Chest CT examinations performed at the University of Crete on at least 90 paediatric and 200 adult patients with well-defined clinical indications will be included in this study.

Using patient CT images as input volume, a 3D model will be created for each patient. 3D dose distributions will be generated for each, using an equipment-specific and patient-specific Monte Carlo code. Two sets of simulations will be performed for each patient using: i) a fixed tube current value and ii) tube current modulation.

Normalized to CTDIvol organ absorbed dose will be determined for all radiosensitive organs located within the primary exposed volume i.e. breast, oesophagus, lungs, bone marrow, heart. At least 3 state-of-the-art CT scanners will be modelled. The scanners’ geometry, x-ray spectrum, composition and dimensions of the filters will be considered in the simulations. The number of photons produced for each simulation is estimated to be 108-109, resulting in a statistical inaccuracy lower than 1%. Radiation doses estimated will be compared to those determined using thermoluminescence dosimetry in a family of anthropomorphic phantoms (4 paediatric phantoms of different sizes and an adult phantom), software packages and data from the literature. Percentage differences in organ radiation doses will be presented and discussed.

A patient-specific method for the estimation of organ doses will be finalised based on Monte Carlo simulation and intercomparison results, taking into account patients’ body size. This will be useful for CT dose optimization and as input for epidemiological research and modelling ofradiation-induced risks.

Organ doses from CTs will be used together with age, sex and organ specific risk models proposed by BEIR VII9 and/or more recent appropriate risk models to derive lifetime attributable risks (and uncertainties) of cancer associated with chest CT scans building on existing risk projection tools.