Volume-weighted Computed Tomography Dose Index Research Articles

Task-based assessment for radiation dose optimization in CT abdominal examinations: A phantom study

Recent advancements in Computed Tomography (CT) imaging technology have significantly enhanced healthcare delivery. However, public concern regarding the safety and health risks associated with increased exposure to ionizing radiation has escalated. In response, this study performs a quantitative analysis comparing the image quality of the standard CT abdomen protocol (P1 protocols) with alternative optimization techniques. Adjustments to standard CT scan parameters, including tube potential (P2 protocols), effective mAs value (P3), and pitch factor (P4, P5, P6 protocols), were made to evaluate the effectiveness of these optimization strategies. A 64-slice CT scanner (Canon, Japan) and a polymethylmethacrylate (PMMA) textural water phantom was utilized in this study. CT dose descriptors, volume weighted CT Dose Index (CTDIvol) and dose-length product (DLP) alongside evaluation parameters such as Hounsfield Unit (HU) number, noise levels, Signal-to-Noise Ratio (SNR), and Contrast-to-Noise Ratio (CNR) were measured and analysed. Furthermore, this research introduced a Figure of Merit (FOM) based on the ratio of image quality parameters (SNR and CNR) to the CTDIvol, establishing a quantitative measure for optimization. A notable reduction in radiation dose—34.85% below the standard protocol (P1)—was observed in protocol P6, attributed to an increased pitch factor. Conversely, increase the effective mAs value has improved SNR and CNR values. The findings reveal that protocols P1 and P2 deliver the highest FOM for soft tissue and fat imaging, respectively. Protocol P1, with its higher attenuation factor, is optimal for abdominal examinations targeting soft tissues. Meanwhile, protocol P2's increase effective mAs value enhances beam intensity, improving CT numbers for fat tissues with their high-density composition. The study also found a strong correlation between FOM based on SNR and CNR values. In conclusion, adjustments to primary CT parameters significantly influence image quality. The FOM serves as an effective tool for measuring the overall performance of image quality, facilitating post-optimization assessment and contributing to the development of safer, more efficient CT imaging protocols.

Evaluation of a new predictive equation for automated calculation of size-specific dose estimate (SSDE) in CT imaging

IntroductionThe adoption of size-specific dose estimate (SSDE) in clinical practice is still limited owing to the tedious and complex manual measurement of individual patient size for the clinical calculation of SSDE. Thus, the automation of SSDE is imperative. This study aims to evaluate a predictive equation for the automated calculation of SSDE. MethodsA user-friendly software was developed to accurately predict the individual size-specific dose estimation of paediatric patients undergoing computed tomography (CT) scans of the head, thorax, and abdomen. The software includes a calculation equation developed based on a novel SSDE prediction equation that used a population's pre-determined percentage difference between volume-weighted computed tomography dose index (CTDIvol) and SSDE with age. American Association of Physicists in Medicine (AAPM RPT 204) method (manual) and segmentation-based SSDE calculators (indoseCT and XXautocalc) were used to assess the proposed software predictions comparatively. ResultsThe results of this study show that the automated equation-based calculation of SSDE and the manual and segmentation-based calculation of SSDE are in good agreement for patients. The differences between the automated equation-based calculation of SSDE and the manual and segmentation-based calculation are less than 3%. ConclusionThis study validated an accurate SSDE calculator that allows users to enter key input values and calculate SSDE. Implication for practiceThe automated equation-based SSDE software (PESSD) seems a promising tool for estimating individualised CT doses during CT scans.

Accuracy, Hemorrhagic Complications and CT Radiation Dose of Emergency External Ventricular Drain (EVD) Placement in Pediatric Patients: A 15-Year Retrospective Analysis.

