Patient Dose In Computed Tomography Research Articles

Establishing Protocol-based Dose Metrics for Common Abdomen and Pelvis Computed Tomography Protocols

The majority of the existing diagnostic reference levels (DRLs) that have been established for computed tomography (CT) are based on various anatomical locations, such as the head, chest, abdomen, etc. However, DRLs are initiated to improve radiation protection by conducting a comparison of similar examinations with similar objectives. The aim of this study was to explore the feasibility of establishing dose baselines based on common CT protocols for patients who underwent enhanced CT abdomen and pelvis exams. Dose length product total (tDLPs), volumetric CT dose index (CTDIvol), size-specific dose estimate (SSDE), effective dose (E), and scan acquisition parameters for a total of 216 adult patients, who underwent an enhanced CT abdomen and pelvis exams over a one-year period, were obtained and retrospectively analyzed. Spearman coefficient and one-way ANOVA tests were used to check significant differences between dose metrics and the different CT protocols. The data exhibited 9 different CT protocols to acquire an enhanced CT abdomen and pelvis exam at our institute. Out of these, 4 were found more common, i.e., CT protocols were acquired for a minimum of 10 cases. Triphasic liver demonstrated the highest mean and median tDLPs across all 4 CT protocols. Triphasic liver protocol registered the highest E followed by gastric sleeve protocol with a mean of 28.7 and 24.7 mSv, respectively. Significant differences (p < 0.0001) were found between the tDLPs of anatomical location and the CT protocol. Evidently, wide variability exists across CT dose indices and patient dose metrics relying on anatomical-based dose baseline, i.e., DRLs. Patient dose optimizations require establishing dose baselines based on CT protocols rather than the anatomical location.

Protocols-based notification versus diagnostic reference levels as an optimization tool in computed tomography

We compare a dose baseline optimization tool built around clinical protocols and notification of dose based on the diagnostic reference level (DRL). In regard to computed tomography (CT), retrospective analysis has been made of the volume CT dose-index (CTDIvol) and dose-length-product (DLP) for a total of 230 adult patients undergoing enhanced CT abdomen and pelvis examinations. From this, a dose baseline was established. The DRL based notification level (NL) was set at twice the Local DRL. The protocol baselines for dose were set at the median and 75th percentiles of dose spectrum. Spearman coefficient and one-way ANOVA tests were used for statistical correlation and differences between DLP and various CT protocols. Significant differences (p < 0.05) were found between DLPs for common CT protocols including routine Abd&Pelv + C, triphasic liver, gastric sleeve, pancreas phases, and tumour. The NL was set at 1194 mGy cm, while the median protocols dose baselines for routine Abd&Pelv + C, triphasic liver, gastric sleeve, pancreas phases, and tumor were 748, 1450, 1530, 1620, and 2040 mGy cm respectively. A significant reduction was observed in the number of dose notification counts when defining dose baselines at the 75th percentile for triphasic liver (26%), gastric sleeve (27%), pancreas phases (25%), and tumour (20%). The observed reductions associated with the established NLs based on CT clinical indications/protocols may limit the counts of notifications alerts and further allow an opportunity for CT protocol standardization and patient dose optimization.

Analysis of a CT patient dose database with an unsupervised clustering approach

PurposeThis study investigated the benefits of implementing a cluster analysis technique to extract relevant information from a computed tomography (CT) dose registry archive. MethodsA CT patient dose database consisting of about 12,000 examinations and 29,000 single scans collected from three CT systems was interrogated. The database was divided into six subsets according to the equipment and the reference phantoms in the definition of the dose indicators. Hierarchical (single, average, and complete linkage, Ward) and not hierarchical (K-means) clustering methods were implemented using R software. The suitable number of clusters for each CT system was determined by analysing the dendrogram, the within clusters sum of squares, and the cluster content. Summary statistics were produced for each cluster, and the outliers of the dose indicator distribution were investigated. ResultsWard clustering identified the most common combinations of scanning parameters for each group. The optimal number of clusters for each CT equipment system ranged from 5 to 15. The main diagnostic applications were then extracted from each cluster. Outlier analysis of the dose indicator distribution of each cluster revealed potential improper settings that resulted in increased patient dose. ConclusionsClustering methods applied to CT patient dose archives provide a quick and effective overview of the main combinations of currently used exposure parameters and the consequences for dose indicator distributions, also when protocol labels and/or study descriptions are not homogeneous.

Doses from cervical spine computed tomography (CT) examinations in the UK.

