Richard D. Nawfel

Recurrent CT, Cumulative Radiation Exposure, and Associated Radiation-induced Cancer Risks from CT of Adults

PURPOSE To estimate cumulative radiation exposure and lifetime attributable risk (LAR) of radiation-induced cancer from computed tomographic (CT) scanning of adult patients at a tertiary care academic medical center. MATERIALS AND METHODS This HIPAA-compliant study was approved by the institutional review board with waiver of informed consent. The cohort comprised 31,462 patients who underwent diagnostic CT in 2007 and had undergone 190,712 CT examinations over the prior 22 years. Each patients cumulative CT radiation exposure was estimated by summing typical CT effective doses, and the Biological Effects of Ionizing Radiation (BEIR) VII methodology was used to estimate LAR on the basis of sex and age at each exposure. Billing ICD9 codes and electronic order entry information were used to stratify patients with LAR greater than 1%. RESULTS Thirty-three percent of patients underwent five or more lifetime CT examinations, and 5% underwent between 22 and 132 examinations. Fifteen percent received estimated cumulative effective doses of more than 100 mSv, and 4% received between 250 and 1375 mSv. Associated LAR had mean and maximum values of 0.3% and 12% for cancer incidence and 0.2% and 6.8% for cancer mortality, respectively. CT exposures were estimated to produce 0.7% of total expected baseline cancer incidence and 1% of total cancer mortality. Seven percent of the cohort had estimated LAR greater than 1%, of which 40% had either no malignancy history or a cancer history without evidence of residual disease. CONCLUSION Cumulative CT radiation exposure added incrementally to baseline cancer risk in the cohort. While most patients accrue low radiation-induced cancer risks, a subgroup is potentially at higher risk due to recurrent CT imaging.

Evaluation of video gray‐scale display

Setting up and maintaining video display monitors properly will help to reduce display variation and improve overall presentation of the radiological image. Display monitor gray-scale characteristics were examined using the SMPTE test pattern. This test pattern may be used as a standard for adjusting brightness and contrast. The controls should be adjusted to display the full dynamic range so that the 5% and 95% signal levels in the pattern are visible. Measured luminance on a laboratory workstation used for radiological perceptual experiments, and on the Siemens CT gray-scale monitor was determined to range from 0.17 to 76.0 nit, and 0.17 to 24.66 nit, respectively. These were compared with the range of approximately 17 to 514 nit for a typical film-viewbox combination. Characteristic curves were determined for both monitors, and CRT gammas were 3.34 and 2.48 for the perceptual workstation and CT console, respectively. The display gamma was determined from fitting luminance data to a log-log plot of luminance versus input gray level. The usefulness of the SMPTE test pattern for visual presentation as well as photometric measurement is demonstrated.

Radiation dose during CT-guided percutaneous cryoablation of renal tumors: Effect of a dose reduction protocol

PURPOSE To estimate and compare the radiation dose using a standard protocol and that of a dose reduction protocol in patients undergoing CT-guided percutaneous cryoablation of renal tumors. MATERIALS AND METHODS An IRB-approved, HIPAA-compliant retrospective study of 97 CT-guided cryoablation procedures to treat a solitary renal tumor in each of 97 patients (64 M, 33 F; range 31-84 yrs) was performed. Fifty patients were treated using a standard dose protocol (kVp=120, mean mAs=180, monitoring scans every 3 min during freezes), and an additional 47 patients were treated using a dose reduction protocol (kVp=100, mean mAs=100, monitoring scans less frequently than every 3 min during freezes). Multiple Wilcoxon Mann-Whitney (rank-sum) tests were used to compare dose-length product (DLP) between the two groups. Fishers exact test was used to compare technique effectiveness at 12 months post ablation between the two groups. RESULTS Median DLP for the standard protocol group was 4833.5 mGy*cm (range, 1667-8267 mGy*cm); median DLP for the dose reduction group was 2648 mGy*cm (range, 850-7169 mGy*cm), significantly less than that of the standard protocol group (p<0.01). The technique effectiveness for the dose reduction group was not significantly different from that of the standard protocol group at 12 month follow up (p=0.434). CONCLUSION The radiation dose during percutaneous CT-guided cryoablation of renal tumors was substantial in both the standard and the dose reduction groups; however, it was significantly lower with the protocol change that reduced dose parameters and decreased the number of CT scans.

