CTDI Values Research Articles

Diagnostic reference levels in spinal CT: Jordanian assessments and global benchmarks.

To reduce radiation dose and subsequent risks, several legislative documents in different countries describe the need for Diagnostic Reference Levels (DRLs). Spinal radiography is a common and high-dose examination. Therefore, the aim of this work was to establish the DRL for Computed Tomography (CT) examinations of the spine in healthcare institutions across Jordan. Data was retrieved from the picture archiving and communications system (PACS), which included the CT Dose Index (CTDI(vol)) and Dose Length Product (DLP). The median radiation dose values of the dosimetric indices were calculated for each site. DRL values were defined as the 75th percentile distribution of the median CTDI(vol) and DLP values. Data was collected from 659 CT examinations (316 cervical spine and 343 lumbar-sacral spine). Of the participants, 68% were males, and the patients' mean weight was 69.7 kg (minimum = 60; maximum = 80, SD = 8.9). The 75th percentile for the DLP of cervical and LS-spine CT scans in Jordan were 565.2 and 967.7 mGy.cm, respectively. This research demonstrates a wide range of variability in CTDI(vol) and DLP values for spinal CT examinations; these variations were associated with the acquisition protocol and highlight the need to optimize radiation dose in spinal CT examinations.

Optimizing Radiation Dose Using Ctdi Value Analysis and Image Quality in the Thorax Low Dose CT Scan (LDCT) Technique with Reduced Dose Variations Using Idose Software

Radiation exposure to patients with higher cumulative effective doses on thorax CT scanning is very detrimental for cancer patients undergoing follow-up and raises the level of concern about the harmful effects of radiation doses received by patients. Reducing the tube voltage will reduce the radiation dose and image quality. To maintain good image quality, the iDose strength level is set. iDose is able to reduce radiation dose and improve image quality by maintaining low noise. Analyze the optimization of radiation dose and image quality in the thorax Low Dose CT Scan (LDCT) examination protocol with tube voltage settings and variations in the use of iDose software. This type of research is True-Experimental research with a Posttest-Only Control Design. The object used is a water phantom with tube voltage settings of 80 kVp, 100 kVp and 120 kVp and the use of iDoe 3 -5. Assessment includes radiation dose, noise, SNR and NPS. After getting optimal results from setting the tube voltage and iDose strength level, these results were applied to a Thorax CT Scan examination in patients, and a subjective assessment of image quality was carried out. Reducing the tube voltage (kVp) from 120 kV to 80 kV was able to reduce the radiation dose by 69.8%, and reducing the tube voltage from 120 kV to 100 kV in the Thorax CT Scan protocol was able to reduce the radiation dose by 34.2 %. There is an influence of setting the tube voltage and setting the iDose strength level on the radiation dose and image quality of the Low Dose CT Scan of the Thorax. Setting tube voltage and high iDose strength levels can improve image quality in CT scans, characterized by decreasing noise and NPS values and increasing SNR values. Tube voltage settings and iDose level settings affect the radiation dose and image quality. The use of a tube voltage of 80 kVp and strength level iDose 5 is able to provide optimal radiation dose and image quality on Thorax Low Dose CT Scan.

Myeloma bone disease imaging on a 1st-generation clinical photon-counting detector CT vs. 2nd-generation dual-source dual-energy CT

