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FRIDAY, Aug. 29 (HealthDayNews) -- American and German researchers say they've developed a new way to treat certain kinds of cancer more effectively.

They've developed a radio-isotope that emits far more high-energy radioactivity than current radio-isotopes used to treat bone metastases that are formed when tumor cells invade bone marrow. For many years, doctors have used radio-isotopes to control bone pain in people with bone metastases.

The radio-isotopes ease pain by accumulating in the area of the tumors. But the radioactivity of standard radio-isotopes currently used in this treatment doesn't have enough energy to slow down or destroy tumors.

In this study, the researchers say they've developed a radio-isotope that emits higher energy radioactivity by combining radioactive rhenium-188 with a diphosphanate. While the substance emits high-energy beta radiation in its immediate vicinity, its energy drops to near harmless levels in areas just a few millimeters away.

Bone metastases act like a magnet to this kind of radioactive phosphorous compound, which collects near the cancer cells and damages or destroys them.

This study included 64 patients with cancer of the prostate and bone metastases who no longer responded to standard hormone therapy. The patients were divided into two groups. Some received one injection of the new radio-isotope medication, while others received two injections at an interval of eight weeks.

There were particularly promising results in the second group, where levels of the tumor marker PSA declined by more than half in 39 percent of the study subjects. The lower PSA levels continued for at least eight weeks.

PSA is a protein substance produced by tumor cells. The more tumor tissue, the higher the PSA levels in the blood.

The study also found that, after one injection, cancer came to a standstill for an average of 2.3 months. After more than one injection, this increased to seven months. The survival rate of patients who received more than one injection increased from seven to 13 months.

The findings appear in the August issue of the Journal of Clinical Oncology.

A follow-up study is planned to investigate whether three or four injections yield even better results.

More information

Here's where you can learn more about treatment of bone metastases.