Systematic scanner variability of patient CT attenuation measurements

CT numbers of the spleen, liver, and trachea air were measured from non-contrast images obtained from 4-channel and 64-channel scanners from the same vendor. Image sections of 1 mm and 5 mm were reconstructed using smooth and sharp kernels. For spleen and liver, no significant differences associated with the variations in kernels or slice thickness could be demonstrated. The increase of the number of channels from 4 to 64 lowered the spleen CT numbers from 53 HU to 43 HU (p <0.00001). The 4-channel spleen CT numbers slightly increased as function of patient size, while the 64-channel CT numbers decreased as function of patient size. Linear regressions predicted for 40-cm patients the spleen 64-channel CT values were 23 HU lower than 4-channel CT numbers. The smooth kernel, 4-channel trachea air CT numbers had mean of -1004 +/-4.8 HU and the 64-channel trachea air CT numbers had a mean of -989+/-4.5 HU. The patient-size dependencies suggest that the CT attenuation variation is associated with increased scatter in 64-channel MSCT. Using CT number to distinguish solid lesions from cysts or quantitative evaluation of COPD disease using CT images may be complicated by inconsistencies between CT scanners.

Use of a 3D-Printed Abdominal Compression Device to Facilitate CT Fluoroscopy–Guided Percutaneous Interventions

OBJECTIVE The purpose of this article is to describe a handheld external compression device used to facilitate CT fluoroscopy-guided percutaneous interventions in the abdomen. CONCLUSION The device was designed with computer-aided design software to modify an existing gastrointestinal fluoroscopy compression device and was constructed by 3D printing. This abdominal compression device facilitates access to interventional targets, and its use minimizes radiation exposure of radiologists. Twenty-one procedures, including biopsies, drainage procedures, and an ablation, were performed with the device. Radiation dosimetry data were collected during two procedures.

TH‐AB‐207A‐03: Skin Dose to Patients Receiving Multiple CTA and CT Exams of the Head

PURPOSE To measure patient skin dose from CT angiography (CTA) and CT exams of the head, and determine if patients having multiple exams could receive cumulative doses that approach or exceed deterministic thresholds. METHODS This study was HIPAA compliant and conducted with IRB approval. Patient skin doses were measured over a 4 month period using nanoDot OSL dosimeters placed on the head of 52 patients for two CT scanners. On each scanner, 26 patients received CT exams (scanner 1: 10 females, 16 males, mean age 64.2 years; scanner 2: 18 females, 8 males, mean age 61.2 years). CT exam dose metrics, CTDIvol and dose-length product (DLP) were recorded for each exam. Additionally, skin dose was measured on an acrylic skull phantom in each scanner and on a neuro-interventional imaging system using clinical protocols. Measured dose data was used to estimate peak skin dose (PSD) for 4 patients receiving multiple exams including CTA, head CT, and cerebral angiography. RESULTS For scanner 1, the mean PSD for CTA exams (98.9 ± 5.3 mGy) and for routine head CT exams (39.2 ± 3.7 mGy) agreed reasonably well with the PSD measured on the phantom, 105.4 mGy and 40.0 mGy, respectively. Similarly for scanner 2, the mean PSD for CTA exams (98.8 ± 7.4 mGy) and for routine head CT exams (42.9 ± 9.4 mGy) compared well with phantom measurements, 95.2 mGy and 37.6 mGy, respectively. In addition, the mean PSD was comparable between scanners for corresponding patient exams, CTA and routine head CT respectively. PSD estimates ranged from 1.9 - 4.5 Gy among 4 patients receiving multiple exams. CONCLUSION Patients having several exams including both CTA and routine head CT may receive cumulative doses approaching or exceeding the threshold for single dose deterministic effects.