ObjectiveSubjective and objective image quality comparison of bone microstructure and disease-related abnormalities in multiple myeloma patients using a 1st-generation dual-source photon-counting detector CT(DS-PCD-CT) and a 2nd-generation dual-source dual-energy (energy-integrating detector) CT (DS-EID-CT).MethodsFifty multiple myeloma patients (mean age 67.7 ± 10.9 years,16 females) were prospectively enrolled. Unenhanced whole-body CTs were clinically indicated and performed on DS-EID-CT and DS-PCD-CT (median time difference: 12 months). DS-PCD-CT was performed in Quantumplus UHR mode and DS-EID-CT was performed using dual-energy mode. DS-PCD-CT kernel was set at Br64 with Quantum iterative reconstruction strength Q1; for DS-EID-CT a comparable I70f kernel with SAFIRE iterative reconstruction strength 1 was used. Two independent radiologists assessed image quality subjectively using a 5-point Likert scale considering delineation and sharpness of trabecular bone and lytic bone lesions in the spine and pelvic bones. Additionally, ImageJ was used for quantification of bony septa inside the cancellous bone and through or the edges of osteolysis.ResultsOverall quality as well as detectability and sharpness in the delineation of lytic bone lesions were superior for DS-PCD-CT compared with DS-EID-CT (p < 0.0001). The inter-reader agreement for subjective image quality readings showed excellent consistency(α = 94.2–98.8). CTDI and DLP mean values for DS-PCD-CT and DS-EID-CT were 1107.4 ± 247.6 mGy*cm and 8.2 ± 1.8 mGy vs. 1344.3 ± 204.6 mGy*cm and 10.1 ± 1.9 mGy. The quantitative metric for bone microstructure in the femoral head showed significantly better visualization of trabeculae in DS-PCD-CT compared with DS-EID-CT (p < 0.0001). Quantitative analyses of edge sharpness of osteolysis showed significant steeper edges for DS-PCD-CT (p < 0.0001).ConclusionDS-PCD-CT significantly improves spatial resolution of bony microstructure and lytic bone lesions compared to DS-EID-CT.Key Points• Application of photon-counting detector CT is superior to dual-source dual-energy integrating detector in clinical workup of multiple myeloma patients.• Compared to energy integrating detectors, photon-counting detectors significantly increase the spatial resolution of bone microstructure including disease-related lytic bone lesions in patients with multiple myeloma.

Is there correlation between measured and console CTDIvol in multislice CT scanners?

This study investigated the relationship between measured and console volume computed tomography dose index (CTDIvol) in multislice CT scanners. The measured CTDI values were determined from kerma length product measured using pencil ionization chamber inserted in the holes of standard CT phantoms with diameters 16 and 32 cm, which respectively mimic adult head and body using the procedures recommended by International Electro-technical Commission. Significantly large deviations were observed between the measured and console CTDI vol values in multislice CT scanners.

Evaluation of computed tomography dose profiler probe for computed tomography dose index and geometric efficiency measurements

The purpose of this study was to evaluate the performance of solid-state sensor based computed tomography dose profiler (CTDP) probe for measurement of standard computed tomography dose metric CTDI100 and free in air geometric efficiency for various beam widths available in a 128-slice CT scanner and also to estimate the efficiency of CTDI100 metric. The response accuracy of CTDP probe was verified using a standard 100 mm long ionization chamber. The geometric efficiency measurements performed by the CTDP probe were validated using XR-QA2 radiochromic film measurements. The efficiency of CTDI100 metric was assessed by calculating the ratio of CTDI100 measured in the center hole position to CTDI∞ measured in the same position of both head and body phantoms. The weighted CTDI values derived from CTDI100 measured by the CTDP probe showed an average difference of 8% from ionization chamber measured values. The efficiency of CTDI100 metric estimated using CTDP probe and 150 mm long phantoms was in the range of 82% to 86% and 76% to 80% for head and body phantom measurements respectively. The differences in the geometric efficiency values for various beam settings and tube voltages measured by the CTDP probe and films were within 7%. Taken together, the results of this study proved that unlike the 100 mm long ionization chamber, the CTDP probe can be efficiently used to determine CTDI for any length over which dose integration is desired and also measure geometric efficiency of MDCT scanners for various beam widths in helical mode of operation.

Radiation Dose Reduction in Contrast-Enhanced Abdominal CT: Comparison of Photon-Counting Detector CT with 2nd Generation Dual-Source Dual-Energy CT in an oncologic cohort

Comparison of radiation dose and image quality in routine abdominal and pelvic contrast-enhanced computed tomography (CECT) between a photon-counting detector CT (PCD-CT) and a dual energy dual source CT (DSCT). 70 oncologic patients (mean age 66 ± 12 years, 29 females) were prospectively enrolled between November 2021 and February 2022. Abdominal CECT were clinically indicated and performed first on a 2nd-generation DSCT and at follow-up on a 1st-generation dual-source PCD-CT. The same contrast media (Imeron 350, Bracco imaging) and pump protocol was used for both scans. For both scanners, polychromatic images were reconstructed with 3mm slice thickness and comparable kernel (I30f[DSCT] and Br40f[PCD-CT]); for PCD-CT data from all counted events above the lowest energy threshold at 20 keV ("T3D") were used. Results were compared in terms of radiation dose metrics of CT dose index (CTDIvol), dose length product (DLP) and size-specific dose estimation (SSDE), objective and subjective measurements of image quality were scored by two emergency radiologists including lesion conspicuity. Median time interval between the scans was 4 months (IQR: 3-6). CNRvessel and SNRvessel of T3D reconstructions from PCD-CT were significantly higher than those of DSCT (all, p < 0.05). Qualitative image noise analysis from PCD-CT and DSCT yielded a mean of 4 each. Lesion conspicuity was rated significantly higher in PCD-CT (Q3 strength) compared to DSCT images. CTDI, DLP and SSDE mean values for PCD-CT and DSCT were 7.98 ± 2.56 mGy vs. 14.11 ± 2.92 mGy, 393.13 ± 153.55 mGy*cm vs. 693.61 ± 185.76 mGy*cm and 9.98 ± 2.41 vs. 14.63 ± 1.63, respectively, translating to a dose reduction of around 32% (SSDE). PCD-CT enables oncologic abdominal CT with a significantly reduced dose while keeping image quality similar to 2nd-generation DSCT.

