Patient Effective Diameter Research Articles

Assessment of image quality and establishment of local acceptable quality dose for computed tomography based on patient effective diameter.

We aim to develop modified clinical indication (CI)-based image quality scoring criteria (IQSC) for assessing image quality (IQ) and establishing acceptable quality doses (AQDs) in adult computed tomography (CT) examinations, based on CIs and patient sizes. CT images, volume CT dose index ( ), and dose length product (DLP) were collected retrospectively between September 2020 and September 2021 for eight common CIs from two CT scanners at a central hospital in the Kingdom of Bahrain. Using the modified CI-based IQSC and a Likert scale (0 to 4), three radiologists assessed the IQ of each examination. AQDs were then established as the median value of and DLP for images with an average score of 3 and compared to national diagnostic reference levels (NDRLs). Out of 581 examinations, 60 were excluded from the study due to average scores above or below 3. The established AQDs were lower than the NDRLs for all CIs, except for oncologic follow-up for large patients (28 versus 26mGy) in scanner A, besides abdominal pain for medium patients (16 versus 15mGy) and large patients (34 versus 27mGy), and diverticulitis/appendicitis for medium patients (15 versus 12mGy) and large patients (33 versus 30mGy) in scanner B, indicating the need for optimization. CI-based IQSC is crucial for IQ assessment and establishing AQDs according to patient size. It identifies stations requiring optimization of patient radiation exposure.

Optimal dose determination for coronary artery calcium scoring CT at standard tube voltage

ObjectivesCoronary artery calcium scoring (CACs) at 120 kVp is the standard practice. It is an important tool for preventative management of asymptomatic patients. However, the current dose delivery, albeit patient-size dependent, does not connect the CACs specific noise requirement to the dose, causing significant dose variations. We propose a new approach for optimal dose determination by incorporating the patient-size dependent noise threshold. MethodsA polyethylene-based Mercury phantom of various diameters was scanned with a dual-source CT using CACs gating at different volume CT dose index (CTDIvol). The relationship of noise to the diameter and CTDIvol was obtained. The phantom diameter was then converted to the patient chest diameter through a retrospective analysis of a clinical cohort (N = 140). Finally, the patient-size dependent noise threshold was applied, and the optimal dose was derived. The prescribed doses were compared with those from a clinical CACs cohort (N = 262). ResultsA power-exponential relationship was found for the noise versus CTDIvol and phantom diameter (R2 = 0.988). The phantom diameter versus the patient effective diameter was found to obey a linear relationship (R2 = 0.998). Two noise threshold settings were made for dose options: one for more dose saving, and another for tighter noise constraint. Retrospective comparisons with clinical CACs studies showed an average dose reduction of 23% in 80.5% of the cases with option 1. The average dose reduction is 23% in 77.9% of the cases with option 2. ConclusionA new optimal dose scheme dictated by the target noise was established for CACs at 120 kVp. The proposed dose modulation can serve as the baseline from which further dose reduction is possible.

U.S. Diagnostic Reference Levels and Achievable Doses for 10 Pediatric CT Examinations.