SU‐GG‐I‐81: Surface Dose of Angular Current‐Modulated CT Exams

Purpose: An analytic procedure was developed and validated to determine why the TLDmeasured lateral skin dose of angular tube‐current‐modulated CT‐urography exams was 7% less than the anterior skin dose even though the tube current in the lateral projection was greater by about a factor of 2 than anterior tube current and the lateral skin was 6 cm closer to the x‐ray focal spot (the closest distance to tube focal spot path). Method and Materials: Exponential attenuation, exponential absorption, and inverse square law were used to estimate the anterior and lateral dose to a miscentered cylindrical test object. The source filter was described by the diameter of a cylindrical object, i.e., the filter would attenuate such that detected intensity is constant when such an object of that size is centered in the data collection field of view. Surface exposure measurements used 16‐cm, 20‐cm, and 32‐cm acyclic test objects. Results: For constant tube current the surface exposure was a decreasing function distance between the center of tube rotation and object surface. Surface doses had a weak dependence on phantom size when the skin surface was greater than 5 cm from center of tube rotation. A 100 cm filter fit surface phantom surface exposures. The analysis predicted that the lateral skin dose would be a factor of 2 lower than the anterior dose. Conclusion: The patient skin dose can be determined by the product CTDImeasured in air at CT scanner center of tube rotation and a factor that is determined by the distance the skin surface is from the center of tube rotation. The comparisons with direct skin dose measurements were a useful QA procedure. Conflict of Interest: Christianne Leidicker is an employee of Siemens.

SU‐FF‐I‐27: CT Urography Radiation Dose Using Automatic Exposure Control

Purpose: To measure and compare patient radiation doses during CT urography with automatic exposure control (both angular and z‐axis tube current modulation) to patient radiation doses without automatic exposure control (tube current modulation alone), and to correlate these doses with corresponding imagenoise measurements. Method and Materials:Skin doses were measured by exposing thermoluminescent dosimeters placed on the abdomen (AP) and side (lateral position) of 18 patients examined with CT urography consisting of automatic exposure control (CARE Dose 4D group), and 20 different patients examined with angular tube current modulation only (CARE Dose group). Mean and standard deviation of patient skin doses were calculated. The CT urography protocol included three volumetric acquisitions of the abdomen and pelvis. Effective doses were calculated and used to compare radiation risk between the two patient groups. The variation in effective dose with patient size was also evaluated. Imagenoise was evaluated by calculating the standard deviation of pixel values from a region of interest in patient liverimages.Results: The mean skin dose for CARE Dose 4D patients (63.4 ± 16.4 mGy) was 14.2% higher than that of CARE Dose patients (54.4 ± 7.39 mGy). The mean effective dose for CARE Dose 4D patients (10.6 ± 2.3 mSv) was 17.1% higher than that of CARE Dose patients (8.8 ± 1.8 mSv). Imagenoise increased with increasing patient size, however the increase was less for patients exposed with automatic exposure control.Conclusion: Patient effective dose, and thus radiation risk was 17.1% higher for CT urography patients examined with automatic exposure control compared to those examined with tube current modulation alone. Using automatic exposure control techniques in CT may be useful in reducing dose in small patients, however, for large patients the dose may actually increase to compensate for the increase in imagenoise.

Classification of mammographic patterns: beyond fraction of dense tissue

Women with mammograms that radiologists classify as dense have been found to have an increased risk of breast cancer. The purpose to this investigation was to determine whether human readers are willing and able to make reliable comparisons of five attributes of pairs of mammograms matched by a quantitative estimate of the fraction of dense tissue (FDT). Forty pairs of CC projections were digitized and presented using a computer workstation. The 40 pairs of mammograms had the same FDT as measured by a visual threshold procedure. Each breast image was from a different woman. The difference in the following 5 attributes were rated: (1) fraction of dense tissue, (2) fraction of homogeneous of the dense tissue, (3) fraction of ductal dense tissue, (4) prominence of scalloping of dense tissue, and (5) prominence of subareolar structures. The rating were replicated to evaluate their reliability. Spearman rank-order correlations of replicated measurements ranged from 0.89 to 0.65 (p was less than 0.0001). Homogeneous dense tissue ratings were negatively correlated with ductal dense tissue ratings (-0.59, p equals 0.0001). The prominence of scalloping rating was not significantly correlated with other attributes. The ratings of the attributes, except scalloping, were significantly correlated to differences mean gray level of breast parenchyma. Readers can make reliable judgments regarding the differences in attributes of mammograms that are matched by FDT. The negative correlation between the homogeneous dense and the ductal dense tissue ratings suggest that homogeneous dense and ductal dense tissues contend for perceived dense breast area. The absence of correlation between scalloping and other image attributes suggests further investigation of scalloping as an independent, breast-cancer risk factor is warranted.