Radiation dose in CT colonography--trends in time and differences between daily practice and screening protocols

Diagnostic accuracy of ultra-low-dose CT colonography for the detection of colorectal polyps: a feasibility study

PURPOSE

The aim of this feasibility study was to evaluate the diagnostic accuracy of ultra-low-dose CT colonography using iterative reconstruction algorithms with reference to standard colonoscopy.

MATERIALS AND METHODS

Prior to this study, a phantom study was performed to investigate the optimal protocol for ultra-low-dose CT colonography. A total of 206 patients with average/high risk of colorectal cancer were recruited. After undergoing full bowel preparation, the patients were scanned in the prone and supine positions with the CT conditions set to 120 kV, standard deviation 45 to 50, and an adaptive iterative reconstruction algorithm applied. Two expert readers read the images independently. The main outcome measures were the per-patient and per-polyp accuracies for the detection of polyps ≥ 10 mm, with colonoscopy results as the reference standard.

RESULTS

Two hundred patients (102 females, mean age 67.5 years) underwent both ultra-low-dose CT colonography and colonoscopy on the same day. The mean radiation exposure dose was 0.64 ± 0.34 mSv. On colonoscopy, 39 patients had 45 polyps ≥ 10 mm (non-polypoid morphology 7), including 4 cancers. Per-patient sensitivity, specificity, and accuracy of CT colonography for polyps ≥ 10 mm were 0.74, 0.96, and 0.92 for reader one, and 0.74, 0.99, and 0.94 for reader two, respectively. Per-polyp sensitivities for polyps ≥ 10 mm were 0.73 for reader one and 0.71 for reader two. On subgroup analysis by morphology, non-polypoid polyps ≥ 10 mm were not detected by both readers.

CONCLUSION

Extreme ultra-low-dose CT colonography had an insufficient diagnostic performance for the detection of polyps ≥ 10 mm, because it was unable to detect non-polypoid polyps. This study showed that the problem with ultra-low-dose CT colonography was the lack of detectability of small-size polyps, especially non-polypoid polyps. To use ultra-low-dose CT colonography clinically, it is necessary to resolve the problems identified by this study.

Assessment of Imaging Protocol and Patients Radiation Exposure in Computed Tomography Colonography

In the screening and identifying of colon and rectum malignancy, computed tomography colonography (CTC) is a highly effective imaging technique, albeit patients receiving a significant effective dose. Accordingly, patient dose evaluation is an important need, seeking to ensure benefits outweigh the projected cancer risk. Objective: For CTC procedures carried out in the Radiology Department, Medical Imaging Operation Services, King Fahad Medical City (KFMC), evaluation is done using the current American College of Radiology (ACR) imaging protocol and concomitant patient-effective doses. Study is carried out on a sample size of 55 CTC procedures, involving 25 males (45%) and 30 females (55%). The patients were classified as follows: two groups based on CT machine; four groups based on the applied protocol; and three groups based on the procedure results. All procedures were carried out using two machines, the products of two different vendors (a GE Healthcare DISCOVERY CT 750 HD 64 slices dual-energy scanner and a Philips Brilliance CT 64 slices scanner). The overall mean, standard deviation (SD), median, and range of the effective dose (in mSv) were 11.57 ± 7.75, 9.25 (2.17–31.93). Automatic tube current modulation (ATCM) shows a significant increase in CTDIvol up to 69% and effective dose (mSv) up to 95% than the manual tube current (mA) compared to the standard protocol. The CT protocol variation results in a three-fold variation in patient-effective dose. The technologist role is crucial in selecting a noise reference based on patient weight and adjusting tube current per slice to avoid overexposure during ATCM protocol.

Improving practice in radiology: a quality-improvement project examining CT colonography patient dose and scanning technique

AIM

To audit scanning technique and patient doses for computed tomography (CT) colonography (CTC) examinations in a large UK region and to identify opportunities for quality improvement.

MATERIALS AND METHODS

Scanning technique and patient dose data were gathered for both contrast-enhanced and unenhanced CTC examinations from 33 imaging protocols across 27 scanners. Measurements of patient weight and effective diameter were also obtained. Imaging protocols were compared to identify technique differences between similar scanners. Scanner average doses were calculated and combined to generate regional diagnostic reference limits (DRLs) for both examinations.

RESULTS

The regional DRLs for contrast-enhanced examinations were volume CT dose index (CTDIvol) of 11 and 5 mGy for the two scan phases (contrast-enhanced and either delayed phase or non-contrast enhanced respectively), and dose-length product (DLP) of 740 mGy·cm. For unenhanced examinations, these were 5 mGy and 450 mGy·cm. These are notably lower than the national DRLs of 11 mGy and 950 mGy·cm. Substantial differences in scan technique and doses on similar scanners were identified as areas for quality-improvement action.

CONCLUSION

A regional CTC dose audit has demonstrated compliance with national DRLs but marked variation in practice between sites for the dose delivered to patients, notably when scanners of the same type were compared for the same indication. This study demonstrates that the national DRL is too high for current scanner technology and should be revised.

British Society of Gastroenterology/Association of Coloproctology of Great Britain and Ireland/Public Health England post-polypectomy and post-colorectal cancer resection surveillance guidelines

