放射治療設備品質保證原理 Comprehensive QA for radiation onlology

1. 放射治療設備品質保證原理Comprehensive QA for radiation onlology • Class date/time: Thursdays, 8:20-10:05 AM, 2002/2/28~6/27 • References: • Quality Assurance in Radiotherapy Physics. • Comprehensive QA for radiation oncology: Report of AAPM Radiation Therapy Committee Task Group 40. Med. Phys. 21 (4), April 1994. Grading: • Roll call and reports: 50%, Examinations: 50%

2. PREFACE • QA activities cover a very broad range, and the work of medical physicists in this regard extends into a number of areas in which the actions of radiation oncologists, radiation therapist, dosimetrists, accelerator engineers, and medical physicists are important. • If quality of care is to be improved, enlightened leadership by hospital management and clinical leaders is required. Within radiation oncology itself, coordination is critical among radiation oncology physicists, dosimetrists, accelerator engineers, radiation oncologists, radiation therapists, and administrators. The various groups are brought into coordinated efforts through well-documented QA procedures administrated by a multidisciplinary QA committee.

3. CONTENTS • Information for radiation oncology administrators • Code of practice • Comprehensive QA program • QA of external beam radiation therapy equipment • Treatment planning computer system • External beam treatment planning • Brachytherapy • QA of clinical aspects

4. Information for radiation oncology administrators • In treating patients with radiation, the radiation oncologist prescribes a treatment regimen ( including the radiation dose ) whose goal is to cure or control the disease while minimizing complications to normal tissue. • The response of tumors and normal tissue t radiation is highly variable. • The radiation dose must be delivered accurately and consistently. • Radiation therapy process is a complex interweaving of a number of related tasks.

5. Information for radiation oncology administrators • Radiation therapy process : • Initial consultation • Determination of patient-specific parameters. ( Acquired from a number of diagnostic imaging sources ) • Treatment planning ( determine the size, extent, and location of the tumor in relation to the normal organs. Distribution of radiation dose to patient ) • Simulating the planned treatment ( Simulator ) • To treat the patient as planned • Verifying the correct delivery of treatment ( portal and verification radiographs, in vivo dosimetry, and record-and-verify systems.

6. Information for radiation oncology administrators • ICRU has recommended that the dose be delivered to within 5% of the prescribed dose. Each step of radiation therapy process must be performed with an accuracy much better than 5%. • To meet such standards required the availability of the necessary facilities and equipment including treatment and imaging units, radiation measuring devices, computer planning systems and the appropriate staffing levels of qualified radiation oncologists, radiation oncology physicists, dosimetrists, and radiation therapists. • Furthermore, the complexity of treatment modalities is increasing.

7. Information for radiation oncology administrators • For Example : • Linacs contain computer control system. • High and low dose-rate remote afterloaders have sophisticated control systems. • Treatment planning systems become larger and more complex. Several sophisticated options have become standard on commercial and locally developed systems. ( 3-D BEV planning, DRR, 3-D dose computation and display, DVH …) • The commissioning and quality assurance of such complex systems requires increasing personnel training and time. • Increasing expectations on the quality of treatment which lead to greater and more complex.

8. Information for radiation oncology administrators • These expectations have arisen from a growing appreciation of the importance of QA, and from the regulations of national, state, and local authorities and accreditation bodies. • QA processes and procedures emanate from a QA committee. • QA committee should include nurses, the department administrator, and • Radiation oncologist may be responsible for • Consultation • Dose prescription • On-treatment supervision • Treatment summary reports

9. Information for radiation oncology administrators • Radiation oncology physicist is responsible for • Calibration of the therapy equipment. • Directs the determination of radiation dose distributions in patients undergoing treatment. • Weekly review of the dose delivered to the patient. • Certifies that the treatment machine is performing according to specifications after it is installed. • Generate the beam data. • Outlines written QA procedures, tolerances, and frequency of the tests. • Understands and appropriately responses to machine malfunctions and related safety issues.

