(USA TODAY) -- Changes in Medicare reimbursement may have led to more prostate cancer patients being surgically castrated instead of being treated with a less invasive alternative, a study shows.

Castration -- either through surgery or hormones that block the testosterone that feeds prostate tumors -- is a common treatment for certain types of prostate cancer. Research shows that both treatments have the same benefits for fighting cancer, as well as the same negative side effects on sexual function, says Otis Brawley, chief medical officer of the American Cancer Society.

Hormone therapy has been far more popular, however, with patients and doctors. The number of patients who got the injections rose sharply in the 1990s and early 2000s as the number of surgical castrations decreased. For doctors, giving the hormone injections also was profitable because the Medicare program reimbursed doctors well, Brawley says.

But doctors gave far fewer hormone injections after Medicare slashed what it paid them by half, according to a study released online today in the journal Cancer. From 2003 to 2005, the number of injections fell by 14% while the number of surgical castrations rose 4%, according to the study, which will appear in the May 15 print issue of the journal.

Author J. Stephen Jones of the Cleveland Clinic says financial pressures probably influenced that change. Although medical practice often changes, such shifts rarely occur so quickly, he notes in the study.

Brawley, who was not involved in the study, notes that urologists now may lose money by prescribing the shots, because Medicare payments don't always cover the cost of a nurse to administer the injections.

But he also notes that doctors have been reconsidering how they use hormones.

Howard Sandler, a cancer specialist at the University of Michigan who wasn't involved in the study, says the increase in surgical castrations -- 254 operations -- is small enough to be a random fluctuation from year to year.

Ethan Basch of New York's Memorial Sloan-Kettering Cancer Center says doctors have begun prescribing hormones intermittently instead of continuously. That could lead to a decrease in injections, even if the number of men getting the treatments didn't change much, says Basch, who also wasn't involved in the study.

Brawley notes that doctors also have become concerned about hormones' side effects. Around 2005, research began to suggest that suppressing testosterone contributes to problems such as osteoporosis.

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