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Organ Dose Estimation Accuracy Using a Modified SSDE for CT Examination in a Pediatric Population
N Deaton1,2 , R Kaufman2 , E Somasundarum2 , S Brady2*, (1) Georgia Institute of Technology, Atlanta, GA, (2) St Jude Children's Research Hospital, Memphis, TN
Presentations
TH-EF-601-11 (Thursday, August 3, 2017) 1:00 PM - 3:00 PM Room: 601
Purpose: Investigate CT size-specific dose estimate (SSDE) in a pediatric population as a viable surrogate for organ dose estimation compared with Monte Carlo calculations.
Methods: CTDIvol was used to calculate SSDE from 290 examinations (191 patients) in order to estimate organ dose based on the method of Moore et al. [Med Phys 41(7) 071917], and was compared to organ doses calculated with and without helical over-ranging using Monte Carlo (MC) and computational phantoms (VirtualDose™CT). Effective dose was calculated from organ doses. A modified SSDE was investigated with weighting factors derived from tube current modulation (TCM) and organ cross-sectional area. The modified SSDE investigated lung organ dose where TCM and organ volume vary the greatest. Paired student t-test was used to assess improvement in SSDE accuracy.
Results: Mean patient weight was 46±29 kg (range 6-133 kg) and age was 12±7 yr (range 0.3-25 yrs). Modifying SSDE by TCM improved lung dose estimation accuracy to better than 16.8% (p<0.001) for CAP (chest-abdomen-pelvis) and NCAP (neck-chest-abdomen-pelvis) examinations. Weighting by lung area improved CAP accuracy by 6.1% (p=0.043). Weighting by both TCM and lung area improved chest accuracy by 3.7% (p=0.049). Effective dose derived from unmodified scan-volume averaged-SSDE agreed to better than 7% with MC results (considering all organs in the body, not just the scan volume), but underestimated MC results incorporating over-ranging by 28% and 44% at the superior/inferior scan boundaries for a single scan and a dual-grouped series (used to scan a CAP or NCAP with contrast), respectively.
Conclusion: Modifying SSDE by TCM and/or lung area improves the lung dose estimation accuracy for some exam protocols, but demonstrates no universal advantage over simple volume averaged-SSDE used for organ dose estimation. As expected, averaged-SSDE underestimated increases in patient dose from helical over-ranging, but agreed to better than 7% with MC calculated patient dose.
Funding Support, Disclosures, and Conflict of Interest: This work was partially funded by American Lebanese Syrian Associated Charities (ALSAC) and the National Cancer Institute (NCI) R25E Grant 5R25CA23944.
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