These consensus guidelines were jointly commissioned by the British Society of Gastroenterology (BSG), the Association of Coloproctology of Great Britain and Ireland (ACPGBI) and Public Health England (PHE). They provide an evidence-based framework for the use of surveillance colonoscopy and non-colonoscopic colorectal imaging in people aged 18 years and over. They are the first guidelines that take into account the introduction of national bowel cancer screening. For the first time, they also incorporate surveillance of patients following resection of either adenomatous or serrated polyps and also post-colorectal cancer resection. They are primarily aimed at healthcare professionals, and aim to address:Which patients should commence surveillance post-polypectomy and post-cancer resection?What is the appropriate surveillance interval?When can surveillance be stopped? two or more premalignant polyps including at least one advanced colorectal polyp (defined as a serrated polyp of at least 10 mm in size or containing any grade of dysplasia, or an adenoma of at least 10 mm in size or containing high-grade dysplasia); or five or more premalignant polyps The Appraisal of Guidelines for Research and Evaluation (AGREE II) instrument provided a methodological framework for the guidelines. The BSG's guideline development process was used, which is National Institute for Health and Care Excellence (NICE) compliant.two or more premalignant polyps including at least one advanced colorectal polyp (defined as a serrated polyp of at least 10 mm in size or containing any grade of dysplasia, or an adenoma of at least 10 mm in size or containing high-grade dysplasia); or five or more premalignant polyps The key recommendations are that the high-risk criteria for future colorectal cancer (CRC) following polypectomy comprise either:two or more premalignant polyps including at least one advanced colorectal polyp (defined as a serrated polyp of at least 10 mm in size or containing any grade of dysplasia, or an adenoma of at least 10 mm in size or containing high-grade dysplasia); or five or more premalignant polyps This cohort should undergo a one-off surveillance colonoscopy at 3 years. Post-CRC resection patients should undergo a 1 year clearance colonoscopy, then a surveillance colonoscopy after 3 more years.

Accuracy of Combined Computed Tomography Colonography and Dual Energy Iiodine Map Imaging for Detecting Colorectal masses using High-pitch Dual-source CT

To evaluate the diagnostic accuracy of combined computed tomography colonography (CTC) and dual-energy iodine map imaging for detecting colorectal masses using high-pitch dual-source CT, compared with optical colonography (OC) and histopathologic findings. Twenty-eight consecutive patients were prospectively enrolled in this study. All patients were underwent contrast-enhanced CTC acquisition using dual-energy mode and OC and pathologic examination. The size of the space-occupied mass, the CT value after contrast enhancement, and the iodine value were measured and statistically compared. The sensitivity, specificity, accuracy rate, and positive predictive and negative predictive values of dual-energy contrast-enhanced CTC were calculated and compared between conventional CTC and dual-energy iodine images. The iodine value of stool was significantly lower than the colonic neoplasia (P < 0.01). The sensitivity of conventional CTC was 95.6% (95% CI = 77.9%–99.2%), combined CTC and dual-energy iodine maps imaging was 95.6% (95% CI = 77.9%–99.2%). The specificity of the two methods was 42.8% (95% CI = 15.4%–93.5%) and 100% (95% CI = 47.9%–100%; P = 0.02), respectively. Compared with optical colonography and histopathology, combined CTC and dual-energy iodine maps imaging can distinguish stool and colonic neoplasia, distinguish between benign and malignant tumors initially and improve the diagnostic accuracy of CTC for colorectal cancer screening.

Effect of Reduced Tube Voltage on Diagnostic Accuracy of CT Colonography

The normal tube voltage in computed tomography colonography (CTC) is 120 kV. Some reports indicate that the use of a low tube voltage (lower than 120 kV) technique plays a significant role in reduction of radiation dose. However, to determine whether a lower tube voltage can reduce radiation dose without compromising diagnostic accuracy, an evaluation of images that are obtained while maintaining the volume CT dose index (CTDI_vol) is required. This study investigated the effect of reduced tube voltage in CTC, without modifying radiation dose (i.e. constant CTDI_vol), on image quality. Evaluation of image quality involved the shape of the noise power spectrum, surface profiling with volume rendering (VR), and receiver operating characteristic (ROC) analysis. The shape of the noise power spectrum obtained with a tube voltage of 80 kV and 100 kV was not similar to the one produced with a tube voltage of 120 kV. Moreover, a higher standard deviation was observed on volume-rendered images that were generated using the reduced tube voltages. In addition, ROC analysis revealed a statistically significant drop in diagnostic accuracy with reduced tube voltage, revealing that the modification of tube voltage affects volume-rendered images. The results of this study suggest that reduction of tube voltage in CTC, so as to reduce radiation dose, affects image quality and diagnostic accuracy.

Computed tomographic colonography compared with colonoscopy or barium enema for diagnosis of colorectal cancer in older symptomatic patients: two multicentre randomised trials with economic evaluation (the SIGGAR trials)

BACKGROUND

Computed tomographic colonography (CTC) is a relatively new diagnostic test that may be superior to existing alternatives to investigate the large bowel.

OBJECTIVES

To compare the diagnostic efficacy, acceptability, safety and cost-effectiveness of CTC with barium enema (BE) or colonoscopy.

DESIGN

Parallel randomised trials: BE compared with CTC and colonoscopy compared with CTC (randomisation 2 : 1, respectively).

SETTING

A total of 21 NHS hospitals.

PARTICIPANTS

Patients aged ≥ 55 years with symptoms suggestive of colorectal cancer (CRC).

INTERVENTIONS

CTC, BE and colonoscopy.

MAIN OUTCOME MEASURES

For the trial of CTC compared with BE, the primary outcome was the detection rate of CRC and large polyps (≥ 10 mm), with the proportion of patients referred for additional colonic investigation as a secondary outcome. For the trial of CTC compared with colonoscopy, the primary outcome was the proportion of patients referred for additional colonic investigation, with the detection rate of CRC and large polyps as a secondary outcome. Secondary outcomes for both trials were miss rates for cancer (via registry data), all-cause mortality, serious adverse events, patient acceptability, extracolonic pathology and cost-effectiveness.

RESULTS

A total of 8484 patients were registered and 5384 were randomised and analysed (BE trial: 2527 BE, 1277 CTC; colonoscopy trial: 1047 colonoscopy, 533 CTC). Detection rates in the BE trial were 7.3% (93/1277) for CTC, compared with 5.6% (141/2527) for BE (p = 0.0390). The difference was due to better detection of large polyps by CTC (3.6% vs. 2.2%; p = 0.0098), with no significant difference for cancer (3.7% vs. 3.4%; p = 0.66). Significantly more patients having CTC underwent additional investigation (23.5% vs. 18.3%; p = 0.0003). At the 3-year follow-up, the miss rate for CRC was 6.7% for CTC (three missed cancers) and 14.1% for BE (12 missed cancers). Significantly more patients randomised to CTC than to colonoscopy underwent additional investigation (30% vs. 8.2%; p < 0.0001). There was no significant difference in detection rates for cancer or large polyps (10.7% for CTC vs. 11.4% for colonoscopy; p = 0.69), with no difference when cancers (p = 0.94) and large polyps (p = 0.53) were analysed separately. At the 3-year follow-up, the miss rate for cancer was nil for colonoscopy and 3.4% for CTC (one missed cancer). Adverse events were uncommon for all procedures. In 1042 of 1748 (59.6%) CTC examinations, at least one extracolonic finding was reported, and this proportion increased with age (p < 0.0001). A total of 149 patients (8.5%) were subsequently investigated, and extracolonic neoplasia was diagnosed in 79 patients (4.5%) and malignancy in 29 (1.7%). In the short term, CTC was significantly more acceptable to patients than BE or colonoscopy. Total costs for CTC and colonoscopy were finely balanced, but CTC was associated with higher health-care costs than BE. The cost per large polyp or cancer detected was £4235 (95% confidence interval £395 to £9656).