Background Diagnostic reference levels (DRLs) and achievable doses (ADs) were developed for the 10 most commonly performed pediatric CT examinations in the United States using the American College of Radiology Dose Index Registry. Purpose To develop robust, current, national DRLs and ADs for the 10 most commonly performed pediatric CT examinations as a function of patient age and size. Materials and Methods Data on 10 pediatric (ie, patients aged 18 years and younger) CT examinations performed between 2016 and 2020 at 1625 facilities were analyzed. For head and neck examinations, dose indexes were analyzed based on patient age; for body examinations, dose indexes were analyzed for patient age and effective diameter. Data from 1 543 535 examinations provided medians for AD and 75th percentiles for DRLs for volume CT dose index (CTDIvol), dose-length product (DLP), and size-specific dose estimate (SSDE). Results Of all facilities analyzed, 66% of the facilities (1068 of 1625) were community hospitals, 16% (264 of 1625) were freestanding centers, 9.5% (154 of 1625) were academic facilities, and 3.5% (57 of 1625) were dedicated children's hospitals. Fifty-two percent of the patients (798 577 of 1 543 535) were boys, and 48% (744 958 of 1 543 535) were girls. The median age of patients was 14 years (boys, 13 years; girls, 15 years). The head was the most frequent anatomy examined with CT (876 655 of 1 543 535 examinations [57%]). For head without contrast material CT examinations, the age-based CTDIvol AD ranged from 19 to 46 mGy, and DRL ranged from 23 to 55 mGy, with both AD and DRL increasing with age. For body examinations, DRLs and ADs for size-based CTDIvol, SSDE, and DLP increased consistently with the patient's effective diameter. Conclusion Diagnostic reference levels and achievable doses as a function of patient age and effective diameter were developed for the 10 most commonly performed CT pediatric examinations using American College of Radiology Dose Index Registry data. These benchmarks can guide CT facilities in adjusting pediatric CT protocols and resultant doses for their patients. © RSNA, 2021 An earlier incorrect version appeared online. This article was corrected on October 29, 2021.

Evaluation of Size-Specific Dose Estimates for Optimizing Pediatric Chest CT Protocol

Introduction: The importance of estimating patient-sized adjusted radiation dose for pediatric computed tomography (CT) has long been accepted. High doses of ionizing radiation to children are often common in chest CT examination, as the volume CT dose index (CTDIvol) is measured by a 32 cm phantom. Our study was aimed to evaluate the effectiveness of size-specific dose estimate (SSDE) to compensate the underestimated pediatric absorbed dose. Materials and methods: CTDIvol and dose-length product (DLP) of 320 pediatric chest CT (<1, 1-5, 5-10, 10-15 years) were obtained from Picture-Archieving and Communication System (PACS) in a hospital affiliated to the Shiraz University of Medical Sciences. CTDIvol was converted to SSDE based on the patient's effective diameter. The Statistical Package for Social Science (SPSS) was used for data analysis. Results: The variations between standard phantom (32cm) and the patients' mean effective diameter were approximately 65%, 57%, 47%, and 38%, across <1, 1-5, 5-10, 10-15 year age groups, respectively. Mean of SSDE for each age group was significantly higher than the corresponding CTDIvol values. Also, mean CTDIvol and SSDE values differed between age groups significantly (p<0.001). Results showed a strong correlation between age and the two dose indicators, CTDIvol (0.361) and SSDE (0.184) with p<0.05. Conclusion: Pediatrics receive radiation doses comparable to the dose for adult-sized patients in chest CT protocol if dosimetry procedure is not individualized. Thus, the application of size-based conversion coefficient is paramount in estimating the absorbed dose in pediatric chest CT.

Thoracic Organ Doses and Cancer Risk from Low Pitch Helical 4-Dimensional Computed Tomography Scans

Purpose To investigate the dose depositions to organs at risk (OARs) and associated cancer risk in cancer patients scanned with 4-dimensional computed tomography (4DCT) as compared with conventional 3DCT. Methods and Materials The radiotherapy treatment planning CT image and structure sets of 102 patients were converted to CT phantoms. The effective diameters of those patients were computed. Thoracic scan protocols in 4DCT and 3DCT were simulated and verified with a validated Monte Carlo code. The doses to OARs (heart, lungs, esophagus, trachea, spinal cord, and skin) were calculated and their correlations with patient effective diameter were investigated. The associated cancer risk was calculated using the published models in BEIR VII reports. Results The average of mean dose to thoracic organs was in the range of 7.82-11.84 cGy per 4DCT scan and 0.64-0.85 cGy per 3DCT scan. The average dose delivered per 4DCT scan was 12.8-fold higher than that of 3DCT scan. The organ dose was linearly decreased as the function of patients' effective diameter. The ranges of intercept and slope of the linear function were 17.17-30.95 and -0.0278--0.0576 among patients' 4DCT scans, and 1.63-2.43 and -0.003--0.0045 among patients' 3DCT scans. Relative risk of cancer increased (with a ratio of 15.68:1) resulting from 4DCT scans as compared to 3DCT scans. Conclusions As compared to 3DCT, 4DCT scans deliver more organ doses, especially for pediatric patients. Substantial increase in lung cancer risk is associated with higher radiation dose from 4DCT and smaller patients' size as well as younger age.