To assess accuracy, the frequency of hemorrhagic complications and computed tomography (CT) radiation dose parameters in pediatric patients undergoing landmark-guided external ventricular drain (EVD) placement in an emergency setting. Retrospective analysis comprised 36 EVD placements with subsequent CT control scans in 29 patients (aged 0 to 17 years) in our university hospital from 2008 to 2022. The position of the EVD as well as the presence and extension of bleeding were classified according to previously established grading schemes. Dose length product (DLP), volume-weighted CT dose index (CTDIvol) and scan length were extracted from the radiation dose reports and compared to the diagnostic reference values (DRLs) issued by the German Federal Office for Radiation Protection. After the initial EVD placement, optimal positioning of the catheter tip into the ipsilateral frontal horn or third ventricle (Grade I), or a functional positioning in the contralateral lateral ventricle or the non-eloquent cortex (Grade II), was achieved in 28 and 8 cases, respectively. In 32 of 36 procedures, no evidence of hemorrhage was present in the control CT scan. Grade 1 (<1 mL) and Grade 2 (≥1 to 15 mL) bleedings were detected after 3 and 1 placement(s), respectively. For control scans after EVD placements, CTDIvol (median [25%; 75% quartile]) was 39.92 [30.80; 45.55] mGy, DLP yielded 475.50 [375.00; 624.75] mGy*cm and the scan length result was 136 [120; 166] mm. Exceedances of the DRL values were observed in 14.5% for CTDIvol, 12.7% for DLP and 65.6% for the scan length. None of these values was in the range requiring a report to the national authorities. Landmark-based emergency EVD placement in pediatric patients yielded an optimal position in most cases already after the initial insertion. Complications in terms of secondary hemorrhages are rare. CT dose levels associated with the intervention are below the reportable threshold of the national DRLs in Germany.

The establishment of national diagnostic reference levels for adult SPECT-CT in Saudi Arabia

This study aims to introduce national diagnostic reference levels (NDRLs) for adult hybrid single photon emission computed tomography (SPECT-CT) in nuclear medicine (NM) departments in the Kingdom of Saudi Arabia. The administered activity (AA) of radiopharmaceuticals, volume-weighted computed tomography dose index (CTDIvol) and dose length product (DLP) for ten hybrid SPECT/CT examinations were collected and analysed for one year. The median of AA, CTDIvol and DLP for each dose quantity was derived and the suggested national DRLs were determined based on the 75th percentile for all identified SPECT-CT examinations. A comparison of the defined adult NDRLs in Saudi Arabia with the published data of other countries was performed. Although there are no significant variations of the proposed NDRL of AA between countries, the proposed NDRLs of the integrated CT metrics exceed the published data in most procedures. NM departments are urged to consider optimisation for both image quality and radiation protection.

Radiation exposure, organ and effective dose of CT-guided liver biopsy as a function of lesion depth and size

Computed tomography (CT)-guided percutaneous biopsies play an important role in the diagnostic workup of liver lesions. Because radiation dose accumulates rapidly due to repeated image acquisition in a relatively small scan area, analysing radiation exposure is critical for improving radiation protection of CT-guided interventions. The aim of this study was to assess the radiation dose of CT-guided liver biopsies and the influence of lesion parameters, and to establish a local diagnostic reference level (DRL). In this observational retrospective cohort study, dose data of 60 CT-guided liver biopsies between September 2016 and July 2017 were analysed. Radiation exposure was reported for volume-weighted CT dose index (CTDIvol), size-specific dose estimate (SSDE), dose-length product (DLP) and effective dose (ED). Radiation dose of CT-guided liver biopsy was (median (interquartile range)): CTDIvol 9.91 mGy (8.33–11.45 mGy), SSDE 10.42 mGy (9.39–11.70 mGy), DLP 542 mGy cm (410–733 mGy cm), ED 8.52 mSv (7.17–13.25 mSv). Radiation exposure was significantly higher in biopsies of deep liver lesions compared to superficial lesions (DLP 679 ± 285 mGy cm vs. 497 ± 167 mGy cm, p = 0.0046). No significant dose differences were observed for differences in lesion or needle size. With helical CT spirals additional to the biopsy-guiding axial CT scans, radiation exposure was significantly increased: 797 ± 287 mGy cm vs. 495 ± 162 mGy cm, p < 0.0001. The local DRL is CTDIvol 9.91 mGy, DLP 542 mGy cm. Radiation dose is significantly increased in biopsies of deeper liver lesions compared with superficial lesions. Interventions with additional biopsy-guiding CT spirals lead to higher radiation doses. This study provides a detailed analysis of local radiation doses for CT-guided liver biopsies and provides a benchmark for optimising radiation protection in interventional radiology.

