Women treated with radiation for breast cancer are more likely to develop heart problems later, even with the lower doses used today, troubling new research suggests. The risk comes from any amount of radiation, starts five years after treatment and lasts for decades, doctors found.

Patients shouldn’t panic – radiation has improved cancer survival, and that is the top priority, doctors say. The chance of suffering a radiation-induced heart problem is fairly small.

For example, 4 to 5 of every 100 women who are 50 years old and free of heart risks will develop a major cardiac problem by age 80, and radiation treatment would add one more case, the research suggests. Women also can do a lot to cut their risk by keeping weight, cholesterol and blood pressure under control.