Comparing Dose-Length Product-Based and Monte Carlo Simulation Organ-Based Calculations of Effective Dose in 16- and 64-MDCT Examinations Using Automatic Tube Current Modulation.

The purpose of this study is to compare dose-length product (DLP)-based calculation of effective dose (EDDLP) with Monte Carlo simulation organ-based calculation of effective dose (EDMCO) in 16- and 64-MDCT examinations, with the use of clinical examinations with automatic tube current modulation. Dose data were obtained from 50 consecutive unenhanced head CT examinations, unenhanced chest CT examinations, and unenhanced and contrast-enhanced abdominopelvic CT examinations performed using 16- and 64-MDCT scanners, as well as from 50 pulmonary CT angiography (CTA) examinations performed using a 64-MDCT scanner and 31 pulmonary CTA examinations performed using a 16-MDCT scanner. The EDMCO and the mean patient effective diameter were calculated using commercially available software. The EDDLP was also calculated. Both the mean difference and percentage difference between EDDLP and EDMCO were calculated, and they were statistically compared according to patient sex, type of examination performed, and type of scanner used. EDDLP significantly underestimated the EDMCO by 0.3 mSv (19%) for men who underwent unenhanced head CT, 0.5 mSv (29%) for women who underwent unenhanced head CT, 0.9-1.4 mSv (9-13%) for men who underwent chest CT, and 4.7-4.8 mSv (39%) for women who underwent chest CT (p < 0.001). The EDDLP overestimated the EDMCO by 1.9-2.0 mSv (12-14%) for men who underwent abdominopelvic CT (p < 0.001), with no significant difference noted for women who underwent abdominopelvic CT's. No significant difference was noted in the percentage difference in ED between the 16- and 64-MDCT scanners (p ≥ 0.13). EDDLP underestimates EDMCO, the reference standard for dose calculation, by 19-39% in unenhanced head CT examinations and, among women, in chest CT examinations. EDDLP deviates from EDMCO by less than 15% for chest CT examinations of men and for abdominopelvic CT. These differences can be attributed to variable patient body habitus, automatic tube current modulation, and sex-neutral k-coefficients, and they should be considered when calculating ED, particularly in women.

Organ Dose and Attributable Cancer Risk in Lung Cancer Screening with Low-Dose Computed Tomography.

PurposeLung cancer screening with CT has been recently recommended for decreasing lung cancer mortality. The radiation dose of CT, however, must be kept as low as reasonably achievable for reducing potential stochastic risks from ionizing radiation. The purpose of this study was to calculate individual patients’ lung doses and to estimate cancer risks in low-dose CT (LDCT) in comparison with a standard dose CT (SDCT) protocol.Materials and MethodsThis study included 47 adult patients (mean age 63.0 ± 5.7 years) undergoing chest CT on a third-generation dual-source scanner. 23/47 patients (49%) had a non-enhanced chest SDCT, 24 patients (51%) underwent LDCT at 100 kVp with spectral shaping at a dose equivalent to a chest x-ray. 3D-dose distributions were obtained from Monte Carlo simulations for each patient, taking into account their body size and individual CT protocol. Based on the dose distributions, patient-specific lung doses were calculated and relative cancer risk was estimated according to BEIR VII recommendations.ResultsAs compared to SDCT, the LDCT protocol allowed for significant organ dose and cancer risk reductions (p<0.001). On average, lung dose was reduced from 7.7 mGy to 0.3 mGy when using LDCT, which was associated with lowering of the cancer risk from 8.6 to 0.35 per 100’000 cases. A strong linear correlation between lung dose and patient effective diameter was found for both protocols (R2 = 0.72 and R2 = 0.75 for SDCT and LDCT, respectively).ConclusionUse of a LDCT protocol for chest CT with a dose equivalent to a chest x-ray allows for significant lung dose and cancer risk reduction from ionizing radiation.

