Dose Evaluation and Reporting
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Learn the importance of dose evaluation and reporting and see how radiation is measured as compared to the radiation from the natural background in a normal environment.
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Dose Evaluation and Reporting
- 1. Dose Evaluation and Reporting Public © 2013, Carestream Health
- 2. p.2 What is the Purpose of Estimating Dose? For radiologists • Determines how changes in techniques impact radiation dose and image quality For patients’ physicians • Determines if the benefits from the diagnostic information outweigh the risks For imaging facilities • Ensures their procedures and protocols are being followed appropriately For professional societies and regulatory agencies • Used for setting or reviewing radiation dose related guidelines • Establishes standards of practice For monitoring and reporting • Dose registries can be used to benchmark imaging practice through establishing dose reference levels • Tracking adverse events can establish trends and allow prospective correction of possible radiation safety problems related to equipment or operator training Public © 2013, Carestream Health
- 3. p.3 What is X-ray Dose? • Radiation dose reported in Gy units is proportional to the amount of absorbed energy per unit mass • Often reported in mGy for radiography, 1mGy=1/1000 Gy • The absorbed energy is proportional to the physical damage on the cell’s chemical bonds (such as DNA double strand breaks) • The quantity most relevant for assessing the risk of cancer is effective dose, which is evaluated in units of sieverts (abbreviated Sv; 1Sv = 1Gy in the case of x rays) • Effective dose allows comparison of the risk estimates associated with partial or whole-body radiation exposures. This quantity also incorporates the different radiation sensitivities of the various organs in the body Public © 2013, Carestream Health
- 4. p.4 Effective Dose Calculation Takes into account the specific organs and areas of the body that are exposed. All parts of the body and organs are not equally sensitive to the possible adverse effects of radiation, such as cancer induction and mutations. Effective dose (mSv) = sum of organ dose (mGy) x tissue weighting factor Public © 2013, Carestream Health tissue weighting factor
- 5. p.5 Comparison with Natural Background Radiation Effective radiation dose: Comparable to the natural background radiation for a period of*: 7 mSv 2 years Computed Tomography (CT)-Chest Low Dose 1.5 mSv 6 months Radiography-Chest 0.1 mSv 10 days 1.5 mSv 6 months 0.001 mSv 3 hours 2 mSv 8 months 0.005 mSv 1 day 0.001 mSv 3 hours 0.4 mSv 7 weeks For this procedure: CHEST: Computed Tomography (CT)-Chest BONE: Radiography (X-ray)-Spine Radiography (X-ray)-Extremity CENTRAL NERVOUS SYSTEM: Computed Tomography (CT)-Head DENTAL: Intraoral X-ray WOMEN'S IMAGING: Bone Densitometry (DEXA) Mammography *That is, how long it would take to receive the same amount of radiation from the natural background in a normal environment. Public © 2013, Carestream Health
- 6. p.6 Dose Metrics Monitored in the Clinic Effective dose is typically not computed for individual patients. As a result, other metrics are reported that is proportional to the absorbed dose and the metric used typically depends on the imaging system: Radiography • Dose Area Product (DAP), Entrance Exposure (EE), Exposure Index (EI), Fluoroscopy • Dose rate, DAP, fluoro time, Maximum Skin Dose (MSD) Computed Tomography (CT) • CT Dose Index (CTDI100, CTDIw, CTDIvol), Dose Length Product (DLP) In addition, the other exam parameters are also important and recorded: • kVp, mAs, collimation, filters, imaging geometry, Patient gender, age, study details etc.. Public © 2013, Carestream Health
- 7. p.7 Entrance Exposure (EE) X-ray source • Source to measurement distance (SMD) EE Dose (mGy) Patient Detector Public © 2013, Carestream Health Typically calculated from system calibration measurements • EE is reported in units of mGy • EE is dependent of distance from the source (SMD) • EE is typically reported at a predefined distance. e.g. 20 cm from detector surface
- 8. p.8 Dose Area Product (DAP) • • DAP is the entrance surface dose (mGy) multiplied by the area irradiated (cm2) • DAP is reported in units of: Gy*cm2, cGy*cm2, or mGy*cm2 • DAP is independent of distance from the source • Public © 2013, Carestream Health Measured using a DAP meter Reported for radiographic and fluoroscopic procedures
- 9. p.9 Exposure Index (EI) • The exposure index calculation is based on the amount of exposure that is not absorbed by the patient X-ray source • EI is based on the average exposure reaching the detector in the area behind exposed anatomy • Patient Detector EI = Exposure behind the patient The calculation excludes radiation attenuated by the collimator • It also excludes areas of direct exposure • EI values are proportional to Log(Exposure) and mR • Doubling of exposure corresponds to +300 count change Public © 2013, Carestream Health
- 10. p.10 What is Dose Reporting? • The Integrated Healthcare Enterprise (IHE) has put together a profile for dose reporting called the IHE REM (Radiation Exposure Monitoring) Integration Profile. • This profile provides a standard mechanism for recording and distributing estimated radiation dose information from imaging procedures using defined DICOM Structured Report (SR) templates appropriate for radiation dose monitoring of CT and projection X-Ray procedures. Public © 2013, Carestream Health
- 11. p.11 What is our Role at the CR or DR Console? • We fulfill the role of the Acquisition Modality in the IHE REM Integration Profile. In this role we will collect radiation dose information at a study level and deliver this information to interested parties in a way that doesn’t disrupt customer workflow • Interested parties may include an Image Manager/Archive (e.g. PACS) and/or a Dose Information Consumer (e.g. RIS) • The dose report will be composed and sent on the completion or discontinuation of a procedure step to interested parties configured to receive DICOM Radiation Dose Structured Reports • The dose report that we deliver will consist of a binary list of tag-value data elements encoded in the same manner in which images are stored and transferred today. The “interested parties” may then present this standardized data in whatever way best suits them Public © 2013, Carestream Health
- 12. p.12 IHE REM Compared to MPPS • The use of Radiation Dose Structured Reports overcomes weaknesses of MPPS as a dose monitoring method • The dose report provides far more complete details and is persisted, whereas MPPS was designed for workflow and is not persisted (e.g. stored, archived) • Dose details are recorded for each irradiation event, which is defined as one continuous occurrence of irradiation being applied to a patient • The dose report is created at the end of each procedure step and contains all the irradiation events from the procedure step Public © 2013, Carestream Health
- 13. p.13 More Information Dose Report • More details on information recorded in the dose report can be found in TID 10001 through TID 10005 of DICOM PS 3.16 http://medical.nema.org/Dicom/2011/11_16pu.pdf MPPS • More details regarding MPPS can be found in DICOM PS 3.4, Table F.7.2-1 • Our role is Service Class Role of SCU http://medical.nema.org/Dicom/2011/11_04pu.pdf Carestream DICOM Conformance Statements • Additional details regarding our conformance can be found at: http://dicom.carestream.com Public © 2013, Carestream Health