Survey of Thoracic CT Protocols and Technical Parameters in Korean Hospitals: Changes before and after Establishment of Thoracic CT Guideline by Korean Society of Thoracic Radiology in 2008

We retrospectively reviewed the thoracic CT scan protocols and technical parameters obtained from hospitals in Korea, one group during May 2007 (n = 100) and the other group during January 2012 (n = 173), before and after the establishment of the thoracic CT Guideline in 2008. Each group was also divided into two subgroups according to the health care delivery level, i.e. the "A" subgroup from primary and the "B" subgroup from secondary and tertiary care hospitals. When comparing the data from 2007 and 2012, the tube current decreased from 179.1 mAs to 137.2 mAs. The scan interval decreased from 6.4 mm to 4.8 mm. Also, the insufficient scan range decreased from 19.0% to 8.7%, and the suboptimal quality scans decreased from 33.0% to 5.2%. Between groups A and B, group B had lower tube voltages, smaller scan thicknesses, and smaller scan intervals. However, group B had more phase numbers. In terms of the suboptimal quality scans, a decrease was seen in both groups. In conclusion, during the five-year time period between 2007 and 2012, a reduction in the tube current values was seen. And the overall image quality improved over the same time period. We assume that these changes are attributed to the implementation of the thoracic CT guideline in 2008.

Patient dose for computed tomography examination: dose reference levels and effective doses based on a national survey of 2013 in Korea

14,620 sets of patient dose data were obtained for 31 different models of computed tomography (CT) equipment (total 73) with 18 types of CT examination in Korea. Specific diagnostic reference levels (DRLs) for this study in terms of third quartile volumetric CT dose index in mGy [and dose-length product (DLP) in mGy.cm] are as follows: head, 53 (910); neck, 20 (770); chest, 14 (710); abdomen, 14 (1000); stomach, 14 (1000); liver, 14 (1700); pancreas, 14 (1700); kidney, 14 (2100); cervical spine, 30 (600); lumbar spine, 25 (760); hip, 17 (600); cardiac CT angiography, 45 (1250); head CT angiography, 43 (1900); liver CT angiography, 14 (1400) and thoraco-abdominal CT angiography, 16 (2000). In the present study, DRLs in terms of volumetric CT dose index were below previously published reference levels, partly because the newer CT equipments have improved technology that facilitates lower patient dose. Meanwhile, DRLs in terms of DLP were higher, because multi-phase scanning protocols with prolonged scan coverage have been widely used.

A survey of organ equivalent and effective doses from diagnostic radiology procedures

The quantification of radiation risks associated with radiological examinations has been a subject of interest with the increased use of X-rays. Effective dose, which is a risk-weighted measure of radiation to organs in the body associated with radiological examination, is considered a good indicator of radiological risk. We have therefore investigated patient effective doses from radiological examinations. Organ and effective doses were estimated for 94 patients who underwent computed tomography examinations and for 338 patients who had conventional radiography examinations. The OrgDose (version 2) program was used for the estimation of effective doses. The tube potential ranges: 57 kVp to 138 kVp depending on the examination and patient size. The entrance surface doses have a wide range even for the same examination: 0.44-10.31 mGy (abdomen) and 0.66-16.08 mGy (lumbar spine) and the corresponding effective dose ranges 0.025-0.77 mSv and 0.025-0.95 mSv respectively. Effective dose for adult abdomen-pelvic CT examinations ranges 5.4-19.8 mSv with a mean of 13.6 mSv and for pediatrics ranges 2.1-5.5 mSv with a mean of 2.7 mSv. The mean effective dose for adult chest and head CT examinations are 7.9 and 1.8 mSv respectively and for pediatrics are 1.7 and 1.1 mSv.

Lung cancer perfusion: can we measure pulmonary and bronchial circulation simultaneously?

OBJECTIVE

To describe a new CT perfusion technique for assessing the dual blood supply in lung cancer and present the initial results.

METHODS

This study was approved by the institutional review board. A CT protocol was developed, and a dual-input CT perfusion (DI-CTP) analysis model was applied and evaluated regarding the blood flow fractions in lung tumours. The pulmonary trunk and the descending aorta were selected as the input arteries for the pulmonary circulation and the bronchial circulation respectively. Pulmonary flow (PF), bronchial flow (BF), and a perfusion index (PI, = PF/ (PF + BF)) were calculated using the maximum slope method. After written informed consent was obtained, 13 consecutive subjects with primary lung cancer underwent DI-CTP.

RESULTS

Perfusion results are as follows: PF, 13.45 ± 10.97 ml/min/100 ml; BF, 48.67 ± 28.87 ml/min/100 ml; PI, 21 % ± 11 %. BF is significantly larger than PF, P < 0.001. There is a negative correlation between the tumour volume and perfusion index (r = 0.671, P = 0.012).