CONCLUSIONS

CTC is superior to BE for detection of cancers and large polyps in symptomatic patients. CTC and colonoscopy detect a similar proportion of large polyps and cancers and their costs are also similar. CTC precipitates significantly more additional investigations than either BE or colonoscopy, and evidence-based referral criteria are needed. Further work is recommended to clarify the extent to which patients initially referred for colonoscopy or BE undergo subsequent abdominopelvic imaging, for example by computed tomography, which will have a significant impact on health economic estimates.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN95152621.

Model-based iterative reconstruction in low-dose CT colonography-feasibility study in 65 patients for symptomatic investigation

RATIONALE AND OBJECTIVES

To compare image quality on computed tomographic colonography (CTC) acquired at standard dose (STD) and low dose (LD) using filtered-back projection, adaptive statistical iterative reconstruction, and model-based iterative reconstruction (MBIR) techniques.

MATERIALS AND METHODS

A total of 65 symptomatic patients were prospectively enrolled for the study and underwent STD and LD CTC with filtered-back projection, adaptive statistical iterative reconstruction, and MBIR to allow direct per-patient comparison. Objective image noise, subjective image analyses, and polyp detection were assessed.

RESULTS

Objective image noise analysis demonstrates significant noise reduction using MBIR technique (P < .05) despite being acquired at lower doses. Subjective image analyses were superior for LD MBIR in all parameters except visibility of extracolonic lesions (two-dimensional) and visibility of colonic wall (three-dimensional) where there were no significant differences. There was no significant difference in polyp detection rates (P > .05). Doses: LD (dose-length product, 257.7), STD (dose-length product, 483.6).

CONCLUSIONS

LD MBIR CTC objectively shows improved image noise using parameters in our study. Subjectively, image quality is maintained. Polyp detection shows no significant difference but because of small numbers needs further validation. Average dose reduction of 47% can be achieved. This study confirms feasibility of using MBIR in this context of CTC in symptomatic population.

Pilot study on image quality and radiation dose of CT colonography with adaptive iterative dose reduction three-dimensional

Objective

To investigate image quality and radiation dose of CT colonography (CTC) with adaptive iterative dose reduction three-dimensional (AIDR3D).

Methods

Ten segments of porcine colon phantom were collected, and 30 pedunculate polyps with diameters ranging from 1 to 15 mm were simulated on each segment. Image data were acquired with tube voltage of 120 kVp, and current doses of 10 mAs, 20 mAs, 30 mAs, 40 mAs, 50 mAs, respectively. CTC images were reconstructed using filtered back projection (FBP) and AIDR3D. Two radiologists blindly evaluated image quality. Quantitative evaluation of image quality included image noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). Qualitative image quality was evaluated with a five-score scale. Radiation dose was calculated based on dose-length product. Ten volunteers were examined supine 50 mAs with FBP and prone 20 mAs with AIDR3D, and image qualities were assessed. Paired t test was performed for statistical analysis.

Results

For 20 mAs with AIDR3D and 50 mAs with FBP, image noise, SNRs and CNRs were (16.4 ± 1.6) HU vs. (16.8 ± 2.6) HU, 1.9 ± 0.2 vs. 1.9 ± 0.4, and 62.3 ± 6.8 vs. 62.0 ± 6.2, respectively; qualitative image quality scores were 4.1 and 4.3, respectively; their differences were all not statistically significant. Compared with 50 mAs with FBP, radiation dose (1.62 mSv) of 20 mAs with AIDR3D was decreased by 60.0%. There was no statistically significant difference in image noise, SNRs, CNRs and qualitative image quality scores between prone 20 mAs with AIDR3D and supine 50 mAs with FBP in 10 volunteers, the former reduced radiation dose by 61.1%.

Conclusion

Image quality of CTC using 20 mAs with AIDR3D could be comparable to standard 50 mAs with FBP, radiation dose of the former reduced by about 60.0% and was only 1.62 mSv.

History, evolution, and current status of radiologic imaging tests for colorectal cancer screening

Colorectal cancer screening is thought to be an effective tool with which to reduce the mortality from colorectal cancer through early detection and removal of colonic adenomas and early colon cancers. In this article, we review the history, evolution, and current status of imaging tests of the colon-including single-contrast barium enema, double-contrast barium enema, computed tomographic (CT) colonography, and magnetic resonance (MR) colonography-for colorectal cancer screening. Despite its documented value in the detection of colonic polyps, the double-contrast barium enema has largely disappeared as a screening test because it is widely perceived as a labor-intensive, time-consuming, and technically demanding procedure. In the past decade, the barium enema has been supplanted by CT colonography as the major imaging test in colorectal cancer screening in the United States, with MR colonography emerging as another viable option in Europe. Although MR colonography does not require ionizing radiation, the radiation dose for CT colonography has decreased substantially, and regular screening with this technique has a high benefit-to-risk ratio. In recent years, CT colonography has been validated as an effective tool for use in colorectal cancer screening that is increasingly being disseminated.

Image quality improvement in submillisievert computed tomographic colonography using a fast 3-dimensional noise reduction method

OBJECTIVE

The objective of this study was to evaluate the image quality in submillisievert computed tomographic colonography (CTC) images using a structure preserving diffusion denoising method.