National indication-based diagnostic reference level values in computed tomography: Preliminary results from Ghana.

This study was conducted to develop national indication-based DRL values for common indications of adult computed tomography (CT) examinations for clinical application in Ghana. The methodological approach recommended by the International Commission on Radiological Protection (ICRP), Publication 135, for the development of DRLs, was employed. Studies on CT infrastructure, common indications and quality control tests were first undertaken. A sample of 20 CT dose descriptor/quantity data sets were collected from each centre for each indication. Overall, 3960 data sets were collected for all identified common indications from 71.4% of the total CT scanners in Ghana (25/35). The data were collected from image folders reported and accepted by radiologists. The objective image quality was assessed through a signal to noise ratio (SNR) analysis prior to using the data and extracting DRL values. Clinical indications and their respective DRL values in terms of volume weighted CT dose index (CTDIvol) and dose length product (DLP) were cerebrovascular accident (CVA)/stroke (77mGy; 1313mGy.cm), head trauma/injury (76mGy; 1596mGy.cm), brain tumour/space occupying lesion (SOL) (77mGy; 2696mGy.cm), lung tumour/cancer (12mGy; 828mGy.cm) and chest lesion with chronic kidney disease (CKD) (13mGy; 467mGy.cm). Others were abdominopelvic lesion (17mGy; 1299mGy.cm), kidney stones (15mGy; 731mGy.cm), urothelial malignancy/CT-intravenous urogram (CT-IVU) (11mGy; 1449mGy.cm) and pulmonary embolism (PE) (14mGy; 942mGy.cm). National Indication-based DRL values developed in this study are recommended to be used to manage CT radiation dose in Ghana.

Diagnostic Reference Level of Radiation Dose and Image Quality among Paediatric CT Examinations in A Tertiary Hospital in Malaysia.

Pediatrics are more vulnerable to radiation and are prone to dose compared to adults, requiring more attention to computed tomography (CT) optimization. Hence, diagnostic reference levels (DRLs) have been implemented as part of optimization process in order to monitor CT dose and diagnostic quality. The noise index has recently been endorsed to be included as a part of CT optimization in the DRLs report. In this study, we have therefore set local DRLs for pediatric CT examination with a noise index as an indicator of image quality. One thousand one hundred and ninety-two (1192) paediatric patients undergoing CT brain, CT thorax and CT chest-abdomen-pelvis (CAP) examinations were analyzed retrospectively and categorized into four age groups; group 1 (0–1 year), group 2 (1–5 years), group 3 (5–10 years) and group 4 (10–15 years). For each group, data such as the volume-weighted CT dose index (CTDIvol), dose-length product (DLP) and the effective dose (E) were calculated and DRLs for each age group set at 50th percentile were determined. Both CT dose and image noise values between age groups have differed significantly with p-value < 0.05. The highest CTDIvol and DLP values in all age groups with the lowest noise index value reported in the 10–15 age group were found in CT brain examination. In conclusion, there was a significant variation in doses and noise intensity among children of different ages, and the need to change specific parameters to fit the clinical requirement.

Effect of iterative reconstruction algorithm levels on noise index and figure-of-merit in CT pulmonary angiography examinations.

To evaluate the influence of iterative reconstruction (IR) levels on Computed Tomography (CT) image quality and to establish Figure of Merit (FOM) value for CT Pulmonary Angiography (CTPA) examinations. Images of 31 adult patients who underwent CTPA examinations in our institution from March to April 2019 were retrospectively collected. Other data, such as scanning parameters, radiation dose and body habitus information from the subjects were also recorded. Six different levels of IR were applied to the volume data of the subjects. Five circles of the region of interest (ROI) were drawn in five different arteries namely, pulmonary trunk, right pulmonary artery, left pulmonary artery, ascending aorta and descending aorta. The mean Signal-to-noise ratio (SNR) was obtained, and the FOM was calculated in a fraction of the SNR2 divided by volume-weighted CT dose index (CTDIvol) and SNR2 divided by the size-specific dose estimates (SSDE). Overall, we observed that the mean value of CTDIvol and SSDE were 13.79±7.72 mGy and 17.25±8.92 mGy, respectively. Notably, SNR values significantly increase with increase of the IR level (p < 0.05). There are also significant differences (p < 0.05) in the FOM for both SNR2/SSDE and SNR2/CTDIvol attained in different IR levels. We successfully evaluate the value of radiation dose and image quality performance and set up a figure of merit for both parameters to further verify scanning protocols by radiology personnel.

