Targeted exome-based predictors of patterns of progression of colorectal liver metastasis after percutaneous thermal ablation.

BACKGROUND: Percutaneous thermal ablation is a curative-intent locoregional therapy (LRT) for selected patients with unresectable colorectal liver metastasis (CLM). Several factors have been identified that contribute to local tumour control after ablation. However, factors contributing to disease progression outside the ablation zone after ablation are poorly understood. METHODS: In this retrospective study, using next-generation sequencing, we identified genetic biomarkers associated with different patterns of progression following thermal ablation of CLM. RESULTS: A total of 191 ablation naïve patients between January 2011 and March 2020 were included in the analysis, and 101 had genomic profiling available. Alterations in the TGFß pathway were associated with increased risk of development of new intrahepatic tumours (hazard ratio [HR], 2.75, 95% confidence interval [95% CI] 1.39-5.45, P = 0.004); and alterations in the Wnt pathway were associated with increased probability of receiving salvage LRT for any intrahepatic progression (HR, 5.8, 95% CI 1.94-19.5, P = 0.003). CONCLUSIONS: Our findings indicate that genomic alterations in cancer-related signalling pathways can predict different progression patterns and the likelihood of receiving salvage LRT following percutaneous thermal ablation of CLM.

Patient Radiation Doses in IR Procedures: The American College of Radiology Dose Index Registry-Fluoroscopy Pilot.

PURPOSE: To update normative data on fluoroscopy dose indices in the United States for the first time since the Radiation Doses in Interventional Radiology study in the late 1990s. MATERIALS AND METHODS: The Dose Index Registry-Fluoroscopy pilot study collected data from March 2018 through December 2019, with 50 fluoroscopes from 10 sites submitting data. Primary radiation dose indices including fluoroscopy time (FT), cumulative air kerma (Ka,r), and kerma area product (PKA) were collected for interventional radiology fluoroscopically guided interventional (FGI) procedures. Clinical facility procedure names were mapped to the American College of Radiology (ACR) common procedure lexicon. Distribution parameters including the 10th, 25th, 50th, 75th, 95th, and 99th percentiles were computed. RESULTS: Dose indices were collected for 70,377 FGI procedures, with 50,501 ultimately eligible for analysis. Distribution parameters are reported for 100 ACR Common IDs. FT in minutes, Ka,r in mGy, and PKA in Gy-cm2 are reported in this study as (n; median) for select ACR Common IDs: inferior vena cava filter insertion (1,726; FT: 2.9; Ka,r: 55.8; PKA: 14.19); inferior vena cava filter removal (464; FT: 5.7; Ka,r: 178.6; PKA: 34.73); nephrostomy placement (2,037; FT: 4.1; Ka,r: 39.2; PKA: 6.61); percutaneous biliary drainage (952; FT: 12.4; Ka,r: 160.5; PKA: 21.32); gastrostomy placement (1,643; FT: 3.2; Ka,r: 29.1; PKA: 7.29); and transjugular intrahepatic portosystemic shunt placement (327; FT: 34.8; Ka,r: 813.0; PKA: 181.47). CONCLUSIONS: The ACR DIR-Fluoro pilot has provided state-of-the-practice statistics for radiation dose indices from IR FGI procedures. These data can be used to prioritize procedures for radiation optimization, as demonstrated in this work.

Patient Radiation Doses in Interventional Radiology Procedures: Comparison of Fluoroscopy Dose Indices between the American College of Radiology Dose Index Registry-Fluoroscopy Pilot and the Radiation Doses in Interventional Radiology Study.

PURPOSE: To compare radiation dose index distributions for fluoroscopically guided interventions in interventional radiology from the American College of Radiology (ACR) Fluoroscopy Dose Index Registry (DIR-Fluoro) pilot to those from the Radiation Doses in Interventional Radiology (RAD-IR) study. MATERIALS AND METHODS: Individual and grouped ACR Common identification numbers (procedure types) from the DIR-Fluoro pilot were matched to procedure types in the RAD-IR study. Fifteen comparisons were made. Distribution parameters, including the 10th, 25th, 50th, 75th, and 95th percentiles, were compared for fluoroscopy time (FT), cumulative air kerma (Ka,r), and kerma area product (PKA). Two derived indices were computed using median dose indices. The procedure-averaged reference air kerma rate (Ka,r¯) was computed as Ka,r / FT. The procedure-averaged x-ray field size at the reference point (Ar) was computed as PKA / (Ka,r × 1,000). RESULTS: The median FT was equally likely to be higher or lower in the DIR-Fluoro pilot as it was in the RAD-IR study, whereas the maximum FT was almost twice as likely to be higher in the DIR-Fluoro pilot than it was in the RAD-IR study. The median Ka,r was lower in the DIR-Fluoro pilot for all procedures, as was median PKA. The maximum Ka,r and PKA were more often higher in the DIR-Fluoro pilot than in the RAD-IR study. Ka,r¯ followed the same pattern as Ka,r, whereas Ar was often greater in DIR-Fluoro. CONCLUSIONS: The median dose indices have decreased since the RAD-IR study. The typical Ka,r rates are lower, a result of the use of lower default dose rates. However, opportunities for quality improvement exist, including renewed focus on tight collimation of the imaging field of view.

