A worldwide shortage of radioactive isotopes used for medical procedures -- including heart tests and cancer treatments -- has affected some midstate hospitals.

Penn State Milton S. Hershey Medical Center has had to delay some procedures. PinnacleHealth, which operates Harrisburg Hospital, is carefully scheduling treatments to be sure it has enough materials for tests and treatments. Hershey and Pinnacle said most patients continue to receive tests and treatments as they normally would, although the shortage has posed problems in emergency cases.

Two nuclear reactors that produce about two-thirds of the world's isotope supply have been shut down for repairs. One reactor is in Canada, and the other is in the Netherlands.

Isotopes are injected into patients and the radiation they produce is recorded by cameras, which feed the information into a computer. An image is then produced of the organ or tissue in question.

A shortage of an isotope called molybdenum-99 is especially problematic for hospitals. The isotope decays into a substance called technetium that is most often used to scan for heart disease, but can also be used to detect cancers.

There are no nuclear reactors in the United States that produce molybdenum.

Some Hershey Medical Center patients can be scheduled for tests, but procedures for patients who need more radioactive materials are being delayed, said Dr. Douglas Eggli, vice chairman of radiology. In some cases, an older isotope, thallium, is used instead, Eggli said. The thallium allows the tests to be done on a vast majority of patients, he said.

Eggli said the biggest impact of the shortage has been felt after hours, in providing emergency services to patients. "In many cases, there are alternative tests that can be done," he said. "But for some patients, there are no alternatives. In those cases, physicians are having to rely on medical judgment rather than diagnostic testing."

He said situations like that represent "a very small number of our total patients," however, and that in most cases, the other diagnostic tests can be done. "Even though the shortage is severe, for us at Penn State Hershey, the clinical impact has been limited," he said.

PinnacleHealth also is being impacted. Karen Botts, director of imaging, and Dave Rheem, assistant supervisor for nuclear medicine, have been experiencing the shortage for about two months. It's affecting procedures such as bone scans, cardiac studies, nuclear stress tests and gastrointestinal studies, Rheem said. "We deal with several pharmacies in the area and as far as we know, everybody's been experiencing the same kind of shortage," she said.

The hospital system still can perform all the tests it's requested to do, Botts said, but has had to carefully plan treatment schedules.

"We know when we get the shipments of the isotope, and we've been trying to schedule these patients on the days we are relatively certain the isotopes are going to be available," Botts said. "If it's an emergent situation, we have been able to get doses if we need them, but no one is really sure how long that's going to continue."

Rheem said that the availability of technetium has improved because reactors in South Africa and Australia are increasing production. But they're still keeping a close eye on the treatment schedules.