Evaluating lead-free alternatives for radiation shielding in diagnostic radiology: a case study from a tertiary general hospital in Korea

With the continued increase in the number of pieces of diagnostic medical radiography equipment being used, radiation shielding in radiology departments is becoming increasingly important. Lead is the most commonly used material for radiation protection; however, there are numerous disadvantages associated with the use of lead, including environmental hazards and harm to the human body. Alternative shielding materials that can be used as replacements include barium sulfate, tungsten, or bismuth. Among alternative materials, barium sulfate appears to be the most cost-effective and easiest to process. In the present study, before constructing shielding barriers, a barrier thickness program for lead-free barrier materials based on National Council on Radiation Protection and Measurements (NCRP) Report No. 147 was used to determine the appropriate barrier thickness. The required thickness for lead-free boards for each type of diagnostic radiography room was calculated based on a tertiary general hospital in the Republic of Korea.

The determination of coefficients for size specific effective dose for adult and pediatric patients undergoing routine computed tomography examinations

The effective dose resulting from computed tomography (CT) scans provides an assessment of the risk associated with stochastic effects but does not account for the patient's size. Advances in Monte Carlo simulations offer the potential to obtain organ dose data from phantoms of varying stature, enabling derivation of a size-specific effective doses (SEDs) representing doses to individual patients. This study aimed to compute size-specific k-conversion factors for SED in routine CT examinations for adult and pediatric patients of different sizes. Radiation interactions were simulated for adult and pediatric phantom models of various sizes using National Cancer Institute CT version 3.0.20211123. Subsequent calculations of SED were performed, and coefficients for SED were derived, considering the variations in body sizes. The results revealed a strong correlation between effective diameter and weight, observed with size-specific k-conversion factors for adult and pediatric phantoms, respectively. While size-specific k-conversion factors for CT brain remained constant in adults, values for pediatric cases varied. When using the tube current modulation (TCM) system, size-specific k-conversion factors increased in larger phantoms and decreased in smaller ones. The extent of this increase or decrease correlated with the set TCM strength. This study provides coefficients for estimating SEDs in routine CT exams. Software utilizing look-up tables of coefficients can be used to provide dose information for CT scanners at local hospitals, offering guidance to practitioners on doses to individual patients and improving radiation risk awareness in clinical practice.

Assessment of knee instability in ACL-injured knees using weight-bearing computed tomography (WBCT): a novel protocol and preliminary results

OBJECTIVE

To propose a protocol for assessing knee instability in ACL-injured knees using weight-bearing computed tomography (WBCT).

MATERIALS AND METHODS

We enrolled five patients with unilateral chronic ACL tears referred for WBCT. Bilateral images were obtained in four positions: bilateral knee extension, bilateral knee flexion, single-leg stance with knee flexion and external rotation, and single-leg stance with knee flexion and internal rotation. The radiation dose, time for protocol acquisition, and patients' tolerance of the procedure were recorded. A blinded senior radiologist assessed image quality and measured the anterior tibial translation (ATT) and femorotibial rotation (FTR) angle in the ACL-deficient and contralateral healthy knee.

RESULTS

All five patients were male, aged 23-30 years old. The protocol resulted in a 16.2 mGy radiation dose and a 15-min acquisition time. The procedure was well-tolerated, and patient positioning was uneventful, providing good-quality images. In all positions, the mean ATT and FTR were greater in ACL-deficient knees versus the healthy knee, with more pronounced differences observed in the bilateral knee flexion position. Mean lateral ATT in the flexion position was 9.1±2.8 cm in the ACL-injured knees versus 4.0±1.8 cm in non-injured knees, and mean FTR angle in the bilateral flexion position was 13.5°±7.7 and 8.6°±4.6 in the injured and non-injured knees, respectively.

CONCLUSION

Our protocol quantitatively assesses knee instability with WBCT, measuring ATT and FTR in diverse knee positions. It employs reasonable radiation, is fast, well-tolerated, and yields high-quality images. Preliminary findings suggest ACL-deficient knees show elevated ATT and FTR, particularly in the 30° flexion position.

CNN application for automated determination of the patient's size to obtain the size-specific dose estimated in CT

Introduction. The currently available dosimetry techniques in computed tomography can be inaccurate which overestimate the absorbed dose. Therefore, we aimed to provide an automated and fast methodology to more accurately calculate the SSDE usingDwobtained by using CNN from thorax and abdominal CT study images.Methods. The SSDE was determined from the 200 records files. For that purpose, patients' size was measured in two ways: (a) by developing an algorithm following the AAPM Report No. 204 methodology; and (b) using a CNN according to AAPM Report No. 220.Results. The patient's size measured by the in-house software in the region of thorax and abdomen was 27.63 ± 3.23 cm and 28.66 ± 3.37 cm, while CNN was 18.90 ± 2.6 cm and 21.77 ± 2.45 cm. The SSDE in thorax according to 204 and 220 reports were 17.26 ± 2.81 mGy and 23.70 ± 2.96 mGy for women and 17.08 ± 2.09 mGy and 23.47 ± 2.34 mGy for men. In abdomen was 18.54 ± 2.25 mGy and 23.40 ± 1.88 mGy in women and 18.37 ± 2.31 mGy and 23.84 ± 2.36 mGy in men.Conclusions. Implementing CNN-based automated methodologies can contribute to fast and accurate dose calculations, thereby improving patient-specific radiation safety in clinical practice.

Patient-specific Effective Dose Estimation from Dose-Length Product in Lung Computed Tomography Using Monte Carlo Simulation

Background

Computed tomography (CT) imaging has a large portion in the dose of patients from radiological procedures; therefore, accurate calculation of radiation risk estimation in this modality is inevitable. In this study, a method for determining the patient-specific effective dose using the dose-length product (DLP) index in lung CT scan using Monte Carlo (MC) simulation is introduced.

Methods

EGSnrc/BEAMnrc MC code was used to simulate a CT scanner. The DOSxyznrc simulation code was used to simulate a specific voxelized phantom from the patient's lungs and irradiate it according to X-ray parameter of routing lung CT scan, and dose delivered to thorax organs was calculated. Three types of phantoms were simulated according to three different body habits (slim, standard, and fat patients) in two groups of men and women. A factor was used to convert the relative dose per particle in MC code to the absolute dose. The dose was calculated in all lung organs, and the effective dose was calculated for all three groups of patient body habits. DLP index and volume CT dose index (CTDIvol) were extracted from the patient's dose report in the CT scanner. The DLP to effective dose conversion factor (k-factor) for patients with different body habitus was calculated.

Results

Lung radiation dose in slim, standard, and fat patients in men was 0.164, 0.103, and 0.078 mGy/mAs and in women was 0.164, 0.105, and 0.079 mGy/mAs, respectively. The k-factor in the group of slim patients, especially in women, was higher than in other groups.

Conclusions

CT scan dose indexes for slim patients are reported to be underestimated in studies. The dose report in CT scan systems should be modified in proportion to the patient's body habitus, to accurately estimate the radiation risk.

