Thousands of elderly women with severe dementia are receiving mammograms, despite recommendations that this group should not be subject to this medical procedure, according to a recent study.

Current guidelines from the American Cancer Society and other groups recommend not performing mammograms on persons with a life expectancy of less than five years. The average lifespan for elderly women with severe dementia is 3.3 years, according to the study from the University of California, San Francisco. Still, in reviewing Medicare claims for more than 2,100 women aged 70 and older, researchers found 18% with severe dementia received the exam. That translates to roughly 120,000 unnecessary mammograms per year, according to the report, with a price tag exceeding $12 million.

The ACS guidelines suggest that any cancerous cells found in an elderly woman with severe dementia would likely not grow fast enough to affect her life expectancy. The potential harms of the procedure—such as diverting time and resources away from therapies that could actually improve quality of life—outweigh the benefits, according to report authors. The study appears in the Jan. 14 edition of the American Journal of Public Health.