10. Information for radiation oncology administrators • Radiation therapist • Be responsible for Accurately delivering a planned course of radiation therapy as prescribed by a radiation oncologist. • Be expected to recognized any change in the patient’s condition and determine when treatment should be withheld until a physician is consulted. • Be able to detect any equipment deviations or malfunctions, understand the safe operating limit of the equipment. • Be able to judge when, due to equipment problems , to withhold or terminate treatment until the problem has been resolved.

11. Information for radiation oncology administrators • Medical radiation dosimetrist • Be responsible for accurate patient data acquisition • Radiation treatment design. ( In consultation with the physicist and oncologist ) • Manual/computer-assisted calculations of radiation dose distribution. • Assist with machine calibrations and ongoing QA under the supervision of the physicist.

12. Information for radiation oncology administrators • It is also important to provide the appropriate dosimetry instrumentation for commissioning and QA of these devices. • Daily QA device • Ion chamber • Electrometer/dosimeter • Barometer • Thermometer • Level • Ruler • Film scanner/ densitometer

13. Information for radiation oncology administrators • Water phantom scanning system • Solid phantom • Survey meter • A comprehensive QA program should not focus just on the analysis of a narrow set of treatment variables, but rather should attempt to understand the cumulative effects of uncertainties. • Medical linear accelerator

14. QA of external beam radiation therapy equipment A. General • QA of radiation therapy equipment is primarily an ongoing evaluation of functional performance characteristics. • The function performance of radiotherapy equipment can change suddenly due to • Electronic malfunction • Component failure • Mechanical breakdown • Or can change slowly due to deterioration and aging of the component.

15. QA of external beam radiation therapy equipment A. General • Therefore, two essential requirement emerge: • QA measurements should be performed periodically on all therapy equipments, including the dosimetry and other QA measurement devices. • There should be regular preventive maintenance monitoring and correction of the performance of therapy machines and measurement equipment. • The overall responsibility for a machine QA program be assigned to one individual : the radiation oncology physicist.

16. QA of external beam radiation therapy equipment A. General • The QA program should be based on a thorough investigation for baseline standards at the time of the acceptance an commissioning of the equipment for clinical use. • Acceptance procedures should be followed to verify the manufacture’s specifications and to establish baseline performance values for new or refurbished equipment, or for equipment following major repair. • Once a baseline standard has be established, a protocol for periodic QA tests should be developed.

17. QA of external beam radiation therapy equipment A. General • Tests for a typical QA program. • Frequency of tests ( daily, weekly, and so on ) • Tolerance values. • Ensuring that the equipment is suitable for high quality and safe radiation treatment. • Machine QA test procedures should be able to distinguish parameter changes smaller than tolerance or action levels. • Within these limits, the tests should also be developed to minimize the test time.

18. QA of external beam radiation therapy equipment B. Test Frequency • Daily tests include those could seriously affect patient positioning and therefore the registration of the radiation field and target volume (lasers, ODI ); patient dose ( output constancy ) and safety ( door interlock and audiovisual contact ) • Monthly include those either have a smaller impact on the patient ( e.g., treatment couch indicators ) or have lower likelihood of changing over a month ( e.g., light and radiation field or beam flatness ).

19. QA of external beam radiation therapy equipment B. Test Frequency • AAPM recommend adherence to the program outlined in the tables unless there is demonstrable reason to modify them. • At this stage there is no accepted method of systematically defining the type and frequency of QA tests that should be performed. • The best guidance that can be given at present is that the QA program should be flexible enough to take into account quality, costs, equipment condition, and institutional needs.

20. QA of external beam radiation therapy equipment C. Guideline for Tolerance Values • The tolerance values are intended to make it possible to achieve an overall dosimetric uncertainty of ±5% and an overall spatial uncertainty of ±5mm. • The tolerances listed in the tables mean that if a parameter either exceeds the tabulated value ( e.g., the measured isocenter under gantry rotation exceeds 2 mm diameter ) or that the change in the parameter exceeds the tabulated value ( e.g., the output changes by more than 2% ), then an action is required.

21. QA of external beam radiation therapy equipment C. Guideline for Tolerance Values • It is important to realize that the tolerance levels presented in this document reflects standards of practice which have evolved in the practice of radiation oncology physics over the past decades, or even longer. These standards may, and probably will to be modified as newer techniques are introduced.