A Study to Determine Whether the Volume-Weighted Computed Tomography Dose Index Gives Reasonable Estimates of Organ Doses for Thai Patients Undergoing Abdomen and Pelvis Computed Tomography Examinations.

Introduction:Values for the CTDIvol, which is displayed on scanner consoles, give doses relative to a phantom much larger than most Thai patients, and the CTDIvol does not take account of differences in patient size, which affect organ doses.Objective:The purpose of this study was to evaluate relationships for size specific dose estimate (SSDE) and volume weighted computed tomography (CT) dose index (CTDIvol) with patient size for CT scanners operating under automatic tube current modulation (ATCM).Methods:Retrospective data from 244 patients who had undergone abdomen and pelvis examination on GE and Siemens CT scanners were included in this study. The combination of anteroposterior (AP) and lateral dimensions at the level of the first lumbar vertebra (L1) was used to represent patient size. Image noise within the liver was measured, and values of the absorbed dose for organs covered by the primary beam such as the liver, stomach and kidney were calculated using methods described in the literature. Values of CTDIvol were recorded and SSDE calculated according to the American Association of Physics in Medicine (AAPM) Report No.204. Linear regression models were used to evaluate the relationship between SSDE, CTDIvol, image noise and patient size.Results:SSDE is 20%-50% larger than the CTDIvol, with values for larger patients being more representative. Both the CTDIvol and image noise decreased with patient size for Siemens scanners, but the decline in SSDE was less significant. For the GE scanner, the CTDIvol was a factor of 3-4 lower in small patients compared to larger ones, while the SSDE only decreased by a factor of two. Noise actually decreased slightly with patient size.Conclusion:Values of SSDE were similar to the doses calculated for the liver, stomach and kidney, which are covered by the primary beam, confirming that it provides a good estimate of organ-absorbed dose.

Practical experiences in the transfer of clinical protocols between CT scanners with different ATCM systems

Automatic tube current modulation (ATCM) systems to aid in optimizing dose and image noise have become standard on computed tomography (CT) scanners over the last decade. ATCM systems of the main vendors modulate tube current in slightly different ways, with some using a control parameter related to image noise (e.g. Toshiba, GE) while others use a quality reference image mAs (e.g. Siemens). The translation of clinical protocols including ATCM operation between CT scanners from different manufacturers in order to obtain similar levels of image quality with optimized exposure variables has become an important issue. In this study, cylindrical phantoms of different sizes representing small, average and large patients, have been combined into one phantom, which has been scanned on Siemens, Toshiba and GE CT scanners with the full ranges of ATCM image quality settings. The volume weighted CT dose index (CTDIvol) and image noise over each section of the phantom were recorded for every setting. Relationships between the image quality level settings, and CTDIvol and measured image noise were analysed in order to investigate ATCM performance. Equations were developed from fits of the data to enable CTDIvol and image noise to be expressed in terms of the image quality parameters for different size phantoms on each scanner. The Siemens scanner protocol was chosen as the reference, as it avoided high doses for large patients, while allowing full modulation of tube current for patients of all sizes, and so was considered to provide optimized performance. The equations derived were used to equate the noise parameters on Toshiba and GE scanners to the quality reference mAs on the Siemens scanner, so that clinical protocols incorporating similar levels of optimization could be obtained on the three CT scanners.