Establishment of diagnostic reference levels in computed tomography in two large hospitals in Oman

This study aimed to estimate diagnostic reference levels (DRLs) for the most frequent computed tomography (CT) imaging examinations to monitor and better control radiation doses delivered to patients. Seven CT imaging examinations: Head, Chest, Chest High Resolution (CHR), Abdomen Pelvis (AP), Chest Abdomen Pelvis (CAP), Kidneys Ureters Bladder (KUB) and Cardiac, were considered. CT dosimetric quantities and patient demographics were collected from data storage systems. Local typical values for DRLs were calculated for CTDIvol (mGy), dose length product (DLP) (mGy·cm) and effective doses (mSv) were estimated for each examination. The calculated DRLs were given as (median CTDIvol (mGy):median DLP (mGy·cm)): Head: 39:657; Chest: 13:451; CHR: 6:228; AP: 12:578; CAP: 20:807; KUB: 7:315, and Cardiac: 2:31. Estimated effective doses for Head, Chest, CHR, AP, CAP, KUB and Cardiac were 1.3, 12.7, 6.3, 12.5, 18.1, 5.8 and 0.8 mSv, respectively. The estimated DRLs will act as guidance doses to prevent systematic excess of patient doses.

An Overview on the Alignment of Radiation Protection in Computed Tomography with Maqasid al-Shari'ah in the Context of al-Dharuriyat

The increasing utilisation of computed tomography (CT) in the medical field has raised a greater concern regarding the radiation-induced health effects as CT imposes high radiation risks on the exposed individual. Adherence to radiation protection measures in CT as endorsed by regulatory bodies; justification, optimisation and dose limit, is essential to minimise radiation risks. Islam values every human being and Maqasid al-Shari'ah helps to protect human beings through its sacred principles which aim to fulfil human beings' benefits (maslahah) and prevent mischief (mafsadah). Alignment of the concept of radiation protection in CT within the framework of al-Dharuriyat; protection of faith or religion (din), protection of life (nafs), protection of lineage (nasl), protection of intellect ('aql) and protection of property (mal) is essential. This strengthens the concept and practices of radiation protection in CT among radiology personnel, particularly Muslim radiographers. The alignment provides supplementary knowledge towards the integration of knowledge fields between Islamic worldview and radiation protection in medical imaging, particularly in CT. This paper is hoped to set a benchmark for future studies on the integration of knowledge between the Islamic worldview and radiation protection in medical imaging in terms of other classifications of Maqasid al-Shari'ah; al-Hajiyat and al-Tahsiniyat.

Estimation of cancer risks due to chest radiotherapy treatment planning computed tomography (CT) simulations

The objective of our study was to determine organ doses to estimate the lifetime attributable risk (LAR) of cancer incidence related to chest tomography simulations for Radiotherapy Treatment Planning (RTTP) using patient-specific information. Patient data were used to calculate organ doses and effective dose. The effective dose (E) was calculated by two methods. First, to calculate effective dose in a standard phantom, the collected dosimetric parameters were used with the ImPACT CT Patient Dosimetry Calculator and E was calculated by applying related correction factors. Second, using the scanner-derived Dose Length Product, LARs were computed using the US National Academy of Sciences (BEIR VII) model for age- and sex-specific risks at each exposure. DLP, CTDI_vol, and scan length were 507 ± 143 mGy.cm, 11 ± 4 mGy, and 47 ± 7 cm, respectively. The effective dose was 10 ± 3 mSv using ImPACT patient dosimetry calculator software and 9 ± 2 mSv using the scanner-derived Dose Length Product. The LAR of cancer incidence for all cancers, all solid cancers and leukemia were 65 ± 29, 62 ± 27, 7 ± 2 cases per 100,000 individuals, respectively. Radiation exposure from the usage of CT for radiotherapy treatment planning (RTTP) causes non-negligible increases in lifetime attributable risk. The results of this study can be used as a guide by physicians to implement strategies based on the As Low As Reasonably Achievable (ALARA) principle that lead to a reduction dose without sacrificing diagnostic information.

A new upper limit for effective dose in patient administered with 18F-FDG for PET/CT whole-body imaging with diagnostic CT parameters

INTRODUCTION

The aim of present study is to estimate effective dose in patient undergoing ¹⁸F-FDG for whole body PET/CT imaging with diagnostic CT parameters and identify the lowest achievable total effective dose.

METHOD

A total of 2247 PET/CT patients with normal glucose level underwent ¹⁸F-FDG-whole body imaging procedures. The ¹⁸F-FDG dose of 3.7MBq per kg of patient weight administered via intravenous infusion. For CT parameters, kilovoltage of 140keV and current of 40 mAs were used for all studies. All the acquired images collected retrospectively and the effective dose was calculated for each patient using algorithm adapted from ICRP Publication 106, modified for patient weight and patient blood volume. The estimated effective doses were evaluated for patients' body weight and BMI.

RESULTS

The mean of total effective dose and standard deviation is approximately 15.08(4.52) mSv using ICRP algorithm. 56% of total patient has normal BMI and their average total effective dose is 13.6mSv. Underweight patients' effective dose can be as low as 9.6mSv even using diagnostic CT protocols.

CONCLUSION

The effective dose of PET/CT procedure in present study is one of the lowest although using diagnostic parameters for CT acquisition compared to published data worldwide. This is due to the improved sensitivity of PET and complex reconstruction technique that maintains the image quality. A significant association between body weight, BMI and effective dose is reported in present study. Therefore, it is suggested that attention must be given for underweight and ideal BMI patients while prescribing FDG activity and CT imaging parameters in order to minimize the effective dose. The effective dose reported in present study can be considered as an upper limit for effective dose in PET/CT patients with normal BMI. This upper limit can be treated as a standard limit when optimizing imaging parameters, developing algorithm for image reconstruction and prescribing activity for patients. This practice could fulfill ALARA principle that could reduce cancer risk.

An in-house step-wedge phantom for the calibration of pixel values in CT localizer radiographs for water-equivalent diameter measurement

Introduction: To develop an in-house acrylic-based step-wedge phantom with several thickness configurations for calibrating computed tomography (CT) localizer radiographs in order to measure the water-equivalent diameter (Dw) and the size-specific dose estimate (SSDE).

Method: We developed an in-house step-wedge phantom using 3 mm thick acrylic, filled with water. The phantom had five steps with thicknesses of 6, 12, 18, 24, and 30 cm. The phantom was scanned using a 64-slice Siemens Definition AS CT scanner with tube currents of 50, 100, 150, 200, and 250 mA. The relationship between pixel value (PV) and water-equivalent thickness (tw) was obtained for the different step thicknesses. This was used to calibrate the CT localizer radiographs in order to measure Dw and SSDE. The results of Dw and SSDE from the radiographs were compared with those calculated from axial CT images.

Results: The relationship between PV and tw from CT localizer radiographs of the phantom step-wedge produced a linear relationship with R2 > 0.990. The linear relationships of the Dw and SSDE values obtained from CT localizer radiographs and axial CT images had R2 values > 0.94 with a statistical test of p-value > 0.05. The Dw difference between those from CT localizer radiographs and axial CT images was 3.7% and the SSDE difference between both was 4.3%.

Conclusion: We have successfully developed a step-wedge phantom to calibrate the relationship between PV and tw. Our phantom can be easily used to calibrate CT localizer radiographs in order to measure Dw and SSDE.