ANALISA PERUBAHAN KV TERHADAP KUALITAS CITRA DAN CTDI

Background : Improved CT Scan image quality with tube variation once reported that higher tube voltage results in better image quality. But the study was conducted to evaluate the tube voltage of 80 kv to lower the dose so that the current of the tube is not increased. Some researchers recommend scanning with low tube voltage and properly adjusted tube current to reduce radiation doses on brain CT scans. However, so far there has never been an evaluation of kV values on image quality and CTDI in the head MSCT and at Sanjawani Hospital to analyze Kv changes to image quality and CTDI multislice computed tomography on phantoms.&#x0D; Methods:The study was conducted on the Phantom using the parameters of the HEAD CT scan examination. This research method is quantitative research with an experimental approach. The study was conducted on the Phantom using the parameters of the HEAD CT scan examination.&#x0D; Results: This study was conducted by collecting kV variation data of 70, 80, 100, 120, and 140 scanned 3 times.&#x0D; Conclusion : The results obtained the output of spss friedman test spatial resolution, contrast resolution, nooise and artifact, the highest rank is at kV tube voltage 120. Ctdi value obtained with kV variari, is in accordance with bapeten / IDRL 2021 recommendations.

Characterization of imaging performance of a novel helical kVCT for use in image-guided and adaptive radiotherapy.

ClearRT helical kVCT imaging for the Radixact helical tomotherapy system recently received FDA approval and is available for clinical use. The system is intended to enhance image fidelity in radiation therapy treatment planning and delivery compared to the prior MV‐based onboard imaging approach. The purpose of this work was to characterize the imaging performance of this system and compare this performance with that of clinical systems used in image‐guided and/or adaptive radiotherapy (ART) or computed tomography (CT) simulation, including Radixact MVCT, TomoTherapy MVCT, Varian TrueBeam kV OBI CBCT, and the Siemens SOMATOM Definition Edge kVCT. A CT image quality phantom was scanned across clinically relevant acquisition modes for each system to evaluate image quality metrics, including noise, uniformity, contrast, spatial resolution, and CT number linearity. Similar noise levels were observed for ClearRT and Siemens Edge, whereas noise for the other systems was ∼1.5–5 times higher. Uniformity was best for Siemens Edge, whereas most scans for ClearRT exhibited a slight “cupping” or “capping” artifact. The ClearRT and Siemens Edge performed best for contrast metrics, which included low‐contrast visibility and contrast‐to‐noise ratio evaluations. Spatial resolution was best for TrueBeam and Siemens Edge, whereas the three kVCT systems exhibited similar CT number linearity. Overall, these results provide an initial indication that ClearRT image quality is adequate for image guidance in radiotherapy and sufficient for delineating anatomic structures, thus enabling its use for ART. ClearRT also showed significant improvement over MVCT, which was previously the only onboard imaging modality available on Radixact. Although the acquisition of these scans does come at the cost of additional patient dose, reported CTDI values indicate a similar or generally reduced machine output for ClearRT compared to the other systems while maintaining comparable or improved image quality overall.

