Size-specific Dose Estimate Research Articles

Dose reference level based on size-specific dose estimate (SSDE) and feasibility of deriving effective body diameter using tube current and time product (mAs) for adult chest and abdomen computed tomography (CT) procedures

This study aimed to establish dose reference level (NDRL) based on size-specific dose estimate (SSDE) derived using effective diameter () for adult chest and abdomen computed tomography (CT) procedures and to explore the feasibility of driving using the product of tube current and time (mAs). In this retrospective study, dose data, scan parameters and patient body dimensions at the mid-slice level from 14 CT units (out of 63 total) were extracted. Additionally, the mAs values of the axial slice at the same z-location where the diameter measurements were made (mAs z ) were recorded. Pearson’s correlation (r) analysis was used to determine the relationship of with patient BMI, weight, and mAs z . The NDRL for the chest and abdomen were 9.72 mGy and 13.4 mGy, respectively. The BMI and body weight were less correlated (r = 0.24 and r = 0.33, respectively) with . The correlation between mAs z and was considerably strong (r = 0.78) and can be used to predict accurately. The absolute dose differences between SSDEs calculated using the AAPM–204 method and mAs z was less than 1.1 mGy (15%). Therefore, mAs z is an efficient parameter to derive . Further, the direct conversion factors to estimate SSDEs at different locations along the z-direction in the scan region from corresponding mAs and CTDI were calculated. The NDRL suggested in the present study can be used as a reference for size-dependent dose optimisation in Sri Lanka, and existing NDRL based on CTDI underestimate the average adult CT dose by 36.0% and 39.7% for chest and abdomen regions respectively. The results show that using mAs z to determine SSDE is a simple and practical approach with an accuracy of 95% and 85% for abdomen and chest scans, respectively. However, the obtained linear relationship between and mAs is highly dependent on the ATCM technique and the user-determined noise levels of the scanning protocol. Finally, the phantom study resulted in the strongest correlation (r = 0.99) between the D and mAs z , and the prediction of patient size would be more precise than method.

Local diagnostic reference levels for paediatric chest computed tomography in Morocco

The present study aimed to establish the local diagnostic reference levels (LDRLs) for paediatric chest computed tomography examinations in Morocco. The data were collected retrospectively from three university hospitals during a two-year period. The proposed LDRLs were expressed in terms of volume CT dose index (CTDIvol), dose-length product (DLP) per series, DLP per procedure, and size-specific dose estimates (SSDE). The effective diameter method was used to estimate SSDE conversion factors based on the middle slice of the scan series. A total of 489 procedures were enrolled including 74% of multiphase scans and 26% of a single series. The LDRLs in terms of CTDIvol (mGy) were 9.5, 9.5, 9.8, and 10.3 for <1 year, 1–<5 years, 5–<10 years, and 10–<15 years age groups, respectively. The LDRLs in terms of DLP (mGy.cm) per series were 188, 243, 276, and 316. In terms of DLP (mGy.cm) per procedure were 373, 491, 583, and 633. The corresponding LDRLs in terms of SSDE (mGy) were 24.4, 21.1, 20.3, and 19 respectively for the four age groups. The findings shed light on higher values compared to international studies for all age groups included.

Estimation of radiation dose associated with bone SPECT/CT and establishing local diagnostic reference levels using size-specific dose estimate

Single-photon emission computed tomography (SPECT) and X-ray computed tomography (CT) is used to diagnose and monitor the skeletal system. However, due to the combination of injected activity and CT radiation dose, its usage is linked to an increase in patient radiation exposure. This study aims to estimate the radiation dose received by patients while undergoing bone SPECT/CT and to establish its local diagnostic reference level (LDRL). In this retrospective study, data from 30 patients who had undergone bone scans were obtained from two hospital imaging devices. The effective doses (E) of the radiopharmaceutical agent and CT components were calculated. Furthermore, the patients' anteroposterior thickness at the midline and lateral widths were measured from their CT images to determine the size-specific dose estimate (SSDE). The mean age of the patients was 53.53 ± 16 years. They were administered an injection activity of 740 MBq of 99mTc-Methyl diphosphonate for SPECT, yielding an E of 2.78 mSv. The mean CTDIvol, DLP, SSDE, and E values for the CT component were 8.76 ± 3.25 mGy, 350 ± 138 mGy cm, 13 ± 4 mGy, and 4.90 ± 1.94 mSv, respectively. Patients received a combined dose of 7.68 mSv from the radiopharmaceuticals and CT. The proposed LDRL for SPECT was comparable to international DRLs, but the CT LDRL was slightly higher. An SSDE-based LDRL is proposed. Moreover, the overall patient dose can be reduced even further by optimizing the injected activity and CT imaging factors.

