# Accuracy of patient-specific CT organ doses from Monte Carlo simulations: influence of CT-based voxel models

## TL;DR

This study evaluates how accurate Monte Carlo simulations are for estimating radiation doses to organs using CT scans, finding that accuracy depends on whether organs are fully within the scan range.

## Contribution

The study introduces a method to assess organ dose accuracy using whole-body and anatomy-specific voxel models in Monte Carlo simulations.

## Key findings

- Organ doses are most accurate when organs are fully within the CT scan field of view.
- Partial organs outside the scan range lead to overestimation of doses due to missing non-irradiated tissue.
- Using ICRP reference masses and densities improves dose estimation accuracy for partially out-of-scan organs.

## Abstract

Monte Carlo simulations using patient CT images as input are the gold standard to perform patient-specific dosimetry. However, in standard clinical practice patient’s CT images are limited to the reconstructed CT scan range. In this study, organ dose calculations were performed with ImpactMC for chest and cardiac CT using whole-body and anatomy-specific voxel models to estimate the accuracy of CT organ doses based on the latter model. When the 3D patient model is limited to the CT scan range, CT organ doses from Monte Carlo simulations are the most accurate for organs entirely in the field of view. For these organs only the radiation dose related to scatter from the rest of the body is not incorporated. For organs lying partially outside the field of view organ doses are overestimated by not accounting for the non-irradiated tissue mass. This overestimation depends strongly on the amount of the organ volume located outside the field of view. To get a more accurate estimation of the radiation dose to these organs, the ICRP reference organ masses and densities could form a solution. Except for the breast, good agreement in dose was found for most organs. Voxel models generated from clinical CT examinations do not include the overscan in the z-direction. The availability of whole-body voxel models allowed to study this influence as well. As expected, overscan induces slightly higher organ doses.