Image quality and dose exposure of contrast-enhanced abdominal CT on a 1st generation clinical dual-source photon-counting detector CT in obese patients vs. a 2nd generation dual-source dual energy integrating detector CT

PurposeTo compare the radiation dose as well as the image quality of contrast-enhanced abdominal 1st-generation Photon-Counting Detector CT (PCD-CT) to a 2nd-generation Dual-Source Dual-Energy-Integrating-Detector CT (DSCT) in obese patients. Method51 overweight (BMI ≥ 25 kgm2) patients (median age: 67.00 years; IQR: 59.00–73.00, median BMI 32.15 kgm2; IQR: 28.70–35.76) who underwent clinically indicated, contrast-enhanced abdominal-CT in portal-venous phase on both 2nd-generation DSCT and on a commercially available 1st-generation PCD-CT were prospectively included the degree of obesity was defined by BMI-calculation (overweight, obesity grade I/30–34.9; obesity grade II/35–39.9; obesity grade III > 40) and by the absolute weight value. The same contrast media and pump protocol were used for both scans. PCD-CT was performed in Quantumplus mode at 120 kVp whereas DSCT used also 120 kVp in single energy mode. Comparable convolution algorithm between DSCT and PCD-CT were set. For both scanners, polychromatic images were reconstructed; for PCD-CT data from all counted events above the lowest energy threshold at 20 keV (termed T3D) were used. Two independent radiologists assessed subjective image quality using a 5-point Likert-scale and quantified the contrast-to-noise ratio of parenchymatous organs and vascular structures. ResultsMedian time interval between the scans was 4 months (IQR 3–7 months). BMI was classified overweight (n = 18, 35.3%), grade I (n = 19, 37.3%), II (n = 9, 17.6%), III (n = 5, 9.8%). Mean CNRrenal_cortex (12.35 ± 3.77 vs. 14.16 ± 3.55) as well as median CNRvessels (9.88 vs. 12.40) and median CNRpancreas (2.81 vs. 4.04) of PCD-CT were significantly higher than those at DSCT (p < 0.05). The inter-reader agreement for all subjective image quality readings was moderate to substantial. Both radiologists independently rated the image quality higher for PCD-CT data sets (p < 0.05). Median CTDI and DLP values for PCD-CT and DSCT were 12.00 mGy (IQR: 10.20–13.50 mGy) vs. 16.05 mGy (IQR: 14.81–17.98) and 608 mGy * cm (IQR: 521.00–748.00 mGy * cm) vs. and 821.90 mGy * cm (IQR: 709.30–954.00 mGy * cm) (p < 0.001). ConclusionSignificant dose reduction by similar or even improved image quality was obtained with abdominal contrast-enhanced CT using PCD-CT in obese patients as compared to 2nd-generation DSCT.

A multi-provincial survey and analysis of radiation doses from pediatric CT in China

ObjectiveTo survey and analyze the radiation doses of pediatric CT in some provinces (autonomous region) or municipalities in China, and compare them with the data released by the relevant domestic and international organizations, so as to identify the current status of Chinese pediatric CT radiation doses. MethodsRadiation doses of pediatric CT were collected during August and December 2016 from 40 hospitals (including 18 children’s hospitals) in 15 provinces, municipalities or autonomous regions across the China. The procedures of head CT, chest CT and abdomen CT were selected in these hospitals, and 10 patients in each group of 0− < 1 y, 1− < 5 y, 5− <10 y and 10− < 15 ​y were collected at random for every procedure. Weighted CT dose index (CTDIw), volumetric CT dose index (CTDIvol) and dose length product (DLP) were used as survey quantities. An independent sample Kruskal-Wallis rank sum test was performed for CTDI and DLP for each procedure for different age groups, and pairwise comparisons were performed for intra-group data. The same statistical method was also conducted for CTDI and DLP of the same procedure and age group in different provinces or municipalities. ResultsThe 75th percentiles of the distribution of CTDI and DLP in different age groups of 0− < 1 y, 1− < 5 y, 5− <10 y and 10− < 15 ​y were as follows: 36.5, 43.4, 49.1, 51.1 ​mGy and 488, 635, 723, 852 ​mGy.cm for head, 6.1, 6.4, 6.8, 9.6 ​mGy and 108, 136, 187, 293 ​mGy.cm for chest, 10.5, 10.3, 11.4, 13.0 ​mGy and 251,284,353, 523 ​mGy.cm for abdomen. The 50th percentiles of the distribution of the radiation doses for the same procedure varied with the ages (head, CTDIw: H ​= ​155.66, DLP: H ​= ​212.35, P ​< ​0.05; chest, CTDIvol: H ​= ​85.43, DLP: H ​= ​197.36, P ​< ​0.05; abdomen: H ​= ​62.29, DLP: H ​= ​173.22, P ​< ​0.05)and with lower dose at lower age. Radiation doses were close for head between 5− <10 y and 10− <15 ​y groups, for chest between 1− <5 ​y and 5− <10 ​y groups and between 5− <10 ​y and 10− <15 ​y groups, and for abdomen between 0− <1 ​y and 1− <5 ​y groups, with no statistically significant difference (the adjusted P ​> ​0.05). The dose levels of different provinces or municipalities in the same procedure and age group were not consistent, and the differences were statistically significant (P ​< ​0.05). The data were different from the domestic and international values of DRL. The 75th percentiles of CTDIw and DLP values of head CT were close to the data from Japan and UK(United Kingdom), higher than the data from Korea and EC(European Commission). The 75th percentiles of CTDI values of all age groups were lower than the values of Japan and UK, and larger than that of Korea and EC in chest CT and abdomen CT. ConclusionsThe 75th percentile values of the distribution of the pediatric CT doses obtained from the survey were inconsistent with those released by the relevant national and international organizations. It is necessary to update the national DRLs for pediatric CT on the basis of the actual survey data.