METHODS

Image quality was compared before and after denoising in 31 patients. One hundred twenty-kilovolt, 30-mAs prone CTC scans were used as reference and compared with submillisievert 140-kV, 10-mAs supine scans. Two readers assessed 2-dimensional and endoluminal image quality. The image noise and the signal-to-noise ratio were measured.

RESULTS

After denoising, image quality scores improved in both supine series and prone series (P < 0.0001), with the submillisievert denoised images being equal to or better than the native prone reference images. In both the supine images and the prone images, the noise was reduced by a factor of 2 and the signal-to-noise ratio was significantly higher (P < 0.001). The signal-to-noise ratio in the denoised submillisievert images was higher than those in the native prone images (P < 0.001).

CONCLUSIONS

The structure preserving diffusion denoising method preserves the image quality in submillisievert CTC images compared with the native 30-mAs reference images.

Abdominal computed tomography, colonography and radiation exposure: what the surgeon needs to know

AIM

Abdominal computed tomography (CT) improves the accuracy of clinical diagnosis and facilitates patient management. Radiation exposure must be considered by requesting clinicians and is especially relevant owing to the increasing use of CT colonography for diagnosis and screening of colorectal disorders. This review describes the radiation dose of abdominopelvic CT and colonography and attempts to quantify the risk for the clinician.

METHOD

Articles were searched in the PubMed and Medline databases using combinations of the MeSH terms 'radiation', 'abdominal computed tomography' and 'colonography'. Electronic English language abstracts were read by two reviewers and the full article was retrieved if relevant to the review.

RESULTS

Abdominopelvic CT and CT colonography convey significant radiation dose to the patient but also have considerable diagnostic potential. In the right clinical context, the radiation risk should not be overestimated. Techniques to reduce the dose should be used. Repeated imaging in certain patients is a concern and should be monitored.

CONCLUSION

Radiation risk can be quantified and presented simply in a manner that both patients and doctors can comprehend and evaluate. This approach will diminish misconceptions and allow a rational choice of diagnostic test.

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).

Dose reduction methods for CT colonography

Patients, referring physicians, the media, and government agencies have all expressed concern over the risks of medical radiation, particularly as it relates to CT. This concern is particularly paramount when associated with a screening examination such as CT colonography. These theoretical risks must be weighed realistically against the substantial benefits of colon cancer screening as well as against the risks inherent in the major alternative screening option, optical colonoscopy. When put into perspective, the risk-benefit ratio is highly in favor of the performance of CT colonography. Nevertheless, in following the ALARA principle, there is an ever increasing armamentarium of options that can be employed in the pursuit of CT radiation dose reduction, all of which can be used in many synergistic combinations allowing for dose reduction while simultaneously preserving image quality and minimizing image noise. After a brief tutorial on estimating radiation dose, various strategies will be discussed including reductions in tube current and tube voltage as well as the use of automatic dose modulation and iterative reconstruction. Other practical considerations will also be reviewed including proper patient isocentering, optimization of colonic insufflation to minimize additional decubitus scans, proper choice of scan volumes to avoid overranging, and variation of slice thickness and window width to minimize perceived image noise. Finally, a strategy for how to incrementally introduce these methods as well as a way to compare dose reduction efforts across institutions throughout the country will be offered.

BMI-based radiation dose reduction in CT colonography

RATIONALE AND OBJECTIVES

There is potential for x-ray dose reduction in computed tomography colonography (CTC) relative to body mass index (BMI). We evaluated the association between BMI and three-dimensional (3D) CTC image quality to assess the potential utility of BMI as the basis for radiation dose reduction in CTC.

MATERIALS AND METHODS

Ninety-six consecutive patients underwent CTC and were randomized for scanning at 15 or 30 mAs. Extremely obese patients (BMI > 50) were excluded. Each patient was scanned supine and prone on a multidetector CT scanner. Postprocessing CTC visualization was performed on a dedicated workstation. Three independent observers assessed 3D image quality using a four-point scale. Image noise was measured in both the abdomen and pelvis. The association between BMI and image noise was examined using random-effects linear regression models. Logistic regression was used to examine the relationship between BMI, mAs, and conspicuity scores.

RESULTS

Statistically significant differences in image noise were observed between 15 and 30 mAs in both the abdomen and pelvis, and the difference was greater with increasing BMI. A positive relationship was detected between BMI and noise in the abdomen (P < .001) and pelvis (P < .001). Inverse correlation was identified between BMI and conspicuity scores in the abdomen (P = .01) and pelvis (P < .001). Overall conspicuity scores were reduced for both 15 and 30 mAs groups as BMI increased.

CONCLUSION

The radiation dose for CTC can be reduced by 40% and 70% below commonly employed doses for overweight and normal BMI patients, respectively, by using a BMI-adjusted dose reduction approach. Conspicuity scores dropped in obese patients with reduced dose suggesting that standard accepted doses should be utilized in that group.

Screening for colorectal cancer with FOBT, virtual colonoscopy and optical colonoscopy: study protocol for a randomized controlled trial in the Florence district (SAVE study)

BACKGROUND

Colorectal cancer (CRC) is the most frequent cancer in Europe. Randomized clinical trials demonstrated that screening with fecal occult blood test (FOBT) reduces mortality from CRC. Accordingly, the European Community currently recommends population-based screening with FOBT. Other screening tests, such as computed tomography colonography (CTC) and optical colonoscopy (OC), are highly accurate for examining the entire colon for adenomas and CRC. Acceptability represents a critical determinant of the impact of a screening program. We designed a randomized controlled trial to compare participation rate and diagnostic yield of FOBT, CTC with computer-aided diagnosis, and OC as primary tests for population-based screening.

METHODS/DESIGN

A total of 14,000 subjects aged 55 to 64 years, living in the Florence district and never screened for CRC, will be randomized in three arms: group 1 (5,000 persons) invited to undergo CTC (divided into: subgroup 1A with reduced cathartic preparation and subgroup 1B with standard bowel preparation); group 2 (8,000 persons) invited to undergo a biannual FOBT for three rounds; and group 3 (1,000 persons) invited to undergo OC. Subjects of each group will be invited by mail to undergo the selected test. All subjects with a positive FOBT or CTC test (that is, mass or at least one polyp ≥ 6 mm) will be invited to undergo a second-level OC. Primary objectives of the study are to compare the participation rate to FOBT, CTC and OC; to compare the detection rate for cancer or advanced adenomas of CTC versus three rounds of biannual FOBT; to evaluate referral rate for OC induced by primary CTC versus three rounds of FOBT; and to estimate costs of the three screening strategies. A secondary objective of the study is to create a biological bank of blood and stool specimens from subjects undergoing CTC and OC.