Radiation Exposure and Lifetime Attributable Risk of Cancer Incidence and Mortality from Low- and Standard-Dose CT Chest: Implications for COVID-19 Pneumonia Subjects

Since the novel coronavirus disease 2019 (COVID-19) outbreak, there has been an unprecedented increase in the acquisition of chest computed tomography (CT) scans. Nearly 616 million people have been infected by COVID-19 worldwide to date, of whom many were subjected to CT scanning. CT exposes the patients to hazardous ionizing radiation, which can damage the genetic material in the cells, leading to stochastic health effects in the form of heritable genetic mutations and increased cancer risk. These probabilistic, long-term carcinogenic effects of radiation can be seen over a lifetime and may sometimes take several decades to manifest. This review briefly describes what is known about the health effects of radiation, the lowest dose for which there exists compelling evidence about increased radiation-induced cancer risk and the evidence regarding this risk at typical CT doses. The lifetime attributable risk (LAR) of cancer from low- and standard-dose chest CT scans performed in COVID-19 subjects is also discussed along with the projected number of future cancers that could be related to chest CT scans performed during the COVID-19 pandemic. The LAR of cancer Incidence from chest CT has also been compared with those from other radiation sources, daily life risks and lifetime baseline risk.

Real-time fully automated dosimetric computation for CT images in the clinical workflow: A feasibility study

Background

Currently, the volume computed tomography dose index (CTDI_vol), the most-used quantity to express the output dose of a computed tomography (CT) patient’s dose, is not related to the real size and attenuation properties of each patient. The size-specific dose estimates (SSDE), based on the water-equivalent diameter (D_W) overcome those issues. The proposed methods found in the literature do not allow real-time computation of D_W and SSDE.

Purpose

This study aims to develop a software to compute D_W and SSDE in a real-time clinical workflow.

Method

In total, 430 CT studies and scans of a water-filled funnel phantom were used to compute accuracy and evaluate the times required to compute the D_W and SSDE. Two one-sided tests (TOST) equivalence test, Bland–Altman analysis, and bootstrap-based confidence interval estimations were used to evaluate the differences between actual diameter and D_W computed automatically and between D_W computed automatically and manually.

Results

The mean difference between the D_W computed automatically and the actual water diameter for each slice is −0.027% with a TOST confidence interval equal to [−0.087%, 0.033%]. Bland–Altman bias is −0.009% [−0.016%, −0.001%] with lower limits of agreement (LoA) equal to −0.0010 [−0.094%, −0.068%] and upper LoA equal to 0.064% [0.051%, 0.077%]. The mean difference between D_W computed automatically and manually is −0.014% with a TOST confidence interval equal to [−0.056%, 0.028%] on phantom and 0.41% with a TOST confidence interval equal to [0.358%, 0.462%] on real patients. The mean time to process a single image is 13.99 ms [13.69 ms, 14.30 ms], and the mean time to process an entire study is 11.5 s [10.62 s, 12.63 s].

Conclusion

The system shows that it is possible to have highly accurate D_W and SSDE in almost real-time without affecting the clinical workflow of CT examinations.

Utilization of artificial intelligence approach for prediction of DLP values for abdominal CT scans: A high accuracy estimation for risk assessment

Purpose

This study aimed to evaluate Artificial Neural Network (ANN) modeling to estimate the significant dose length product (DLP) value during the abdominal CT examinations for quality assurance in a retrospective, cross-sectional study.

Methods

The structure of the ANN model was designed considering various input parameters, namely patient weight, patient size, body mass index, mean CTDI volume, scanning length, kVp, mAs, exposure time per rotation, and pitch factor. The aforementioned examination details of 551 abdominal CT scans were used as retrospective data. Different types of learning algorithms such as Levenberg-Marquardt, Bayesian and Scaled-Conjugate Gradient were checked in terms of the accuracy of the training data.

Results

The R-value representing the correlation coefficient for the real system and system output is given as 0.925, 0.785, and 0.854 for the Levenberg-Marquardt, Bayesian, and Scaled-Conjugate Gradient algorithms, respectively. The findings showed that the Levenberg-Marquardt algorithm comprehensively detects DLP values for abdominal CT examinations. It can be a helpful approach to simplify CT quality assurance.

Conclusion

It can be concluded that outcomes of this novel artificial intelligence method can be used for high accuracy DLP estimations before the abdominal CT examinations, where the radiation-related risk factors are high or risk evaluation of multiple CT scans is needed for patients in terms of ALARA. Likewise, it can be concluded that artificial learning methods are powerful tools and can be used for different types of radiation-related risk assessments for quality assurance in diagnostic radiology.

Low-Dose Abdominal CT for Evaluating Suspected Appendicitis: Recommendations for CT Imaging Techniques and Practical Issues

A vast disparity exists between science and practice for CT radiation dose. Despite high-level evidence supporting the use of low-dose CT (LDCT) in diagnosing appendicitis, a recent survey showed that many care providers were still concerned that the low image quality of LDCT may lead to incorrect diagnoses. For successful implementation of LDCT practice, it is important to inform and educate the care providers not only of the scientific discoveries but also of concrete guidelines on how to overcome more practical matters. Here, we discuss CT imaging techniques and other practical issues for implementing LDCT practice.

Factors affecting dose-length product of computed tomography component in whole-body positron emission tomography/computed tomography

In whole-body positron emission tomography (PET)/computed tomography (CT), it is important to optimise the CT radiation dose. We have investigated factors affecting the dose-length product (DLP) of the CT component of whole-body PET/CT and derived equations to predict the DLP. In this retrospective study, 1596 whole-body oncology PET/CT examinations with¹⁸F-fluorodeoxyglucose were analysed. Automatic exposure control was used to modulate radiation dose in CT. Considering age, weight, sex, arm position (up, down, one arm up), scan range (up to the mid-thigh or feet), scan mode (spiral or respiratory-triggered nonspiral) and the presence of a metal prosthesis as potential factors, multivariate analysis was performed to identify independent predictors of DLP and to determine equations to predict DLP. DLP values were predicted using the obtained equations, and compared with actual values. Among body size indices, weight best correlated with DLP in examinations performed under the standard imaging conditions (arms: up; scan range: up to the mid-thigh; scan mode: spiral; and no metal prosthesis). Multivariate analysis indicated that weight, arm position, scan range and scan mode were substantial independent predictors; lowering the arms, extending the scan range and using respiratory-triggered imaging, as well as increasing weight, increased DLP. The degree of the DLP increase tended to increase with increasing weight. The DLP values were predicted using equations that considered these parameters were in excellent agreement with the actual values. The DLP for the CT component of whole-body PET/CT is affected by weight, arm position, scan range and scan mode, and can be predicted with excellent accuracy using these factors.

Organs' absorbed dose and comparison of different methods for effective dose calculation in computed tomography of parathyroid glands

Objective:To estimate organs' absorbed dose from the two-phase CT of parathyroid glands, effective dose (ED) based on three different methods, and compare the dose values with those reported by other published protocols.Methods:Volumetric-computed-tomography-dose-index (CTDIvol), dose-length-product (DLP), and the corresponding scan length during each phase of a parathyroid protocol were recorded, for seventy-six patients. One k-factor, and two different k-factors for the neck and chest area were used to estimate the ED from DLP. A Monte Carlo software, VirtualDoseCT, was also used for the estimation of organs' absorbed dose and ED.Results:Two-phase parathyroid CT resulted in a mean ED of 3.93 mSv, 4.29 mSv and 4.21 mSv according to the one k-factor, two k-factors, and VirtualDoseCT methods, respectively. The two k-factors method resulted in a slight overestimation of 1.9% in total ED compared to VirtualDoseCT. No statistically significant difference was found in ED values between these methods (Wilcoxon test, p>0.05), except for female patients in the pre-contrast phase. The organs inside the SFOV received the following doses: thymus 23.3 mGy, lungs 11.5 mGy, oesophagus 9.2 mGy, thyroid 6.9 mGy, and breast 6.3 mGy. The ED and organs' dose (OD) values were significantly lower in the pre-contrast than in the arterial phase (Wilcoxon test, p<0.001). A statistically significant difference was observed between male and female patients for the pre-contrast phase (Mann-Whitney test, p<0.05), regarding the ED values obtained with the two k-factors method and VirtualDoseCT software.Conclusions:The two k-factors method could be applied for the ED estimation in clinical practice, if appropriate software is not available. An extensive range of ED values derived from the literature, mainly depending on the acquisition protocol parameters and the estimation method.