Revisiting the need for radiation output measurements after X-ray tube replacement in computed tomography.

PURPOSE: State regulations require that CT radiation output be measured using a dosimeter after major service. The most common major service is tube replacement. We hypothesized that historical QC data could be used instead to determine if output measurements are necessary, potentially reducing the need for output measurements that require an on-site visit by a qualified medical physicist. METHODS: Records of 65 original equipment manufacturer (OEM) tube replacements were reviewed to determine with what frequency output was outside the manufacturer's specifications. The previous 7 days of historical quality control (QC) data prior to a tube change was used to establish a baseline mean noise level and 95% inferential confidence intervals (ICIs) about the mean. This was compared to an ICI constructed using 7 days of QC data post-tube change and the region of indifference. Different methods for acquiring samples of image noise were compared using a single factor analysis of variance (ANOVA). RESULTS: None of the 65 tube replacements reviewed in this study resulted in an output change that exceeded the manufacturer's specifications. In all but one case, the results of the ICI analysis matched the measured output results. In the single case where results were discordant, the mean image noise was slightly higher after the tube change, which may have indicated the need for a larger sample size or service unrelated to the X-ray tube, for example, system calibration. The method used to sample image noise did not significantly affect the calculated mean noise. CONCLUSIONS: This review of historical OEM tube replacement data indicated the likelihood of output falling outside manufacturer specifications is low. Considering this, it is likely that using QC data from programs required by regulation and the American College of Radiology (ACR), medical physicists can reliably verify radiation output stability remotely instead of making measurements using a dosimeter.

Validation of a method for estimating peak skin dose from CT-guided procedures.

A method for estimating peak skin dose (PSD) from CTDIvol has been published but not validated. The objective of this study was to validate this method during CT-guided ablation procedures. Radiochromic film was calibrated and used to measure PSD. Sixty-eight patients were enrolled in this study, and measured PSD were collected for 46 procedures. CTDIvol stratified by axial and helical scanning was used to calculate an estimate of PSD using the method [1.2 × CTDIvol (helical) + 0.6 × CTDIvol (axial)], and both calculated PSD and total CTDIvol were compared to measured PSD using paired t-tests on the log-transformed data and Bland-Altman analysis. Calculated PSD were significantly different from measured PSD (P < 0.0001, bias, 18.3%, 95% limits of agreement, -63.0% to 26.4%). Measured PSD were not significantly different from total CTDIvol (P = 0.27, bias, 3.97%, 95% limits of agreement, -51.6% to 43.7%). Considering that CTDIvol is reported on the console of all CT scanners, is not stratified by axial and helical scanning modes, and is immediately available to the operator during CT-guided interventional procedures, it may be reasonable to use the scanner-reported CTDIvol as an indicator of PSD during CT-guided procedures. However, further validation is required for other models of CT scanner.

The American College of Radiology Fluoroscopy Dose Index Registry Pilot: Technical Considerations and Dosimetric Performance of the Interventional Fluoroscopes.

PURPOSE: To characterize the accuracy and consistency of fluoroscope dose index reporting and report rates of occupational radiation safety hardware availability and use, trainee participation in procedures, and optional hardware availability at pilot sites for the American College of Radiology (ACR) Fluoroscopy Dose Index Registry (DIR). MATERIALS AND METHODS: Nine institutions participated in the registry pilot, providing fluoroscopic technical and clinical practice data from 38 angiographic C-arm-type fluoroscopes. These data included measurements of the procedure table and mattress transmission factors and accuracy measurements of the reference-point air kerma (Ka,r) and air kerma-area product (PKA). The accuracy of the radiation dose indices were analyzed for variation over time by 1-way analysis of variance (ANOVA). Sites also self-reported information on availability and use of radiation safety hardware, hardware configuration of fluoroscopes, and trainee participation in procedures. RESULTS: All Ka,r and PKA measurements were within the ±35% regulatory limit on accuracy. The mean absolute difference between correction factors for a given system in fluoroscopic and acquisition mode was 0.03 (95% confidence interval, 0.03-0.03). For the 28 fluoroscopic imaging planes that provided data for 3 time points, ANOVA yielded an F value of 0.134 with an F-critical value of 3.109 (P = .875). CONCLUSIONS: This publication provides the technical and clinical framework pertaining to the ACR Fluoroscopy DIR pilot and offers necessary context for future analysis of the clinical procedure radiation-dose data collected.

