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Part 7 Optimization of Protection in Medical Exposure

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Part 7 Optimization of Protection in Medical Exposure

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  1. Part 7Optimization of Protection in Medical Exposure IAEA Training Material on Radiation Protection in Nuclear Medicine Diagnostic Procedures

  2. Objective To be able to apply the principles of radiation protection including design, operational considerations, calibration, clinical dosimetry and quality control for diagnostic procedures using these major equipment: Activity meter, monitoring equipment, probes, scanners, gamma cameras, SPECT-system including coincidence option, and PET. Part 7. Medical Exposure Diagnostic Procedures

  3. Contents • Activity meter and calibration of sources • Probes and counters • Equipment for morphological and functional studies Scanner Gammacamera PET • Clinical dosimetry Part 7. Medical Exposure Diagnostic Procedures

  4. Quality Assurance (BSS: Interim Edition) “3.169. Registrants and licensees, in applying the requirements of these Standards in respect of management systems, shall establish a comprehensive programme of quality assurance for medical exposures with the active participation of medical physicists, radiological medical practitioners, medical radiation technologists and, for complex nuclear medicine facilities, radiopharmacists and radiochemists, and in conjunction with other health professionals as appropriate. Principles established by the World Health Organization, the Pan American Health Organization and relevant professional bodies shall be taken into account.” Part 7. Medical Exposure Diagnostic Procedures

  5. Quality Assurance (BSS: Interim Edition) “3.170. Registrants and licensees shall ensure that programmes of quality assurance for medical exposure include, as appropriate to the medical radiation facility: • (a) Measurements of the physical parameters of medical radiological equipment made by, or under the supervision of, a medical physicist: (i) At the time of acceptance and commissioning of the equipment prior to its clinical use on patients; (ii) Periodically thereafter; (iii) After any major maintenance procedure that could affect protection and safety of patients; (iv) After any installation of new software or modification of existing software that could affect protection and safety of patients;” Part 7. Medical Exposure Diagnostic Procedures

  6. Quality Assurance (BSS contd..) • (b) Implementation of corrective actions if measured values of the physical parameters mentioned in (a) are outside established tolerance limits; • (c) Verification of the appropriate physical and clinical factors used in radiological procedures; • (d) Maintaining records of relevant procedures and results; • (e) Periodic checks of the calibration and conditions of operation of dosimetry equipment and monitoring equipment. Part 7. Medical Exposure Diagnostic Procedures

  7. Optimized Use of Equipment • Well trained staff with access to relevant manuals • Quality control programme • Regular maintenance Part 7. Medical Exposure Diagnostic Procedures

  8. Optimization of Imaging • Use of appropriate image acquisition and processing protocols Part 7. Medical Exposure Diagnostic Procedures

  9. Part 7Optimization of Protection in Medical Exposure IAEA Training Material on Radiation Protection in Nuclear Medicine Module 7.1. Activity Meter and Calibration of Sources

  10. Activity Meter/Dose Calibrator Part 7. Medical Exposure Diagnostic Procedures

  11. Calibration of Sources(BSS: Interim Edition) • “3.166. In accordance with para. 3.153(d) and (e), the medical physicist shall ensure that: • (a) All sources giving rise to medical exposure are calibrated in terms of appropriate quantities using internationally accepted or nationally accepted protocols; • (b) Calibrations are carried out at the time of commissioning a unit prior to clinical use, after any maintenance procedure that could affect the dosimetry and at intervals approved by the regulatory body;” Part 7. Medical Exposure Diagnostic Procedures

  12. ActivityMeter Well-shaped ionization chamber filled with a gas of high atomic number (e.g. Xenon) and keptunder pressure Proportionality between the number of photons emitted and the ionization current SC97 Part 7. Medical Exposure Diagnostic Procedures

  13. Activity Meter • The response of the detector will depend on: • Radionuclide (energy and abundance of photons). • Geometry of the detector. • Geometry of the source. • The condition of the instrument (QC). Part 7. Medical Exposure Diagnostic Procedures

  14. Activity Meter Calibration should be made at factory using reference sources that are traceable to a standard laboratory Part 7. Medical Exposure Diagnostic Procedures

  15. Activity Measurements Setting Measured activity Tc-99m 1.00 Co-57 1.19 In-111 2.35 Tl-201 1.76 Ga-67 1.12 I-123 2.19 I-131 1.43 Measured activity/True activity of Tc.99m if the indicated settings are used Part 7. Medical Exposure Diagnostic Procedures

  16. Geometric Efficiency The quotient: number of photons reaching the detector over the number of photons emitted from the sample Increasing geometric efficiency Part 7. Medical Exposure Diagnostic Procedures

  17. Sample Holder(Reproducible Geometry) Part 7. Medical Exposure Diagnostic Procedures

  18. Activity Meter Operational considerations Radionuclide settings Background Reproducibility Part 7. Medical Exposure Diagnostic Procedures

  19. Quality Control of Activity Meter(what should be done and who should do it) Acceptance Daily Monthly Yearly High voltage/display P T T P Zero adjust P T T P Background P T T P Accuracy P P Precision P T P Relative responses P T P Subsidiary calibrations P Linearity P P Electrical safety P P Leakage radiation P P P: physicist The accuracy should be +/- 5% T: technician Traceability to a national standard. Interlaboratory comparisons. Part 7. Medical Exposure Diagnostic Procedures

  20. Sealed Sources for Calibration of Activity Meters • Long half-life • Range of photon energies • Range of activities • Calibrated within 5% Co57, Ba133, Cs137, Co60 Part 7. Medical Exposure Diagnostic Procedures