O-Arm-Navigated, Robot-Assisted Versus Conventional CT Guided Radiofrequency Ablation in Treatment of Osteoid Osteoma: A Retrospective Cohort Study

Background

Osteoid osteoma is a common benign bone tumor, and clinically there is severe local pain that typically worsens at night. The conventional CT-guided radiofrequency ablation (RFA) was widely used in the treatment of osteoid osteoma (OO), which could result in some radiation-related and imprecise complications due to the overdose of radiation exposure. This study aimed to compare the surgical effect of robot-assisted RFA with O-arm navigation and conventional CT-guided RFA in the treatment of OO.

Methods

Sixty-two patients who underwent robot-assisted RFA with O-arm navigation (Robot-RFA, n = 24) or CT-guided RFA (CT-RFA, n = 38) were included in this retrospective cohort study. The mean follow-up time was 23.3 months. The intra-operative data, primary technical success rate, visual analog scale (VAS), and post-operative complications were analyzed.

Results

Primary technical success was obtained in 23 patients who had robot-assisted RFA, and 35 patients who had conventional CT-guided RFA. One patient in Robot-RFA group and three patients in CT-RFA group with pain recurrence received repeat-RFA and had a secondary success. Mean operation time and dose of radiation exposure were lower in Robot-RFA group than that in CT-RFA group. The Robot-RFA group took fewer K-wire adjustment times for each patient than the CT-RFA group. There was a statistically significant difference in the mean operation time, dose of radiation exposure, and K-wire adjustment times between the groups (p &lt; 0.05). No complications associated with the procedure were reported in the two groups during the follow-up period.

Conclusion

Robot-assisted RFA with O-arm navigation is a safer and more precise strategy in the treatment of osteoid osteoma with less operation time and radiation exposure compared with the conventional CT-guided radiofrequency ablation.

Conversion from dose-length product to effective dose in computed tomography venography of the lower extremities

For radiation dose assessment of computed tomography (CT), effective dose (ED) is often estimated by multiplying the dose-length product (DLP), provided automatically by the CT scanner, by a conversion factor. We investigated such conversion in CT venography of the lower extremities performed in conjunction with CT pulmonary angiography. The study subjects consisted of eight groups imaged using different scanners and different imaging conditions (five and three groups for the GE and Siemens scanners, respectively). Each group included ten men and ten women. The scan range was divided into four anatomical regions (trunk, proximal thigh, knee and distal leg), and DLP was calculated for each region (regional DLP). Regional DLP was multiplied by a conversion factor for the respective region, to convert it to ED. The sum of the ED values for the four regions was obtained as standard ED. Additionally, the sum of the four regional DLP values, an approximate of the scanner-derived DLP, was multiplied by the conversion factor for the trunk (0.015 mSv mGy cm^-1), as a simplified method to obtain ED. When using the simplified method, ED was overestimated by 32.3%-70.2% and 56.5%-66.2% for the GE and Siemens scanners, respectively. The degree of overestimation was positively and closely correlated with the contribution of the middle and distal portions of the lower extremities to total radiation exposure. ED/DLP averaged within each group, corresponding to the conversion factor, was 0.0089-0.0114 and 0.0091-0.0096 mSv mGy cm^-1for the GE and Siemens scanners, respectively. In CT venography of the lower extremities, ED is greatly overestimated by multiplying the scanner-derived DLP by the conversion factor for the trunk. The degree of overestimation varies widely depending on the imaging conditions. It is recommended to divide the scan range and calculate ED as a sum of regional ED values.

Radiation Dose Modulation of Computed Tomography Component in Positron Emission Tomography/Computed Tomography

In oncology practice, the CT component of PET/CT may be used for attenuation correction, lesion localization, and CT diagnosis, and significantly enhances the clinical benefit of PET. However, acquisition of CT covering the whole body increases radiation dose and consequently the risk of cancer induction, and optimization should be pursued. In CT, radiation dose is a major determinant of image quality, and is mainly adjusted by modulation of tube current. Automatic exposure control (AEC) is widely used for tube current modulation, and increases tube current in a large patient and in strongly attenuating regions of a given patient to preserve image quality despite strong X-ray attenuation. Radiation dose determined by AEC depends on various factors, such as the type of AEC software, scout imaging direction, arm positioning, and patient centering. Because radiation dose reduction increases image noise and may degrade clinical utility, image quality should be assessed together with radiation dose in the process of optimization. Clinical demands for image quality vary largely depending on the aim of the CT component, with lower quality being sufficient for lesion localization than for CT diagnosis. Therefore, optimal radiation dose differs according to the aim. Determining optimal dose is a somewhat subjective and difficult task, and use of the diagnostic reference level, determined based on national or regional survey, is recommended to recognize need for optimization. The volume CT dose index and dose-length product are used as indices of CT radiation dose, and effective dose may also be calculated for comparison of stochastic effects among different radiation sources and among different imaging procedures. Wide coverage from the head to the lower extremities causes problems in estimating these indices in whole-body PET/CT. CT definitely enhances clinical benefits of PET but simultaneously increases potential detriments due to radiation exposure. In the era of hybrid imaging, nuclear medicine practitioners should be aware of the technology and radiation dose management of CT.

DOSIMETRIC EVALUATION OF THE TWO-PHASE COMPUTED TOMOGRAPHY IN PARATHYROID GLANDS IMAGING

This study evaluates the patient radiation dose from the two-phase protocols of two different computed tomography (CT) systems and compares this with that delivered by the other similar protocols previously published. Two hundred and fourteen patients with primary hyperparathyroidism were included in the study with a two-phase CT scan between 2008 and 2020 by using a Toshiba Aquilion Prime 80 and a GE Light Speed 16. The standard 'neck' or a modified 'parathyroid' protocol was used. The patient dose was evaluated in terms of volumetric computed tomography dose index (CTDIvol), dose length product (DLP) and effective dose (ED) per acquisition protocol and CT system. CTDIvol and DLP were recorded retrospectively, while the ED was calculated based on DLP and an appropriate conversion coefficient. Comparisons of patient dose between the two protocols and two CT systems and the corresponding published values were established. A significantly lower patient dose (40.2-43.2%) than the GE system (p < 0.0001) resulted from the Toshiba system. The 'parathyroid' protocol resulted in a 6.5-9.6% lower patient dose than the standard 'neck' protocol. Compared with the literature, the lowest ED value (3.6 mSv) was observed since this protocol consists of a lowered tube voltage of 100 kVp, a reduced scan length for the pre-contrast phase and implementation of an iterative reconstruction algorithm.