Potential Radiation-Related Effects on Radiologists.

OBJECTIVE: The risk of injury associated with long-term occupational exposure to ionizing radiation is low for radiologists. The purpose of this article is to systematically review and inform radiologists about radiation-related effects to which they are potentially susceptible. CONCLUSION: Formal education and training on radiation safety and management, careful attention to good radiation protection habits, and continued emphasis on radiation management and the as low as reasonably achievable principle are recommended for all radiologists.

JOURNAL CLUB: Standardizing CT-Guided Biopsy Procedures: Patient Dose and Image Noise.

OBJECTIVE: The objective of this study was to standardize our image acquisition protocol for CT-guided biopsy procedures. MATERIALS AND METHODS: The records of consecutive patients who underwent CT-guided biopsy 3 months before (n = 598 biopsies) and 3 months after (n = 540 biopsies) standardization of our image acquisition protocol were retrospectively reviewed. CT technical parameters were individualized on the basis of the sum of the anteroposterior and transverse dimensions of the patient. Information on patient demographic characteristics, biopsy site, complications associated with the procedure, and diagnostic yield was collected. The radiation dose metrics that were evaluated included the volume CT dose index, dose-length product, and size-specific dose estimate. Image noise was quantified using the SD of the CT number measured in subcutaneous fat. Fisher exact test and one-way ANOVA were used to evaluate statistical significance. RESULTS: The mean dose-length product decreased by 72.3% (from 699.7 to 193.9 mGy × cm; p < 0.0001), and statistically significant decreases in dose-length product were observed when data were stratified according to biopsy site (i.e., lung, solid organ, lymph node, or bone; for all sites, p < 0.0001). The mean size-specific dose estimate decreased by 58.9% (from 125 to 51.4 mGy), which was statistically significant (p < 0.001). Image noise increased during the study period, but this increase was not statistically significantly different among the four biopsy sites (p = 0.46). CONCLUSION: Standardization of the image acquisition protocol used in CT-guided biopsy procedures significantly reduced patient radiation dose and decreased variability in image noise.

In vivo CT dosimetry during CT colonography.

OBJECTIVE: The purpose of this study was to develop a method of measuring rectal radiation dose in vivo during CT colonography (CTC) and assess the accuracy of size-specific dose estimates (SSDEs) relative to that of in vivo dose measurements. MATERIALS AND METHODS: Thermoluminescent dosimeter capsules were attached to a CTC rectal catheter to obtain four measurements of the CT radiation dose in 10 volunteers (five men and five women; age range, 23-87 years; mean age, 70.4 years). A fixed CT technique (supine and prone, 50 mAs and 120 kVp each) was used for CTC. SSDEs and percentile body habitus measurements were based on CT images and directly compared with in vivo dose measurements. RESULTS: The mean absorbed doses delivered to the rectum ranged from 8.8 to 23.6 mGy in the 10 patients, whose mean body habitus was in the 27th percentile among American adults 18-64 years old (range, 0.5-67th percentile). The mean SSDE error was 7.2% (range, 0.6-31.4%). CONCLUSION: This in vivo radiation dose measurement technique can be applied to patients undergoing CTC. Our measurements indicate that SSDEs are reasonable estimates of the rectal absorbed dose. The data obtained in this pilot study can be used as benchmarks for assessing dose estimates using other indirect methods (e.g., Monte Carlo simulations).

Guidelines for anti-scatter grid use in pediatric digital radiography.