To review doses to patients undergoing cervical spine CT examinations in the UK. A data collection form was developed and distributed to medical physicists and radiographers via e-mail distribution lists. The form requested details of CT scanners, exposure protocols and patient dose index information. Data were received for 73 scanners. It was seen that 97% of scanners used automatic exposure control, and 60% of scanners used an iterative reconstruction technique for cervical spine examinations. The majority of scans were taken at 120 kV. The average patient dose indicators in terms of CT dose index (CTDIvol) ranged from 3.5 to 39.7 mGy (mean value 16.7 mGy), and for the DLP, ranged from 87 to 1030 mGy cm (mean value 379 mGy cm) as quoted for the standard 32 cm phantom. The rounded third quartile value of the mean dose distributions from this study were a CT dose index (CTDIvol) of 20 mGy and a dose-length product of 440 mGy cm as quoted for a 32 cm body phantom. These are significantly higher than those in the 2011 Public Health England CT dose survey when adjusted for phantom size. It is suggested that the existing national diagnostic reference levels for cervical spine CT should be amended, both with the new values and also to quote according to the 32 cm phantom. Advances in knowledge: Proposed new national diagnostic reference levels are presented for cervical spine CT examinations.

Abstract ID: 167 Assessing the CTDIVOL and SSDE from dose profiles in cylindrical phantoms of water equivalent materials

The assessment of the Computed Tomography (CT) radiation output has become a challenge to researchers and technicians due to the rapid evolution of the technology incorporated in CT machines. To guarantee the correct performance and to avoid accidents in CT examinations, the novel CT units require the use of specific phantoms for dosimetry and imaging evaluations. Nevertheless, such phantoms are expensive or they are unavailable in the market. In this work, water equivalent materials produced in the Medical Physics and Radiation Dosimetry Group of the University of Sao Paulo [1] will be evaluated in order to demonstrate their use in phantom fabrication for dosimetry and imaging purposes. Dose profiles along the central and peripheral axis of cylindrical phantoms of water equivalent material were computed in order to assess the quantities: volume CT Dose Index ( CTDI vol ) and Size Specific Dose Estimate (SSDE). The CTDI vol and SSDE are used as CT radiation output and patient dose descriptors, respectively. Three water equivalent materials: H2O_1 (Propylene + Chloroethylene + Sodium hydroxide), H2O_2 (Propylene + Phosphorous acid + Sodium hydroxide) and H2O_3 (Polyethylene + Sodium hydroxide + Calcium Fluoride) were evaluated in this work. X-ray source models based on phase space files generated by Monte Carlo simulation for 80, 100, 120 and 140 kV. The X-ray source model was implemented following the technical specification of the GE Lightspeed Ultra CT machine (General Electric Company, Boston, USA) and it incorporates the anode self-attenuation, anode tilt and the bowtie filters for head and body examination. The CTDI vol was computed in a cylindrical phantom of 15 cm length and the SSDE was achieved varying phantom diameters of 5–40 cm. CTDI vol and SSDE results were compared with literature data for reference materials. Finally, the results of this work will be used as reference to guarantee the usefulness of the materials developed in the GDFM in the manufacture of simulators for CT quality control.

Radiological protection in computed tomography and cone beam computed tomography.

The International Commission on Radiological Protection (ICRP) has sustained interest in radiological protection in computed tomography (CT), and ICRP Publications 87 and 102 focused on the management of patient doses in CT and multi-detector CT (MDCT) respectively. ICRP forecasted and 'sounded the alarm' on increasing patient doses in CT, and recommended actions for manufacturers and users. One of the approaches was that safety is best achieved when it is built into the machine, rather than left as a matter of choice for users. In view of upcoming challenges posed by newer systems that use cone beam geometry for CT (CBCT), and their widened usage, often by untrained users, a new ICRP task group has been working on radiological protection issues in CBCT. Some of the issues identified by the task group are: lack of standardisation of dosimetry in CBCT; the false belief within the medical and dental community that CBCT is a 'light', low-dose CT whereas mobile CBCT units and newer applications, particularly C-arm CT in interventional procedures, involve higher doses; lack of training in radiological protection among clinical users; and lack of dose information and tracking in many applications. This paper provides a summary of approaches used in CT and MDCT, and preliminary information regarding work just published for radiological protection in CBCT.

