Conference Coverage

Abbreviated MRI equals standard protocol for high-risk breast cancer screens


 

REPORTING FROM RSNA 2019

– An abbreviated magnetic resonance imaging (MRI) protocol for screening individuals at high risk for breast cancer performed as well as a standard protocol, in about half the time and with greater patient satisfaction.

The abbreviated protocol also resulted in fewer false positive findings, with 5% fewer patients receiving biopsies for benign lesions than with a standard protocol (8.4% versus 13.7%, P less than .001).

Findings from the prospective 10-month trial conducted in the province of Ontario were presented by Jean Seely, MD, professor of radiology at the University of Ottawa, at the annual meeting of the Radiological Society of North America.

“The abbreviated protocol was shown to be as effective as the standard protocol in high-risk screening breast MRI, supporting previous studies,” said Dr. Seely. The shorter protocol took 16.3 minutes on average, compared with 27 minutes for the standard MRI protocol. This difference resulted in a 50% increase in institutional capacity, or a jump from two to three patients screened per hour.

In the province of Ontario, said Dr. Seely, women assessed at being at a 25% or greater lifetime risk of breast cancer receive MRIs as part of the Ontario Breast Screening Program (OBSP), which calculates risk by using the International Breast Cancer Intervention Study model.

For high-risk patients, the OBSP model provides annual mammography and an MRI for women between the ages of 30 and 60 years. Not only is the half-hour duration of the standard protocol resource-intensive, especially in regions with limited scanner availability, but patients may either be reluctant to undergo a half-hour scan, or not tolerate a lengthy scan very well.

Dr. Seely cited previous work (J Clin Oncol. 2014 Aug 1;32[22]:2304-10) showing that an abbreviated MRI protocol has similar accuracy as the full standard protocol. With the foundation of evidence from this study, Dr. Seely and her collaborators compared outcomes for high-risk patients who were screened with an abbreviated versus a standard protocol.

The abbreviated protocol, approved by the American College of Radiology, omits a final round of image acquisition sequences at the 9-minute mark after gadolinium administration, instead performing acquisition at 1, 2, 3, and 4 minutes after contrast delivery. Total time required for this protocol is just over 13 minutes, said Dr. Seely, and additional diagnostic MRIs were not required.

The trial was constructed so that the abbreviated protocol was used for the entire OBSP cohort for 10 months in 2018. Results were compared with those from the 12 previous months, when OBSP patients’ MRIs were performed using the standard protocol.

A total of 881 patients received standard-protocol MRIs; about three quarters (651) of those patients had previous MRI screening, while the remaining 230 patients had a baseline screen via the standard protocol.

Of the 658 patients in the abbreviated protocol group, 135, or about 20%, received the briefer scans as a baseline screen; the remast of the patients in this arm had received earlier MRI screening.

In addition to tracking scanning times, Dr. Seely and her collaborators also compared cancer detection rates, Breast Imaging Reporting and Data System (BI-RADS) assessment categories, positive predictive values, and the abnormal interpretation rate – that is, how many scans fell into BI-RADS categories 0, 4, and 5.

No significant difference was found between the rates of BI-RADs 0, 3, or 5 studies between the groups. Significantly fewer abbreviated scans fell into the BI-RADS 4 category, however (9.3% vs. 14.9%; P less than .001).

Similarly, the abnormal interpretation rate was 12.5% for the abbreviated protocol, compared with 17.5% for the standard protocol (P less than .007), with a correspondingly lower biopsy rate of 8.4% for the abbreviated protocol, compared with 13.7% for the standard protocol (P less than .001). The overall cancer detection rate did not differ between groups.

The net effect of the abbreviated protocol, said Dr. Seely, was an increase in positive predictive value without a drop in cancer detection rates. She and her colleagues will continue to track outcomes for those receiving abbreviated screening within the province of Ontario to track performance over time.

Dr. Seely reported that she had no relevant conflicts of interest. She reported no funding source beyond the province of Ontario.

SOURCE: Seely J et al. RSNA 2019, Session RC-215-04.

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