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CT Radiation Dose: Units and Measurement Methods Walter Huda PhD SUNY Upstate Medical University, Syracuse NY

Computed Tomography Dose Index (CTDI)Effective DoseWhy is CT dose important?. x-ray skin dose 2 mGy/0.2 rad. Conventional radiography. Head CT scan. Body CT scan. CataractsDeterministic effect. CarcinogenesisStochastic effect. In CT, CTDI is "radiation concentration"Effective dose is the "total radiation" .

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CT Radiation Dose: Units and Measurement Methods Walter Huda PhD SUNY Upstate Medical University, Syracuse NY

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    1. CT Radiation Dose: Units and Measurement Methods Walter Huda PhD SUNY Upstate Medical University, Syracuse NY

    13. CTDIw (weighted) CTDIw = (1/3 CTDI100)center + (2/3 CTDI100)periphery

    14. CTDI100 is Proportional to mAs Approximately independent of slice thickness

    18. Volume CTDIvol

    23. Dose-length product (DLP) DLP = CTDIvol x Scan Length DLP has units of mGy-cm Given on console of some CTs Can be used to obtain effective dose E

    25. Dose (risk) in CT is best measured by effective dose (E)

    26. Sensitive organs (wi = 0.12) Red bone marrow Colon Lung Stomach

    27. Moderately sensitive organs (wi = 0.05) Bladder Breast Liver Esophagus Thyroid

    29. Effective doses can be estimated using DLP conversion factors mSv/mGy-cm

    30. Model patient as cylinder of water Determine energy imparted Convert energy imparted into effective dose

    33. Abdominal CT scan ~4 mSv

    37. In US Hospitals CT ~10% of exams CT contributes 2/3rd of patient dose Fred Mettler 2000 study in New Mexico

    38. Individual and collective doses will continue to increase

    43. Conclusions

    44. CTDI parameters quantify CT scanner dose characteristics, not patient doses CTDIw & CTDIvol

    45. Stochastic risks are important in CT Deterministic risk should not occur Doses should be kept ALARA

    46. Effective doses in CT ~1 mSv for head ~5 mSv for body CT doses dominate medical exposures

    47. Radiation Dose in CT MF McNitt-Gray Radiographics (2002) 22:1541-1553

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