DISCUSSION

This study will provide information about participation/acceptability, diagnostic yield and costs of screening with CTC in comparison with the recommended test (FOBT) and OC.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT01651624.

Advances in CT Colonography for Colorectal Cancer Screening and Diagnosis

CT colonography (CTC) is a validated colorectal cancer test that provides an additional minimally-invasive screening option which is likely to be preferred by some patients. Important examination prerequisites include adequate colonic cleansing and distention. Tagging of residual material aids in the differentiation of true polyps from stool. Low radiation dose technique should be employed routinely for screening studies. Readers must be skilled in the use of both 2D and 3D interpretation methods.

Screening computed tomography colonography with 256-slice scanning: should patient radiation burden and associated cancer risk constitute a major concern?

OBJECTIVES

The aim of this study was to determine the radiation burden and the lifetime attributable risk (LAR) of radiation-induced cancer in patients undergoing screening 256-slice computed tomography colonography (CTC) and compare CTC-related radiogenic risks to corresponding nominal lifetime intrinsic risk of cancer.

MATERIALS AND METHODS

A Monte Carlo simulation software dedicated for computed tomography (CT) dosimetry was used to determine absorbed doses to primarily exposed radiosensitive organs of 31 women and 29 men subjected to screening CTC on a 256-slice CT scanner. Effective dose was estimated from (a) organ dose data and (b) dose-length product. Organ-specific and total LARs of cancer were estimated using published risk factors. Cumulative LARs from repeated CTC studies on individuals participating in a colorectal cancer screening program were compared with corresponding lifetime intrinsic risks.

RESULTS

The mean organ dose-derived effective dose was estimated to be 2.92 and 2.61 mSv for female and male individuals, respectively. The dose-length product method was found to overestimate effective dose from CTC by 26% and 13% in female and male individuals, respectively. Compared with previously published results for 64-slice CT scanners, 256-slice CTC was found to be associated with up to 45% less radiation burden. The cumulative LAR of radiation-induced cancer from repeated quinquennial screening CTC studies between the ages of 50 and 80 years was estimated to increase the lifetime intrinsic risk of cancer by less than 0.2%.

CONCLUSION

The level of patient radiation burden and theoretical radiogenic cancer risks associated with screening CTC performed using modern low-dose protocols and techniques may not justify disapproval of CTC as a mass screening tool.

Validation of dual-source single-tube reconstruction as a method to obtain half-dose images to evaluate radiation dose and noise reduction: phantom and human assessment using CT colonography and sinogram-affirmed iterative reconstruction (SAFIRE)

OBJECTIVE

To evaluate a method for obtaining half-dose CT images for observer studies evaluating lower-dose CT.

METHODS

Phantoms of varying sizes were scanned at multiple tube potentials using dose-matched dual-source (DS) and single-source (SS) protocols. Images from single-tube reconstruction of DS data were compared with SS images acquired at half-original CTDIvol. Thirty patients underwent supine SS and dose-matched prone DS CT colonography (CTC). Half-dose prone images were reconstructed with sinogram-affirmed iterative reconstruction (SAFIRE). Two radiologists scored image quality on 2-dimensional (2D) and 3D images.

RESULTS

Image noise was similar between half-dose SS images and DS images reconstructed from one tube only with tube potential of 120 kV or more for phantoms 40 cm or smaller (P < 0.05). For both readers, the patients' CTC image quality scores were more than 84% concordant between SS or DS CTC images, and half-dose-prone CTC images with SAFIRE had 84% or more concordance with routine-dose CTC except for 3D image noise.

CONCLUSIONS

In appropriately sized patients, DS acquisition with single-tube reconstruction can create half-dose images, permitting comparison to full-dose images. For CTC, there is comparable image quality for colonic evaluation between full-dose and half-dose images reconstructed with SAFIRE.

The second ESGAR consensus statement on CT colonography

Objective

To update quality standards for CT colonography based on consensus among opinion leaders within the European Society of Gastrointestinal and Abdominal Radiology (ESGAR).

Material and methods

A multinational European panel of nine members of the ESGAR CT colonography Working Group (representing six EU countries) used a modified Delphi process to rate their level of agreement on a variety of statements pertaining to the acquisition, interpretation and implementation of CT colonography. Four Delphi rounds were conducted, each at 2 months interval.

Results

The panel elaborated 86 statements.

In the final round the panelists achieved complete consensus in 71 of 86 statements (82 %). Categories including the highest proportion of statements with excellent Cronbach's internal reliability were colon distension, scan parameters, use of intravenous contrast agents, general guidelines on patient preparation, role of CAD and lesion measurement.

Lower internal reliability was achieved for the use of a rectal tube, spasmolytics, decubitus positioning and number of CT data acquisitions, faecal tagging, 2D vs. 3D reading, and reporting.

Conclusion

The recommendations of the consensus should be useful for both the radiologist who is starting a CTC service and for those who have already implemented the technique but whose practice may need updating.

Key Points

• Computed tomographic colonography is the optimal radiological method of assessing the colon

• This article reviews ESGAR quality standards for CT colonography

• This article is aimed to provide CT-colonography guidelines for practising radiologists

• The recommendations should help radiologists who are starting/updating their CTC services

Effective radiation dose in CT colonography: is there a downward trend?

RATIONALE AND OBJECTIVES

Radiation dose is an important drawback of computed tomography (CT) colonography, especially for its use as a screening tool for colorectal cancer. It is therefore important to know the present radiation dose. Our objective is to assess the effective radiation doses used for CT colonography and its trend over time.

