Low-Dose Chest CT Protocols for Imaging COVID-19 Pneumonia: Technique Parameters and Radiation Dose

Chest computed tomography (CT) plays a vital role in the early diagnosis, treatment, and follow-up of COVID-19 pneumonia during the pandemic. However, this raises concerns about excessive exposure to ionizing radiation. This study aimed to survey radiation doses in low-dose chest CT (LDCT) and ultra-low-dose chest CT (ULD) protocols used for imaging COVID-19 pneumonia relative to standard CT (STD) protocols so that the best possible practice and dose reduction techniques could be recommended. A total of 564 articles were identified by searching major scientific databases, including ISI Web of Science, Scopus, and PubMed. After evaluating the content and applying the inclusion criteria to technical factors and radiation dose metrics relevant to the LDCT protocols used for imaging COVID-19 patients, data from ten articles were extracted and analyzed. Technique factors that affect the application of LDCT and ULD are discussed, including tube current (mA), peak tube voltage (kVp), pitch factor, and iterative reconstruction (IR) algorithms. The CTDIvol values for the STD, LDCT, and ULD chest CT protocols ranged from 2.79-13.2 mGy, 0.90-4.40 mGy, and 0.20-0.28 mGy, respectively. The effective dose (ED) values for STD, LDCT, and ULD chest CT protocols ranged from 1.66-6.60 mSv, 0.50-0.80 mGy, and 0.39-0.64 mSv, respectively. Compared with the standard (STD), LDCT reduced the dose reduction by a factor of 2-4, whereas ULD reduced the dose reduction by a factor of 8-13. These dose reductions were achieved by applying scan parameters and techniques such as iterative reconstructions, ultra-long pitches, and fast spectral shaping with a tin filter. Using LDCT, the cumulative radiation dose of serial CT examinations during the acute period of COVID-19 may have been inferior or equivalent to that of conventional CT.

Photoneutrons and Gamma Capture Dose Rates at the Maze Entrance of Varian TrueBeam and Elekta Versa HD Medical Linear Accelerators

Herein, we evaluated the neutron and gamma capture dose equivalent rates at the maze entrance of Varian TrueBeam and Elekta Versa HD™ medical linear accelerators (linacs) using experimental measurements as well as empirical calculations. Dose rates were measured using calibrated neutron and gamma area survey meters placed side-by-side at the measurement point of interest. Measurements were performed at a source-to-detector distance of 100 cm, with a 10 × 10 cm² field size therapeutic X-ray beam, and a 30 × 30 × 15 cm³ solid water patient equivalent phantom, with a linac operating at 15, 10 MV, and 10 MV flattened filter-free (FFF). Dose rates were also measured at different points at the centerline along the maze towards the maze entrance. The measured dose equivalent rates at the maze entrance were comparable to those reported in the literature. The dose rates along the maze decreased exponentially towards the maze entrance and were significant for short maze lengths. The evaluated empirical methods for estimating neutron dose rates at the maze entrance of a linac proposed by Kersey, the modified Kersey method and Falcão method, agree by a factor of two from the experimental measurements. The results revealed vital radiation protection considerations owing to neutron contamination in external beam therapy.

An approach for the online determination of Entrance Surface Air Kerma (ESAK) from Kerma Area product (PKA) in digital radiology

We propose determining the entrance surface air kerma (ESAK) from the kerma area product (P_KA) in digital radiology. ESAK values were derived from the X-ray tube outputs and patient exposure factors across five X-ray departments. Using linear regression between ESAK and P_KA values, the slope and intercept coefficients were determined for each X-ray equipment and procedure. The method was examined using the data collected from patients who underwent chest PA/LAT, abdomen, pelvic AP, and lumbar spine AP/LAT X-ray examinations. The results showed a highly significant correlation between ESAK and P_KA values and correlation coefficients, ranging from 0.77 to 1 with P-value < 0.001 in most studies. This method can be employed by incorporating dose data and related parameters into the X-ray device's software, similar to other dose-displayed information. The online determination of ESAK from P_KA could help with quality assurance and patient dose management in digital radiology.