BACKGROUND: Pediatric radiography presents unique challenges in balancing image quality and patient dose. Removing the anti-scatter grid reduces patient dose but also reduces image contrast. The benefit of using an anti-scatter grid decreases with decreasing patient size. OBJECTIVE: To determine patient thickness thresholds for anti-scatter grid use by comparing scatter-to-primary ratio for progressively thinner patients without a grid to the scatter-to-primary ratio for a standard adult patient with a grid. MATERIALS AND METHODS: We used Solid Water™ phantoms ranging in thickness from 7 cm to 16 cm to simulate pediatric abdomens. The scatter-to-primary ratio without a grid was measured for each thickness at 60 kVp, 70 kVp and 80 kVp for X-ray fields of view (FOV) of 378 cm(2), 690 cm(2) and 1,175 cm(2) using indirect digital radiography (iDR) and computed radiography (CR). We determined thresholds for anti-scatter grid use by comparing the intersection of a fit of scatter-to-primary ratio versus patient thickness with a standard adult scatter-to-primary ratio measured for a 23-cm phantom thickness at 80 kVp with an anti-scatter grid. Dose area product (DAP) was also calculated. RESULTS: The scatter-to-primary ratio depended strongly on FOV and weakly on kVp; however DAP increased with decreasing kVp. Threshold thicknesses for grid use varied from 5 cm for a 14 × 17-cm FOV using iDR to 12 cm for an 8 × 10-cm FOV using computed radiography. CONCLUSIONS: Removing the anti-scatter grid for small patients reduces patient dose without a substantial increase in scatter-to-primary ratio when the FOV is restricted appropriately. Radiologic technologists should base anti-scatter grid use on patient thickness and FOV rather than age.

Time to take the gloves off: the use of radiation reduction gloves can greatly increase patient dose.

Sterile radiation reduction gloves have been widely used over the past several decades in an effort to reduce hand doses during fluoroscopically guided proce- dures. While multiple studies have quantified the potential dose reduction to the fluoroscope operator from the use of such gloves, possible effects on the patient have not yet been quantified. The aim of this study was to examine the impact on patient dose when radiation reduction gloves are used. The impact on patient dose when using radiation reduction gloves in the field of view (FOV) was evalu- ated by measuring patient entrance surface dose rates (ESDR) using three C-arm fluoroscopes for a range of patient sizes and different operating and magnification modes. Multiple measuring fields were used in combination with both peripheral and central glove placement. ESDR were measured with no glove in the FOV, with one radiation reduction glove, and with double gloves in the FOV, to replicate the actions of some fluoroscope operators. Compared to an ungloved hand, the use of a single radiation reduction glove in the measuring field resulted in up to a 2.8-fold increase in ESDR. The use of double radiation reduction gloves resulted in up to a 4.9-fold increase in ESDR. In both cases, the increase in ESDR was dependent on the size of the patient and on the operating and magnification modes used, and ranged from no increase up to the aforementioned maximum. When used in the FOV, and particularly within the measuring field, radiation reduction gloves can substantially increase ESDR. This increase in dose, when considered against the relatively small published reduction in dose to the operator's hands, may mean that the increased risks from the use of radiation reduction gloves outweigh the benefits. In any case, hands should not be placed in the FOV if not required by the goals of the procedure. 

Use of Contrast Media During CT-guided Thermal Ablation of Colorectal Liver Metastasis for Procedure Planning is Associated with Improved Immediate Outcomes.

PURPOSE: The aim of this study was to analyze the impact of using intra-procedural pre-ablation contrast-enhanced CT prior to percutaneous thermal ablation (pre-ablation CECT) of colorectal liver metastases (CLM) on local outcomes. MATERIALS AND METHODS: This retrospective analysis of a prospectively collected liver ablation registry included 144 consecutive patients (median age 57 years IQR [49, 65], 60% men) who underwent 173 CT-guided ablation sessions for 250 CLM between October 2015 and March 2020. In addition to oncologic outcomes, technical success was retrospectively evaluated using a biomechanical deformable image registration software for 3D-minimal ablative margin (3D-MAM) quantification. Bayesian regression was used to estimate effects of pre-ablation CECT on residual unablated tumor, 3D-MAM, and local tumor progression-free survival (LTPFS). RESULTS: Pre-ablation CECT was acquired in 71/173 (41%) sessions. Residual unablated tumor was present in one (0.9%) versus nine tumors (6.6%) ablated with versus without using pre-ablation CECT, respectively (p = 0.024). Pre-ablation CECT use decreased the odds of residual disease on first follow-up by 78% (CI95% [5, 86]) and incomplete ablation (3D-MAM ≤ 0 mm) by 58% (CI95% [13, 122]). The odds ratio for residual unablated tumor for larger CLM was lower when pre-ablation CECT was used (odds ratio 1.0 with pre-ablation CECT vs. 2.52 without). Pre-ablation CECT use was not associated with improvements on LTPFS. CONCLUSIONS: Pre-ablation CECT is associated with improved immediate outcomes by significantly reducing the incidence of residual unablated tumor and by mitigating the risk of incomplete ablation for larger CLM. We recommend performing baseline intra-procedural pre-ablation CECT as a standard imaging protocol. LEVEL OF EVIDENCE: Level 3 (retrospective cohort study).