Application of computed tomography dose index as dosimetric parameter in dental tomography

ABSTRACT Objective Quantify the CTDI from a reference beam, correcting this value for several beam widths from the ratio of CTDI100 values measured in the air, and verifying the underestimation of the dose comparing CTDI100 and CTDI300, applied to dental CBCT. Methods i-CAT and Prexion 3D tomographs, 100mm pencil ionization chamber, electrometer. Firstly for beam above 40 mm, CTDIW,NT from CTDIW,Ref, multiplied by the ratio of CTDIAR measurements to N.T widths and reference, was estimated. In second, CTDI100 and CTDI300 are obtained by displacing the ionization chamber along the beam with spacing intervals equal to 100 mm to cover sufficiently large integration intervals for CBCT protocols, and a comparison is made through the modified efficiency. Results CTDIAR,100,Ref averaged 53% higher than CTDIW,Ref, due to attenuation of the beam by the simulator object, and the ratio between CTDIAR,100,Ref and CTDIW,Ref is greater than 1, being this constant relationship and validating the method for dosimetry in quality control tests. For the second method, CTDI100 greatly underestimates the dose deposited on the central axis, where CTDI300 covers all beam sizes and stands out in relation to CTDI100 to more accurately quantify the radiation levels emitted. Conclusions The IEC method is applicable to quality control, facilitating practice, and optimizing time and resources. CTDI300 is a better dose descriptor than CTDI100, and should be implemented for CBCT modalities when used.

Integration of An Information System to Suggest A Drl Model in Radiology Department at Azadi Hospital in Duhok–kurdistan Region, Iraq

Computer Tomography is a useful technique in diagnostic radiology. However, it emits high radiation doses which may cause harm to patients. For this, a quality management system, Diagnostic Reference Levels (DRL) is used in European countries. The aim of this study was to suggest a DRL system in Duhok Hospitals. Patient’s data (70 – 80) were collected from Azadi Hospital for three main protocols head, chest and abdomen. Only 15 patients had complete data for calculations for the three protocols. The DRL results were then compared with the ones reported in several European countries. For example, in the head protocol for the a CTDI value of 81, the results of the calculated DLP and ED values were 1504 and 3.16 respectively. These values were found to be much higher than the corresponding values reported in Italy 13.12 and 2.76 respectively. As a result, the DRL using 75th percentiles corresponding to these three dosimetric values were also high. Similar high results for the abdomen protocol were recorded, however, the results of the chest protocol showed to be within the average range. Part two of this work involved designing a Flow Chart based on an Information System to help running the CT scan procedure more effectively. Additionally, an extra repository system was added to this model to solve the short capacity issue in Duhok Hospitals.