Size-Specific Dose Estimates for Evaluation of Individual Patient Dose in CT Protocol for Renal Colic.

The purpose of this study is to retrospectively evaluate size-specific dose estimates of a renal-colic CT protocol and to assess the quality and diagnostic value of obtained images. The study population included 82 consecutive adult patients with acute renal colic undergoing CT with a reduced radiation dose (noise index, 59.1). The control group included 82 consecutive patients who underwent clinically indicated CT examination of the abdomen and pelvis with a routine-dose CT protocol (noise index, 22.0). The size-specific dose estimate was calculated with volume CT dose index and patient effective diameter. Subjective image quality analysis was based on visibility of the ureter. Ureters were tracked from the renal pelvis to the vesicoureteral junction. Objective image quality was based on the signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR). The size-specific dose estimates in the renal-colic group were 2.7 times lower than those in the control group. A linear relationship between patient size and size-specific dose estimate was noted. In the smallest patient, the conversion factor for the size-specific dose estimate calculation was 1.65. Overall image quality was better for the control patients, but there was no statistically significant difference in ureter visibility. The SNR was higher for the control group, whereas no difference in CNR was found. Small patients need the biggest correction for body size and require special attention in radiation dose estimation. We suggest the modification of scanning parameters on the basis of size-specific dose estimate to decrease patient dose in large patients.

Comparison of radiation dose and image quality from single-energy and dual-energy CT examinations in the same patients screened for hepatocellular carcinoma

To compare radiation dose surrogates [volume CT dose index (CTDIvol), dose-length product (DLP), size-specific dose estimate (SSDE), and effective dose] and image noise in a cohort of patients undergoing hepatocellular carcinoma screening who underwent both single-energy CT (SECT) and dual-energy CT (DECT). In this institutional review board-approved, Health Insurance Portability and Accountability Act-compliant retrospective study, 74 adults (mean age 59.5 years) underwent 64 section SECT (120 kVp and weight-based reference mAs) and 128 section dual-source DECT (100/Sn 140 kVp and CTDIvol, adjusted to match the CDTIvol of the SECT protocol) on different occasions. Noise levels were measured in the liver, inferior vena cava (IVC), retroperitoneal (RP) fat, and aorta. Generalized linear models were constructed to compare dose and noise, adjusting for effective diameter. The total DLP (1371.11 mGy-cm, SD = 527.91) and effective dose (20.57 mSv, SD = 7.92) with SECT were significantly higher than the DLP (864.84 mGy-cm, SD = 322.10) and effective dose (12.97 mSv, SD = 4.83) with DECT (p < 0.001). The differences between SECT and DECT increased as the patient's effective diameter increased (p < 0.001). Noise levels in the liver (22.4 versus 21.9 HU), IVC (22.3 versus 23.4 HU), and RP fat (23.5 versus 23 HU) were similar for DECT and SECT (p > 0.05) but were significantly lower in the aorta for DECT (25.3 versus 26.4 HU; p = 0.006). DECT imaging of the abdomen can achieve noise levels comparable to those seen with SECT imaging without a dose penalty to patients.

MO‐E‐17A‐10: Evaluation of Body and Head Dimensions of Pediatric Patients as a Function of Age

Purpose:Phantom development in medical physics plays an important role in radiation dose assessment and image quality evaluation, and this is especially true in the pediatric patient population. The purpose of this investigation was to establish the relationship between patient age and patient size, focusing on the abdomen‐pelvis and head effective diameters, for patients ranging in age from newborn to 18 years.Methods:A dose reporting tool for computed tomography systems was installed at our institution to achieve compliance with state law commencing on July 1, 2012. The software records a number of patient‐specific data, and also reports CT dose metrics (CTDIvol and DLP) into the patients interpretive report. The database generated by the software was mined to determine patient effective diameter as a function of age for pediatric patients aged 0–18 years. CT protocols including abdomen‐pelvis and routine head were evaluated, and specific to this study the patients age, gender and equivalent diameter were recorded.Results:Six age ranges were evaluated: A(0–3), B(4–6), C(7–9), D(10–12),E(13–15),F(16–18). For the torso in these groups based upon 694 patients, median effective diameters were 147, 167, 184, 214, 231, 246 mm, respectively. For the head (N=1833), median diameters were 143, 157, 162, 168, 174, and 174, respectively.Conclusion:A solid understanding of the approximate dimensions of pediatric patients as a function of age is useful in the development of age‐based imaging protocols and dose assessments. CT dose‐reporting tools generate a great deal of data with respect to body dimensions automatically. In this study, median equivalent diameters for the abdomen‐pelvis and head of pediatric patients were evaluated. These data may prove useful in the development of both mathematical and physical phantoms for dosimetry and image quality assessment.

