The benefits of CT to the practice of medicine are indisputable but concerns regarding increased cancer risk from CT continue to escalate. Of the 67 million CT examinations performed in the United States in 2006, more than 21 million were abdominal and pelvic CT examinations—over 30% of all CT studies. Although CT accounts for only about 17% of imaging examinations, CT is reportedly responsible for almost half of the collective effective dose from medical procedures in the United States [1]. According to risk projection models, in a few decades 1.5–2% of all cancers in the United States may be attributable to the use of CT [2]. Cancer risk from CT may no longer be theoretic because a recent study reports, for the first time, a direct increase in cancer rates related to radiation exposure from CT [3].

Radiologists should adhere to both the principle of ALARA (as low as reasonably achievable—referring to radiation dose) and the principle of AHARA (as high as reasonably achievable—referring to benefit) [4]. The objective is to achieve diagnostic-quality images addressing the clinical concern in the most dose-efficient manner. Although equipment manufacturers continue to make progress toward automating CT dose optimization, radiologists must accept the primary responsibility for minimizing radiation dose to patients from CT. To apply dose reduction strategies in body CT, radiologists must know how to interpret radiation dosimetric data available on a CT dose report and understand the effects of key CT technical parameters on patient radiation exposure. The purpose of this article is to provide this necessary background information.