NATIONAL DIAGNOSTIC REFERENCE LEVELS AND ACHIEVABLE DOSES FOR STANDARD CT EXAMINATIONS IN SUDAN

Radiation doses were determined to propose national diagnostic reference levels (NDRLs) and achievable doses (ADs) for computed tomography (CT) examinations in Sudan. Doses were estimated from retrospectively collected scan parameters for 1336 CT examinations of adult patients from 14 Sudanese hospitals using CT Expo 2.5 software. ADs and NDRLs were set at the 50th and 75th percentile of the hospital median dose distribution, respectively. The proposed CTDIvol (mGy) ADs ranged from: 10 (chest) to 64 (head), and that of the dose-length product (DLP; mGy.cm) ranged from 366 (chest) to 1225 (head). The proposed CTDIvol (mGy) NDRLs ranged from 15 kidney-ureter-bladder (KUB) to 79 (head), whereas that of the DLP (mGy.cm) ranged from 690 (chest) to 1490 (head). Current doses fell within the upper range of the doses presented in the literature emphasizing the need for implementation of the current ADs and NDRLs for CT to enhance patient protection and dose optimization in Sudan.

Nusinersen injections in adults and children with spinal muscular atrophy: a single-center experience

PURPOSE

Nusinersen is a drug approved in December 2016 for treatment of spinal muscular atrophy (SMA). We want to share our initial experience with image-guided, non-image-guided, and port-delivered nusinersen injections in a large single-center SMA patient cohort, treating both pediatric and adult patients with focus on technical considerations and other patient concerns from a combined perspective of patient, neurologist, and radiologist.

METHODS

All nusinersen injections between February 2017 and September 2018 were retrospectively reviewed. We obtained age, sex, SMA type and technical details of the injections and postprocedure complications for each procedure.

RESULTS

A total of 52 patients (24 women [46%]; 4 patients with SMA-1 [7.6%]; 30 patients with SMA-2 [57.8%]; 18 patients with SMA-3 [34.6%]; mean age, 25.5 years [7 months to 62 years]) with a total of 265 injections were included. Of the 265 injections, 206 (77.9%) were performed with local anesthetic, 25 (9.4%) with moderate sedation, and 23 (8.6%) under general anesthesia. We performed 65 CT-guided transforaminal injections in 13 patients, 106 fluoroscopy-guided lumbar punctures in 24 patients and 83 lumbar punctures in 16 patients using conventional technique. Only 6 of 265 injections (2.2%) ended up with a post-lumbar puncture headache (PLPH) requiring medical treatment. None required an epidural blood patch. Fourteen PLPH (5.2%) occurred and resolved at the same day without any treatment. After 6 of 265 injections (2.2%), patients reported soreness at the injection site which resolved spontaneously. Three elected to have an intrathecal reservoir placement (2 lumbar, 1 intraventricular) with a total of 11 injections. One patient with lumbar catheter developed infection after surgery with subsequent meningitis and treatment delay. After the resolution of meningitis, a new intraventricular reservoir was placed without any complication in the following injections.

CONCLUSION

With the introduction of nusinersen treatment, neurologists and radiologists play an important role in treatment of SMA patients and therefore should be familiar with different techniques and complications of drug administration. Using good technique, it is possible to have very low complication rates even in this complex patient population, and various image-guided procedures can be a safe alternative to surgical approach, even in the most difficult cases.

CT pulmonary angiography in pregnancy: Specific conversion factors to estimate effective radiation dose from dose length product: A retrospective cross-sectional study across a multi-hospital integrated healthcare network

PURPOSE

Effective dose describes radiation-related cancer risk from CT scans and is estimated using a readily available conversion factor (k-factor), which varies by body part and study type. To purpose of this study is to determine the specific k-factor for CTPA in pregnant patients and its predictive factors.

METHODS

This retrospective cross-sectional study evaluates CTPA in pregnancy across a multihospital integrated healthcare network from January 2012 to April 2017. Patient and CTPA-related data were obtained from the electronic health record and a radiation dose index monitoring system. Each patient's effective dose was determined by patient-specific Monte-Carlo simulation with Cristy phantoms and divided by patient dose-length-product to determine the k-factor. K-factor for pregnant patients was compared to the k-factor for adults of standard physique with a one-sample t-test. Bivariate and multivariable analyses were performed for patient and CT predictors of k-factor.

RESULTS

A total of 534 patients were included. The mean k-factor for all patients was 0.0249 (mSv·mGy^-1·cm^-1), 78% greater than k-factor of 0.014 (p < 0.001) suggested for the general adult population. Multivariable analysis demonstrated lower k-factors with increasing pitch (p = 0.0002), patient size (p < 0.001), and scan length (p < 0.0001). The 120 kVp (p < 0.001) and 140 kVp (p = 0.0028) analyses showed a larger k-factor than 80 and 100 kVp studies combined.

CONCLUSIONS

Specific k-factor for CTPA in pregnant patients is greater than the previously used generic chest CT k-factor and should be used to estimate the effective dose for CTPA exams in pregnancy.

The effective and water-equivalent diameters as geometrical size functions for estimating CT dose in the thoracic, abdominal, and pelvic regions

Purpose: The aim of this work was to establish the relationships of patient size in terms of effective diameter (Deff) and water-equivalent diameter (Dw) with lateral (LAT) and anterior-posterior (AP) dimensions in order to predict the specific patient dose for thoracic, abdominal, and pelvic computed tomography (CT) examinations.

Methods: A total of 47 thoracic images, 79 abdominal images, and 50 pelvic images were analyzed in this study. The patient’s images were retrospectively collected from Dr. Kariadi and Kensaras Hospitals, Semarang, Indonesia. The slices measured were taken from the middle of the scan range. The calculations of patient sizes (LAT, AP, Deff, and Dw) were automatically performed by IndoseCT 20b software. Deff and Dw were plotted as functions of LAT, AP, and AP+LAT. In addition, Dw was plotted as a function of Deff.

Results: Strong correlations of Deff and Dw with LAT, AP, and AP+LAT were found. Stronger correlations were found in the Deff curves (R2 > 0.9) than in the Dw curves (R2 > 0.8). It was found that the average Deff was higher than the average Dw in the thoracic region, the average values were similar in the abdominal and pelvic regions.

Conclusion: The current study extended the study of the relationships between Deff and Dw and the basic geometric diameter LAT, AP, and AP+LAT beyond those previously reported by AAPM. We evaluated the relationships for three regions, i.e. thoracic, abdominal, and pelvic regions. Based on our findings, it was possible to estimate Deff and Dw from only the LAT or AP dimension.

An improved method for automated calculation of the water-equivalent diameter for estimating size-specific dose in CT

PURPOSE

The aim of this study is to propose an algorithm for the automated calculation of water-equivalent diameter (D_w ) and size-specific dose estimation (SSDE) from clinical computed tomography (CT) images containing one or more substantial body part.

METHODS

All CT datasets were retrospectively acquired by the Toshiba Aquilion 128 CT scanner. The proposed algorithm consisted of a contouring stage for the D_w calculation, carried out by taking the six largest objects in the cross-sectional image of the patient's body, followed by the removal of the CT table depending on the center position (y-axis) of each object. Validation of the proposed algorithm used images of patients who had undergone chest examination with both arms raised up, one arm placed down and both arms placed down, images of the pelvic region consisting of one substantial object, and images of the lower extremities consisting of two separated areas.