Radiation Attenuation Assessment of Serpentinite Rocks from a Geological Perspective

Serpentinites are metamorphic rocks that are widely applied as aggregates in the production of radiation-shielding concrete. Different varieties of massive serpentinite mountains located in Egypt exist without real investment. Hence, this study aims to evaluate the radiation shielding efficacy of three varieties of serpentinite rocks from different geological perspectives: mineralogical, geochemical, and morphological characteristics. X-ray diffraction, transmitted-light microscopy, and thermal analysis were required to characterize their mineralogical composition, while X-ray fluorescence was necessary to investigate their geochemical features. Moreover, scanning electron microscopy was used to detect their morphological characteristics. On the other hand, the PuBe source and stilbene detector were employed for the experimental determination of fast neutrons and γ-ray attenuations, which were conducted at energy ranges of 0.8−11 and 0.4−8.3 MeV, respectively. Based on the mineralogical, geochemical, and morphological characteristics of these rocks, the radiation attenuation capacity of lizardite > antigorite > chrysotile. However, these serpentinites can be applied as a natural alternative to some radiation-shielding concrete in radiotherapy centers and other counterpart facilities.

Comparison of Dosimetry Protocols for Electron Beam Radiotherapy Calibrations and Measurement Uncertainties

This paper presents guidelines for the calibration of radiation beams that were issued by the International Atomic Energy Agency (IAEA TRS 398), the American Association of Physicists in Medicine (AAPM TG 51) and the German task group (DIN 6800-2). These protocols are based on the use of an ionization chamber calibrated in terms of absorbed dose to water in a standard laboratory’s reference quality beam, where the previous protocols were based on air kerma standards. This study aims to determine uncertainties in dosimetry for electron beam radiotherapy using internationally established high-energy radiotherapy beam calibration standards. Methods: D_w was determined in 6-, 12- and 18 MeV electron energies under reference conditions using three cylindrical and two plane-parallel ion chambers in concert with the IAEA TRS 398, AAPM TG 51 and DIN 6800-2 absorbed dose protocols. From mean measured D_w values, the ratio TRS 398/TG 51 was found to vary between 0.988 and 1.004, while for the counterpart TRS 398/DIN 6800-2 and TG 51/DIN 6800-2, the variation ranges were 0.991–1.003 and 0.997–1.005, respectively. For the cylindrical chambers, the relative combined uncertainty (k = 1) in absorbed dose measurements was 1.44%, while for the plane-parallel chambers, it ranged from 1.53 to 1.88%. Conclusions: A high degree of consistency was demonstrated among the three protocols. It is suggested that in the use of the presently determined dose conversion factors across the three protocols, dose intercomparisons can be facilitated between radiotherapy centres.

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.

PROPOSED NATIONAL DIAGNOSTIC REFERENCE LEVELS FOR STANDARD RADIOGRAPHIC X-RAY PROCEDURES IN SUDAN

This study aimed to calculate patient radiation doses for adults during the seven most commonly performed conventional X-ray procedures, and to propose national diagnostic reference levels (DRLs). A representative sample of patients from 29 hospitals was included. The entrance surface air kerma (ESAK) was calculated by measuring X-ray tube output and the corresponding technical and exposure factors for each patient. Third-quartile values of the mean ESAK distributions were proposed as DRL values. The DRLs in mGy were as follows: 0.6 for chest postero-anterior (PA), 3.5 for skull AP, 1.7 for skull lateral (LAT), 2.7 for abdominal, 2.6 for pelvic AP, 3.7 for lumbar spine AP and 8 for lumbar spine LAT. Compared with literature, the maximum percentages increase were in chest PA (329%) and skull AP (187%). Since the suggested DRL for chest PA was higher than literature values, dose optimization and a review of its value is recommended.

Estimates of Patient Radiation Doses in Digital Radiography Using DICOM Information at a Large Teaching Hospital in Oman

In this study, we sought to estimate the patient radiation doses in the digital radiography X-ray examinations conducted in a large hospital. The patient exposure factors and kerma-area product (PKA) were retrospectively recorded via the Digital Imaging and Communications in Medicine (DICOM) header for 547 patients. The entrance surface air kerma (ESAK) was estimated from the measurements of the X-ray tube output and recorded exposure factors, as well as from the console that displayed PKA as an alternative method. Effective doses were estimated from ESAK and PKA values using the appropriate conversion coefficient. In the chest PA, chest LAT, cervical spine AP, cervical spine LAT, abdomen AP, pelvis AP, lumbar spine AP, and lumbar spine LAT, the median ESAK (mGy) was found to be 0.13, 0.27, 0.35, 0.52, 0.70, 1.06, 2.33, and 4.18 mGy, respectively. Median PKA values were 0.10, 0.26, 0.14, 0.17, 0.77, 0.68, 0.81, and 1.11 Gy cm2, respectively. The estimated effective dose from ESAK and PKA values yielded comparable results. The comparison revealed that the ESAK and PKA values fell far below the reported in the literature. The results showed that the information of the DICOM deader is valuable for dosimetry and optimization.