CONCLUSION

The dual-input CT perfusion analysis method can be applied successfully to lung tumours. Initial results demonstrate a dual blood supply in primary lung cancer, in which the systemic circulation is dominant, and that the proportion of the two circulation systems is moderately dependent on tumour size.

KEY POINTS

A new CT perfusion technique can assess lung cancer's dual blood supply. A dual blood supply was confirmed with dominant bronchial circulation in lung cancer. The proportion of the two circulations is moderately dependent on tumour size. This new technique may benefit the management of lung cancer.

CT radiation dose optimization and estimation: an update for radiologists

In keeping with the increasing utilization of CT examinations, the greater concern about radiation hazards from examinations has been addressed. In this regard, CT radiation dose optimization has been given a great deal of attention by radiologists, referring physicians, technologists, and physicists. Dose-saving strategies are continuously evolving in terms of imaging techniques as well as dose management. Consequently, regular updates of this issue are necessary especially for radiologists who play a pivotal role in this activity. This review article will provide an update on how we can optimize CT dose in order to maximize the benefit-to-risk ratio of this clinically useful diagnostic imaging method.

Population dose from medical diagnostic exposure in Taiwan

Medical exposure showed a continuous increasing trend. This trend was due to the growth of diagnostic procedures such as computed tomography (CT) and interventional fluoroscopy (IVF). In the present work, results of a recent study on medical exposure in Taiwan are reported. This study analysed data from the National Health Insurance Research Database. Surveyed data on the dose indices, including the entrance surface dose in radiography, dose area product in fluoroscopy, CT dose index in CT and mean glandular dose in mammography, were applied. Using programmes and databases, dose indices were converted to the effective dose. For the year 2008, individual effective doses in Taiwan were estimated as 0.16, 0.37, 0.12 and 0.12 mSv for conventional radiography and fluoroscopy, CT, IVF and nuclear medicine, respectively. The total collective effective dose and the effective dose per individual for medical exposure were 17 788 person-Sv and 0.77 mSv, respectively.

A review of patient dose and optimisation methods in adult and paediatric CT scanning

An increasing number of publications and international reports on computed tomography (CT) have addressed important issues on optimised imaging practice and patient dose. This is partially due to recent technological developments as well as to the striking rise in the number of CT scans being requested. CT imaging has extended its role to newer applications, such as cardiac CT, CT colonography, angiography and urology. The proportion of paediatric patients undergoing CT scans has also increased. The published scientific literature was reviewed to collect information regarding effective dose levels during the most common CT examinations in adults and paediatrics. Large dose variations were observed (up to 32-fold) with some individual sites exceeding the recommended dose reference levels, indicating a large potential to reduce dose. Current estimates on radiation-related cancer risks are alarming. CT doses account for about 70% of collective dose in the UK and are amongst the highest in diagnostic radiology, however the majority of physicians underestimate the risk, demonstrating a decreased level of awareness. Exposure parameters are not always adjusted appropriately to the clinical question or to patient size, especially for children. Dose reduction techniques, such as tube-current modulation, low-tube voltage protocols, prospective echocardiography-triggered coronary angiography and iterative reconstruction algorithms can substantially decrease doses. An overview of optimisation studies is provided. The justification principle is discussed along with tools that assist clinicians in the decision-making process. There is the potential to eliminate clinically non-indicated CT scans by replacing them with alternative examinations especially for children or patients receiving multiple CT scans.

Radiation Dose from Diagnostic Computed Tomography in Saskatchewan

Objective

To calculate the effective dose from diagnostic computed tomography (CT) scans in Saskatchewan, Canada, and compare with other reported dose levels.

Methods

Data from CT scans were collected from 12 scanners in 7 cities across Saskatchewan. The patient age, scan type, and selected technique parameters including the dose length product and the volume computed tomography dose index were collected for a 2-week period. This information then was used to calculate effective doses patients are exposed to during CT examinations. Data from 2,061 clinically indicated CT examinations were collected, and of them 1,690 were eligible for analysis. Every examination during a 2-week period was recorded without selection.

Results

The average provincial estimated patient dose was as follows: head, 2.7 mSv (638 scans; standard deviation [SD], ±1.6); chest, 11.3 mSv (376 scans; SD, ±8.9); abdomen-pelvis, 15.5 mSv (578 scans; SD, ±10.0); abdomen, 11.7 mSv (80 scans; SD, ±11.48), and pelvis, 8.6 mSv (18 scans; SD, ±6.04). Significant variation in dose between the CT scanners was observed ( P = .049 for head, P = .001 for chest, and P = .034 for abdomen-pelvis).