Low dose pediatric chest computed tomography on a photon counting detector system – initial clinical experience

BackgroundWith the clinical release of a photon counting detector-based computed tomography (CT) system, the potential benefits of this new technology need to be evaluated clinically. Literature concerning this new generation of detector is sparse, especially in the field of pediatric radiology. Therefore, this study outlines our initial experience with ultra-low dose chest CT imaging on the new photon counting CT system.Materials and methodsA pediatric phantom (1-year old, CIRS ATOM phantom, model 704 [CIRS-computerized imaging reference system, Norfolk, VA]) was scanned at different dose levels and different image quality levels to define a protocol for clinical examinations. Next, 20 consecutive pediatric non-contrast ultra-low dose chest CT examinations were evaluated for radiation dose and diagnostic image quality using a 4-point Likert-scale—1 = excellent, 4 = bad image quality—by two radiologists in a consensus reading. This retrospective analysis was approved by the local research ethics committee.ResultsChest CT examinations performed at ultra-low radiation dose (effective dose 0.19 ± 0.07 mSv; size-specific dose estimate 0.45 ± 0.14 mGy) in pediatric patients ages (2.6 ± 1.8 years) show good to excellent image quality for lung structures (1.4 ± 0.4) and moderate image quality for soft tissue structures (2.8 ± 0.2).ConclusionPediatric ultra-low dose chest CT examinations are feasible with the new generation photon counting detector-based CT system. The benefits of this technology must be evaluated for pediatric patients from the outset.

Relative Error between Organ Doses and Size-specific Dose Estimates for a Specific Location When the Mean CTDIvol Value Is Used for Calculation

Size-specific dose estimates (SSDEs) are dose indices that account for differences in body shape in computed tomography (CT) scans, allowing the evaluation of approximate absorbed doses in any cross section that could not be obtained with the volume CT dose index (CTDIvol). When using automatic exposure control (AEC), CTDIvol is modulated in the body axis direction, but the value displayed after the examination is the mean CTDIvol for the entire scan, and it is expected that the SSDE value will change depending on which value is used in the calculation. In this study, using a human body phantom, we examined the influence of whether the mean CTDIvol or the modulation value for each slice is used to calculate the SSDE on local organ dose evaluation. A program to calculate water equivalent diameter according to the procedure in the American Association of Physicists in Medicine Report No. 220 was developed and compared. As a result, SSDE calculated using the mean CTDIvol (local-SSDEmean) overestimated organ doses in the lung region by 18%-56% compared with those calculated by a web system for evaluating CT exposure doses (WAZA-ARIv2, Japan). In contrast, local-SSDEmodulated, which was calculated using the modulated value of the CTDIvol, was able to estimate the organ dose with a relative error of 10%-13%. The average local-SSDE over the entire body axis direction was not significantly different between the two methods, regardless of which method was used for CTDIvol. If the mean CTDIvol is stored in the Digital Imaging and Communications in Medicine (DICOM) header tag (0018, 9345) of the CT image and the modulated CTDIvol value is not available for each slice, the calculated local SSDE will contain many errors and will not correctly reflect the organ doses at the scan region. In such cases, it is available to use the method of evaluating local organ doses by multiplying the SSDE, which is the average of the SSDE for the entire scan, by a factor for each organ.

Estimation of Radiation Dose in CT Chest and Abdomen Examinations Using Size-Specific Dose Estimates

Estimation of Radiation Dose in CT Chest and Abdomen Examinations Using Size-Specific Dose Estimates

Detectability of Small Low-Attenuation Lesions With Deep Learning CT Image Reconstruction: A 24-Reader Phantom Study.