SU-C-12A-02: CTDIvol Variability in Tube-Current Modulated Body CT: The Role of Patient Diameter

Purpose: Researchers have used the large variability in CTDIvol as an example of inconsistent and inappropriate protocols for CT imaging. However, CTDIvol variability can exist for many sound reasons pertaining to protocol needs (slice thickness, etc.) or patient size. This investigation focused on the role that patient effective diameter plays in CTDIvol variability. Methods: A database associated with a commercial CT dose reporting tool was mined, and the protocol parameters from 3136 patients who were scanned on one CT scanner (GE VCT) at our institution were evaluated. All patients were imaged using an abdomen-pelvis protocol, and tube current modulation was employed. A graph of CTDIvol versus diameter was fit using an exponential function (CTDIvol = a EXP(b x DIAMETER), and the parameters of this fit were used to subtract away the diameter dependence. Evaluation of variance before and after this correction was performed. Results: Abdomen-pelvis CT scans performed between February 28, 2013 and February 28, 2014 were evaluated corresponding to a timeframe where x-ray tube current modulation was used consistently. Average patient age was 50.0 years (SD=18.1), and ranged from 0 to 97 years. Mean patient diameter was 306.2 mm (SD=52.0), and CTDIvol values ranged from 2.8 mGy to 56.0 mGy, with a mean of 11.1 mGy (SD=6.68 mGy). After the dependency of patient diameter was removed from the data, the remainder data averaged 0.28 mGy (SD=3.01 mGy). A 2.2 fold reduction in standard deviation was observed, and the reduction in variance achieved by removing the size dependence of CTDIvol was (6.68/3.01)∧2 = 4.93. Conclusion: In a modern CT scanner using contemporary TCM protocols, a large component of CTDIvol variance can be attributed to patient size. The reduction of variance by a factor of 4.9 demonstrates that significant variability in CTDIvol is related to patient size. This study was partially funded by a grant from the University of California Office of the President

SU-E-I-42: Size-Specific Dose Estimates (SSDE) Modified for Lung Inhomogeneities: A Practical Approach

Purpose: his work recommends a method of estimating the patient effective diameter (ED) parameter in the thoracic area in order to compute the Size‐Specific Dose Estimates (SSDE) for both adult and pediatric patients, taking into account the lung inhomogeneities. Methods: A well‐established method of estimating effective distance/depth (sometimes called radiological depth) in radiotherapy treatment planning for lung inhomogeneities, is recommended here. The method requires the use of an average relative electron density for the lung tissue of rho(Lung)=0.3 to be used so a corrected lateral (LAT) patient thickness and ED is determined. Based on the new ED the dose correction factor, as per TG‐204, can be selected. This method was compared with the current recommendation by TG‐204 and another correction method for lung inhomogeneities from the literature. Results: Improved estimation of patient ED that incorporates lung inhomogeneities was compared to that computed by a radiotherapy treatment planning system. The two methods agreed to within 5% for the cases studied. This difference is smaller than the 12–20% between the recommended method by TG‐204 and another published correction method. In addition, the results showed that the effective AP thickness is not necessary to be accounted for by this approach. Conclusions: A fast and easy method of computing patient effective LAT thickness and ED in order to estimate SSDE is based on the use of a relative electron density for the lung tissue. The more accurate LAT thickness and patient ED allow the selection of a dose correction factor out of the TG‐204 tables that would take into account in some way the tissue heterogeneities in the thoracic area. This method may potentially be used in cone‐beam CT image guided radiotherapy where estimation of patient imaging doses is required.