Conclusions

Overall, the estimated dose from diagnostic CT examinations was similar to other previously published Canadian data from British Columbia. This dose varied slightly from some other published standards, including being higher than those found in a review conducted in the United Kingdom in 2003.

Overview of patient dosimetry in diagnostic radiology in the USA for the past 50 years

This review covers the role of medical physics in addressing issues directly related to patient dosimetry in radiography, fluoroscopy, mammography, and CT. The sections on radiography and fluoroscopy radiation doses review the changes that have occurred during the last 50 to 60 years. A number of technological improvements have contributed to both a significant reduction in patient and staff radiation doses and improvements to the image quality during this period of time. There has been a transition from film-screen radiography with hand dip film processing to electronic digital imaging utilizing CR and DR. Similarly, fluoroscopy has progressed by directly viewing image intensifiers in darkened rooms to modern flat panel image receptor systems utilizing pulsed radiation, automated variable filtration, and digitally processed images. Mammography is one of the most highly optimized imaging procedures performed, because it is a repetitive screening procedure that results in annual radiation exposure. Mammography is also the only imaging procedure in the United States in which the radiation dose is regulated by the federal government. Consequently, many medical physicists have studied the dosimetry associated with screen-film and digital mammography. In this review, a brief history of mammography dose assessment by medical physicists is discussed. CT was introduced into clinical practice in the early 1970s, and has grown into one of the most important modalities available for diagnostic imaging. CT dose quantities and measurement techniques are described, and values of radiation dose for different types of scanner are presented. Organ and effective doses to adult patients are surveyed from the earliest single slice scanners, to the latest versions that include up to two x-ray tubes and can incorporate as many as 256 detector channels. An overview is provided of doses received by pediatric patients undergoing CT examinations, as well as methods, and results, of studies performed to assess the radiation absorbed by the conceptus of pregnant patients.

On the use of Monte Carlo-derived dosimetric data in the estimation of patient dose from CT examinations

The purpose of this work was to investigate the applicability and appropriateness of Monte Carlo-derived normalized data to provide accurate estimations of patient dose from computed tomography (CT) exposures. Monte Carlo methodology and mathematical anthropomorphic phantoms were used to simulate standard patient CT examinations of the head, thorax, abdomen, and trunk performed on a multislice CT scanner. Phantoms were generated to simulate the average adult individual and two individuals with different body sizes. Normalized dose values for all radiosensitive organs and normalized effective dose values were calculated for standard axial and spiral CT examinations. Discrepancies in CT dosimetry using Monte Carlo-derived coefficients originating from the use of: (a) Conversion coefficients derived for axial CT exposures, (b) a mathematical anthropomorphic phantom of standard body size to derive conversion coefficients, and (c) data derived for a specific CT scanner to estimate patient dose from CT examinations performed on a different scanner, were separately evaluated. The percentage differences between the normalized organ dose values derived for contiguous axial scans and the corresponding values derived for spiral scans with pitch = 1 and the same total scanning length were up to 10%, while the corresponding percentage differences in normalized effective dose values were less than 0.7% for all standard CT examinations. The normalized organ dose values for standard spiral CT examinations with pitch 0.5-1.5 were found to differ from the corresponding values derived for contiguous axial scans divided by the pitch, by less than 14% while the corresponding percentage differences in normalized effective dose values were less than 1% for all standard CT examinations. Normalized effective dose values for the standard contiguous axial CT examinations derived by Monte Carlo simulation were found to considerably decrease with increasing body size of the mathematical phantom used. When the body-mass index was increased from 23.0 to 32.7 kg/m2 discrepancies in patient effective dose were up to 34%. The error in estimating effective dose from a CT exposure performed on a specific CT scanner using Monte Carlo data derived for a different CT scanner was estimated to be up to 25%. A simple method was proposed and validated for the determination of scanner-specific normalized dosimetric data from data derived from Monte Carlo simulation of a specific scanner. In conclusion, computed tomography dose index (CTDI) to effective dose conversion coefficients derived by Monte Carlo simulation of axial CT scans may provide a good approximation of corresponding coefficients applicable in helical scans. However, the use of Monte Carlo conversion coefficients for the estimation of patient dose from a CT examination involves a remarkable inaccuracy when the body size of the mathematical anthropomorphic phantom used in Monte Carlo simulation differs from the body of the patient. Therefore, separate sets of Monte Carlo dosimetric CT data shall be generated for different patient body sizes. Besides calculation of different sets of Monte Carlo data for each commercially available scanner is not necessary, since scanner specific data may be derived with acceptable accuracy from the Monte Carlo data calculated for a specific scanner appropriately modified for the different CTDI(W)/CTDI(air) ratio.