Patient centering effects on Size-Specific Dose Estimates (SSDE)

Congress:

EuroSafe Imaging 2017

Poster Number:

ESI-0048

Type:

EuroSafe Imaging

Keywords:

Computer Applications-General, CT, Radioprotection / Radiation dose, Radiation physics, Action 5 - Performance indicators for radiation protection management, Action 10 - EuroSafe Imaging Stars, Action 2 - Clinical diagnostic reference levels (DRLs), Action 9 - Development of criteria for safe imaging procedures, Action 8 - EuroSafe Imaging Stars network and data collection, Action 3 - Optimisation, diagnostic reference levels, image quality, Physics, Radiation safety, Quality assurance

Authors:

K. Ahlström Riklund, J. S. Andersson, C. Granberg, J. Lundman

DOI:

10.1594/esi2017/ESI-0048

DOI-Link:

https://dx.doi.org/10.1594/esi2017/ESI-0048

Fig. 1: Scatter plot of CTDIvol corresponding to the 218 CT thorax examinations...

Fig. 2: Example of an original CT examination image from PACS used in this study...

Fig. 3: Calculation results of SSDE based on WED for the CT examinations investigated....

Fig. 6: SSDE as a function of Y-axis offset, i.e. patient centring compared to CT...

Background/Introduction

The concept of Size-Specific Dose Estimates (SSDE) for refining computed tomography (CT) dosimetry has been proposed in the Report of the American Association of Physicists in Medicine (AAPM) Task Group 204.[1] The present conventional metrics for determining patient exposure in CT applications are the volume Computed Tomography Dose Index (CTDIvol) and Dose Length Product (DLP), which do not take patient size into account. Tube current modulation (TCM) functionality is used in most CT examinations to achieve consistent clinical image quality independent of patient size, resulting...

Description of activity and work performed

The present work employs a script from the REMbox framework (Dicom Port AB, Umeå, Sweden) written in Python™ where the patient contour is automatically segmented, i.e. removing the patient table and mattress. Based on recommendations from the Report of AAPM Task Group 220[2], the script then use the segmented patient volume to determine the WED. To validate script functionality with regard to segmentation, determination of WED and centring errors, a Catphan® 500 was used (The Phantom Laboratory, USA). Phantom images were evaluated from known size...

Conclusion and Recommendations

The SSDE is superior to the CTDIvol for any optimization and clinical audit work involving CT. The true novelty of the SSDE concept can only be realized when working with automated workflows allowing evaluation of large data sets. When working with reconstructed axial CT images, WED is superior to a patient physical size metric (EAD) for determining the SSDE with regard to patient specificity. The evaluation of patient centring effects on patient dose, i.e. the SSDE calculated in the present work, show that centring offsets...

Personal/Organisational information

Jonas Andersson and Josef A Lundman represent Dicom Port AB (Umeå, Sweden).

References

1. The American Association of Physicists in Medicine (AAPM), “Size-Specific Dose Estimates (SSDE) in Pediatric and Adult Body CT Examinations,” Report of AAPM Task Group 204, AAPM (2012). 2. The American Association of Physicists in Medicine (AAPM), “Use of Water Equivalent Diameter for calculating patient size and Size-Specific Dose Estimates (SSDE) in CT,” Report of AAPM Task Group 220, AAPM (2014). 3. Supawitoo Sookpeng, Patsuree Cheebsumon, Thanyawee Pengpan, and Colin Martin, “Comparison of computed tomography dose index in polymethyl methacrylate and nylon dosimetry phantoms,” J....