MATERIALS AND METHODS

Institutions performing CT colonography research were asked to provide their CT colonography protocols. Median effective doses were calculated and compared with a 2007 inventory. Separate analyses were performed for protocols using intravenous contrast medium and for academic versus nonacademic institutions. Differences in effective dose were tested for significance, using Wilcoxon rank-sum or Wilcoxon signed-rank test.

RESULTS

Sixty-two of 109 (57%) institutions responded, providing protocols for 58 institutions. Median effective dose for daily practice protocols was 7.6 mSv (4.3 mSv and 2.0 mSv for supine and prone, respectively) and for screening 4.4 mSv (2.6 mSv and 2.0 mSv, respectively; P = .01). For daily practice with and without contrast medium, the median effective doses were 10.5 mSv and 4.0 mSv (P < .001), respectively. Academic and nonacademic institutions used similar doses (all comparisons P > .05). For institutions also participating in the 2007 inventory, effective dose for both daily practice and screening protocols were similar (P > .05).

CONCLUSION

In 2011 the median effective radiation dose for daily practice protocols was 7.6 mSv and for screening 4.4 mSv. Median effective doses have not decreased as compared to 2007. Academic and nonacademic institutions use similar radiation dose.

Complications of CT colonography: a review

Since its inception, one of the main advantages of computed tomography colonography (CTC) over colonoscopy has been its assumed superior safety profile. However CTC is not without complication and adverse events are well described. Although the risks of insufflation, bowel preparation, contrast media and radiation dose are very small, they are not insignificant. This review discusses the potential hazards and complications associated with the technique, and discuss precautions, which may lessen the risk of occurrence.

Does CT colonography have a role for population-based colorectal cancer screening?

Colorectal cancer (CRC) is the second most common cancer and second most common cause of cancer-related deaths in Europe. CRC screening has been proven to reduce disease-specific mortality and several European countries employ national screening programmes. These almost exclusively rely on stool tests, with endoscopy used as an adjunct in some countries. Computed tomographic colonography (CTC) is a potential screening test, with an estimated sensitivity of 88 % for advanced neoplasia ≥10 mm. Recent randomised studies have shown that CTC and colonoscopy have similar yields of advanced neoplasia per screened invitee, indicating that CTC is potentially viable as a primary screening test. However, the evidence is not fully elaborated. It is unclear whether CTC screening is cost-effective and the impact of extracolonic findings, both medical and economic, remains unknown. Furthermore, the effect of CTC screening on CRC-related mortality is unknown, as it is also unknown for colonoscopy. It is plausible that both techniques could lead to decreased mortality, as for sigmoidoscopy and gFOBT. Although radiation exposure is a drawback, this disadvantage may be over-emphasised. In conclusion, the detection characteristics and acceptability of CTC suggest it is a viable screening investigation. Implementation will depend on detection of extracolonic disease and health-economic impact. Key Points • Meta-analysis of CT colonographic screening showed high sensitivity for advanced neoplasia ≥10mm. • CTC, colonoscopy and sigmoidoscopy screening all have similar yields for advanced neoplasia. • Good quality information regarding the cost-effectiveness of CTC screening is lacking. • There is little good quality data regarding the impact of extracolonic findings. • CTC triage is not clinically effective in first round gFOBT/FIT positives.

Colon distension and scan protocol for CT-colonography: an overview

This article reviews two important aspects of CT-colonography, namely colonic distension and scan parameters. Adequate distension should be obtained to visualize the complete colonic lumen and optimal scan parameters should be used to prevent unnecessary radiation burden. For optimal distension, automatic carbon dioxide insufflation should be performed, preferably via a thin, flexible catheter. Hyoscine butylbromide is - when available - the preferred spasmolytic agent because of the positive effect on insufflation and pain/burden and its low costs. Scans in two positions are required for adequate distension and high polyp sensitivity and decubitus position may be used as an alternative for patients unable to lie in prone position. The great intrinsic contrast between air or tagging and polyps allows the use of low radiation dose. Low-dose protocol without intravenous contrast should be used when extracolonic findings are deemed unimportant. In patients suspected for colorectal cancer, normal abdominal CT scan protocols and intravenous contrast should be used in supine position for the evaluation of extracolonic findings. Dose reduction can be obtained by lowering the tube current and/or voltage. Tube current modulation reduces the radiation dose (except in obese patients), and should be used when available. Iterative reconstructions is a promising dose reducing tool and dual-energy CT is currently evaluated for its applications in CT-colonography. This review also provides our institution's insufflation procedure and scan parameters.

Feasibility of simultaneous computed tomographic colonography and fully automated bone mineral densitometry in a single examination

PURPOSE

To show the feasibility of calculating the bone mineral density (BMD) from computed tomographic colonography (CTC) scans using fully automated software.

MATERIALS AND METHODS

Automated BMD measurement software was developed that measures the BMD of the first and second lumbar vertebrae on computed tomography and calculates the mean of the 2 values to provide a per patient BMD estimate. The software was validated in a reference population of 17 consecutive women who underwent quantitative computed tomography and in a population of 475 women from a consecutive series of asymptomatic patients enrolled in a CTC screening trial conducted at 3 medical centers.

RESULTS

The mean (SD) BMD was 133.6 (34.6) mg/mL (95% confidence interval, 130.5-136.7; n = 475). In women aged 42 to 60 years (n = 316) and 61 to 79 years (n = 159), the mean (SD) BMDs were 143.1 (33.5) and 114.7 (28.3) mg/mL, respectively (P < 0.0001). Fully automated BMD measurements were reproducible for a given patient with 95% limits of agreement of -9.79 to 8.46 mg/mL for the mean difference between paired assessments on supine and prone CTC.

CONCLUSIONS

Osteoporosis screening can be performed simultaneously with screening for colorectal polyps.

Radiation-related cancer risks from CT colonography screening: a risk-benefit analysis

OBJECTIVE

The purpose of this study was to estimate the ratio of cancers prevented to induced (benefit-risk ratio) for CT colonography (CTC) screening every 5 years from the age of 50 to 80 years.

MATERIALS AND METHODS

Radiation-related cancer risk was estimated using risk projection models based on the National Research Council's Biological Effects of Ionizing Radiation (BEIR) VII Committee's report and screening protocols from the American College of Radiology Imaging Network's National CT Colonography Trial. Uncertainty intervals were estimated using Monte Carlo simulation methods. Comparative modeling with three colorectal cancer microsimulation models was used to estimate the potential reduction in colorectal cancer cases and deaths.

