Recently published AAPM Task Group 204 developed conversion coefficients that use scanner reported CTDIvol to
estimate dose to the center of patient undergoing fixed tube current body exam. However, most performed CT exams use
TCM to reduce dose to patients. Therefore, the purpose of this study was to investigate the correlation between organ
dose and a variety of patient size metrics in adult chest CT scans that use tube current modulation (TCM).
Monte Carlo simulations were performed for 32 voxelized models with contoured lungs and glandular breasts tissue,
consisting of females and males. These simulations made use of patient's actual TCM data to estimate organ dose. Using
image data, different size metrics were calculated, these measurements were all performed on one slice, at the level of
patient's nipple. Estimated doses were normalized by scanner-reported CTDIvol and plotted versus different metrics.
CTDIvol values were plotted versus different metrics to look at scanner's output versus size.
The metrics performed similarly in terms of correlating with organ dose. Looking at each gender separately, for male
models normalized lung dose showed a better linear correlation (r2=0.91) with effective diameter, while female models
showed higher correlation (r2=0.59) with the anterior-posterior measurement. There was essentially no correlation
observed between size and CTDIvol-normalized breast dose. However, a linear relationship was observed between
absolute breast dose and size. Dose to lungs and breasts were consistently higher in females with similar size as males
which could be due to shape and composition differences between genders in the thoracic region.