Abstract TP340: Imaging Related Radiation Dose and Cancer Risk Assessment of Brain in Acute Ischemic Stroke Patients

Background and aims: Recently, safety concerns were raised about the radiation dose for acute ischemic stroke (AIS) patients undergoing computed tomography (CT), CT angiography (CTA) and CT perfusion (CTP). We evaluated precise radiation dose to the brain during various imaging studies in our AIS patients. Methods: Brain imaging was performed with 64-detector row CT scanner (Phillips-iCT256) using standard protocols recommended by American Association of Physicist in Medicine. For each procedure, volume weighted CT dose index (CTDIvol, mGy) and dose-length product DLP (mGy.cm) were obtained from dose reports generated at the time of acquisition. Organ specific dose to brain, eye, bone marrow and thyroid were also obtained. The estimates of cancer risk were interpolated. Results: In this prospective study, a total of 18 patients who underwent CT, CTA as well as CTP were included. Mean DLP for non-enhanced CT, CTA and CTP were 1068.25, 1150 and 1197 mGy.cm, respectively. Corresponding whole body effective dose for the CT, CTA and CTP were calculated as 2.57, 2.6, 2.4 mSv, respectively. Cumulative doses to the brain, eyes, bone marrow and thyroid gland were 33.81, 32.8, 1.21 and 1.31 mGy for the non-contrast brain CT. CTDIvol measurements for different protocols tested by the phantom were in agreement with values given in dose reports. Conclusions: The effective radiation doses are less than previously reported and much below the radiation threshold level for deterministic effects for brain and optic lens (500-2000mGy). Estimated life-time attributable cancer risks are very low with the current radiation doses.

Preliminary study on effective dose of patients in SPECT/CT fusion imaging

Objective To assess the patient effective dose during SPECT/CT imaging. Methods A total of 157 patients (85 males, 72 females; mean age: (60.46±13.44) years, range: 24-88 years) who underwent SPECT/CT from April 2013 to September 2014 were retrospectively analyzed. They were divided into 3 groups: 99Tcm-MDP bone scan group (n=113), 99Tcm -MIBI parathyroid imaging group (n=23) and 99Tcm-MAA pulmonary perfusion imaging group (n=21). The injection dose (MBq) was recorded and the effective dose (mSv) was estimated according to the International Commission on Radiological Protection (ICRP) guideline. The volume-weighted computed tomography dose index (CTDIvol) and dose length product (DLP) of CT were also recorded and the effective dose (mSv) due to CT was calculated. The effective doses among different groups were statistically compared by Kruskal-Wallis rank sum test and Wilcoxon rank sum test. Results The effective dose from radiopharmaceuticals were (4.02±0.35) mSv for 99Tcm-MDP bone scan, (6.13±0.53) mSv for 99Tcm-MIBI parathyroid imaging and (1.66±0.13) mSv for 99Tcm-MAA pulmonary perfusion imaging (χ2=96.853; Z=7.533, 7.262 and 5.676; all P<0.05). The effective dose due to CT were (3.84±1.98), (1.04±0.19), (4.05±0.47) mSv respectively (χ2=41.225, P<0.05), and there were significant differences between 99Tcm-MIBI parathyroid imaging group and 99Tcm-MDP bone scan group, 99Tcm-MAA pulmonary perfusion imaging group(Z=6.046 and 5.672, both P<0.05). The total effective dose during SPECT/CT imaging were (7.86±1.98), (7.21±0.81) and (5.71±0.45) mSv (χ2=28.988, P<0.05). There were significant differences between 99Tcm-MAA pulmonary perfusion imaging group and 99Tcm-MDP bone scan group, 99Tcm-MIBI parathyroid imaging group(Z=4.967 and 4.994, both P<0.05). Conclusions The increase in effective dose due to spiral CT during SPECT/CT examination should be concerned. Appropriate utilization and optimization of SPECT/CT is needed. Key words: Radiation dosage; Tomography, emission-computed, single-photon; Tomography, X-ray, computed; MDP; MIBI; MAA

National diagnostic reference level initiative for computed tomography examinations in Kenya.

The purpose of this study was to estimate the computed tomography (CT) examination frequency, patient radiation exposure, effective doses and national diagnostic reference levels (NDRLs) associated with CT examinations in clinical practice. A structured questionnaire-type form was developed for recording examination frequency, scanning protocols and patient radiation exposure during CT procedures in fully equipped medical facilities across the country. The national annual number of CT examinations per 1000 people was estimated to be 3 procedures. The volume-weighted CT dose index, dose length product, effective dose and NDRLs were determined for 20 types of adult and paediatric CT examinations. Additionally, the CT annual collective effective dose and effective dose per capita were approximated. The radiation exposure during CT examinations was broadly distributed between the facilities that took part in the study. This calls for a need to develop and implement diagnostic reference levels as a standardisation and optimisation tool for the radiological protection of patients at all the CT facilities nationwide.

