CT colonography/MR colonography

Current Situation and Future Perspective of for Colorectal Screening:CT Colonography and MR Colonography

要旨●CTC（CT colonography）の診断精度は，大腸スクリーニングの標的である腫瘍径6mm以上の病変では良好であり，径10mm以上では大腸検査のgold standardとされている全大腸内視鏡検査とほぼ同等である．CTCは低侵襲で診断精度が高く，大腸スクリーニングとして有用である．臨床面でのCTCの有用性は大腸癌診療において確立していると言える．今や術前検査としてCTCは注腸X線造影検査（BE）にとって代わろうとしている．大腸スクリーニングとして，本邦の大腸がん検診の精密検査法としてCTCの本格的導入が間近となっており，任意型検診では一次スクリーニングからCTCを導入する施設が増加してきている．CTCをスクリーニング法として確固たるものにするためには，診断精度・処理能力・偶発症を評価し，医療被曝低減・診断施設基準を明確化し，前処置法・撮影法・読影法などの標準化を図り，認定制度（医師，一次読影技師）を整備することが喫緊の課題である．これに対してMR colonographyを大腸がん検診に導入する機運はほとんどないのが本邦の現状である．

　CTC（computed tomographic colonography）is used to detect colorectal tumors, and the diagnostic accuracy is better for lesions with a diameter of ≧6mm, which are targets for screening. For tumors with a diameter of ≧10mm, the accuracy is almost the same as that of colonoscopy, which is regarded as the gold standard in colorectal screening. CTC is less invasive, and it has a relatively high diagnostic accuracy rate, making it a useful colorectal screening method. The clinical utility of CTC has been established in the field of colorectal cancer. Moreover, CTC is becoming the preferred preoperative examination over barium enema X-ray examination. In Japan, CTC will soon be a major part of the work-up examination for organized colorectal cancer screening. Recently, the number of facilities using CTC for opportunistic screening has increased. In order to firmly establish CTC as a screening method, we need to undertake the following tasks：clearly evaluate diagnostic accuracy, determine the processing capacity, identify adverse events, limit the radiation exposure of medical personnel, establish criteria for diagnostic facilities, standardize the pretreatment procedure, develop a method for taking and interpreting images, and establish an accreditation system for doctors and radiological technicians. Currently, there is little interest in trying to incorporate magnetic resonance colonography into the colorectal cancer screening procedure in Japan.