BACKGROUND. Iterative reconstruction (IR) techniques are susceptible to contrast-dependent spatial resolution, limiting overall radiation dose reduction potential. Deep learning image reconstruction (DLIR) may mitigate this limitation. OBJECTIVE. The purpose of our study was to evaluate low-contrast detectability performance and radiation-saving potential of a DLIR algorithm in comparison with filtered back projection (FBP) and IR using a human multireader noninferiority study design and task-based observer modeling. METHODS. A dual-phantom construct, consisting of a low-contrast detectability module (21 low-contrast hypoattenuating objects in seven sizes [2.4-10.0 mm] and three contrast levels [-15, -10, -5 HU] embedded within liver-equivalent background) and a phantom, was imaged at five radiation exposures (CTDIvol range, 1.4-14.0 mGy; size-specific dose estimate, 2.5-25.0 mGy; 90%-, 70%-, 50%-, and 30%-reduced radiation levels and full radiation level) using an MDCT scanner. Images were reconstructed using FBP, hybrid IR (ASiR-V), and DLIR (TrueFidelity). Twenty-four readers of varying experience levels evaluated images using a two-alternative forced choice. A task-based observer model (detectability index [d']) was calculated. Reader performance was estimated by calculating the AUC using a noninferiority method. RESULTS. Compared with FBP and IR methods at routine radiation levels, DLIR medium and DLIR high settings showed noninferior performance through a 90% radiation reduction (except DLIR medium setting at 70% reduced level). The IR method was non-inferior to routine radiation FBP only for 30% and 50% radiation reductions. No significant difference in d' was observed between routine radiation FBP and DLIR high setting through a 70% radiation reduction. Reader experience was not correlated with diagnostic accuracy (R2 = 0.005). CONCLUSION. Compared with FBP or IR methods at routine radiation levels, certain DLIR algorithm weightings yielded noninferior low-contrast detectability with radiation reductions of up to 90% as measured by 24 human readers and up to 70% as assessed by a task-based observer model. CLINICAL IMPACT. DLIR has substantial potential to preserve contrast-dependent spatial resolution for the detection of hypoattenuating lesions at decreased radiation levels in a phantom model, addressing a major shortcoming of current IR techniques.

A new approach to dose reference levels in pediatric CT: Age and size-specific dose estimation

BackgroundAlthough paediatrics' are more radio-sensitivity than adults, the number of requested paediatric CT examinations is increasing globally. Significant efforts have been focused on achieving the lowest possible radiation dose for paediatric patients, particularly adjusting for size differences. This study aims to establish Diagnostic Reference Levels (DRLs) for paediatric patients based on size-specific dose estimates (SSDE). MethodIn this retrospective national study, CT scans for brain, chest, abdominopelvic, and chest, abdomen, and pelvis (CAP) were collected from four hospitals in Jordan undergoing paediatric CT scans. A total of 1818 cases were randomly selected in four age categories (<1 year, 1–4 years, 5–10 years, 11–18 years). The SSDE values were determined by multiplying the volume CT dose index (CTDIvol) with the conversion factor extracted from the American Association of Physicists in Medicine Report 204. ResultsVariations exist between the DRLs between the different hospitals, age groups, and variations in protocols with different types of CT scanners. The DRL values (CTDIvol, dose-length product (DLP) and SSDE) for the four age categories were as follows; <1 year: brain (47.88 mGy, 741.67 mGy cm and 58.40 mGy), chest (5.65 mGy, 124 mGy cm and 13.91 mGy), abdominopelvic (12.65 mGy, 321.5 mGy cm and 28.72 mGy) and CAP (16.12 mGy, 507.72 mGy cm and 38.04 mGy). 1–4 years, brain (54.79 mGy, 979.12 mGy cm and 55.88 mGy), chest (7.37 mGy, 220.85 mGy cm and 14.68 mGy), abdominopelvic (16.16 mGy, 424.72 mGy cm and 32.68 mGy) and CAP (16.13 mGy, 742.1 mGy cm and 33.54 mGy). 5–10 years: brain (65.03 mGy, 1129.94 mGy cm and 55.92 mGy), chest (12.57 mGy, 383.9 mGy cm and 22.45 mGy), abdominopelvic (12.34 mGy, 450.75 mGy cm and 22.23 mGy) and CAP (13.46 mGy, 748.85 mGy cm and 25.69 mGy). 11–18 years, brain (60.7 mGy, 1207.9 mGy cm and 41.81 mGy), chest examination (12.94 mGy, 496.2 mGy cm and 20.49 mGy), abdominopelvic (16.13 mGy, 803.07 mGy cm and 23.06 mGy) and CAP (16.13 mGy, 1101.5 mGy cm and 23.85 mGy). ConclusionThere were increases in CTDIvol, DLP, and SSDE with ascending age groups. SSDE and age are closely matched to delivered radiation in paediatric CT; however, radiation dose levels remain high in Jordan. This work highlights the need for caution when administering radiation in the paediatric population.