MO‐D‐134‐06: A Preliminary Method Correlating Patient‐Specific Parameters with Direct Measurements to Estimate Organ Doses in CT

Purpose: In the field of Computed Tomography (CT) dosimetry, there remains a need to accurately measure organ doses. Such measurements are only meaningful if they are performed under actual clinical scanning conditions, for this purpose, a cadaver can serve as the measurement subject that most closely mimics a living patient. Organ doses were measured in 7 adult female cadaveric subjects with varying body mass indices (BMIs) and for various CT protocols. Methods: A tube placement system allowed external access to internal organs, in which optically‐stimulated luminescent dosimeters (OSLDs) were placed and used to measure dose. Dosimeter placement and location was based on organ size and distribution. In order to determine organ doses of real patients, a correlation between various patient size parameters and the measured organ doses was explored. Only measurements that could be performed on a CT image or subject‐specific parameters or data which could otherwise be obtained for an actual patient were considered for this correlation. The size parameters that were examined included: body mass index (BMI), the AP and lateral dimensions of the patient, and patient perimeter. Results: The BMIs for the 7 subjects ranged from 16.6–43.9, spanning from underweight to extreme obesity. Overall average organ doses from a CAP exam for all subjects ranged from 11.8–24.4 mGy. Generally, organ doses were shown to increase with all size parameters examined. Conclusion: For the purpose of accuracy, the estimation of patient dose in CT must be based on actual physical measurements. A complete set of direct organ dose measurements for 7 adult female cadavers has been accomplished for common CT exams with this research. It has been shown before that patient size parameters can be indicative of patient dose. This work has shown further validation of this concept.

Patient dose and image quality in low-dose abdominal CT: a comparison between iterative reconstruction and filtered back projection

In computed tomography (CT), there is increasing concern for potential CT radiation hazards. Several raw-data-based iterative reconstruction techniques attempt to facilitate low-dose imaging without compromising image quality, which raises the question whether these techniques may allow further dose reduction. To compare image quality of iterative reconstruction and filtered back projection in low-dose abdominal CT and study the potential for further dose reduction. Forty-five patients underwent CT of the abdomen twice: with standard low-dose technique and with 30% reduced dose, using both iterative reconstruction and filtered back projection. Four radiologists made pair-wise image quality assessment using five visual criteria. Visual grading regression (VGR) and weighted kappa (κ w) were used to analyze the data. There were significant effects of log(mAs) (P <0.001) and reconstruction algorithm (P <0.01) on all image quality criteria with an estimated potential dose reduction of 5-9%. Inter-observer agreement ranged from 70% to 91% and κ w from -0.01 to 0.57. An iterative reconstruction algorithm improved image quality in abdominal CT, but the estimated dose reduction was rather small. The full potential of the algorithm remains unclear.

WE-E-144-01: The Management of Imaging Procedure Dose 3: Computed Tomography

WE-E-144-01: The Management of Imaging Procedure Dose 3: Computed Tomography

Survey of practice in paediatric computed tomography

The purpose of this study was to explore the frequency of paediatric computed tomography (CT) examinations in several hospitals in Bulgaria and to assess the current practice. The standard forms provided by the International Atomic Emergency Agency for survey of the paediatric CT practice were used. Six hospitals provided data on frequency of paediatric CT examinations performed in 2009. Large variations in dose, up to a factor of 4, were found among the centres within the same age group for a given procedure, and in one of the hospitals the paediatric dose was twice higher than the adult dose. Seven departments use dedicated CT protocols for children. Only 4 in 12 departments keep records of patient dose. Dose information for previous examinations is not required by the radiologists. The collected detailed data provided preliminary information how the patient doses in paediatric CT can be reduced. Recommendations were given based on the findings.

Patient doses in paediatric CT: feasibility of setting diagnostic reference levels

Despite the fact that doses to paediatric patients from computed tomography (CT) examinations are of special concern, only few data or studies for setting of paediatric diagnostic reference levels (DRLs) have been published. In this study, doses to children were estimated from chest and head CT, in order to study the feasibility of DRLs for these examinations. It is shown that for the DRLs, patient dose data from different CT scanners should be collected in age or weight groups, possibly for different indications. For practical reasons, the DRLs for paediatric chest CT should be given as a continuous DRL curve as a function of patient weight. For paediatric head CT, DRLs for a few age groups could be given. The users of the DRLs should be aware of the calibration phantom applied in the console calibration for different paediatric scanning protocols. The feasibility of DRLs should be re-evaluated every 2-3 y.

CT Dose Index and Patient Dose: They AreNotthe Same Thing

Estimates of individual patient risk, and epidemiologic studies assessing potential late effects, must use patient size–specific dose estimates—they cannot use only scanner output (volume CT dose index or dose-length product).

