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CT dose data by CT radiation treatment planning scans versus CT diagnosis Poster No.: C-0561 Congress: ECR 2015 Type: Scientific Exhibit Authors: S. Johansen, A. Sanderud; Oslo/NO Keywords: Breast, CT, Radiation safety, Dosimetric comparison DOI: 10.1594/ecr2015/C-0561 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. www.myESR.org Page 1 of 9 Aims and objectives 1) to compare the absorbed dose from Computed Tomography (CT) scans used for pre radiotherapy planning (RP#CT) against those from diagnostic CT (DG#CT) examinations. 2) to explore the possible reasons for any dose differences. Methods and materials Two groups of patients underwent CT scans of the thorax with either DG-CT or RP-CT. Each group consisted of 55 patients; patients from each group had similar weight and body mass index (BMI) (Table 1). Patients were scanned using a GE Light speed PRO CT machines across two sites.Parameters including CTDIvol, DLP and scan length from the RP#CT imaging were compared with parameters obtained from DG#CT imaging (Table 2). A two-tailed T-test with independent samples indicated that the distributions of weight and BMI were not significantly different between groups (p>0.05). However, there was a significant difference for the height distribution, mean/SD height for RP-CT group was 170/9 cm whereas for the DG-CT group it was 174/8 cm (p=0.009). Images for this section: Table 1 Page 2 of 9 Table 2 Page 3 of 9 Results The mean CTDIvol and DLP values from RP-CT (38.1 mGy, 1472 mGy·cm) are approximately four times higher than for DG-CT (9.63 mGy, 376.5 mGy·cm). The CT scan length for both RP-CT (mean 37.8 cm) and DG-CT (mean 37.5cm) were similar (p=0.549). The CTDIvol in both RP-CT and DG#CT CTDIvol increase with higher BMI, but the dependence is much stronger in the DG-CT studies than in the RP-CT (DG-CT r=0.852,p<0.001; RP-CT r=0.279,p=0.044). Variations in CTDIvol with BMI indicates the ability of the CT system to modulate the mA according to the patient size and that the DG-CT scans are able to better optimize the mA to the patient size when compared to the RP-CT (Figure 1). In the DG-CT scans a strong negative linear correlation between noise index (NI) and mean CTDIvol was also observed (r =-0.954, p=0.004); the higher NI, the lower CTDIvol. This was not the case in the RP-DG scans. Images for this section: Table 1 Page 4 of 9 Table 2 Page 5 of 9 Fig. 1: Figure 1: CTDIvol as function of Height, Weight and BMI in CT-thorax and Scan length as function of BMI from radiation treatment RP CT scans (orange) and DG CT examinations (blue) Page 6 of 9 Conclusion Our study found that absorbed radiation doses given to patients in RP-CT thorax scans are four times higher, on average, than the doses given in DG-CT scans. The differences are largest between patients with a low BMI. It is important to emphasis the use of patient size modified CT protocols even when high quality images are required. More research to understand and improve reduce the differences in CT dose between DG-CT and RPCT should be a priority. Personal information Corresponding author: [email protected] References 1. Almén A, Friberg EG, Widmark A, Olerud HM. Radiologiske undersøkelser i Norge per 2008 : trender i undersøkelsesfrekvens og stråledoser til befolkningen. 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