RESULTS

The proposed algorithm gave the same results for D_w and SSDE as the previous algorithm when images consisted of one substantial body part. However, when images consisted of more than one substantial body part, the new algorithm was able to detect all parts of the patient within the image. The D_w values from the proposed algorithm were 9.5%, 15.4%, and 39.6% greater than the previous algorithm for the chest region with one arm placed down, both arms placed down, and images with two legs, respectively. The SSDE values from the proposed algorithm were 8.2%, 11.2%, and 20.6% lower than the previous algorithm for the same images, respectively.

CONCLUSIONS

We have presented an improved algorithm for automated calculation of D_w and SSDE. The proposed algorithm is more general and gives accurate results for both D_w and SSDE whether the CT images contain one or more than one substantial body part.

Evaluating our progress with trauma transfer imaging: repeat CT scans, incomplete imaging, and delayed definitive care

PURPOSE

Many trauma patients present at non-trauma centers and require transfer. CT imaging obtained at the initial hospital (IH) may lead to delays in definitive trauma care, and previous studies have shown imaging is often repeated at the trauma center (TC).

METHODS

A retrospective review was performed of all tier 1 trauma patients transferred to our TC between May 2018 and April 2019. Patients that did and did not undergo CT imaging at the IH were compared (n = 147). Of those with IH CT imaging (n = 68), we identified 4 imaging "inadequacies": (1) repeat CT scans: CT scan of the same body region performed at IH and at TC; (2) C-spine inadequacies: severely injured patients who underwent head CT without a C-spine CT; (3) incomplete chest-abdomen-pelvis (CAP): patients with partial CAP CT imaging at IH that underwent an additional portion of CAP imaging at TC; (4) CAP CT without IV contrast.

RESULTS

IH time was significantly prolonged when CT imaging was obtained. Of those that had IH imaging, 13 patients (19%) required repeat CT, ten (15%) had a C-spine inadequacy, 11 (16%) had incomplete CAP, and 28 (41%) had one or more inadequacy. Patients with any inadequacy underwent more CT imaging. Most patients (76%) with imaging at the IH returned to the CT scan at the TC.

CONCLUSION

In severely injured trauma patients transferred to our TC, we identified many continuing issues with IH CT imaging. The imaging inadequacies detailed above lead to delays in definitive care and subject patients to increased radiation.

Radiation Dose to the Fetus From Computed Tomography of Pregnant Patients-Development and Validation of a Web-Based Tool

OBJECTIVE

Estimations of radiation dose absorbed by the fetus from computed tomography (CT) in pregnant patients is mandatory, but currently available methods are not feasible in clinical routine. The aims of this study were to develop and validate a tool for assessment of fetal dose from CT of pregnant patients and to develop a user-friendly web interface for fast fetal dose calculations.

METHODS

In the first study part, 750 Monte Carlo (MC) simulations were performed on phantoms representing pregnant patients at various gestational stages. The MC code simulating vendor-independent dose distributions was validated against CT dose index (CTDI) measurements performed on CT scanners of 2 vendors. The volume CTDI-normalized fetal dose values from MC simulations were used for developing the computational algorithm enabling fetal dose assessments from CT of various body regions at different exposure settings. In the institutional review board-approved second part, the algorithm was validated against patient-specific MC simulations performed on CT data of 29 pregnant patients (gestational ages 8-35 weeks) who underwent CT. Furthermore, the tool was compared with a commercially available software. A user-friendly web-based interface for fetal dose calculations was created.

RESULTS

Weighted CTDI values obtained from MC simulations were in excellent agreement with measurements performed on the 2 CT systems (average error, 4%). The median fetal dose from abdominal CT in pregnant patients was 2.7 mGy, showing moderate correlation with maternal perimeter (r = 0.69). The algorithm provided accurate estimates of fetal doses (average error, 11%), being more accurate than the commercially available tool. The web-based interface (www.fetaldose.org) enabling vendor-independent calculations of fetal doses from CT requires the input of gestational age, volume CTDI, tube voltage, and scan region.

CONCLUSIONS

A tool for fetal dose assessments from CT of pregnant patients was developed and validated being freely available on a user-friendly web interface.

Impact of an Augmented Reality Navigation System (SIRIO) on Bone Percutaneous Procedures: A Comparative Analysis with Standard CT-Guided Technique

(1) Background: The purpose of this study is to evaluate the impact of an augmented reality navigation system (SIRIO) for percutaneous biopsies and ablative treatments on bone lesions, compared to a standard CT-guided technique. (2) Methods: Bioptic and ablative procedures on bone lesions were retrospectively analyzed. All procedures were divided into SIRIO and Non-SIRIO groups and in <2 cm and >2 cm groups. Number of CT-scans, procedural time and patient’s radiation dose were reported for each group. Diagnostic accuracy was obtained for bioptic procedures. (3) Results: One-hundred-ninety-three procedures were evaluated: 142 biopsies and 51 ablations. Seventy-four biopsy procedures were performed using SIRIO and 68 under standard CT-guidance; 27 ablative procedures were performed using SIRIO and 24 under standard CT-guidance. A statistically significant reduction in the number of CT-scans, procedural time and radiation dose was observed for percutaneous procedures performed using SIRIO, in both <2 cm and >2 cm groups. The greatest difference in all variables examined was found for procedures performed on lesions <2 cm. Higher diagnostic accuracy was found for all SIRIO-assisted biopsies. No major or minor complications occurred in any procedures. (4) Conclusions: The use of SIRIO significantly reduces the number of CT-scans, procedural time and patient’s radiation dose in CT-guided percutaneous bone procedures, particularly for lesions <2 cm. An improvement in diagnostic accuracy was also achieved in SIRIO-assisted biopsies.

Strategy to reduce radiation exposure in postoperative spinal computed tomography scans

Background:

When diagnosing and treating spinal disorders, spine surgeons commonly utilize computed tomography (CT) scans preoperatively, intraoperatively, and postoperatively.

Methods:

This article reviews the literature regarding the potentially harmful effects of X-rays, specifically from CT scans.

Results:

The risk for damaging DNA and developing cancer increases with increasing scan length (e.g., increasing amount of radiation received).

Conclusion:

When assessing postoperative status, CT scans should be directed only through the area of specific interest to limit the total dose of radiation received by the patient.

A review on chest CT scanning parameters implemented in COVID-19 patients: bringing low-dose CT protocols into play

Background

This study aims to review chest computed tomography (CT) scanning parameters which are utilized to evaluate patients for COVID-19-induced pneumonia. Also, some of radiation dose reduction techniques in CT would be mentioned, because using these techniques or low-dose protocol can decrease the radiation burden on the population.

Main body

Chest CT scan can play a key diagnostic role in COVID-19 patients. Additionally, it can be useful to monitor imaging changes during treatment. However, CT scan overuse during the COVID-19 pandemic raises concerns about radiation-induced adverse effects, both in patients and healthcare workers.

Conclusion

By evaluating the CT scanning parameters used in several studies, one can find the necessity for optimizing these parameters. It has been found that chest CT scan taken using low-dose CT protocol is a reliable diagnostic tool to detect COVID-19 pneumonia in daily practice. Moreover, the low-dose chest CT protocol results in a remarkable reduction (up to 89%) in the radiation dose compared to the standard-dose protocol, not lowering diagnostic accuracy of COVID-19-induced pneumonia in CT images. Therefore, its employment in the era of the COVID-19 pandemic is highly recommended.

