PMID- 34309040 OWN - NLM STAT- MEDLINE DCOM- 20211105 LR - 20211105 IS - 2473-4209 (Electronic) IS - 0094-2405 (Linking) VI - 48 IP - 10 DP - 2021 Oct TI - Evaluating Size-Specific Dose Estimate (SSDE) as an estimate of organ doses from routine CT exams derived from Monte Carlo simulations. PG - 6160-6173 LID - 10.1002/mp.15128 [doi] AB - PURPOSE: Size-specific dose estimate (SSDE) is a metric that adjusts CTDI(vol) to account for patient size. While not intended to be an estimate of organ dose, AAPM Report 204 notes the difference between the patient organ dose and SSDE is expected to be 10-20%. The purpose of this work was therefore to evaluate SSDE against estimates of organ dose obtained using Monte Carlo (MC) simulation techniques applied to routine exams across a wide range of patient sizes. MATERIALS AND METHODS: Size-specific dose estimate was evaluated with respect to organ dose based on three routine protocols taken from Siemens scanners: (a) brain parenchyma dose in routine head exams, (b) lung and breast dose in routine chest exams, and (c) liver, kidney, and spleen dose in routine abdomen/pelvis exams. For each exam, voxelized phantom models were created from existing models or derived from clinical patient scans. For routine head exams, 15 patient models were used which consisted of 10 GSF/ICRP voxelized phantom models and five pediatric voxelized patient models created from CT image data. For all exams, the size metric used was water equivalent diameter (D(w) ). For the routine chest exams, data from 161 patients were collected with a D(w) range of ~16-44 cm. For the routine abdomen/pelvis exams, data from 107 patients were collected with a range of D(w) from ~16 to 44 cm. Image data from these patients were segmented to generate voxelized patient models. For routine head exams, fixed tube current (FTC) was used while tube current modulation (TCM) data for body exams were extracted from raw projection data. The voxelized patient models and tube current information were used in detailed MC simulations for organ dose estimation. Organ doses from MC simulation were normalized by CTDI(vol) and parameterized as a function of D(w) . For each patient scan, the SSDE was obtained using D(w) and CTDI(vol) values of each scan, according to AAPM Report 220 for body scans and Report 293 for head scans. For each protocol and each patient, normalized organ doses were compared with SSDE. A one-sided tolerance limit covering 95% (P = 0.95) of the population with 95% confidence (alpha = 0.05) was used to assess the upper tolerance limit (T(U) ) between SSDE and normalized organ dose. RESULTS: For head exams, the T(U) between SSDE and brain parenchyma dose was observed to be 12.5%. For routine chest exams, the T(U) between SSDE and lung and breast dose was observed to be 35.6% and 68.3%, respectively. For routine abdomen/pelvis exams, the T(U) between SSDE and liver, spleen, and kidney dose was observed to be 30.7%, 33.2%, and 33.0%, respectively. CONCLUSIONS: The T(U) of 20% between SSDE and organ dose was found to be insufficient to cover 95% of the sampled population with 95% confidence for all of the organs and protocols investigated, except for brain parenchyma dose. For the routine body exams, excluding the breasts, a wider threshold difference of ~30-36% would be needed. These results are, however, specific to Siemens scanners. CI - (c) 2021 American Association of Physicists in Medicine. FAU - Hardy, Anthony James AU - Hardy AJ AD - Materials Engineering Division/Non-destructive Evaluation Group, Livermore National Laboratory, Livermore, California, USA. FAU - Bostani, Maryam AU - Bostani M AD - Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, Livermore, USA. AD - Physics and Biology in Medicine Graduate Program, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, USA. FAU - Kim, Grace Hyun J AU - Kim GHJ AD - Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, Livermore, USA. FAU - Cagnon, Christopher H AU - Cagnon CH AD - Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, Livermore, USA. AD - Physics and Biology in Medicine Graduate Program, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, USA. FAU - Zankl, Maria Agnes AU - Zankl MA AD - Institute of Radiation Medicine, Helmholtz Zentrum Munchen, German Research Center for Environmental Health (GmbH, Neuherberg, Germany. FAU - McNitt-Gray, Michael AU - McNitt-Gray M AD - Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, Livermore, USA. AD - Physics and Biology in Medicine Graduate Program, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, USA. LA - eng GR - T32-EB002101/GF/NIH HHS/United States PT - Journal Article DEP - 20210809 PL - United States TA - Med Phys JT - Medical physics JID - 0425746 SB - IM MH - *Abdomen MH - Child MH - Humans MH - Monte Carlo Method MH - Phantoms, Imaging MH - Radiation Dosage MH - *Tomography, X-Ray Computed OTO - NOTNLM OT - Monte Carlo dose simulations OT - TCM OT - routine CT exams OT - size-specific dose estimate EDAT- 2021/07/27 06:00 MHDA- 2021/11/06 06:00 CRDT- 2021/07/26 09:00 PHST- 2021/06/11 00:00 [revised] PHST- 2021/04/04 00:00 [received] PHST- 2021/07/09 00:00 [accepted] PHST- 2021/07/27 06:00 [pubmed] PHST- 2021/11/06 06:00 [medline] PHST- 2021/07/26 09:00 [entrez] AID - 10.1002/mp.15128 [doi] PST - ppublish SO - Med Phys. 2021 Oct;48(10):6160-6173. doi: 10.1002/mp.15128. Epub 2021 Aug 9.