Comparison of Water-Equivalent Diameter Measured from CT Localizer Radiograph Based on Two phantoms of the Step-Wedge and Computed Tomography Dose Index

The purpose of this study is to compare the water-equivalent diameter (Dw) and size-specific dose estimate (SSDE) obtained from CT localizer radiograph based on the step-wedge and computed tomography dose index (CTDI) phantoms. The two phantoms were scanned using a 64-slice SIEMENS Somatom CT Scanner with tube currents of 100 mA and 120 kV. The CT localizer radiographs of two phantoms were obtained. Subsequently, relationships between pixel values (PV) and water-equivalent thickness (tw) were developed. Based on those relationships, the Dw and SSDE of twenty patients were calculated from the CT localizer radiographs. The results of the Dw and SSDE measured using CT localizer radiographs based on the two phantoms were compared. The relationships between PV and tw obtained from both CT localizer radiographs of the phantoms of step-wedge and CTDI are established. The Dw and SSDE values from the CT localizer radiograph calibrated with the CTDI phantom and step-wedge phantom also have linear relationship with R2 &gt; 0.99. The statistical test value with p-value &gt; 0.05 indicating that the two measurements of Dw and SSDE based on two phantoms are not statistically different. The results from the step-wedge phantom are comparable with those from the CTDI phantom. The relationship PV and tw with CT localizer radiograph from the step-wedge phantom can produce accurate calibration results. The results of the calibration of the step-wedge phantom can then determine the value of Dw and SSDE.

Size-specific dose estimate (SSDE) in pediatric chest and abdominal CT scans: water equivalent diameter vs. patient body weight

Size-specific dose estimate (SSDE) in pediatric chest and abdominal CT scans: water equivalent diameter vs. patient body weight

Size specific dose estimates for Computed Tomography cancer patients at an Oncology hospital.

Size specific dose estimates for Computed Tomography cancer patients at an Oncology hospital.

Accuracy of patient dose estimation in cone beam computed tomography in breast irradiation by size-specific dose estimates with position correction.

This study aims to investigate the effects of the position correction of size-specific dose estimates (SSDE) on patient dose estimation in cone beam computed tomography (CBCT). The relationship between the phantom position and absorbed dose in the right breast was studied using optically stimulated luminescence dosimeters and a simulated human body phantom. The effect of position correction for CT dose index (CTDI) on SSDE was investigated in 51 patients who underwent right breast irradiation by comparing the SSDE with position correction and SSDE without position correction. The absorbed dose in the right breast tended to decrease by 10.2% as the phantom was placed away from the center of CBCT. The mean and standard deviation of SSDE were 2.54±0.29 and 2.92±0.30 mGy with and without position correction, respectively. The SSDE with position correction was 13.1% lower than that without position correction (p<0.05). SSDE was different when the patient's torso center was located at the isocenter of CBCT, and when it was not. The same tendency was seen in the case of the breast. Therefore, if the center of the patient is not at the acquisition center of the CT scanner, position correction is required when estimating SSDE.

Deep Learning-based calculation of patient size and attenuation surrogates from localizer Image: Toward personalized chest CT protocol optimization

