Abstract

Presented at the annual meeting of the Radiological Society of North America (RSNA) in 2018 (November 2018, Chicago, USA)
PARTICIPANTS:

An Dedulle, MSc Leuven, Belgium
Disclosure: Researcher, Qaelum NV
Niki Fitousi Leuven, Belgium
Disclosure: Research Director, Qaelum NV
Guozhi Zhang Leuven, Belgium
Disclosure: Nothing to Disclose
Jurgen Jacobs, MSc Leuven, Belgium
Disclosure: Co-founder and CEO, Qaelum NV
Hilde Bosmans, PhD Leuven, Belgium
Disclosure: Co-founder, Qaelum NV Research Grant, Siemens AG

PURPOSE

To evaluate a patient-specific approach for organ dose estimation in conventional posterior-anterior (PA) chest radiography.

METHOD AND MATERIALS

The methodology included three steps and was applied to 423 chest PA exams (191 female and 232 male patients). First, the standard ICRP female and male phantom were used in a Monte Carlo (MC) framework to simulate a chest PA exam. These ICRP reference dose conversion factors were applied on the 423 patients to calculate the organ doses (lung, breast). Secondly, a new patient-specific approach was implemented that starts from real time calculated water equivalent diameter (WED) from 3 readily available parameters of the exam (dose area product, exposed area, standardized exposure index). Voxel models had been created from 20 female and 20 male patients. MC was used to generate WED-specific organ dose conversion factors. The equations that correlated WED with WED-specific conversion factors were then applied to the same 423 patients to provide patient-specific organ doses. In the third step, the ICRP-based and patient-specific doses were compared and the percentage difference (D) was calculated.

RESULTS

The WED ranged from 19cm to 33cm for the females and from 22cm to 32cm for the males. The median patient-specific doses for the females were 26uGy and 6uGy for the lung and breast, while for the males this was 26uGy and 5uGy respectively. Patient-specific organ doses were found significantly different from the ICRP-based values (p<0.01). For the lowest WED in this study, ICRP-based doses were underestimated up to 40%, while for the highest WED doses were overestimated by 106%. This would further increase for more obese patients. For increasing WED, the difference between the ICRP-based and patient-specific doses increased for the lungs and breasts (p<0.01) and this effect was most pronounced for the breasts (Fig.). Due to differences in anatomy, the ICRP lung dose was always an overestimation for females and an underestimation for males. 

CONCLUSION

The described methodology provides a good solution for a patient-specific dosimetric approach on a large-scale. More conventional approaches deviate up to ±100% for some subgroups like obese patients. 

CLINICAL RELEVANCE/APPLICATION

The proposed methodology leads to personalized dosimetry in 2D projection imaging, implementable in a dose monitoring platform, by using selected DICOM tags and size-based conversion factors.