ABSTRACT Although optical col oscopy is the criterion standard for co - PDF document

ABSTRACT: Although optical col oscopy is the criterion standard for colorectal cancer screening, CTcolonography is now accepted to be useful when screening average-indicated poor sensitivity for CTly refuted. Recent improvements inthat permit primary 3D viewing ofimages have increas ed screeningaccuracy. Access to CT colonogra-phy is still somewhat limited, butsome advantages of CT colonogra-phy over optical co clude the lack of side effects fromDisadvantages of screening with CTcolonography include the need to schedule a subsequent opticalcolonoscopy if images indicate abiopsy or polypectomy is required,and the reduced ability of CT co lonography to identify small polypswhich rarely, but occasionally, areolorectal cancer (CRC) isthe number one cause ofcancer death among nonsmokers inThe incidence in -creases significantly after age 50.More than 700 people die of CRCestimated 10 years of productive life,over 7000 productive years.quarters of all CRC occurs in asymp-tomatic average-risk individuals, thatis, patients older than 50, without afamily history of the disease, and withno other risk factors such as inflam-matory bowel disease or familial poly-CRC: The ideal disease for screeningBecause CRC exists initially as pre-malignant polyps in virtually all cases,and because early CRC is more cur-able than late CRC (90% cure rateswhen patient is asymptomatic vs 50%cure rates when patient is sympto-matic), this disease is ideally suitedfor a screening program. However,two Canadian studies have shownvery poor compliance rates for CRC screening. A study by Rabeneck of nearly 1 million screen-eligible Ontario patients age 50 to 59determined that fewer than 20.5% hadundergone any form of CRC screen-ing during a 6-year follow-up period.A more recent phone surveyof 1808of these average-risk patients hadgo CRC screening and only 3% hadundergone endoscopy within the past5 years, despite the fact that screeningfor CRC is supported by both theCanadian Cancer Society and theAmerican Cancer Society. Multiple procedures for CRCenema, and flexible sigmoidoscopy.CT colonography: A newcancer screeningAverage-risk patients may be candidates for a less invasive imagingtechnology.Borys Flak, MD, FRCPC, Bruce B. Forster, MD, FRCPC, Michael E. Pezim, MD, FRCSC, FACSDr Flak provides professional services on a contract basis to Canadian Diagnostic Centres, where CT colonography studiesare performed for screening purposes. DrForster is an associate professor and vice-chairman of research in the Department of Radiology at the University of BritishColumbia, and medical director of CanadaDiagnostic Centres (BC). Dr Pezim is themedical director of the Pezim Clinic, a col-orectal diagnostic centre in Vancouver, andThe Intelligent Patient Guideto Colorectal Cancer. BCMEDICALJOURNALMAY of resorption, and thus diminishesp

reparation and distention is absolute-ly vital to ensure an adequate study.Inadequate prep and colonic disten-tion are the most common causes ofThe patient is scanned in both thesupine and prone positions. In prob-lem cases, the decubitus position maybe used as well. These maneuversimprove the probability of adequatelyhelp to differentiate stool, which tendsremain static. Intravenous contrast istions as it is not felt that the increasedbut still very small risk associated withpossible contrast reactions is justifiedics are also not routinely utilized asseveral studies have shown them to beof little value.A Toshiba 64 multislice scanner isused by the authors. Scans are acquiredaging and improve multiplanar refor-mats and 3D reconstructions, thusCT colonography: A new technique for colorectal cancer screening Figure 1. Image obtained with patient in the prone position. Colonic fluid appears white because of prepwith Telepaque (arrowhead). Polyp (long arrow) is shown as a soft tissue mass outlined by a thinrim of contrast. Rectal tube with inflatable balloon is also visible (short white arrow).Image courtesy of Dr Perry Pickhardt Other procedures on the horizoninclude video colon capsules andDNA testing. However, at presentoptical colonoscopy (OC) remains thewhen assessing any new techniques.One such technique, CT colonogra-phy (CTC), is now accepted to haveaverage-risk patients. At present, ac -cess to CTC is still somewhat limited,although there are now a number ofpublic imaging facilities providing theservice in BC. Any local population-ever, is likely to be some years away.CT colonography CT colonography was first introducedby Vining and Gelfand in 1994. CTCis now the preferred name, althoughvirtual colonoscopyŽ is also com-monly used. Since its introduction,CTC has benefited immensely fromtechnological improvements such asmultidetector CT scanners and im -proved workstations. At present anoptimal CTC examination still re -quires a bowel cleansing regimenidentical to that used for colonoscopy,with the addition of dilute barium Telepaque) taken orally. Barium, remaining stool, helps differentiatepolyps from stool. Telepaque, byincreasing the density of any residualcolonic fluid, helps reveal polyps thatmeans of taggingŽ stool in concertniques may mean that in future less or no colonic preparation will beThe CTC procedure begins whena rectal tube is inserted and the colonis insufflated manually with carbondioxide, which is preferred to roomair because it has a much greater rateMAYBCMEDICALJOURNAL smaller polyps.This technique resultsin an estimated effective radiationdose of 5.9 mSv, which compares withannual background radiation of 2.3mSv in the Lower Mainland and aenema of 4 to 8 mSv. A reasonable ruleof thumb for considering radiationrisk is that for every 10 mSv of expo-sure, a pa

tient has a 1 in 1000 lifetimerisk of developing cancer. This statis-tic compares with an annual risk ofmortality in a motor vehicle accidentin the US of 1 in 5900,ural incidence of fatal cancer, which isinduction takes many years, the riskobviously diminishes with age, andscreening for average-risk subjects isonly recommended for patients olderThere has been some controversywhich method of primary reading ofCTC studies, 2D or 3D, is the mostaccurate and efficient. Initially, work-stations and CT scanners were less so -phisticated and most radiologists wereand referring to 3D images in problemareas. This method is tedious andtime-consuming. Pickhardts land-was the first to utilize primary 3D read and report excellentaccuracy. Using a revolutionary work-station that enabled user-friendly auto-matedfly-thrmary 3D read. Radiologists will varyin their approach, based on their ownavailable to them. The authors use theViatronix workstation that Pickhardtused and a combination of 2D and 3Dviewing, but rely on primary 3D inter-pretation. An example of a CTC studyis shown in .CT colonography versus standard optical colonoscopy There is a steep learning curve whenusing either CTC or OC technology.For CTC, meticulous attention to tech-sis, and up-to-date equipment are cru-cial to the production of acceptablededication to absolute patient safetyand a safe and comfortable patientOC has very high sensitivity andspecificity, making it the criterionIn addition, OC images can often beplastic and adenomatous polyps on thebasis of appearance or with the use offluorescence imaging, and OC has thesignificant advantage of permittingimmediate biopsy, polypectomy, orboth if required. The procedure is notperfect and lesions can be missed.Reports show miss rates of 26% to27% for polyps less than 5 mm, 13%for polyps 6 to 9 mm, and 2% to 6%for polyps greater than 10 mm.Overall OC is felt to have an accuracyof approximately 97%. It does sufferfrom a less than 100% completionrate, although incompletion rates arevery low in the hands of expert co -lonoscopists with the availability ofdouble-balloon variable-stiffness adult Figures 1, 2 and 3 CT colonography: A new technique for colorectal cancer screening Image courtesy of Dr Perry Pickhardt Figure 2. 3D view from CTC. Image shows the same polyp (arrow) revealed in 2D view and isvery similar to the image obtained by OC shown in Figure 3. BCMEDICALJOURNALMAY same size. Disparities may be relatedto differences in experience and thequality of equipment used by thesetwo research groups. In line with Pick-hardts results, several recent largeevidence that CTC is capable of highaccuracy.Unpublished and preliminary re -sults from the NIH-funded AmericanCollege of Radiology Imaging Net-work (ACRIN) study were presentedby Dr Johnson at this falls ACRINmeeting. The study inv