PurposeExtracting water equivalent diameter (DW), as a good descriptor of patient size, from the CT localizer before the spiral scan not only minimizes truncation errors due to the limited scan field-of-view but also enables prior size-specific dose estimation as well as scan protocol optimization. This study proposed a unified methodology to measure patient size, shape, and attenuation parameters from a 2D anterior-posterior localizer image using deep learning algorithms without the need for labor-intensive vendor-specific calibration procedures. Methods3D CT chest images and 2D localizers were collected for 4005 patients. A modified U-NET architecture was trained to predict the 3D CT images from their corresponding localizer scans. The algorithm was tested on 648 and 138 external cases with fixed and variable table height positions. To evaluate the performance of the prediction model, structural similarity index measure (SSIM), body area, body contour, Dice index, and water equivalent diameter (DW) were calculated and compared between the predicted 3D CT images and the ground truth (GT) images in a slicewise manner. ResultsThe average age of the patients included in this study (1827 male and 1554 female) was 53.8 ± 17.9 (18–120) years. The DW, tube current ,and CTDIvol measured on original axial images in the external 138 cases group were significantly larger than those of the external 648 cases (P < 0.05). The SSIM and Dice index calculated between the prediction and GT for body contour were 0.998 ± 0.001 and 0.950 ± 0.016, respectively. The average percentage error in the calculation of DW was 2.7 ± 3.5 %. The error in the DW calculation was more considerable in larger patients (p-value < 0.05). ConclusionsWe developed a model to predict the patient size, shape, and attenuation factors slice-by-slice prior to spiral scanning. The model exhibited remarkable robustness to table height variations. The estimated parameters are helpful for patient dose reduction and protocol optimization.

Truncation Effects on Effective Diameter Measurement for Size-specific Dose Estimation in Computed Tomography (CT) Imaging

The determination of size specific dose estimation (SSDE) has been proposed for accurate CT dose assessment. The SSDE introduction has prompted numerous manufacturers and researchers to develop various methodologies that have progressed from manual to automated methods in SSDE determination. Few studies reported on truncation effects with respect to specific size and SSDE determination and CT manufacturers are yet to incorporate truncation correction in their system [1,2].&#x0D; This study aimed to evaluate the effects of truncation artifacts on the measurement of effective diameter (Deff) and SSDE in CT imaging. A phantom study was performed using CTDI phantom of different diameters, 22 and 32 cm with Siemens SOMATOM Definition AS+ CT scanner. Phantom images of different truncation percentage (TP) of 5%, 10%, 15%, and 20% were simulated and acquired. The Deff and SSDE were determined based on the displayed CTDIvol, and the AAPM correction factor table was used to calculate the SSDE accurately [3]. The percentage error for each TP in comparison with non-truncated image (TP 0%) was computed.&#x0D; Results showed the percentage error (PE) for both Deff and SSDE increased as the TP increased. The PE was determined by comparing the Deff and SSDE of each TP with non-truncated (TP 0%) image. Table 1 shows the values of PE of truncated images of different TP (5%, 10%, 15%, and 20%) for both Deff and SSDE in phantom sizes of 22 and 32 cm. However, it can be observed that PE values for SSDE of 5% and 10% truncation were similar for both phantom sizes. This is because the correction factors for 5% and 10% were similar and had resulted in similar calculated SSDE. The highest recorded PE was observed in 20% truncation that determined the largest difference in Deff and SSDE with non-truncated image.&#x0D; This study demonstrates that there is a linear relationship between truncation percentage with measured Deff and SSDE computation. It can be concluded that the percentage error in Deff measurement and calculated SSDE will increase as TP increased. Therefore, the effects of truncation artefacts should be carefully considered in SSDE calculation for accurate estimation especially in development of automated calculation.

SIZE-specific dose estimate for lower-limb CT.

The Computed Tomography Dose Index (CTDI) is an indicator for dose management in computed tomography (CT), but has limited use for patient dosimetry. To evaluate the patient dose, the size-specific dose estimate (SSDE), reported by the American Association of Physics in Medicine task groups 204, 220, and 293, must be calculated by the CTDIvol(z) displayed on the CT console, and the conversion factor f(D(z)) from the effective diameter (DEff) or water equivalent diameter (Dw). However, no reports have verified the appropriateness of using the 320-mm diameter phantom for dose assessment in CT examinations involving the lower limbs. Therefore, we validated a new method for evaluating the SSDE(z) of the lower limbs, using two 160-mm diameter phantoms instead of the 320-mm diameter phantom. The CTDIvol(z) obtained from Monte Carlo (MC) simulation study was reliable because they were almost the same as obtained in a dosimetry study. The conversion factor f (D (zl.l.)) for the lower limbs was evaluated based on the CTDIvol(z) obtained by MC simulation performed using two polymethyl methacrylate cylinder phantoms of 160-mm diameter. The MC simulation was performed by the International Commission on Radiological Protection publication 135 reference adult phantom and was used to evaluate the absorbed dose of the pelvis, thighs, knees, and ankles. The dose showing the greatest difference was the thighs, which was 8.3mGy (16%) lower than the absorbed dose. Thus, the SSDE (zl.l.) could be estimated from the [Formula: see text] displayed on the CT scanner console.