RADIATION PROTECTION IN THE RELEASE OF PATIENTS RECEIVING 131I TREATMENT

Radiation measurements were made to support radiation protection decisions and instructions concerning the release of patients receiving 131I treatment in Sudan. In hyperthyroidism, administered activity ranged from 370 to 1110 MBq (average: 817.8 MBq), and air-absorbed dose rate at 1 m in front of the patients varied from 20 to 66 μGy h-1 (average: 47.0 μGy h-1). For thyroid cancer patients, the administered activity ranged from 3700 to 7400 MBq (average: 4816.2 MBq), and the air-absorbed dose rate at 1 m in front of the patients ranged from 3 to 55 μSv h-1 (average: 19.2 μSv h-1). On average, the contamination activity was highest in the patients' clothes: 11.0 Bq cm-2, followed by the toilet: 6.6 Bq cm-2 and the front bed: 2.9 Bq cm-2. The estimated release times from the confinement were well with the radiation safety criteria, whereas instruction are given concerning precaution times to limit radiation exposure to family members and co-worker.

RETROSPECTIVE ANALYSIS OF PATIENT RADIATION DOSES IN DIGITAL CORONARY ANGIOGRAPHY AND INTERVENTIONS

This study sought to assess patient and operator eye lens doses in diagnostic coronary angiography (DCA) and percutaneous coronary interventions (PCI) in a University hospital in Oman. Kerma area product (PkA), cumulative air kerma (CAK) and fluoroscopic time (FT) were retrospectively recorded from the DICOM header for 264 patients. The median (interquartile range) of FT, PKA and CAK were: 5.3 min (2.6-10.5), 60.9 Gy cm2 (41.3-91.4) and 0.86 Gy (0.61-1.29), respectively, for DCA procedures, and they were 20.2 min (13.3-30.1), 174.0 Gy cm2 (113.7-253.3) and 2.6 Gy (1.8-3.9), respectively, for PCI procedures. The results revealed wide variability in patient doses among individual patients. Monitoring and recording patient dose data can be valuable for quality assurance and patient safety purposes. Feedback to the operator may help optimize radiation doses to patients and prompt further action, as needed.

RADIATION DOSE DETERMINATION IN ABDOMINAL CT EXAMINATIONS OF CHILDREN AT SUDANESE HOSPITALS USING SIZE-SPECIFIC DOSE ESTIMATES

In this study, we thought to estimate the radiation exposure of children undergoing multi-detector CT examinations using size-specific dose estimates (SSDE). Console-displayed volume computed tomography dose index (CTDIvol) were recorded for a total of 78 paediatric abdominal CT examinations performed in six hospitals. Measurements of the patient diameters were taken from the mid-slice location on the transverse and scout CT images. Size-specific conversion coefficients were used to translate CTDIvol to the SSDE, according AAPM Report 204. For children aged 0-1 y, CTDIvol, SSDEtrans (from transverse images) and SSDEsco (from scout images) were: 12.80 ± 16.10, 14.43 ± 13.22; and 14.37 ± 13.03 mGy; respectively. For children aged 1-5 y, CTDIvol, SSDEtrans and SSDEsco were: 12.11 ± 14.47, 18.8 ± 18.61 and 16.51 ± 13.55 mGy; respectively. The obtained doses are higher than the corresponding diagnostic reference levels. SSDE increase with patient size as results of tube current modulation and is therefore a valuable tool for dose optimisation.

Patient radiation doses in intraoral and panoramic X-ray examinations in Sudan

Radiation doses were measured for the first time in intraoral and panoramic dental radiology at Sudanese hospitals. Doses were determined using various exposure settings for adults and children in 8 intraoral and 6 panoramic X-ray devices. The study sample was equally divided between devices using a digital image receptor (DR) and those using conventional screen film (SF). Radiation doses are reported in terms of incident air kerma (IAK) (intraoral radiology) and kerma area product (P_KA) (panoramic radiology). IAK values in intraoral radiology were: 1.45 mGy (DR), 4.45 mGy (SF), and 3.01 mGy (combined). For panoramic radiology, P_KA values ranged: from 35.8 to 103.2 mGy cm² (average: 70.4 mGy cm²) for children and from 65.7 to 151.4 mGy cm² (average: 103.4 mGy cm²) for adults. The results showed that the downward trend in patient doses can be achieved using digital imaging. The study revealed important concerns surrounding radiation protection, such as the lack of regular quality assurance programs and the use of circular collimators.