Radiation protection of patients in diagnostic radiology: Status of practice in five Eastern-European countries, based on IAEA project

The purpose of this work was to investigate status of imaging technology and practice in five countries in Eastern-European region and evaluate the impact of IAEA projects on radiation protection of patients. Information collected using standardized IAEA protocol included status of technology, practices and patient dose levels in interventional procedure, radiography, mammography and computed tomography (CT). In spite of increased number of digital units, single phase generators or units older than 30 year are still in use. Examples of obsolete practice such as using fluoroscopy for positioning, photofluorography, chest fluoroscopy and soft-beam technique for chest radiography are also in use. Modern multi-slice CT or digital mammography units are available; however, there is lack of adequate radiation protection and medical physics support in hospitals. Information on patient doses in interventional procedures, conventional radiography, mammography and CT was collected to have baseline data and corrective measures were proposed with appropriate follow up actions taken.

Patient-size-dependent radiation dose optimisation technique for abdominal CT examinations

Since patient doses from computed tomography (CT) are relatively high, risk-benefit analysis requires dose to patients and image quality be optimised. The aim of this study was to develop a patient-dependent optimisation technique that uses patient diameter to select a combination of CT scanning parameters that minimise dose delivered to patients undergoing abdominal CT examinations. The study was performed using cylindrical phantoms of diameters ranging from 16 to 40 cm in order to establish the relationship between image degradation, CT scanning techniques, patient dose and patient size from two CT scanners. These relationships were established by scanning the phantoms using standard scanning technique followed by selected combinations of scanning parameters. The image noises through phantom images were determined using region of interest software available in both scanners. The energy depositions to the X-ray detector through phantoms were determined from measurements of CT dose index in air corrected for attenuation of the phantom materials. The results demonstrate that exposure settings (milliampere seconds) could be reduced by up to 82 % for smaller phantom relative to standard milliampere seconds, while detector signal could be reduced by up to 93 % for smaller phantom relative to energy depositions required when scanned using standard scanning protocols. It was further revealed that the use of the object-specific scanning parameters on studies performed with phantom of different diameters could reduce the incident radiation to small size object by up to 86 % to obtain the same image quality required for standard adult object. In view of the earlier mentioned fact, substantial dose saving from small-sized adults and children patients undergoing abdomen CT examinations could be achieved through optimal adjustment of CT scanning technique based on the patient transverse diameter.

Poster - Thur Eve - 68: Computed Tomography Patient Dose and National Diagnostic Reference Levels in Iran

Objective: To measure radiation doses from Computed Tomography(CT) in the head, chest and abdomen techniques and compare them with the international diagnostic reference levels, as part of National Research project, attempting to establish National Diagnostic Reference Levels (NDRL's). Materials and Methods: 50 CTscanners from all private and none private hospitals or clinics around the country were selected. All scanners were conventional or helical single‐slice or multi— detectors row CT systems. Five thousand patients undergoing above mentioned techniques were included. Collected data included patient height, weight, sex, and age; tube voltage and tube current—time product settings; pitch; slice thickness; number of slices. Weighted or volumetric CT dose index (CTDI); and dose‐length product (DLP) were measured using a pencil shape ionizing chamber with standard rod Plexiglas's with16, 32 cm in diameters for head and body respectively. Results: Mean volumetric CT dose index and DLP values were below the European diagnostic reference levels: 31 mGy and 1135 mGy‐ cm, respectively, at head CT; 12.8 mGy and 514 mGy‐cm, respectively, at chest CT; and 13.4 mGy and 537 mGy‐ cm, respectively, at abdominal CT. Estimated effective doses were 2.61, 8.74, and 8.06 mSv, respectively. Conclusion: NDRL's for CT is going to be established in the country and comparison of our results with EU revealed that we are in a good conditions but we have to reconsider CT techniques parameters for children.

The development of a guidance level for patient dose for CT examinations in Korea

The primary goal of this study was to analyse the state of patient doses in the field of computed tomography (CT) examinations in the Republic of Korea. All survey data including the CT applications and patient dose details were obtained from general hospitals registered in the Korean Hospital Association. The systematic analysis of the patient dose survey gives target values of the weighted computed tomography dose index (CTDI(w)) and the dose-length product (DLP). The targeted CTDI(w) values were 69, 69, 31, 19, 44, 25, 24, 20, 2, 19 and 19 mGy for the brain non-contrast enhancement (BNCE), brain contrast enhancement (BCE), neck, chest, spine, liver, pancreas, stomach, kidneys, abdomen routine and abdomen trauma protocols, respectively. The targeted DLP values were 1056, 2112, 762, 1234, 1338, 2794, 2742, 2378, 2836, 1844 and 1939 mGy cm for the BNCE, BCE, neck, chest, spine, liver, pancreas, stomach, kidneys, abdomen routine and abdomen trauma protocols, respectively. Comparing with the EUR recommendation, especially in the DLP, the adjustment of the total scan phase frequency and the shortening of the scan phase in each scan phase are needed to reduce the patients radiation exposure to international standards.

