CT Quality Control Manual FAQs

Transcription

1 CT Quality Control Manual FAQs General Question: How often will the QC Manual be updated and how will those updates be communicated? Answer: The ACR CT Physics Subcommittee will review any comments, issues or concerns regarding the ACR CT QC Manual. Formal modifications to the manual will be made at the discretion of the CT Physics Subcommittee and will be made on an annual basis as needed. The new versions of the manual will be ed to all CT accredited facilities and to all who have purchased a copy from the ACR education catalog. If the issues need to be addressed before the routine update, an FAQ will be added to the website. Additional mechanisms are being explored so that changes are communicated to affected facility staff in a timely manner. Question: We have a dual source CT scanner, but the secondary tube is only used for dual energy imaging protocols, cardiac protocols and some other non-routine protocols. Does the secondary tube need to be evaluated during the annual system performance evaluation? Does the secondary tube need to be used for the accreditation testing? Answer: The primary and secondary tubes should both be evaluated in the annual system performance evaluations as the goal of the annual evaluations is to ensure that the scanner is functioning as designed in all respects and that it is being used optimally. However, the secondary tube is not typically used in the ACR Accreditation physics testing as it is not normally used for the diagnostic protocols (adult head, adult abdomen, pediatric head and pediatric abdomen) that are used for the accreditation testing. Important Points Radiologic Technologist Section I. Scanner Repairs Question: The ACR 2012 CT QC manual indicates that QC procedures should be performed at acceptance testing, during an ongoing QC program following parameter specific frequencies and following major repairs. What is a major repair and does the QC procedure need to be performed by the medical physicist on site and within what timeframe?

2 Answer: A major repair includes or repair of components such as an x-ray tube or detector assembly. The evaluation should be determined by the medical physicist based on the type of component repaired or replaced. A matrix of response is provided below for guidance for several major repairs or s: Item Major repair MP Response Time frame X-ray Tube CT service calibrations HV generator HV generator service calibration Control console Detector assembly Collimator adjustments Software upgrade ma/kv modulation install Maybe MP must discuss with vendor for effected parameters.

3 Protocol change N *MP oversight with Radiologist and Technologist Follow normal QC guidelines *MP oversight means that the medical physicist directs the site to follow established QC procedures and to share these results with the MP in order to determine that the equipment is functioning properly. The medical physicist does not need to conduct this on site. A. Water CT Number Standard Deviation (Noise) Question: Does the technologist daily water CT number and standard deviation QC have to be performed in both the helical and axial mode? Answer: It is recommended that this be performed in both the axial and helical scan mode and the QC manual suggests performing these scans on alternate days to speed up the process. This is a recommendation and not a requirement. Qualified Medical Physicist s Annual Quality Control Section E. Radiation Beam Width Question: Can the solid state CT probe provided by a manufacturer be used to measure the radiation beam width that is required in the Medical Physicist s Section of the CT QC Manual? Answer: As stated in the Manual, beam width may be measured in a number of different ways. The methodologies listed each have their strengths and weaknesses, and some are currently only appropriate for measurement in axial mode, while others are only designed for helical mode. Note that specific CT scanners may have beam widths that are only available in one mode or the other. Some manufacturers of probes designed for helical data acquisition are currently developing devices to move the probe through the beam during an axial scan. It is imperative to verify that these "probe movers" are properly calibrated to yield accurate results. The table below lists various measurement devices and the scan modes in which they can be used. Measurement Devices Axial Helical CR es No Film es No

4 OSL es No Small ion chamber Solid State probe Only with fully calibrated probe moving device* Only with fully calibrated probe moving device* es, when mounted to scanner table es, when mounted to scanner table * If probe moving device does not yield accurate velocity values, then beam width estimates will be off and will most likely differ from specifications and/or values obtained with other methods. F. Low Contrast Performance Question: There is a discrepancy between the 2012 CT QC manual low contrast performance CNR values and those stated in the CT Accreditation phantom instructions. Which ones are correct? Answer: As of July 1, 2013, the CNR values changed to 0.7 and 0.4 for the pediatric head and pediatric abdomen protocols. In addition, pediatric head and abdomen CTDIvol reference values and pass/fail criteria changed. These new values should be used for the accreditation testing immediately and used for the annual system performance evaluations effective December 1, The changes will be made in the CT QC Manual upon the next annual update. Scan protocol Pass/Fail Criteria CTDIvol (mgy) Reference Value CTDIvol (mgy) CNR Adult Head Pediatric Head Adult Abdomen Pediatric Abdomen H. CT Number Accuracy Question: Does annual CT number accuracy need to be evaluated for adult and pediatric head and abdomen protocols or just the adult abdomen protocol as for accreditation testing? Answer: At a minimum, the scans performed should include an adult head, adult abdomen, pediatric head and pediatric abdomen protocol unless the site does not scan any pediatric patients.

5 . Formal Updates since December 2012 release: Page 25: Item L. Monitors Used for Interpretation should be deleted. Quality control for monitors that are used for primary interpretation is not within the scope of this manual. Performance testing and monitoring of official or primary interpretation display devices should be performed in accordance with any relevant quality control manual recommendations from the ACR Accreditation Program, equipment manufacturer s specifications, applicable industry guidelines, and state and federal regulations. In the absence of adequate manufacturer s procedures, guidelines, or standards, you should follow recommendations for the performance evaluation and testing methods and frequencies of display devices from the American Association of Physicists in Medicine Task Group 18: Assessment of Display Performance for Medical Imaging Systems. Page 62: The Recommended Performance Criteria and Corrective Action should be revised as follows: "ou may use the manufacturer s specifications as the performance criteria. However, if these are not available, then the measured radiation beam width should be accurate to within 3 mm or 30% of the total nominal collimated beam width (N T), whichever is GREATER."