Body mass index (BMI) is not only the most widely used anthropometric tool for defining overweight and obesity, but it is also the most commonly reported body index for adjusting low dose in MDCT.Despite this popularity of BMI, it is becoming increasingly more clear that BMI is not a good surrogate for regional adiposity. Regional fat deposition, especially in the upper body region, is a better predictor of some obesity related complications than BMI. Accordingly, it has been reported that several anthropometric parameters of the chest might serve as a surrogate instead of BMI for individualized dose settings Neck circumference(NC) is a kind of somatometric parameter like wrist or hip circumference that reflects the upper body size. NC may be an important landmark in the determination of the low dose protocols for upper body CT examinations such as neck, chest and coronary CT. Although investigators have not encountered studies in the literature, this point will be evaluated in our study.The purpose of this study is to evaluate if NC is an appropriate and a novel parameter for adjusting and reduction of the effective chest CT radiation doses in comparison with BMI or not.