SU‐FF‐I‐08: Ramping and Overscanning Contributions to Patient Dose in Helical CT

Purpose: In helical computed tomography (CT) scans, slices adjacent to the clinical volume of interest, known as z overscanning lengths, are acquired for reconstruction. Additionally, CT machines undergo a transient power state, known as tube ramping, to reach full power. This investigation will characterize the dependence of tube ramping time and z overscanning length on pitch, rotation time, beam collimation, and reconstruction slice width. These relationships will be utilized to determine the contributions to patient dose. Methods and Materials: A real‐time fiber optic coupled dosimetry system with 10 ms temporal resolution is interfaced with three organic scintillators with 0.157 mm3 volumes. A Siemens Somatom Sensation 16 multislice helical CT scanner is used for the study with pitches varying from 0.5 to 1.5; rotation speeds between 0.5 and 1.5 seconds per rotation; reconstructed slice widths of 2.0 to 10.0 mm; and beam collimation of either 12 or 24 mm. One dosimeter remains stationary while two dosimeters are translated through the beam to provide real‐time profiles of the x‐ray field. Results: The ramping time was found to be independent of pitch and represented 0.5% of the total scan time. The z overscanning length was found to be monotonically increasing with pitch and represents anywhere from 14.3% to 35.9% of the total scan length. Conclusions: While ramping time remained constant, it has been demonstrated that z overscanning length is heavily dependent upon pitch — a high pitch added 7.1 cm to a 20.3 cm clinical scan length. Both z overscanning and ramping time must be taken into consideration when planning and managing patient dose. The effect of rotation time, beam collimation, and reconstruction slice width on ramping time and z overscanning length will be investigated in future work.

Optimizing dosage in thoracic computerized tomography

Radiation exposure in computed tomography (CT) by far exceeds radiation dose in chest radiography. Dose requirements in CT of the chest, however, are much smaller than for the abdomen because of low x-ray absorption in the lungs. This article describes scanner parameters that influence patient exposure and image quality. Suitable compromises will be explained that allow for dose reduction in chest CT without jeopardising image quality. Dose reduction in chest CT should be performed depending on the clinical indication and requires active reduction of mAs settings. For helical CT, a pitch of 1.5 to 2 should be employed. Dedicated low-dose techniques for screening of bronchogenic carcinoma are described. Dose reduction decreases image quality but the detrimental effects can be reduced by applying proper parameters for scanning and image reconstruction. Thus, images of the mediastinum should be reconstructed with a smoothing filter, while a higher resolution filter should be used for the lungs. In multislice CT, reconstruction of thicker axial or multiplanar sections retains spatial resolution but keeps image noise and thus dose requirements low. The effective, weighted CT dose index (CTDIw,eff) can serve as a rough estimate of the effective patient dose (E) in helical or multislice CT of the whole chest: for most scanners and age groups the conversion factors are 0.5 mSv/mGy for females and 0.4 mSv/mGy for males.

Dose reduction in CT by anatomically adapted tube current modulation. II. Phantom measurements.

Theoretical considerations and simulation studies have led to the expectation that patient dose in CT (computed tomography) can be reduced significantly without a concomitant loss in image quality if tube current is modulated according to rotation angle-dependent x-ray attenuation. In this study, the simulation results presented in Part I were validated with phantoms. We used one cylindrical, two oval, and one elliptical phantom, available both as mathematical descriptions and in physical form, to mimic different parts of the human anatomy. Prototype hardware was available to control tube current on a commercial clinical CT scanner. The potential for dose reduction was evaluated for sinusoidal and attenuation-based current modulation for variable modulation amplitudes. Agreement between simulations and measured results was better than within 10%. Dose reduction values of 8%-56% were found depending on the phantom geometry and tube current modulation function. Attenuation-based tube current modulation consistently yielded higher reduction than fixed-shape sinusoidal modulation functions. For the shoulder phantom and 70% modulation amplitude, 44.6% dose reduction was measured as compared to 34.1% for sinusoidal modulation. A maximum of 56% was measured for the shoulder phantom including inserts. Specifying mAs reduction as an estimate for dose reduction proved to be a valid and conservative estimate; measured dose is reduced more strongly than the total mAs product both centrally and on average. First patient studies confirm the results of simulation and phantom studies. We conclude that attenuation-based online tube current control has great potential for reducing patient dose in CT and that it should be made generally available for clinical use.