Purpose:To summarize data on computed tomographic (CT) radiation doses collected from consecutive CT examinations performed at 12 facilities that can contribute to the creation of reference levels. Materials and Methods:The study was approved by the institutional review boards of the collaborating institutions and was compliant with HIPAA. Radiation dose metrics were prospectively and electronically collected from 199 656 consecutive CT examinations in 83 181 adults and 3871 consecutive CT examinations in 2609 children at the five University of California medical centers during 2013. The median volume CT dose index (CTDI vol ), dose-length product (DLP), and effective dose, along with the interquartile range (IQR), were calculated separately for adults and children and stratified according to anatomic region. Distributions for DLP and effective dose are reported for single-phase examinations, multiphase examinations, and all examinations. Results:For adults, the median CTDI vol was 50 mGy (IQR, 37-62 mGy) for the head, 12 mGy (IQR, 7-17 mGy) for the chest, and 12 mGy (IQR, 8-17 mGy) for the abdomen. The median DLPs for single-phase, multiphase, and all examinations, respectively, were as follows: head, 880 mGy · cm (IQR, 640-1120 mGy · cm), 1550 mGy · cm (IQR, 1150-2130 mGy · cm), and 960 mGy · cm (IQR, 690-1300 mGy · cm); chest, 420 mGy · cm (IQR, 260-610 mGy · cm), 880 mGy · cm (IQR, 570-1430 mGy · cm), and 550 mGy · cm (IQR 320-830 mGy · cm); and abdomen, 580 mGy · cm (IQR, 360-860 mGy · cm), 1220 mGy · cm (IQR, 850-1790 mGy · cm), and 960 mGy · cm (IQR, 600-1460 mGy · cm). Median effective doses for single-phase, multiphase, and all examinations, respectively, were as follows: head, 2 mSv (IQR, 1-3 mSv), 4 mSv (IQR, 3-8 mSv), and 2 mSv (IQR, 2-3 mSv); chest, 9 mSv (IQR, 5-13 mSv), 18 mSv (IQR, 12-29 mSv), and 11 mSv (IQR, 6-18 mSv); and abdomen, 10 mSv (IQR, 6-16 mSv), 22 mSv (IQR, 15-32 mSv), and 17 mSv (IQR,(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26). In general, values for children were approximately 50% those for adults in the head and 25% those for adults in the chest and abdomen. Conclusion:These summary dose data provide a starting point for institutional evaluation of CT radiation doses.q RSNA, 2015

Purpose:To determine patient, vendor, and institutional factors that influence computed tomography (CT) radiation dose. Materials and Methods:The relevant institutional review boards approved this HIPAA-compliant study, with waiver of informed consent. Volume CT dose index (CTDI vol ) and effective dose in 274 124 head, chest, and abdominal CT examinations performed in adult patients at 12 facilities in 2013 were collected prospectively. Patient, vendor, and institutional characteristics that could be used to predict (a) median dose by using linear regression after log transformation of doses and (b) high-dose examinations (top 25% of dose within anatomic strata) by using modified Poisson regression were assessed. Results:There was wide variation in dose within and across medical centers. For chest CTDI vol , overall median dose across all institutions was 11 mGy, and institutional median dose was 7-16 mGy. Models including patient, vendor, and institutional factors were good for prediction of median doses (R 2 = 0.31-0.61). The specific institution where the examination was performed (reflecting the specific protocols used) accounted for a moderate to large proportion of dose variation. For chest CTDI vol , unadjusted median CTDI vol was 16.5 mGy at one institution and 6.7 mGy at another (adjusted relative median dose, 2.6 mGy [95% confidence interval: 2.5, 2.7]). Several variables were important predictors that a patient would undergo high-dose CT. These included patient size, the specific institution where CT was performed, and the use of multiphase scanning. For example, while 49% of patients (21 411 Conclusion:CT doses vary considerably within and across facilities. The primary factors that influenced dose variation were multiphase scanning and institutional protocol choices. It is unknown if the variation in these factors influenced diagnostic accuracy.q RSNA, 2016

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Radiotherapy treatment planning calculations of the chest wall are complex due to missing tissue, the thin chest wall and the presence of lung. The accuracy of calculated dose is dependent on the type of algorithm employed. This work evaluates a collapsed cone (CC) and a pencil beam (PB) convolution model for radiotherapy planning of the chest wall. Various irradiation geometries simulating the chest wall have been examined and calculations were compared with measurements with an ionization chamber in epoxy resin water substitute and in low-density lung substitute blocks. A retrospective treatment planning study comprising 6 patients was carried out to evaluate the differences in the dose distributions and monitor units predicted by the two algorithms. The calculated dose in unit density medium was within +/-1% for the CC model and up to +/-2% for PB. In low density medium and under full scatter conditions, CC overestimated the dose by 1% whereas PB overestimated the dose by 9%. In the tangential irradiation geometry with water and lung media, the PB overestimated dose to the isocentre by up to 10%, whereas the dose from CC was within 3%. From the treatment planning study calculated monitor units (MU) and doses were consistent with the experimental findings. The CC model is more accurate for radiotherapy treatment planning of the chest wall and especially when there is significant involvement of lung tissue.