SU-D-103-03: Converting Size Specific Dose Estimate (SSDE) to Patient Specific Organ Dosimetry: Application to a Pediatric Population

Purpose: Develop a methodology to convert size specific dose estimate (SSDE) to pediatric patient specific organ dosimetry. Methods: Each thoracic and abdominal-pelvic organ within a family of four anthropomorphic phantoms (ATOM, CIRS) developed to emulate a wide range of pediatric patient body habitus was measured for absolute dose using MOSFET dosimeters; e.g., a series of 884 measurements were made in 21 different organs spanning the thorax of an anthropomorphic phantom developed to emulate a 10 yr patient. A Scout scan was performed for each phantom wherein the phantoms thoracic and abdominal-pelvic effective diameters were calculated pursuant to the AAPM Report 204 methodology. The phantoms effective diameter was matched with a pediatric patient population average effective diameter, and imaged according to that patient populations weight based CT scan parameters; thus, normalizing CTDIvol between phantom and representative patient populations. A correction factor was developed for each phantoms organ dose as it related to the phantoms calculated SSDE (both thoracic and abdominal-pelvic). The SSDE-to-Absolute dose correction factors were then applied to an IRB approved patient cohort of 492 patients (7.6 ± 5.4 yrs; range 2 mo to 28 yrs and mean weight was 35 ± 33 kg; range 4–147 kg) to convert patient specific SSDE to organ dose. Results: Organ dose linearly correlated with patient effective diameter with an average R2 of 0.96. In general, chest organ doses were greater than the chest SSDE by 10–40%, the abdomen organ doses were greater than the abdomen SSDE by 10–20%, but organ doses in the pelvis were lower by 0–20%. Conclusion: Correction factors were established to convert SSDE to absolute organ dose. Organ dose values linearly correlated with patient size. SSDE, when calculated based on Report 204, generally underestimates actual patient chest and abdomen organ dosimetry from 10–40%, but overestimates pelvic organ dose by 0–20%.

WE‐A‐218‐05: Do Weight‐Based Pediatric CT Abdomen Protocols Provide Similar Size‐Specific Dose Estimates for Similar Patient Effective Diameters?

Purpose: The use of weight‐based acquisition techniques for CT examinations of pediatric patients is a common practice in the imaging community. AAPM Report 204 reported on conversion factors for Size Specific Dose Estimates (SSDE) based on patient effective diameter. This study examines the relationship between the use of weight‐based Pediatric CT abdominal acquisitions at one institution and the resultant SSDE. Methods: A total of 36 Pediatric Abdomen and Pelvis CTs acquired on scanners from 2 different manufacturers at 120 kVp and using fixed tube current based on reported patient weight were analyzed. The fixed tube currents at each weight range were chosen to match CTDIvol (32 cm phantom) across scanners. Effective diameter was established by thresholding the mid‐scan range image to determine patient area and was calculated using eXposureTM from Radimetrics. The area is then converted to a circle of equivalent diameter. SSDE was determined using the effective diameter for each study and the recorded CTDIvol. The eXposureTM software utilized AAPM Report 204 look‐up‐tables (LUTs) of conversion factors and interpolation to determine the correct normalization factor for each study which is then used to scale the CTDIvol to the final SSDE value. Results: Weak correlation was observed between effective diameter and SSDE, with SSDE values varying by as much as a factor of 2 for effective diameters within 0.5 cm. A slight decrease in average SSDE was observed at larger effective diameters. Conclusion:The weight‐based acquisition protocols analyzed in this study do not effectively match patient effective diameter and radiation dose. Technique parameters based on patient effective diameter should provide better dose equivalence for patients of equal cross‐sectional area. Assessment of image quality and the evaluation of acquisition protocols based on diameter will be pursued in the future. The Presenting Author is the PI on a Research Grant funded by Siemens Medical Solutions.