Investigations of CT Dose with Contrast Agent and Its Effects on the CTDI

Purpose: Computed tomography is a leading imaging technique for head & neck and brain and most of these imaging protocols iodine-based contrast media are utilised. The chief aim of this research is to utilize the effects of the contrast media “CM” used in computed tomography “CT” which is used to enhance subject contrast on the delivered CT via its inclusion into the CT dose index “CTDI”, and to introduce a simple method to determine this effect via the available CT numbers at the imaged targets. Method: The CT dose increase is estimated theoretically and measured experimentally and then related to the average CT number in the volume of CM uptake. A factor dependent on CM concentration and beam energy is added to the CTDI equation to represent the increased dose burden. A simple holed Perspex phantom was built to measure the variation of imaged CT number. CT Gafchromic type film was alternately imaged in a reservoir of CM and water. The relative difference in the dose burden as obtained by scanning the two films represents the dose difference and hence the CM dependent increase. Results: Measured dose effects due to the inclusion of the CM varied depending on the concentration. The increase in dose is estimated to be about 17% for 20% contrast media in the target while that for 10% by volume is around 6.6%. These are estimated from the CT numbers. Patients’ data also shows influence of the CM on the CTDI values. Conclusion: The dosimetric effects of the contrast media are included into the CTDI and can be estimated by using the CT numbers obtained.

Assessment of the Radiation Dose during 16 Slices CT Examinations

In this work. Two studies were presented. The first one is an experimental study of the influence of different scan parameters (potential tube. current tube and pitch) on the radiation dose is presented. It has been demonstrated that the radiation dose increases if we increase the tube current or the potential current. Contrary to the pitch. the radiation dose is reduced when the pitch increases. The second study is a Monte Carlo validation of a CT named SOMATION emotion from Siemens using GATE. Results were carried out for different voltage 80.110.130 kVp. Results of the simulation are presented and good agreements are observed (less than 2.6% for head phantom. and less than 4.6% for body phantom for all applied voltages). The influence of changing the phantom diameter on the CTDIw was also presented. the CTDIw decreased nonlinearly with increasing the phantom diameter. Moreover. the CTDIw differences decreased if the phantom diameter increased. It was demonstrated that the CTDI100 values can be characterized as functions of the kVp. mAs and diameter of phantoms. Based on these results. it is possible to optimize the CT parameters in clinical applications. Finally the effective dose was calculated using the method dose length product and the conversion factors for four clinical protocols.

Utilization of sinogram affirmed iterative reconstruction on 128 multi slice computed tomography scan to reduce radiation dose and improve image quality on thorax multi slice computed tomography scan: chest phantom study

Background: Thorax MSCT examination is a diagnostic imaging that is capable of displaying both normal and pathological lung and respiratory organs. MSCT examination also has a better level of sensitivity and specificity compared to other modalities, but the radiation exposure given is very high, so the radiation dose given to patients is high. The reduction in radiation dose is very important because of the direct exposure to sensitive tissue. One method of reducing radiation dose is by reducing the tube voltage. However, the decrease in tube voltage causes a decrease in image quality as indicated by increased noise and decreased CNR. To maintain the quality of the image at low tube voltage setting, an IR reconstruction of SAFIRE was used. The purpose of this research is to know the impact of using SAFIRE on dose radiation and image quality of thorax MSCT.Methods: This study was an experimental study with a quasi-experimental study design. The object used was the N-1 Lungman chest phantom in which an artificial tumor was attached. Radiation dose assessment used CTDI value, while image quality assessment used noise and CNR. Data processing was conducted using linear regression test.Results: There was an effect of tube voltage setting and SAFIRE setting on radiation dose and image quality.Conclusions: Tube voltage ssetting and SAFIRE setting had an effect on radiation dose and image quality. Tube voltage setting and SAFIRE strength level setting that were able to provide optimal radiation dose and image quality were tube voltage of 80 kVp and SAFIRE strength levels 3 and 4 (S3 and S4).

Patient centring and scan length: how inaccurate practice impacts on radiation dose in CT colonography (CTC).

The aim of this study was to acknowledge errors in patients positioning in CT colonography (CTC) and their effect in radiation exposure. CTC studies of a total of 199 patients coming from two different referral hospitals were retrospectively reviewed. Two parameters have been considered for the analysis: patient position in relation to gantry isocentre and scan length related to the area of interest. CTDI vol and DLP were extracted for each patient. In order to evaluate the estimated effective total dose and the dose to various organs, we used the CT-EXPO® software version 2.2. This software provides estimates of effective dose and doses to the other various organs. Average value of the patients' position is found to be below the isocentre for 48 ± 25mm and 29 ± 27mm in the prone and supine position. It was observed that the increase in CTDI and DLP values for patients in Group 1, due to the inaccurate positioning, was estimated at about 30% and 20% for prone and supine position, respectively, while in Group 2, a decrease in CTDI and DLP values was estimated at about 16% and 18% for prone and supine position, respectively, due to an average position above isocentre. A dose increase ranging from 4 up to 13% was calculated with increasing the over-scanned region below anal orifice. Radiographers and radiologists need to be aware of dose variation and noise effects on vertical positioning and over-scanning. More accurate training need to be achieved even so when examination protocol varies from general practice.