Measurements of computed tomography dose index for clinical scans

Dose assessment in computed tomography is nowadays based on indicators such as the weighted computed tomography dose index (CTDIw) and the volume-weighted computed tomography dose index (CTDIvol), both measured only on single-axial scans. The aim of this study is to extend the set of CT protocols suitable in CTDIvol,w evaluation and therefore to perform measurements directly on clinical CT scans. With this purpose, the present work follows the methodology proposed by the American Association of Physicists in Medicine in the Report No. 111 and focuses on the central cumulative dose DL(0), which predicts CTDIvol,w values for scan length equal to 100 mm. All measurements performed with ion chamber and gafchromic films suggest that it is possible to achieve accurate CTDIvol,w values without selecting single-axial scans tailored to dosimetry. Therefore, it is not always necessary to split dosimetric and clinical CT scanner set-up.

Cardiac Computed Tomography Angiography With Automatic Tube Potential Selection

Automatic exposure control (AEC) algorithms are widely available in coronary computed tomography angiography (CTA) and have been shown to reduce radiation doses by adjusting tube current to patient size. However, the effects of anthropometry-based automatic potential selection (APS) on image quality and radiation dose are unknown. We sought to investigate the effect of an APS algorithm on coronary CTA radiation dose and image quality. For this retrospective case-control study we selected 38 patients who had undergone coronary CTA for coronary artery assessment in whom tube potential and tube current were selected automatically by a combined automatic tube potential and tube current selection algorithm (APS-AEC) and compared them with 38 controls for whom tube voltage was selected according to standard body mass index (BMI) cutoffs and tube current was selected using automatic exposure control (BMI-AEC). Controls were matched for BMI, heart rate, heart rhythm, sex, acquisition mode, and indication for cardiac CTA. Image quality was assessed as contrast-to-noise ratio and signal-to-noise ratio in the proximal coronary arteries. Subjective reader assessment was also made. Total radiation dose (volume-weighted computed tomography dose index) was measured and compared between the 2 groups. In the study group, comparison was made with conventional BMI-guided prior protocols (site protocols and Society of Cardiovascular Computed Tomography recommendations) through disagreement analysis. The APS-AEC cases received 29.8% lower overall radiation dose compared with controls (P=not significant). APS-AEC resulted in a significantly higher signal-to-noise ratio of the proximal coronary arteries (P<0.01) and contrast-to-noise ratio of the left main (P=0.01). In the study cases, the APS resulted in a change in tube potential versus site protocols and Society of Cardiovascular Computed Tomography recommendations in 45% (n=17) and 50% (n=19) of patients, respectively. Automated tube potential selection software resulted in significantly improved objective image quality versus standard BMI-based methods of tube potential selection, without increased radiation doses.