22. QA of external beam radiation therapy equipment Daily QA of medical accelerator • Dosimetry • X-ray output constancy 3% • Electron output constancy 3% • Mechanical • Localizing lasers 2 mm • Distance indicator ( ODI ) 2 mm • Safety • Door interlock Functional • Audiovisual monitor Functional

23. QA of external beam radiation therapy equipment Monthly QA of medical accelerator • Dosimetry • X-ray output constancy 2% • Electron output constancy 2% • X-ray central axis dosimetry parameter ( TPR) constancy 2% • Electron central axis dosimetry parameter ( PDD) constancy 2mm • X-ray beam flatness constancy 2% • Electron beam flatness constancy 3% • X-ray and electron symmetry 3%

24. QA of external beam radiation therapy equipment Monthly QA of medical accelerator • The beam uniformity and dose stability should be check at different angular positions of the gantry, since recent reports indicate that accelerator beam characteristics can vary with gantry position. • Beam scanners which mount directly on the treatment head of the machine are useful in measuring beam output and symmetry as a function of gantry angle. • Instruments for daily “spot checks” use arrays of ionization chambers or solid state detectors which can be perform multiple tests with one radiation exposure.

25. QA of external beam radiation therapy equipment Monthly QA of medical accelerator • Monthly output checks are performed by a physicist with an ionometric dosimetry system that is acceptable for calibration by an Accredited Dosimetry Calibration Laboratory. • For daily output checks, clinical action level = 5%. If exceeded, no further Tx. should be given. If the output difference is within 3% and 5%, then Tx. may continue and the radiation oncology physicist is notified. • It is essential that the physicist review these daily measurements and keep the output under surveillance.

26. QA of external beam radiation therapy equipment Monthly QA of medical accelerator • Field symmetry and flatness may be affected by both mechanical and electronic parameters. Small changes in beam energy, beam alignment, bending magnet function, target position, flattening filter selection and position, as well as other machine parameters, may result in unacceptable beam profile. • Field symmetry and flatness are both characteristics of a beam profile measures either in air or at some given depth in water.

27. QA of external beam radiation therapy equipment Monthly QA of medical accelerator • Flatness • Defined as the max. difference from the dose on the central axis over 80% of the field dimension ( length or width ). 80% of Field Width Ymax 100% Ymin Y0 ( Ymax-Y0 ) / Y0 100 % ( Ymin-Y0 ) / Y0 100 % Flatness = ± 50% Field Width

28. QA of external beam radiation therapy equipment Monthly QA of medical accelerator • Symmetry • Defined as the difference in dose rate between any two symmetric points within 80% of the field size ( length or width ). 80% of Field Width Y1 100% Y2 Y0 ( Y1-Y2 ) / Y0 100 % Symmetry = 50% Field Width

30. QA of external beam radiation therapy equipment Monthly QA of medical accelerator • Safety Interlocks • Emergency off switches Functional • Wedge, Electron cone interlocks Functional • Mechanical Checks • Light/Radiation field coincidence 2mm or 1% on a side • Gantry/Collimator angle indicator 1 deg • Wedge position 2 mm ( or 2% change in transmission factor ) • Tray position 2 mm • Applicator position 2 mm

31. Light/Radiation field coincidence Light and radiation fields coincident Light and radiation fields not coincident

32. QA of external beam radiation therapy equipment Monthly QA of medical accelerator • Mechanical Checks • Field size indicators 2mm • Cross-hair centering 2 mm diameter • Treatment couch position indicators 2 mm / 1 deg • Latching of Wedges, Blocking tray Functional • Jaw symmetry 2 mm • Field light intensity Function

33. QA of external beam radiation therapy equipment Monthly QA of medical accelerator • Cross-hair centering A Mid-point of line AB is a point on the collimator axis of rotation. A and B correspond to collimator angular positions 180 degrees apart. B