P155] Exposure levels from CT scanning for treatment planning in radiotherapy

Purpose CT-scanning for treatment planning in radiotherapy is often hampered by the fact that scan parameter optimization may be limited due to treatment planning system constraints. The current work reviews the exposure levels for a selected group of treatment locations, i.e. head, head&neck, thorax, breast, abdomen and prostate. Methods Equal scan protocols, based on filtered back projection, are set on the two scanners (Siemens Definition AS+). Scan parameters from the CT scanners are automatically transferred, using the DICOM SR protocol, after each scanning sequence to a dose monitoring system (Sectra DoseTrack). These data include, but are not limited to CTDI, DLP, weight and age. For adult patients with weights between 60 and 80 kg the median CTDI (mGy) and DLP (mGycm) values as well as standard deviation (1 SD) have been calculated for the treatment locations. 20 or more patients are included for each location. Results The exposure levels for the selected sites are more or less equal between the two scanners. CTDI and DLP values (CTDI/DLP) for CT 1 are: Head 41 ± 4/1125 ± 145, Head&neck 11 ± 1/452 ± 61, Thorax 9 ± 3/390 ± 161, Breast ca 9 ± 2/355 ± 61, Abdomen 17 ± 3/815 ± 239, Prostate ca respectively. Corresponding values for CT 2 are: Head 42 ± 6/1168 ± 222, Head&neck 11 ± 1/458 ± 89, Thorax 9 ± 2/412 ± 136, Breast ca 9 ± 1/357 ± 60, Abdomen 17 ± 3/801 ± 177, Prostate ca 17 ± 2/813 ± 110 for each scan site. CTDI values are well below current national dose reference levels (DRL) in diagnostic radiology were these are given. DLP values are however slightly outside the diagnostic DRL values were these exist. Increased scan length requirements due to treatment planning flexibility, dose calculation accuracy and DVH evaluation of complete organs add to higher DLP values. Conclusions Exposure levels have been evaluated for the head, head&neck, thorax, breast, abdomen and prostate regions. These exposure levels turn out to be lower for CTDI than current national diagnostic radiology dose reference levels indicating well adapted scan protocols. Scan length requirements for treatment planning do however add to DLP making them slightly higher than current DRL levels.

Variability of the discrepancy between manufacturer and measured CTDI100 values by scanner type, acquisition parameters and phantom size

According to the EU directive 2013/59, the computed tomography (CT) equipments shall be able to inform the practitioner of parameters for assessing the patient dose. The aim of this study was to measure the accuracy of the CTDI100 with respect to the values stipulated in the manufacturer manual for different manufacturers/models of CT and to assess the impact of acquisition parameters on CTDI100 accuracy.Ten CT from 4 different manufacturers were included in the study. The discrepancy with the manufacturer value CTDI100 was checked with a dosimeter with traceable calibration. Manufacturer values for the CTDI100 were derived from the equipment’s manual. The impact of the kVp, CT model, primary collimation and phantom size on the discrepancy of the CTDI100, was assessed by a four-way ANOVA.All the factors had a statistically significant impact on CTDI100 discrepancy (P < 0.05). In a head to head comparison, the greater discrepancies were found on average for 80 kV (15.4 ± 10.7%), sixteen channels CT (10.3 ± 5.1%) and for thick collimations (13.2 ± 6.8%), whilst no significant differences were found between head and body phantoms.For sixteen channels CT and acquisition protocols involving the use of low kV or thick primary collimation, the discrepancies with the manufacturer value CTDI100 can be higher than 20%, which is the suspension level indicated in the EC RP N.162 Publication. This suggests the need of individual calibration of CT X-ray tubes by the manufacturers and the necessity of including this check in the quality control programs for CT.

New weighting factor of weighted CTDI equation for PMMA phantom diameter from 8 to 40 cm: A Monte Carlo study.