The Impact of Data Management on the Achievable Dose and Efficiency of Computed Tomography During the COVID-19 Era: A Facility-Based Ambispective Study.

PurposeThis study primarily aimed to evaluate the effectiveness of computational data management and analytical software for establishing departmental diagnostic reference levels (DRLs) for computed tomography (CT) scanning in clinical settings, and monitor achievable doses (ADs) for CT imaging, particularly during the coronavirus disease 2019 (COVID-19) era. Secondarily, it aimed to correlate these standards with national and international benchmarks.Patients and MethodsThis ambidirectional cohort study enrolled 4668 patients (6419 CT-based examinations) who visited King Fahd Hospital of the University from May 25, 2021, to November 4, 2021. Participants’ demographic data were acquired from their electronic medical charts, in addition to all corresponding CT-dose determinant parameters. The study was divided into two phases (pre- and post-data management) based on the implementation of digital data management software.ResultsIn both phases of the study, the size-specific dose estimate (SSDE) was the most significant confounder of dose determination compared to the dose-length product (DLP) and computed tomography dose index (CTDI) (P = 0.003). The head was the most frequently imaged body region (pre-implementation, 1051 examinations [35.1%]; post-implementation, 1071 examinations [31.3%]; P = 0.001), followed by the abdominal region (pre-implementation, 616 examinations [20.6%]; post-implementation, 256 examinations [7.48%]; P = 0.001). Based on the SSDE, DLP, and volume CTDI, the average per-section radiation exposure among organ-based scanning type was highest for the lumbar spine during the pre- and post-implementation periods.ConclusionData management software enabled the establishment of DRLs and reduction of ADs in CT examinations, which consequently improved key performance indicators, despite the ergonomic complexities of COVID-19. Institutions are encouraged to apply DRLs and ADs via automatic systems that monitor patient dose indices to evaluate aggregate results.

Computed Tomography Diagnostic Reference Levels for Brain, Chest, and Abdominal/Pelvis Examinations

Radiation dosage variance is one of the topics that arise when dealing with computed tomography (CT) devices within medical imaging centers. In this article, a review was done to enlighten the causes of such dosage variance and the degree of variation for pediatric patients. The article focuses on the diagnostic reference levels (DRLs) for the brain, chest, and abdomen CT images. The reviewed studies were categorized depending on the type of the cases of pediatric patients, which include head, chest, and abdominal examinations. There were 9 studies using human data, 1 with phantom data, and 2 with combined human and phantom data. The dosage indices used in the studies were the DRLs, which were used as a key comparison between studies. The classification was likewise done at the expense of the radiation dose, with a secondary classification based on the patients' age, weight, and size. The type of scanner, differences in protocols, variations in patients, and variations in research design are all considered sources of variation. The following dosage indices were found in different combinations: volume CT dose index (CTDIvol), dose length product (DLP), and size-specific dose estimate (SSDE). The use of different dose indices limited the dose comparison between 11 studies.

The role of topogram views on dose indices and image quality in thorax and abdomen-pelvis CT scan

This study was designed to investigate the effect of the different topograms (AP and dual AP/Lateral) on patient dose indices and image quality in thorax and abdomen-pelvis CT. Size-specific dose estimation (SSDE), volumetric CT dose index (CTDIvol), milliampere seconds (mAs), effective dose, as well as signal to noise ratio (SNR) and contrast to noise ratio (CNR) of 60 thorax and 60 abdomen-pelvis CT scans were analyzed. In thorax CT, SSDE, mAs, CTDIvol and effective dose were significantly reduced by using dual topograms (p &lt; 0.05) but not significantly reduced in abdominal-pelvic scans (p &gt; 0.05). There was no significant difference between CNR parameter in the two groups for thorax CT (p &gt; 0.05) and SNR parameter in abdomen-pelvic CT (p &lt; 0.05) and all images were diagnostically acceptable. The use of two topograms in thorax CT is an efficient approach to reduce dose indices without decreasing the image quality.

