Do not want to do a ct scan because of radiation, would an mri show any and all cancers in the body ?

No.: No test/tests can achieve complete accuracy. Additionally, full body cancer screenings are generally not indicated for people of average risk. The cost would be prohibitive. Additionally, when the chance of a false positive outweighs the chance of a true positive result, unnecessary work ups result. That said, other than PET imaging, MRI would probably be the most sensitive to detect occult CA