Assessment of Effective Dose Received in Various Computed Tomography Protocols and Factors Affecting It

PURPOSE OF STUDY

The purpose of the study was to evaluate the effect of patient characteristics and equipment-related factors on the computed tomography (CT) dose received by patients from positron emission tomography-CT (PET-CT) using system-generated dose-length product (DLP) values and also to check the effective dose (ED) received from various CT protocols at our institute.

MATERIALS AND METHODS

This retrospective study included 78 adult patients who underwent F-18 fluorodeoxyglucose whole-body PET-CT and were divided into three groups based on the area of primary cancerous lesion. In Group A, we had 44 patients who underwent PET-CT (head-and-neck protocol), in Group B, we had 24 patients who underwent PET-CT (whole body with brain protocol), and in Group C, we had 10 patients who underwent PET-CT (pelvis protocol). All of the patients under the study are of South Asian ethnicity. A majority of patients 53.85% were males and remaining 46.15% were females. The product of conversion factor (k-coefficient), as described in "American Association of Physicists in Medicine Report No. 96" and DLP value generated by the scanner, was used to calculate the ED. Moreover, we also performed regression analysis to check relation between body weight, height, scan range, tube current, Volume computed tomography dose index (CTDIvol), DLP, and ED.

RESULTS

The regression analysis shows that scan range, patient height, weight, tube current, and DLP were significantly correlated with ED (P < 0.05 for all). Moreover, the DLP and conversion factor method estimated the ED from various groups. Patients under Group A (head-and-neck protocol), Group B (whole body with brain protocol), Group C (pelvis protocol) received an average ED of 22.45 mSv, 22.40 mSv, and 21.24 mSv, respectively.

CONCLUSION

ED from CT component of PET-CT can be assessed as the product of scanner-generated DLP and conversion factor for selected range. Moreover, body weight, scan range, and tube current had an independent significant effect on ED received from CT.

Radiation doses from head, neck, chest and abdominal CT examinations: an institutional dose report

PURPOSE

We aimed to obtain typical values for head, neck, chest, and abdominal computed tomography (CT) examinations from routine patients in 2018, and to review our data with national and international diagnostic reference levels (DRLs).

METHODS

Single-phase head, neck, chest, and abdominal CT scans of adults performed in 64-slice CT in 2018 were included in this study. Radiation dose parameters of CT scans were obtained from the picture archiving and communication system of our hospital. Volumetric CT dose index (CTDIvol) and dose length product (DLP) values were recorded. Effective dose (ED) and scan length was calculated. A 16 cm diameter phantom is referenced for head CT, and 32 cm diameter phantom is referenced for neck, chest, and abdominal CT. Descriptive statistics of the variables were given according to the normality testing.

RESULTS

Median CTDIvol value was 53 mGy for the head, 13.1 mGy for the neck, 8.3 mGy for the chest, and 8.6 mGy for the abdomen. Median DLP value was 988 mGy.cm for the head, 299 mGy.cm for the neck, 314 mGy.cm for the chest, and 457 mGy.cm for the abdomen. Median ED value was 2.07 mSv for the head, 1.76 mSv for the neck, 4.4 mSv for the chest, and 6.8 mSv for the abdomen. Considering national DRLs, median CTDIvol values of head, chest, and abdomen were lower, whereas median DLP and ED values of head and chest were higher. For the abdomen, the median DLP and ED values were lower.

CONCLUSION

Overall radiation dose parameters obtained in this study points out the need for optimization of head CT examinations in our institution.

Automated size-specific dose estimates using deep learning image processing

An automated vendor-independent system for dose monitoring in computed tomography (CT) medical examinations involving ionizing radiation is presented in this paper. The system provides precise size-specific dose estimates (SSDE) following the American Association of Physicists in Medicine regulations. Our dose management can operate on incomplete DICOM header metadata by retrieving necessary information from the dose report image by using optical character recognition. For the determination of the patient's effective diameter and water equivalent diameter, a convolutional neural network is employed for the semantic segmentation of the body area in axial CT slices. Validation experiments for the assessment of the SSDE determination and subsequent stages of our methodology involved a total of 335 CT series (60 352 images) from both public databases and our clinical data. We obtained the mean body area segmentation accuracy of 0.9955 and Jaccard index of 0.9752, yielding a slice-wise mean absolute error of effective diameter below 2 mm and water equivalent diameter at 1 mm, both below 1%. Three modes of the SSDE determination approach were investigated and compared to the results provided by the commercial system GE DoseWatch in three different body region categories: head, chest, and abdomen. Statistical analysis was employed to point out some significant remarks, especially in the head category.

New Fast kVp Switching Dual-Energy CT: Reduced Severity of Beam Hardening Artifacts and Improved Image Quality in Reduced-Iodine Virtual Monochromatic Imaging

RATIONALE AND OBJECTIVES

To compare degradation of the image quality due to beam hardening artifacts in reduced-iodine-dose virtual monochromatic imaging (VMI) between a new fast kVp switching dual-energy computed tomography (CT) scanner (Revolution CT) and the conventional dual-energy scanner (Discovery CT).

MATERIALS AND METHODS

First, a phantom study was performed to quantitatively evaluate beam hardening artifacts in images obtained by VMI reconstruction at different energy levels. In the second study, we performed a retrospective evaluation of the images of 28 patients who had undergone reduced-iodine (300 mg/kg) dual-energy scanning in both Revolution CT and Discovery CT. We evaluated each image quantitatively by measuring the contrast-to-noise ratio (CNR) and qualitatively by scoring the artifacts and image quality. We also calculated the modulation transfer function (MTF) and noise power spectrum (NPS) of the two scanners.

RESULTS

In the phantom study, VMI reconstruction of the CT images at 40-70 keV was associated with a significantly greater reduction in the severity of the artifacts in the Revolution CT images as compared to the Discovery CT images. In the retrospective study, there were no significant differences in the CT value of the aorta, noise, or CNR between the two scanners, but the scores for image quality were significantly higher in the Revolution CT images as compared to the Discovery CT images. The MTF of Revolution CT was higher than that of Discovery CT, reflecting the better spatial resolution.

CONCLUSION

In Revolution CT, beam hardening artifacts were reduced in reduced-iodine VMI at lower energy levels compared to Discovery CT, contributing to better image quality.

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.

Low-Dose Computed Tomographic Scans for Postoperative Evaluation of Craniomaxillofacial Fractures: A Pilot Clinical Study

Computed tomographic scans are frequently obtained following craniomaxillofacial fracture reconstruction. The additive radiation from such scans is not trivial; cumulative radiation exposure poses stochastic health risks. In this article, the authors postulate that a low-dose computed tomography protocol provides adequate image quality for postoperative evaluation of reconstructed craniomaxillofacial fractures. This study included patients for whom a computed tomographic scan was indicated following craniomaxillofacial fracture repair at a Level I trauma center. Postoperative craniomaxillofacial computed tomography was performed using a low-dose protocol, rather than standard protocols. A craniomaxillofacial surgeon and a radiologist interpreted the images to determine whether they were of sufficient quality. It was decided a priori that any inadequate low-dose computed tomography would require repeated scanning using standard protocols. The primary endpoint was the need for repeated computed tomography. In addition, the clarity of clinically significant anatomical landmarks on the images was graded on a five-point Likert scale. Twenty patients were scanned postoperatively using the low-dose protocol. Mean radiation dose (total dose-length product) from the low-dose protocol was 71 mGy · cm versus 532 mGy · cm for the preoperative computed tomographic scans that were obtained using conventional protocols (p < 0.001). All 20 low-dose computed tomographic scans were determined to provide satisfactory image quality. No patients required repeated computed tomography secondary to poor image quality. Low-dose computed tomography received high image-quality scores. A low-dose computed tomography protocol that delivers approximately 7.5-fold less radiation than the standard protocols was found to be adequate for postoperative evaluation of craniomaxillofacial fractures. Larger prospective studies may be warranted. CLINICAL QUESTION/LEVEL OF EVIDENCE:: Therapeutic, IV.