  21. Sealed Sources for Calibration of Activity Meters Part 7. Medical Exposure Diagnostic Procedures

  22. Measurement of Precision and Accuracy Source (sealed): Cs-137 or Co-57 Procedure: Select settings for the radionuclide and adjust background. Insert source in holder and make 10 measurements. Data analysis: To assess precision, calculate for each source (i) the percentage difference between the measured activity Ai and their mean Amv. (+/-5%) To assess accuracy, calculate the percentage difference between the mean activity and the certified activity. (+/- 10%). Part 7. Medical Exposure Diagnostic Procedures

  23. Measurement of Reproducibility Measure the activity of a sealed reference source e.g. every morning. Use Tc-99m settings. Part 7. Medical Exposure Diagnostic Procedures

  24. Measurement of Linearity Use a radionuclide with short half-life e.g. Tc-99m Make repeated measurements during several half-lives. Part 7. Medical Exposure Diagnostic Procedures

  25. Part 7Optimization of Protection in Medical Exposure IAEA Training Material on Radiation Protection in Nuclear Medicine Module 7.2. Sample Counters and Probes

  26. Sample Counters Gamma counter Liquid scintillation counter Part 7. Medical Exposure Diagnostic Procedures

  27. Examples of Use of Sample Counters RIA 125I Kidney clearance 51Cr Vitamin B12 deficiency 57Co,58Co Ferrokinetic studies 59Fe Total body water 3H Blood volume 125I, 51Cr, 99mTc Biomedical research 3H, 14C Part 7. Medical Exposure Diagnostic Procedures

  28. Gamma Counter Detector Sample Timer Scaler Ampl. PHA Rate- meter Gain Base Window HV Voltage Lead shield PM-tube Part 7. Medical Exposure Diagnostic Procedures

  29. Scintillation Detector Amplifier PHA Scaler Proportionality between thesignal and the energy absor- bed in the detector Part 7. Medical Exposure Diagnostic Procedures

  30. Pulse Height Analyzer Pulse height (V) UL LL Time The pulse height analyzer allows only pulses of a certain height (energy) to be counted. counted not counted Part 7. Medical Exposure Diagnostic Procedures

  31. Pulse-Height DistributionNaI(Tl) Part 7. Medical Exposure Diagnostic Procedures

  32. Probe System • Thyroid uptake measurements • Radionuclide angiography • Renography Part 7. Medical Exposure Diagnostic Procedures

  33. Probe System Timer Collimator Scaler Ampl. PHA D Rate- meter Gain Base Window PM Recorder HV Voltage Part 7. Medical Exposure Diagnostic Procedures

  34. Gamma CounterProbe Operational considerations • Window setting • Geometry • Reproducibility • Count losses • Background Part 7. Medical Exposure Diagnostic Procedures

  35. Window Setting Energy window setting depends on the energy resolution of the detector and the photon energies Part 7. Medical Exposure Diagnostic Procedures

  36. Gamma CounterDifferent design of the detector Part 7. Medical Exposure Diagnostic Procedures

  37. Reproducibility Measure the activity of a reference source e.g. every morning or every week. Use window settings corresponding to the radionuclide Part 7. Medical Exposure Diagnostic Procedures

  38. Count Losses(Linearty of Activity Response) • Decaying source method • Graded source method Part 7. Medical Exposure Diagnostic Procedures

  39. Liquid Scintillation Counter Sample PM PM Coinc No window 100% geometric efficiency Scaler Timer PHA Ampl Part 7. Medical Exposure Diagnostic Procedures

  40. Liquid Scintillation Counter Operational considerations • Counting efficiency • Quenching • Sample preparation • Window setting • Reproducibility • Background Part 7. Medical Exposure Diagnostic Procedures

  41. Quality Control • Scaler/timer/rate meter function • Energy calibration • Energy resolution • Preset analyser facilities • Sensitivity, counting efficiency • Counting precision • Count rate losses • Linearity of energy response • Background • Linearity of activity response • Geometrical response • Quench correction methods (LSC) Part 7. Medical Exposure Diagnostic Procedures

  42. Part 7. Medical Exposure Diagnostic Procedures

  43. Part 7Optimization of Protection in Medical Exposure IAEA Training Material on Radiation Protection in Nuclear Medicine Module 7.3. Equipment for Morphological and Functional Studies

  44. Rectilinear Scanner Scaler Ampl. PHA Display processor Rate- meter Gain Base Window HV Voltage Display device Scanner drive mechanism Part 7. Medical Exposure Diagnostic Procedures

  45. Rectilinear Scanner Used to measure the spatial distribution of a radiopharmaceutical Rollo 1977 Part 7. Medical Exposure Diagnostic Procedures

  46. Collimator NaI (Tl) crystal Collimator crystal side Lead septa Collimator patient side Focal distance Focal plane Focal point Part 7. Medical Exposure Diagnostic Procedures

  47. Collimator Part 7. Medical Exposure Diagnostic Procedures

  48. Scanner Images Part 7. Medical Exposure Diagnostic Procedures

  49. Scanner • Operational Considerations: • Scanning speed (optimum count density) • Collimator • Collimator mounting • Tapper function • Window setting • Background Part 7. Medical Exposure Diagnostic Procedures

  50. Scanner Quality Control Acceptance Daily Weekly Yearly Energy window P T T P Energy resolution P P Sensitivity P T P Counting precision P P Linearity of energy response P P Test of integral background P T P Test of preset analyzer facilities P P System linearity P T P Background subtraction P P Contrast enhancement P P Scanner drive P P Total performance P T P P: physicist, T:technician Part 7. Medical Exposure Diagnostic Procedures