olved 2531patients in 15 US centres who had OC and CTC on the same day. Thefrom the study include a 90% perpatient sensitivity for polyps greaterthan 10 mm„on par with OC sensi-tivity. This study also reported verycentages, which are vital for an effec-tive screening study. A second large study publishedCTC in 3120 consecutive adults (meanage 57) with primary OC in 3163 con-secutive adults (mean age 58). Theresults shown in the include theOther relevant findings from thispolyps less than 10 mm were histo-logically advanced in 15 patients (arate of 0.2%). Also, only three patientswith a total of four polyps less than Table CT colonography: A new technique for colorectal cancer screening 3D view from OC. Image obtained by OC of the same polyp (arrow) shown in Figures 1 and 2.Image courtesy of Dr Perry Pickhardt perforation is rare in experienced hands,Intravenous sedation is generally usedtions are extremely rare. Most patientsmore of a challenge than the actualprocedure. Colonoscopy has the addi-tional advantage of zero radiation.CTC does not require sedation,venous line, the potential side effectsof sedation, and the need for monitor-ing. This allows patients to be releasedmal activity, including driving aninations is difficult as OC patients arelection of the study. Perforation ratesduring CTC are even lower than dur-study is also rare, although a poorlydistensible segment of colon may ham-per CTC interpretation. Such segmentsAn advantage of CTC over OC isits ability to detect significant extra-(4%), abdominal aortic aneurysms(5%), and lymphadenopathy (6%).The evaluation of solid organs in theabdomen is limited when comparedscan because of the nonintravenousnature of contrast agents and low-doseradiation protocols used in CTC.Studies comparing the accuracy ofCTC and OC have previously shownan en -doscopist, found a sensitivity of only55% for polyps greater than 10 mmand 39% for polyps greater than 6 mm,whereas Pickhardt,reported sensitivities of 93.8% and88.7%, respectively, for polyps of theMAYBCMEDICALJOURNAL rate of 0.05%) and no subcentimetrecancers were found. The authors con-cluded that CTC and OC screeningmethods resulted in similar detectionrates for advanced neoplasms withinthe same general population.Ž The pri-optical colonoscopies and polypec-used effectively as a screening filterfor therapeutic OC. Perhaps such agreater overall compliance for CRCLooking aheadOf the imaging technologies used toview the entire colorectum, opticalcolonoscopy is still considered the criterion standard. However, whenscreening average-risk patients forCRC, CT colonography should be con-sidered. Earlier studies that showedpoor sensitivity for CTC have nowbeen largely refuted. Assuming thereis state-of-the-art equipment and tech-nical expertise in performing and in -terpreting the studies, CTC ha

s highsensitivity. The primary methodolog-ical issue that has prevented endo-scopists from fully embracing CTC isless, the extremely low prevalence ofadvanced neoplasia or frank carcino-ma in these small lesions may justifying these patients with a repeat exam-As of March 2008, the AmericanCancer Society has added CTC to itslist of acceptable front-line screeningFuture developments in CTC willuser-friendly workstation tools, whichwill reduce interpretation times andallow the incorporation of computer-aided diagnosis as a primary review toidentify suspicious areas for the radi-ologist to reconcile. Advances will alsopermit less vigorous colon cleansing.Already some studies show promiseAdvances on the horizon for OC in -refraction systems that can identifyareas of dysplasia not previously visi-ble, wider angle lenses permittinggreater view around folds to improveaccuracy, instruments that will walkŽinto the colon on their own motorizedlegs and negotiate colonic angulationsmore easily, and further improve-ments in analgesia to eliminate patientAs well as improving the accuracyof both OC and CTC images, it ishoped that these developments willimprove the currently poor screeningrates in BC and Canada for a prevalentand deadly cancer. Competing interestsDr Flak receives fees for consultancy withvate clinic that provides screening CTcolonography. Dr Forster is the salariedmedical