BOSTON, MA – Patients with clinically localized prostate cancer have a better chance of beating the disease with higher doses of radiation, which can be safely and precisely delivered to the tumor with few side effects using three-dimensional conformal radiation therapy. While dose escalation has been shown to improve patient prognosis across all disease stages and risk groups, doctors at Memorial Sloan-Kettering Cancer Center have been able to substantiate the success of the treatment using biopsy results.
In a biopsy, several needles are inserted into the prostate to withdraw cells, which are then examined under a microscope. According to preliminary findings from a study being presented at the American Society for Therapeutic Radiology and Oncology (ASTRO) meeting in Boston this week, prostate cancer patients who received higher doses of radiation therapy were more likely to have a negative biopsy, indicating the disease had been controlled or cured. Tumors that received lower doses of radiation were less likely to be eliminated.
The lower doses delivered in the study were the standard prescription for radiation therapy when it began in 1989. As three-dimensional technology proved to be the most precise method to deliver radiation, doctors slowly escalated the dose levels when appropriate. This study used biopsy as a barometer to determine whether dose escalation eliminated the disease in the prostate three years after treatment.
Doctors have traditionally monitored levels of Prostate Specific Antigen (PSA) to test the effectiveness of radiation therapy after prostate cancer patients have completed treatment. However, a rise in a patient’s PSA level does not always reveal whether the cancer-cell activity detected is in the prostate or somewhere else in the body. "Biopsy provides very accurate information about local disease specifically in the prostate gland, whereas PSA level gives a more general picture," said Michael Zelefsky, MD, a radiation oncologist with expertise in the treatment of prostate cancer at Memorial Sloan-Kettering Cancer Center and lead author of the study.
The research found that lower radiation dose was the strongest predictor of a positive biopsy, indicating the prostate cancer had not been eliminated. The findings also suggest that higher radiation dose was critical in eradicating the disease, even among patients with aggressive prostate cancers – those patients with high Gleason scores in whom cancer cells are more resistant to radiation and more likely to spread to other areas of the body. In the study, which was conducted between 1989 and 1998, 1,100 patients were treated with varying doses of three-dimensional conformal radiation therapy for clinically localized cancer that had not spread beyond the prostate. Three years after treatment, 63 percent of eligible patients received a prostate biopsy. The incidence of positive biopsy was 54 percent among patients who had the lowest radiation dose in the study, compared with only 10 percent among those who had the highest dose. Overall, the vast majority of patients whose biopsy indicated their cancer was controlled or cured were cancer-free and had normal PSA levels five years after treatment.
"The improved biopsy and PSA results support the effectiveness of higher doses of radiation therapy, which translates into a better chance of eliminating the disease in the prostate," said Steven Leibel, MD, chairman of Radiation Oncology at Memorial Sloan-Kettering and senior author of the study.
The use of hormone therapy with radiation treatment was also shown to be a strong predictor of biopsy outcome. Of the 252 patients evaluated in the study, 33 percent were treated with three months of hormone therapy to shrink the size of the tumor prior to radiation treatment. The findings show that patients who were treated with hormone therapy and three-dimensional conformal radiation therapy were less likely to have a positive biopsy compared to patients treated with radiation therapy alone.
According to the American Cancer Society, 179,000 men in the US will be diagnosed with prostate cancer this year, and 37,000 will die of the disease. It is the second leading cause of cancer deaths (after lung cancer) among American men.
Memorial Sloan-Kettering Cancer Center is the world’s oldest and largest private institution devoted to prevention, patient care, research, and education in cancer. Throughout its long and distinguished history, the Center has played a leadership role in defining the standard of care for patients with cancer.