Radiation exposure during paediatric CT in Sudan: CT dose, organ and effective doses

The purpose of this study was to assess the magnitude of radiation exposure during paediatric CT in Sudanese hospitals. Doses were determined from CT acquisition parameters using CT-Expo 2.1 dosimetry software. Doses were evaluated for three patient ages (0-1, 1-5 and 5-10 y) and two common procedures (head and abdomen). For children aged 0-1 y, volume CT air kerma index (Cvol), air Kerma-length product and effective dose (E) values were 19.1 mGy, 265 mGy.cm and 3.1 mSv, respectively, at head CT and those at abdominal CT were 8.8 mGy, 242 mGy.cm and 7.7 mSv, respectively. Those for children aged 1-5 y were 22.5 mGy, 305 mGy.cm and 1.1 mSv, respectively, at head CT and 12.6 mGy, 317 mGy.cm, and 5.1 mSv, respectively, at abdominal CT. Dose values and variations were comparable with those reported in the literature. Organ equivalent doses vary from 7.5 to 11.6 mSv for testes, from 9.0 to 10.0 mSv for ovaries and from 11.1 to 14.3 mSv for uterus in abdominal CT. The results are useful for dose optimisation and derivation of national diagnostic reference levels.

A comparative study of adult patient doses in film screen and computed radiography in some Sudanese hospitals

A study was performed to compare adult patient doses in film screen (FS) and computed radiography (CR) diagnostic X-ray examinations in some hospitals in Sudan over a period of 1 y; during this period of time, the CR systems were introduced to replace FS systems. Radiation doses were estimated for 354 patients in five hospitals (two FS units and three CR units). Entrance surface air kerma (ESAK) was estimated from incident air kerma using patient exposure parameters and tube output. Dose calculations were performed using CALDOSE X 3.5 Monte Carlo-based software. In FS, third quartile of ESAK values for skull PA, skull LAT, chest PA, pelvis AP, lumbar spine AP and lumbar spine LAT were 1.5, 1.3, 0.3, 1.9, 2.8 and 5.9 mGy, respectively, while in CR, third quartile of ESAK values for the same examinations were 2.7, 1.7, 0.18, 1.7, 3.2 and 10.8 mGy, respectively. Comparable ESAK values were presented in FS and CR units. The results are important for future dose optimisation and setting national diagnostic reference levels.

Performance evaluation of two computed radiography systems and patient dose in pelvic examination

This study was carried out to evaluate the performance of two computed radiography (CR) units. These evaluations became necessary following the introduction of CR systems in Sudan. Evaluation of the CR systems was performed using physical image quality parameters: signal transfer property, modulation transfer function, normalised noise power spectrum, detective quantum efficiency and the subjective contrast detail detectability. Patient dose was measured in terms of entrance surface air kerma estimated from tube output and exposure factors for 100 patients who had undergone pelvic X-ray examinations. Fuji computed radiography velocity system with columnar screen dose results was much lower than those using CR975 system with granular screen. Patient doses delivered by both systems were within the international diagnostic reference levels.

Examination frequency and population dose from medical X-ray examinations in Sudan in 2010

This study was performed to estimate examination frequency and collective and per caput effective doses arising from medical X-ray procedures in Sudan, 2010. Information was collected from 30 hospitals performing radiography, computed tomography (CT), fluoroscopy and interventional radiology (IR) procedures. The estimated annual number of examinations was 33 million radiographic X-ray procedures (99 %), 0.34 million CT exams per year (14 % paediatrics CT), 0.02 million fluoroscopy and IR procedures. The estimated annual number of examinations was 326 per 1000 people. The estimated annual collective and per caput effective doses from medical X-ray procedures mount 7197 man Sv and 0.18 mSv, respectively. The study offered the first projection of frequency and population dose from medical X-ray examinations in Sudan and provides estimates of the impact of the medical X-ray procedures at the national level.