The weighted computed tomography dose index (CTDIw ) uses measured CTDI values at the center and periphery of a cylindrical phantom. The CTDIw value is calculated using conventional, Bakalyar's, and Choi's weighting factors. However, these weighting factors were produced from only 16- and 32-cm-diameter cylindrical phantoms. This study aims to devise new weighting factors to provide more accurate average dose in the central cross-sectional plane of cylindrical phantoms over a wide range of object diameters, by using Monte Carlo simulations. Simulations were performed by modeling a Toshiba Aquilion ONE CT scanner, in order to compute the cross-sectional dose profiles of polymethyl methacrylate (PMMA) cylindrical phantoms of each diameter (8-40 cm at 4-cm steps), for various tube voltages and longitudinal beam widths. Two phantom models were simulated, corresponding to the CTDI100 method and the method recommended by American Association of Physicists in Medicine (AAPM) task group 111. The dose-computation PMMA cylinders of 1 mm diameter were located between the phantom surfaces and the centers at intervals of 1 mm, from which cross-sectional dose profiles were calculated. By using linear least-squares fits to the obtained cross-sectional dose profiles data, we determined new weighting factors to estimate more accurate average doses in the PMMA cylindrical phantoms by using the CTDIw equation: CTDIw = Wcenter ・ CTDIcenter + Wperiphery ・ CTDIperiphery . In order to demonstrate the validity of the devised new weighting factors, the percentage difference between average dose and CTDIw value was evaluated for the weighting factors (conventional, Bakalyar's, Choi's, and devised new weighting factors) in each calculated cross-sectional dose profile. With the use of linear least-squares techniques, new weighting factors (Wcenter = 3/8 and Wperiphery = 5/8 where Wcenter and Wperiphery are weighting factors for CTDIcenter and CTDIperiphery ) were determined. The maximum percentage differences between average dose and CTDIw value were 16, -12, -8, and -6% for the conventional, Bakalyar's, Choi's, and devised new weighting factors, respectively. We devised new weighting factors (Wcenter = 3/8 and Wperiphery = 5/8) to provide more accurate average dose estimation in PMMA cylindrical phantoms over a wide range of diameter. The CTDIw equation with devised new weighting factors could estimate average dose in PMMA cylindrical phantoms with a maximum difference of -6%. The results of this study can estimate the average dose in PMMA cylindrical phantoms more accurately than the conventional weighting factors (Wcenter = 1/3 and Wperiphery = 2/3).

Application of low-dose dual-source computed tomography angiography in children with complex congenital heart disease.

The objective of the present study was to evaluate image quality and radiation dosage using a low-dose prospectively electrocardiogram (ECG)-gated computed tomography (CT) protocol for dual-source angiography in children with complex congenital heart disease. A total of 206 patients with complex congenital heart disease were equally assigned into two groups at random. The children in group A underwent low-dose retrospective ECG-gated CT scanning with an ECG-pulsing technique, and group B underwent prospective ECG-gated scanning with an ECG-pulsing technique. Radiation dose volume computed tomography dose index (CTDI vol), dose length product (DLP) and effective dose (ED) were recorded after scanning. Raw data were transferred to workstations for post-processing, diagnosis, grading, comparison with intra-operation findings or cardiac catheterisation, and the coincidence, false negative rate and misdiagnosis rates of groups A and B, respectively, were subsequently recorded. The results of the present study indicated that the height, age and weight of the children in the two groups exhibited no significant differences. The image quality of group A was graded as 3.94±0.08, whereas the grade for the image quality in group B was 4.05±0.08; no significant difference was detected. The coincidence rates of groups A and B were 89.37 and 88.48%, respectively; the false negative rates of groups A and B were 9.66 and 10.60%, respectively; the misdiagnosis rates of groups A and B were 0.97 and 0.92%. No significant differences between the two groups were detected. The CTDI value of group A was 3.24±1.62 mGy, the DLP value was 47.53±33.28 mGy·cm2, the ED value was 0.93±0.42 mSv. By contrast, the CTDI value of group B was 2.27±0.94 mGy, the DLP value was (27.03±17.64) mGy·cm2, and the ED value was 0.53±0.23 mSv. Significant differences were detected between the two groups (CTDI t=5.287, P<0.05; DLP t=5.523, P<0.05; ED t=8.497, P<0.05), and the radiation dose of group B was markedly decreased, compared with group A. In conclusion, the present study demonstrated that prospectively ECG-gated scanning of dual-source CT is an effective method of examination for dose reduction in children with congenital heart disease without impairment of image quality, which suggests that this protocol may be suitable for future application and dissemination.