director for Canada DiagnosticCentres, but neither he nor his profession-al practice group hold an equity position. DrPezim owns a clinic that undertakes co lonoscopy examinations. Dr Pezim occa-sionally sends and receives referrals to andfrom Canada Diagnostic Services; in nei-ther case is a fee exchanged. References1.National Cancer Institute of Canada.Review of trends in colorectal cancer.www.ncic.cancer.ca/ncic/internet/standard/0,3621,84658243_85787780_91035926_langId-en,00.html (accessed16 March 2008).2.British Columbia Vital Statistics Agency.Ministry of Health Planning. Death-related statistics. In: Selected vital sta-tistics and health status indicators.129th annual report, 2000. 130th annu-al report, 2001.3.Rabeneck L, Paszat LF. A population-CT colonography: A new technique for colorectal cancer screening Table.Findings from Kim study comparing optical colonoscopy with CT colonography. 10 mm or having tubular, tubulovillous, villous, or serrated characteristics and/or containing areas of high grade dysplasiaIn 107 patients (3.4%)In 100 patients (3.2%) Optical colonoscopy CT colonography Patients Mean age 58 Advanced neoplasms* Invasive cancer 4 High grade dysplasia 7 Polypectomies performed or recommended 2434 Polyps 2006 Advanced neoplasms 4 Requiring surgical repair 4 Referrals for OC N/A BCMEDICALJOURNALMAY based estimate of the extent of colorec-tal cancer screening in Ontario. Am J Gas-troenterol

2004;99:1141-1144.4.McGregor SE, Hilsden RJ, Li FX, et al.Low uptake of colorectal cancer screen-ing three years after release of nationalrecommendations for screening. Am JGastroenterol 2007;102:1736-1738. 5.Callstrom MR, Johnson CD, Fletcher JG,et al. CT colonography without catharticpreparation: Feasibility study. Radiology2001;219:693-698.6.Shinners TJ, Pickhardt PJ, Taylor AJ, et al.Patient-controlled room air insufflationversus automated carbon dioxide deliv-ery for CT colonography. AJR Am JRoentgenol 2006;186:1491-1496.7.Park SH, Ha HK, Kim MJ. False-negativeresults at multi-detector row CT colonog-raphy: Multivariate analysis of causes formissed lesions. Radiology 2005;235:8.Morrin MM, Farrell RJ, Keogan MT, et al.CT colonography: Colonic distentionimproved by dual positioning but notintravenous glucagon. Eur Radiol 2002;12:525-530.9.Macari M, Bini EJ, Xue X, et al. Colorec-tal neoplasms: Prospective comparisonof thin-section low-dose multi-detectorrow CT colonography and conventionalcolonoscopy for detection. Radiology2002;332:383-392.10.Brenner DJ, Elliston CD. Estimated radia-tion risks potentially associated with full-body CT screening. Radiology 2004;11.Brenner DJ. Estimating cancer risks frompediatric CT: Going from the qualitative tothe quantitative. Pediatr Radiol 2002;32:228-231.12.Pickhardt PJ, Choi JR, Hwang I, et al.Computed tomographic virtual colon oscopy to screen for colorectal neoplasiain asymptomatic adults. N Engl J Med2003;349:2191-2200.13.Rex DK, Cutler CS, Lemmel GT, et al.Colonoscopic miss rates of adenomasdetermined by back-to-back colono-scopies. Gastroenterology 1997;112:14.van Rijn JC, Reitsma JB, Bossuyt PM, etal. Polyp miss rate determined by tan-dem colonoscopy: A systematic review.Am J Gastroenterol 2006;101:343-350.15.Cotton PB, Durkalski VL, Pineau BC, et al.Computed tomographic colonography(virtual colonoscopy): A multicenter com-parison with standard colonoscopy fordetection of colorectal neoplasia. JAMA2004;291:1713-1719.16.Kim DH, Pickhardt PJ, Taylor AJ, et al. CTcolonography versus colonoscopy for thedetection of advanced neoplasia. N EnglJ Med 2007;357:1403-1412.17.Hellstrom M, Svensson MH, Lasson A.Extracolonic and incidental findings onCT colonography (virtual colonoscopy).AJR Am J Roentgenol 2004;182:631-18.Health Groups Issue Updated Colorec tal Cancer Screening Guidelines. www.cancer.org/docroot/MED/content/Updated_Colorectal_Cancer_19.Lefere P, Gryspeerdt S, Baekelandt M, etal. Laxative-free CT colonography. AJRAm J Roentgenol 2004;183:945-948. CT colonography: A new technique for colorectal cancer screeningOf the imaging technologies used toview the entire colorectum, opticalcolonoscopy is still considered thecriterion standard. However, whenscreening average-risk patients for CRC,CT colonography should be considered.MAYBCMEDICALJOU