AUTOMATIC BRAIN DOSE ESTIMATION IN COMPUTED TOMOGRAPHY USING PATIENT DICOM IMAGES

This study aims to develop an Automatic Brain Dose Estimation (ABDE) methodology for head computed tomography examinations. The ABDE is to be applied first to an anthropomorphic Alderson phantom to obtain a Correction factor (Cf) between the ABDE and the direct absorbed brain dose using dosemeters positioned within the anthropomorphic phantom. Then, in order to estimate the correct brain dose for patient, the Cf was multiplied by the mean ABDE values for each patient. Results were compared to those registered with a mathematical simulation phantom using CT-Expo V 2.4 software. Results showed no significant difference between the correct ABDE values and the CT-Expo values with a mean percent difference of 2.54 ± 0.01%. In conclusion, ABDE yields a correct estimation of brain dose, taking into account the size and attenuation of the irradiated region. Thus, it is clinically recommended for accurate patient brain dose assessment.

ESTIMATION OF RADIATION DOSE IN CT VENOGRAPHY OF THE LOWER EXTREMITIES: PHANTOM EXPERIMENTS USING DIFFERENT AUTOMATIC EXPOSURE CONTROL SETTINGS AND SCAN RANGES

We performed phantom experiments to assess radiation dose in computed tomography (CT) venography of the lower extremities. CT images of a whole-body phantom were acquired using different automatic exposure control settings and scan ranges, simulating CT venography. Tube current decreased in the lower extremities compared to the trunk. The scout direction and dose modulation strength affected tube current, dose length product (DLP) and effective dose. The middle and distal portions of the lower extremities contributed substantially to DLP but not to effective dose. When effective dose was estimated by multiplying DLP by a single conversion factor, overestimation was evident; this became more pronounced as the scan range narrowed. In CT venography of the lower extremities, the scout direction and modulation strength affect radiation dose. Use of DLP severely overestimates radiation dose and underestimates effects of scan range narrowing.

Individual Calculation of Effective Dose and Risk of Malignancy Based on Monte Carlo Simulations after Whole Body Computed Tomography

Detailed knowledge about radiation exposure is crucial for radiology professionals. The conventional calculation of effective dose (ED) for computed tomography (CT) is based on dose length product (DLP) and population-based conversion factors (k). This is often imprecise and unable to consider individual patient characteristics. We sought to provide more precise and individual radiation exposure calculation using image based Monte Carlo simulations (MC) in a heterogeneous patient collective and to compare it to phantom based MC provided from the National Cancer Institute (NCI) as academic reference. Dose distributions were simulated for 22 patients after whole-body CT during Positron Emission Tomography-CT. Based on MC we calculated individual Lifetime Attributable Risk (LAR) and Excess Relative Risk (ERR) of cancer mortality. ED_MC was compared to ED_DLP and ED_NCI. ED_DLP (13.2 ± 4.5 mSv) was higher compared to ED_NCI (9.8 ± 2.1 mSv) and ED_MC (11.6 ± 1.5 mSv). Relative individual differences were up to -48% for ED_MC and -44% for ED_NCI compared to ED_DLP. Matching pair analysis illustrates that young age and gender are affecting LAR and ERR significantly. Because of these uncertainties in radiation dose assessment automated individual dose and risk estimation would be desirable for dose monitoring in the future.

Liver Tumor Ablation Procedure Duration and Estimated Patient Radiation Dose: Comparing Positron Emission Tomography/CT and CT Guidance

PURPOSE

To compare procedure duration and patient radiation dose in positron emission tomography/computed tomography (PET/CT) and CT-guided liver tumor ablation procedures.

MATERIALS AND METHODS

In this retrospective, case-control study, 275 patients underwent 368 image-guided ablation procedures to treat 537 tumors. Radiologists used PET/CT guidance for 117 procedures and CT guidance for 251 procedures. PET/CT-guided procedures were performed by one radiologist (C: P.B.S.). All 3 radiologists (A: J.G.S., B: a radiologist who is not an author on this article, and C: P.B.S.) performed CT-guided procedures. Potential confounders included patient demographics, clinical and tumor characteristics, and procedural variables.

RESULTS

The mean duration and estimated patient radiation dose of PET/CT-guided procedures performed by radiologist C were 21.5 ± 4.9 minutes longer and 0.7 ± 2.8 mSv higher than CT-guided procedures performed by all radiologists in an unadjusted comparison. Adjusting for confounding, mean duration and estimated dose of PET/CT-guided procedures performed by radiologist C were 28.3 ± 3.8 minutes longer (P < .0001) and 6.2 ± 2.9 mSv higher (P = .03) than CT-guided procedures performed by the same radiologist. Comparing CT-guided procedures performed by all 3 radiologists, adjusted mean durations and estimated patient doses of procedures by the least experienced radiologist, radiologist A, and the second most experienced radiologist, radiologist B, were 24.2 ± 5.1 (P < .0001) and 18.1 ± 8.9 (P = .04) minutes longer and 13.1 ± 3.7 (P < .001) and 14.5 ± 6.4 (P = .02) mSv higher, respectively, than procedures performed by the most experienced radiologist, radiologist C.

CONCLUSIONS

PET/CT-guided liver ablations had a slightly longer duration with slightly higher estimated patient radiation dose than similar CT-guided liver ablations. Procedure duration and patient dose do not appear to be major impediments to the emerging field of PET/CT-guided tumor ablation.

A prospective study comparing water only with positive oral contrast in patients undergoing abdominal CT scan

Consecutive adults scheduled to undergo abdominal CT with oral contrast were asked to choose between 1000 ml water only or positive oral contrast (50 ml Télébrix-Gastro diluted in 950 ml water). Two abdominal radiologists independently reviewed each scan for image quality of the abdomen, the diagnostic confidence per system (gastrointestinalsystem/organs/peritoneum/retroperitoneum/lymph nodes) and overall diagnostic confidence to address the clinical question (not able/partial able/fully able). Radiation exposure was extracted from dose reports. Differences between both groups were evaluated by Student’s t-test, Mann-Whitney-U-test or chi-square-test. Of the 320participants, 233chose water only. All baseline characteristics, image quality of the abdomen and the diagnostic confidence of the organs were comparable between groups and both observers. Diagnostic confidence in the water only group was more commonly scored as less than good by observer1. The results were as follows: the gastrointestinal system(18/233vs1/87; p = 0.031), peritoneum (21/233vs1/87; p = 0.012), retroperitoneum (11/233vs0/87; p = 0.040) and lymph nodes (11/233vs0/87; p = 0.040). These structures were scored as comparable between both groups by observer2. The diagnostic confidence to address the clinical question could be partially addressed in 6/233 vs 0/87 patients (p = 0.259). The water only group showed a tendency towards less radiation exposure. In summary, most scan ratings were comparable between positive contrast and water only, but slightly favored positive oral contrast for one reader for some abdominal structures. Therefore, water only can replace positive oral contrast in the majority of the outpatients scheduled to undergo an abdominal CT.