Fetal Dose from PET and CT in Pregnant Patients.

When pregnancy is discovered during or after a diagnostic examination, the physician or the patient may request an estimate of the radiation dose received by the fetus as per guidelines and standard operating procedures. This study provided the imaging community with dose estimates to the fetus from PET/CT with protocols that are adapted to University of Michigan low-dose protocols for patients known to be pregnant. Methods: There were 9 patients analyzed with data for the first, second, and third trimesters, the availability of which is quite rare. These images were used to calculate the size-specific dose estimate (SSDE) from the CT scan portion and the SUV and 18F-FDG uptake dose from the PET scan portion using the MIRD formulation. The fetal dose estimates were tested for correlation with each of the following independent measures: gestational age, fetal volume, average water-equivalent diameter of the patient along the length of the fetus, SSDE, SUV, and percentage of dose from 18F-FDG. Stepwise multiple linear regression analysis was performed to assess the partial correlation of each variable. To our knowledge, this was the first study to determine fetal doses from CT and PET images. Results: Fetal self-doses from 18F for the first, second, and third trimesters were 2.18 mGy (single data point), 0.74-1.82 mGy, and 0.017-0.0017 mGy, respectively. The combined SSDE and fetal self-dose ranged from 1.2 to 8.2 mGy. These types of images from pregnant patients are rare. Conclusion: Our data indicate that the fetal radiation exposure from 18F-FDG PET and CT performed, when medically necessary, on pregnant women with cancer is low. All efforts should be made to minimize fetal radiation exposure by modifying the protocol.

Calculation of scan length and size-specific dose at longitudinal positions of body CT scans using dose equilibrium function.

Dose evaluation at longitudinal positions of body computed tomography (CT) scans is useful for CT quality assurance programs and patient organ dose evaluation. Accurate estimates depend on both patient size and scan length. To propose practical evaluation of the average dose to the transverse slab of an axial image slice for adult body CT examinations, considering not only patient size but also scan length, and to compare the results with those of Monte Carlo (Geant4) simulation [Dsim (z)] and size-specific dose estimates at longitudinal positions of scans [SSDE(z)] from international standards (IEC publication no. 62985). In a scan series, the total dose at each z-axis location was calculated using the input information identical to the SSDE(z) evaluation. Each axial image slice (slice thickness, 2.5 or 5mm) was first considered independently. Its z-axis coverage and CTDIvol (from the DICOM headers) were used to directly calculate a z-axis dose profile for the average dose over the cross-section of a water phantom, using the approach to equilibrium function. The phantom diameter was taken to be equal to the patient water equivalent diameter at that slice. The above was repeated at all slices and the dose at each z-axis location was accumulated from all profiles, referred to as Dcalc (z). For validation, we considered a cohort of 65 patients, who underwent chest and abdominopelvic examinations. The resultant Dcalc (z) was compared with Dsim (z) and SSDE(z), both available in a previous paper. Dcalc (z) evaluation could be used to accurately assess the scan range average dose, with an accuracy of 7.1%-8.7% for 65 patients in two examinations. On individual image slices, the maximum difference in magnitude between Dcalc (z) and Dsim (z) [and between SSDE(z) and Dsim (z) in parentheses] was 37.5% (85%) [two edges (2×5cm) of chest scan range], 17.8% (35.2%) (the remaining central region of chest scan), 26.8% (74.1%) [two edges (2×5cm) of abdominopelvic scan range], and 14.2% (22.5%) (the remaining central region of abdominopelvic scan). Identical input data are used for Dcalc (z) and SSDE(z) evaluations. The latter is limited to the z-axis locations within scan range. At each image slice, SSDE(z) is equivalent to the midpoint dose of a fixed-mA scan of 15-30cm (scan length). In contrast, Dcalc (z) considers dose accumulation from varying scan length (from sub-centimeter to about 1m) and tube current, and dose profile is also computed outside scan range. Besides greatly improving dose evaluation for individual image slices, Dcalc (z) allows for evaluating dose accumulation from multiple series, which typically span different scan ranges. Our proposal may assist CT manufacturers and dose index monitoring software in assessing dose at longitudinal positions of body CT scans.