Effects of protocol and obesity on dose conversion factors in adult body CT

In computed tomography (CT), organ dose, effective dose, and risk index can be estimated from volume-weighted CT dose index (CTDI(vol)) or dose-length product (DLP) using conversion coefficients. Studies have investigated how these coefficients vary across scanner models, scan parameters, and patient size. However, their variability across CT protocols has not been systematically studied. Furthermore, earlier studies of the effect of patient size have not included obese individuals, which currently represent more than one-third of U.S. adults. The purpose of this study was to assess the effects of protocol and obesity on dose and risk conversion coefficients in adult body CT. Whole-body computational phantoms were created from clinical CT images of six adult patients (three males, three females), representing normal-weight patients and patients of three obesity classes. Body CT protocols at our institution were selected and categorized into ten examination categories based on anatomical region examined. A validated Monte Carlo program was used to estimate organ dose. Organ dose estimates were normalized by CTDI(vol) and size-specific dose estimate (SSDE) to obtain organ dose conversion coefficients (denoted as h and h(ss) factors, respectively). Assuming each phantom to be 20, 40, and 60 years old, effective dose and risk index were calculated and normalized by DLP to obtain effective dose and risk index conversion coefficients (denoted as k and q factors, respectively). Coefficient of variation was used to quantify the variability of each conversion coefficient across examination categories. The effect of obesity was assessed by comparing each obese phantom with the normal-weight phantom of the same gender. For a given organ, the variability of h factor across examination categories that encompassed the entire organ volume was generally within 15%. However, k factor varied more across examination categories (15%-27%). For all three ages, the variability of q factor was small for male (<10%), but large for female phantoms (21%-43%). Relative to the normal-weight phantoms, the reduction in h factor (an average across fully encompassed organs) was 17%-42%, 17%-40%, and 51%-63% for obese-class-I, obese-class-II, and obese-class-III phantoms, respectively. h(ss) factor was not independent of patient diameter and generally decreased with increasing obesity. Relative to the normal-weight phantoms, the reduction in k factor was 12%-40%, 14%-46%, and 44%-59% for obese-class-I, obese-class-II, and obese-class-III phantoms, respectively. The respective reduction in q factor was 11%-36%, 17%-42%, and 48%-59% at 20 years of age and similar at other ages. In adult body CT, dose to an organ fully encompassed by the primary radiation beam can be estimated from CTDI(vol) using a protocol-independent conversion coefficient. However, fully encompassed organs only account for 50% ± 19% of k factor and 46% ± 24% of q factor. Dose received by partially encompassed organs is also substantial. To estimate effective dose and risk index from DLP, it is necessary to use conversion coefficients specific to the anatomical region examined. Obesity has a significant effect on dose and risk conversion coefficients, which cannot be predicted using body diameter alone. SSDE-normalized organ dose is not independent of diameter. SSDE itself generally overestimates organ dose for obese patients.

SPECT-CT in routine clinical practice

To assess the patient radiation dose during routine clinical single-photon emission computed tomography-computed tomography (SPECT-CT) and measure the increase as compared with SPECT alone. Data pertaining to 357 consecutive patients who had undergone radioisotope imaging along with SPECT-CT of a selected volume were retrospectively evaluated. Dose of the injected radiopharmaceutical (MBq) was noted, and the effective dose (mSv) was calculated as per International Commission on Radiological Protection (ICRP) guidelines. The volume-weighted computed tomography dose index (CTDIvol) and dose length product of the CT were also assessed using standard phantoms. The effective dose (mSv) due to CT was calculated as the product of dose length product and a conversion factor depending on the region of investigation, using ICRP guidelines. The dose due to CT was compared among different investigations. The increase in effective dose was calculated as CT dose expressed as a percentage of radiopharmaceutical dose. The per-patient CT effective dose for different studies varied between 0.06 and 11.9 mSv. The mean CT effective dose was lowest for 99mTc-ethylene cysteine dimer brain SPECT-CT (0.9 ± 0.7) and highest for 99mTc-methylene diphosphonate bone SPECT-CT (4.2 ± 2.8). The increase in radiation dose (SPECT-CT vs. SPECT) varied widely (2.3-666.4% for 99mTc-tracers and 0.02-96.2% for 131I-tracers). However, the effective dose of CT in SPECT-CT was less than the values reported for conventional CT examinations of the same regions. Addition of CT to nuclear medicine imaging in the form of SPECT-CT increases the radiation dose to the patient, with the effective dose due to CT exceeding the effective dose of RP in many instances. Hence, appropriate utilization and optimization of the protocols of SPECT-CT is needed to maximize benefit to patients.

Intercomparison of patient CTDI surveys in three countries

The results of large-scale computed tomography (CT) patient dose surveys from the USA, UK and Germany undertaken during the period 1999-2001 were reviewed. The mean values for volume-weighted CT dose index (CTDI(vol)) and dose length product (DLP) were extracted. For head CT examinations, the reported values for the three surveys were similar with a mean CTDI(vol) of 59±6 mGy and a mean DLP of 760±90 mGy cm. For the body, the values for CTDI(vol) in the USA (21±5 mGy) were nearly double those in the European countries (12±2 mGy). Average head CTDI(vol) values are comparable with the diagnostic reference levels (DRLs) recommended by the European Commission and the UK Health Protection Agency, but lower than the value of 75 mGy, which is currently used in the USA. DRLs for abdominal imaging are nearly a factor of 2 lower in the UK (14 mGy) than in other parts of the European Community and the USA (25 mGy).