RESULTS

The estimated mean effective dose per CTC screening study was 8 mSv for women and 7 mSv for men. The estimated number of radiation-related cancers resulting from CTC screening every 5 years from the age of 50 to 80 years was 150 cases/100,000 individuals screened (95% uncertainty interval, 80-280) for men and women. The estimated number of colorectal cancers prevented by CTC every 5 years from age 50 to 80 ranged across the three microsimulation models from 3580 to 5190 cases/100,000 individuals screened, yielding a benefit-risk ratio that varied from 24:1 (95% uncertainty interval, 13:1-45:1) to 35:1 (19:1-65:1). The benefit-risk ratio for cancer deaths was even higher than the ratio for cancer cases. Inclusion of radiation-related cancer risks from CT examinations performed to follow up extracolonic findings did not materially alter the results.

CONCLUSION

Concerns have been raised about recommending CTC as a routine screening tool because of potential harms including the radiation risks. Based on these models, the benefits from CTC screening every 5 years from the age of 50 to 80 years clearly outweigh the radiation risks.

Colorectal cancer screening in women: an underutilized lifesaver

OBJECTIVE

Colorectal cancer (CRC) represents the third most common cancer diagnosed and a major cause of cancer-related deaths in women. Despite strong evidence that early screening decreases colorectal cancer incidence and mortality rates, colorectal cancer screening rates in women still lag significantly behind screening rates for breast and cervical cancers. Additionally, women have been found to be less likely than men to undergo CRC screening. This is despite the fact that the overall lifetime risk for the development of colorectal carcinoma is similar in both sexes. Barriers to screening have been found to be different for women compared with men. Screening adherence in women also appears to be associated with various social and demographic factors.

CONCLUSION

CT colonography (CTC) is an accurate, minimally invasive, and well-tolerated examination that is newly endorsed by the American Cancer Society, U.S. Multisociety Task Force, and the American College of Radiology. Improved screening compliance may occur in women with further dissemination of CTC.

Colorectal cancer screening: The role of CT colonography

Computed tomography colonography (CTC) in colorectal cancer (CRC) screening has two roles: one present and the other potential. The present role is, without any further discussion, the integration into established screening programs as a replacement for barium enema in the case of incomplete colonoscopy. The potential role is the use of CTC as a first-line screening method together with Fecal Occult Blood Test, sigmoidoscopy and colonoscopy. However, despite the fact that CTC has been officially endorsed for CRC screening of average-risk individuals by different scientific societies including the American Cancer Society, the American College of Radiology, and the US Multisociety Task Force on Colorectal Cancer, other entities, such as the US Preventive Services Task Force, have considered the evidence insufficient to justify its use as a mass screening method. Medicare has also recently denied reimbursement for CTC as a screening test. Nevertheless, multiple advantages exist for using CTC as a CRC screening test: high accuracy, full evaluation of the colon in virtually all patients, non-invasiveness, safety, patient comfort, detection of extracolonic findings and cost-effectiveness. The main potential drawback of a CTC screening is the exposure to ionizing radiation. However, this is not a major issue, since low-dose protocols are now routinely implemented, delivering a dose comparable or slightly superior to the annual radiation exposure of any individual. Indirect evidence exists that such a radiation exposure does not induce additional cancers.

Performance improvements of imaging-based screening tests

Endoscopic and radiologic tests appear to be more accurate than stool-tests in detecting advanced neoplasia because of direct visualisation of colorectal mucosa. Further technological advances are expected to improve the performance and acceptability of these tests. Several attempts at increasing the adenoma detection rate of colonoscopy have been tested, and in vivo histologic differentiation between neoplastic and hyperplastic polyps may lead to substantial saving in economic and medical resources. Low-volume and non-cathartic bowel preparations may improve CT colonography acceptability, whilst computer-aided detection and low-dose protocols may result in a higher accuracy and safety of this procedure. Despite the lack of ionising radiation, significant drawbacks will likely to limit the role of MR colonography in screening programs. Colon capsule endoscopy appears to be a safe and technically feasible procedure. The suboptimal accuracy of the first generation seems to be substantially improved by the second generation of this device.

CT colonography: perforation rates and potential radiation risks

Computed tomographic colonography (CTC) has emerged as an alternative screening tool for colorectal cancer due to the potential to provide good efficacy combined with greater acceptability than optical colonoscopy or fecal occult blood testing. However, some organizations have raised concerns about the potential harms, including perforation rates and radiation-related cancer risks, and have not recommended that it currently be used as a screening tool in the general population in the US. In this article the authors review the current evidence for these potential harms from CTC and compare them to the potential harms from the alternatives including colonoscopy and double-contrast barium enema.

Current techniques in the performance, interpretation, and reporting of CT colonography

The technical objective of computed tomographic colonography (CTC) is to acquire high-quality computed tomography images of the cleansed, well-distended colon for polyp detection. In this article the authors provide an overview of the technical components of CTC, from preparation of the patient to acquisition of the imaging data and basic methods of interpretation. In each section, the best evidence for current practices and recommendations is reviewed. Each of the technical components must be optimized to achieve high sensitivity in polyp detection.

Dose optimisation of double-contrast barium enema examinations

The purpose of the present work was to optimise the filtration and dose setting for double-contrast barium enema examinations using a Philips MultiDiagnost Eleva FD system. A phantom study was performed prior to a patient study. A CDRAD phantom was used in a study where copper and aluminium filtration, different detector doses and tube potentials were examined. The image quality was evaluated using the software CDRAD Analyser and the phantom dose was determined using the Monte Carlo-based software PCXMC. The original setting [100 % detector dose (660 nGy air kerma) and a total filtration of 3.5 mm Al, at 81 kVp] and two other settings identified by the phantom study (100 % detector dose and additional filtration of 1 mm Al and 0.2 mm Cu as well as 80 % detector dose and added filtration of 1 mm Al and 0.2 mm Cu) were included in the patient study. The patient study included 60 patients and up to 8 images from each patient. Six radiologists performed a visual grading characteristics study to evaluate the image quality. A four-step scale was used to judge the fulfillment of three image quality criteria. No overall statistical significant difference in image quality was found between the three settings (P > 0.05). The decrease in the effective dose for the settings in the patient study was 15 % when filtration was added and 34 % when both filtrations was added and detector dose was reduced. The study indicates that additional filtration of 1 mm Al and 0.2 mm Cu and a decrease in detector dose by 20 % from the original setting can be used in colon examinations with Philips MultiDiagnost Eleva FD to reduce the patient dose by 30 % without significantly affecting the image quality. For 20 exposures, this corresponds to a decrease in the effective dose from 1.6 to 1.1 mSv.