Radiation dose measurements for optimisation of chest X-ray examinations of children in general radiography hospitals

This study was performed to measure the entrance surface air kerma (ESAK) for optimisation of chest X-ray examination of children in general radiography hospitals in Khartoum. ESAK was estimated using the X-ray tube output exposure and patient-specific exposure parameters collected during routine examinations. The estimated ESAK values per radiography ranged from 17 to 89 μGy, 32 to 161, 67 to 242, 77 to 278; and from 95 to 389 μGy for Newborn, 1, 5, 10 and 15 y children, respectively. Doses are comparable with a previous study and are somewhat higher than the UK reference dose levels. The study demonstrated the necessity to follow guidelines for quality radiograph as a key element in the optimisation of X-ray examination of children. Frequent dose measurements are of particular importance for the optimisation of X-ray examination of children in general radiography hospitals.

Equipment performance and radiation protection status in X-ray fluoroscopy units in Sudan

The number of fluoroscopy and fluoroscopically guided procedures has been substantially growing in developing countries at the same time advanced and sophisticated equipment are used in some hospitals. However, radiation protection requirements are not necessarily well adopted. In this study nine fluoroscopy X-ray units in Sudan were examined for compliance with international standards. The tests included: beam quality, entrance surface air kerma, image quality and radiation field measurements. Staff radiation protection tools such as lead aprons and eye glasses were also visually examined to find out whether international recommendations were fulfilled and to determine the level of staff awareness. The measured peak tube voltage deviation exceeded the recommended tolerance level in 30 % of the measurements. The results of patient doses measurements exceeded the recommended reference dose levels in 43 % of the measurements; however image quality and radiation field generally fulfilled the requirements for most units. The study revealed that a considerable number of fluoroscopy units were not performing according to the international standards and highlights the need of optimisation of radiation protection.

Radiation doses from some common paediatric X-ray examinations in Sudan

Radiation doses to patients from some common paediatric X-ray examinations were studied in three hospitals in Khartoum state, Sudan. Entrance surface dose (ESD) was determined from exposure settings using DosCal software. Totally, 459 patients were included in this study. Mean ESDs obtained from anteroposterior projection for chest, skull, abdomen and pelvis for neonates falls in the range of 52-100, 115-169, 145-183, 204-242 microGy, respectively. For a 1-y-old infant, mean ESD range was 80-114, 153-202, 204-209, 181-264 microGy, respectively. Some doses for neonates and infants were exceeding the reference doses by >20%. The results highlighted that a good technique has to adhere to guidelines necessarily. As demonstrated elsewhere, patients' doses were high in departments using single-phase generators compared with those using constant potential. The results presented will serve as a baseline data needed for deriving reference doses for paediatric X-ray examinations in Sudan.

Entrance surface doses to patients undergoing selected diagnostic X-ray examinations in Sudan

The aim of the study was to evaluate the entrance surface doses (ESDs) to patients undergoing selected diagnostic X-ray examinations in major Sudanese hospitals. ESD per examination was estimated from X-ray tube output parameters in four hospitals comprising eight X-ray units and a sample of 346 radiographs. Hospital mean ESDs estimated range from 0.17 to 0.27 mGy for chest AP, 1.04-2.26 mGy for Skull AP/PA, 0.83-1.32 mGy for Skull LAT, 1.31-1.89 mGy for Pelvis AP, 1.46-3.33 mGy for Lumbar Spine AP and 2.9-9.9 mGy for Lumbar Spine LAT. With exception of chest PA examination at two hospitals, mean ESDs were found to be within the established international reference doses. The results are useful to national and professional organisations and can be used as a baseline upon which future dose measurements may be compared.

Quality control of equipment used in digital and interventional radiology

Digital and interventional radiology are increasingly important areas of radiology. Quality control (QC) of such equipment is of particular importance to avoid unnecessary high doses and to help to achieve good image quality. Within the DIMOND III project, equipment requirements and specifications for digital and interventional radiology have been formulated. A protocol for QC tests has been drafted based on various national and international recommendations. Tests are included for various parts of the imaging chain, i.e. X-ray tube and generator, X-ray tube control system, laser printer and display station, and image quality and patient dose. Preliminary tolerance levels have been set for the various tests, after initial measurements. To check the suitability of QC tests and stated tolerance levels, measurements were made at the University Hospital Gasthuisberg in Leuven for equipment used for paediatric radiology and a unit used for chest examinations. The results of the various tests are reported.