Improving Health Through Medical Physics

AAPM Newsletter — Volume 42 No.2 — March | April 2017


Picture of Tyler Fisher
Practical Advice for Implementing the Changes to the ACR CT Accreditation Program

Within the past few months, the ACR CT Accreditation program has been updated with a few minor, but important changes. The changes were made to raise awareness and understanding of Size-Specific Dose Estimates (SSDE) and give flexibility to the medical physicist with respect to pediatric abdomen CTDI, as well as align with the IEC standard. The ACR notified all accredited facilities with an email on December 12 and released the new standards the same week. The changes include an option to measure pediatric abdomen CTDIvol using the phantom reported by the scanner, Pass/Fail criteria when using the 32 cm phantom for the pediatric abdomen, the inclusion of scanner reported CTDIvol data with a calculation of the percent difference between measured and reported CTDIvol, a place to report the Dose Notification value from XR-29, and a calculation of the SSDE for the adult abdomen and pediatric abdomen.

The option to measure the pediatric abdomen CTDIvol using the 32 cm phantom allows for a direct comparison of scanner reported to measured CTDIvol for scanners that report pediatric CTDIvol using the 32 cm phantom. The new Reference Value and Pass/Fail criteria for the pediatric abdomen, when measured on the 32 cm phantom, is 7.5 mGy and 10 mGy, respectively. When scanning the 32 cm phantom using a pediatric abdomen protocol, it is important to keep the Scan FOV the same as it is in the clinical protocol, which may be smaller than 32 cm. This will keep the appropriate filter in place, rather than switching out to a filter used for a larger body scan field of view. ACR reviewers will expect to see these CTDI phantom images with the phantom beyond the field of view under these circumstances. A drop down field titled "Size of phantom the scanner uses to report CTDIvol for routine pediatric abdomen protocol (40-50 lb)" must be filled in on the online Pediatric Abdomen CTDI dose calculator spreadsheet. It is important to note that this field must match the size of the CTDI phantom being submitted. If the medical physicist scanned the CTDI images for submission prior to the implementation of these changes, and the CT scanner reports the pediatric abdomen CTDIvol using the 32 cm CTDI phantom, the images do not need to be rescanned with the 32 cm CTDI phantom. The 16 cm CTDI phantom can be submitted and 16 cm should be selected in the drop down field for the pediatric abdomen.

The inclusion of scanner reported CTDIvol and the calculation of the percent difference between measured and scanner reported CTDIvol is in line with what has been done in a majority of CT physics reports as recommended by the ACR CT QC Manual and in order to meet Joint Commission standards. The Joint Commission requires that reported CTDIvol be within 20% of measured CTDIvol. Although the ACR CT QC manual indicates that the scanner reported CTDIvol should be within 20% of the measured, it will not contribute to deficiencies for accreditation submissions if the scanner does not meet this criteria. The ACR provided CTDI dose calculator spreadsheet and the ACRedit website CTDI dose calculator spreadsheet automatically calculate the percent difference. The use of the ACR provided forms is highly recommended as they match the data that must be reported on the ACRedit website for accreditation submission. The scanner reported CTDIvol is an optional field and is not required to be completed if the scanner does not report it.

Another additional field within the ACR provided forms is for the Dose Notification Value (mGy) as described in XR-29. This is an optional field, meaning that the ACR does not require this field to be filled in. This data is currently being used for informational purposes only. However, many of the CT systems across the country do not have these Dose Notification Values configured. The most helpful resource available at this time is the AAPM CT Protocols page under the dose check tab. The AAPM provides recommended values as well as manufacturer specific information on how to configure the Dose Notification Values. The recommended Dose Notification Values will help facilities to meet Joint Commission standards and can be easily implemented by most facilities. Note that XR-29 compliance is not a requirement for ACR CT accreditation.

The inclusion of a field for SSDE for abdomen scans in the ACR provided dose calculator spreadsheets as well as in the ACRedit website dose calculator forms will help to establish SSDE as a corollary to CTDIvol and provide comparison data for pediatric abdomen scans performed with the 16 cm or 32 cm CTDI phantoms. These data fields, again, are optional and will not contribute to deficiencies for accreditation submissions if they are not included. For details regarding SSDE, refer to AAPM Reports No. 204 and No. 220.

A few changes also occurred to the ACRedit website. The "Available Slice Thicknesses" section of the Phantom Site Scanning Data form has been removed. This information is no longer required to be submitted. Additionally, it is important to note that the ACRedit website forms have reversed the order of T (z-axis collimation) & N (number of data channels used) into the way we normally think of them as N & T. Speaking from experience, I had to change a lot of links within my forms to accommodate this change, but once done, it makes the reports easier for inspectors and technologists to follow.

For anyone who would like more information on the changes to the program, the ACR website has very helpful FAQ's. The CT Accreditation Program Requirements, CT Accreditation Program Testing Instructions, and CTAP Phantom Data/Dose Forms links have been updated to include the changes. While the CT Quality Control manual is not available directly from the website, all accredited facilities have free access to this document.

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