Computed tomographic colonography: Hope or hype?

Computed tomographic colonography (CTC) is a promising emerging technology for imaging of the colon. This concise review discusses the currently available data on CTC technique, test characteristics, acceptance, safety, cost-effectiveness, follow-up strategy, and extracolonic findings. In summary, CTC technique is still evolving, and further research is needed to clarify the role of automated colonic insufflation, smooth-muscle relaxants, intravenous and oral contrast, software rendering, and patient positioning. Currently, full bowel preparation is still required to achieve optimal results. The sensitivity for detecting large polyps (> 1 cm) can be as high as 85%, with specificity of up to 97%. These test characteristics are almost comparable to those of conventional colonoscopy. Patient acceptance of CTC is generally higher than that for colonoscopy, especially in patients who have never undergone either procedure. CTC is generally safe, although uncommon instances of colonic perforation have been documented. In terms of cost-effectiveness, most decision analyses have concluded that CTC would only be cost-effective if it were considerably cheaper than conventional colonoscopy. The proper follow-up strategy for small polyps or incidental extracolonic findings discovered during CTC is still under debate. At present, the exact clinical role of virtual colonoscopy still awaits determination. Even though widespread CTC screening is not available today, in the future there may eventually be a role for this technology. Technological advances in this area will undoubtedly continue, with multi-detector row CT scanners allowing thinner collimation and higher resolution images. Stool-tagging techniques are likely to evolve and may eventually allow for low-preparation CTC. Perceptual and fatigue-related reading errors can potentially be minimized with the help of computer-aided detection software. Further research will define the exact role of this promising technology in our diagnostic armamentarium.

ACR Colon Cancer Committee white paper: status of CT colonography 2009

PURPOSE

To review the current status and rationale of the updated ACR practice guidelines for CT colonography (CTC).

METHODS

Clinical validation trials in both the United States and Europe are reviewed. Key technical aspects of the CTC examination are emphasized, including low-dose protocols, proper insufflation, and bowel preparation. Important issues of implementation are discussed, including training and certification, definition of the target lesion, reporting of colonic and extracolonic findings, quality metrics, reimbursement, and cost-effectiveness.

RESULTS

Successful validation trials in screening cohorts both in the United States with ACRIN and in Germany demonstrated sensitivity > or = 90% for patients with polyps >10 mm. Proper technique is critical, including low-dose techniques in screening cohorts, with an upper limit of the CT dose index by volume of 12.5 mGy per examination. Training new readers includes the requirement of interactive workstation training with 2-D and 3-D image display techniques. The target lesion is defined as a polyp > or = 6 mm, consistent with the American Cancer Society joint guidelines. Five quality metrics have been defined for CTC, with pilot data entered. Although the CMS national noncoverage decision in May 2009 was a disappointment, multiple third-party payers are reimbursing for screening CTC. Cost-effective modeling has shown CTC to be a dominant strategy, including in a Medicare cohort.

CONCLUSION

Supported by third-party payer reimbursement for screening, CTC will continue to further transition into community practice and can provide an important adjunctive examination for colorectal screening.

CT and radiation-related cancer risk-time for a paradigm shift?

The use of CT in the US has been increasing exponentially over the past decade. The greatest increases in CT use have been in pediatric diagnosis and adult screening. Unfortunately, there is little cognizance among health-care providers (or their patients) about the relative latent cancer risks associated with repetitive exposure to ionizing radiation. Given the exposure of a relatively high proportion of the population to these tests, it is incumbent on health-care providers to have an improved understanding of these risks and discuss them accordingly with their patients. The risks and benefits of these tests should be carefully analyzed and radiation exposure risk assessment should be conducted as part of the selection of diagnostic and screening tests. Appropriate discussion between physicians and patients of the risks associated with radiographic studies is warranted to inform patients of the longitudinal risks of subsequent testing.

CT colonography versus double-contrast barium enema for screening of colorectal cancer: comparison of radiation burden

Our aim is to compare the radiation dose associated with a low-dose CT colonography (CTC) protocol for colorectal cancer screening with that delivered by double-contrast barium enema (DCBE). CTC of twenty asymptomatic individuals (M:F = 10:10) participating to a colorectal cancer screening program and DCBE of fifteen patients (M:F = 6:9) were evaluated. For CTC, absorbed dose was determined by calculating the dose-length product for each CTC examination from measurements on a CT dose phantom equipped with a CT ion chamber. For DCBE, the free-in-air Kerma at the patient's X-ray entry surface and the Kerma-area product during fluoroscopy and fluorography were measured with a Barracuda system, with fluoroscopy times being recorded blinded to the performing operator. Effective dose at CTC was 2.17 ± 0.12 mSv, with good and excellent image quality in 14/20 (70%) and 6/20 cases (30%), respectively. With DCBE, effective patient dose was 4.12 ± 0.17 mSv, 1.9 times greater than CTC (P < 0.0001). Our results show that effective dose from screening CTC is substantially lower than that from DCBE, suggesting that CTC is the radiological imaging technique of the large bowel with the lowest risk of stochastic radiation effects.

CT colonography: techniques and applications

CT colonography (CTC), also termed virtual colonoscopy, is increasingly accepted at sites throughout the world as a new effective tool for the diagnosis and screening of colorectal carcinoma. This article presents information of related issues of bowel cleansing, stool and fluid tagging, bowel distention and multidetector CT scanning parameters. The author presents discussion of interpretation of CTC, appropriate applications of CTC and potential complications.