34. QA of external beam radiation therapy equipment Monthly QA of medical accelerator • Jaw symmetry

35. QA of external beam radiation therapy equipment Annual QA of medical accelerator • Dosimetry • X-ray/electron output calibration constancy 2% • Field size dependence of x-ray output constancy 2% • Output factor constancy for electron applicators 2% • Central axis parameter constancy ( PDD, TPR) 2% • Off-axis factor constancy 2% • Transmission factor constancy for all Tx.accessories 2% • Wedge transmission factor constancy 2% • Monitor chamber linearity 1% • X-ray output constancy vs gantry angle 2%

36. QA of external beam radiation therapy equipment Annual QA of medical accelerator • Dosimetry • Electron output constancy vs gantry angle 2% • Off-axis factor constancy vs gantry angle 2% • Arc mode Functional • Safety Interlock • Follow manufacturers test procedures Functional • Mechanical Checks • Collimator rotation isocenter 2 mm dia. • Gantry rotation isocenter 2 mm dia. • Couch rotation isocenter 2 mm dia. • Coincidence of collimator, gantry, 2 mm dia. couch axes with isicenter

37. QA of external beam radiation therapy equipment Annual QA of medical accelerator • Mechanical Checks • Coincidence of radiation and mechanical isocenter 2 mm • Table top sag 2 mm • Vertical travel of table 2 mm

38. QA of Newer Innovation on Medical Accelerators • Computer controlled and monitored operation ; motorized autowedge; dynamic wedge; multileaf collimators; record and verified systems; portal imaging devices; stereotactic radiosurgery; and intraoperative radiotherapy. • The guidelines of these systems that established by the manufacturers for safe operation should be strictly followed.

39. QA of Simulators • Subjected to the same mechanical checks as accelerators. • In addition, the simulator should be checked for image quality. • QA of CT Scanners • A flat top insert on the CT table to reproduce the radiation therapy treatment couch top. • A laser system mimicking that used in the simulation and treatment units should be mounted in the CT suite and the alignment of the lasers should be checked daily.

40. QA of CT Scanners • The correlation of CT numbers with electron densities and the variation of CT numbers with position and phantom size should be determined. This correlation should be checked yearly. • Image quality and other parameters described in the QA protocol provided by the manufacturer should be checked. • QA of Measurement Equipment • As important as that of the radiation treatment equipment and should be part of a QA program.

41. QA of Measurement Equipment • Redundancy in dose calibration equipment is recommended to assure that instruments are holding their calibration. • By comparing the response of the measurements equipment with an appropriate long-lived radioactive source ( Sr-90 ). • A two-system redundancy method provides better accuracy than one system with check source.

42. Documentation and Records of QA • This is very important that test procedures are well documented for all units under the QA program. • The results of initial baseline testing ( commissioning ) and future periodic testing be recorded and dated. • QA records must be kept on file for a minimum specified time ( typically 5 years, although sometimes longer ).

47. Treatment Planning Computer System • Commissioning and QA for external beam : • The calculation of relative dose distributions for relative machine, energy, and modality. • The summation of relative doses from different beams • The calculation of monitor units for a given prescribed dose. • Production of clear and accurate output data, including graphical isodose distributions. • Independent computer “MU” programs.

48. Treatment Planning Computer System • Concerns for Brachytherapy : • The dose distribution is correct for the source type in use. • The spatial reproduction of the implant is appropriate • Dose summations are calculated correctly. • A treatment planning system should be tested over a range of parameters which would be typical of those used in the clinic, and should be tested on a periodic basis.

49. Treatment Planning Computer System • Program Documentation • Beam Data Library • The manufacturer should provide clear documentation on the procedures for acquiring and transferring beam and other necessary data to the treatment planning system’s data library. • Users should acquire their own basic beam data sets • Dose Calculation Models • The documentation should describe the required dosimetric input data set and the expected accuracy of the dosimetric calculations for various conditions.

50. Treatment Planning Computer System • Program Documentation • Dose Calculation Models • Discuss the limitations of the dose calculation models. • Operating Instructions and Data I/O • Test Procedures • Initial Manufacturer’s Tests • Initial User Test Procedures • Commissioned for each treatment machine. Energy. Modality and for each isotope at the time of purchase of the software, annually, and every time a software upgrade is installed.