Seeds, conformal proton beam treatment show similar results

July 1, 2005

Orlando, FL--In men with early-stage prostate cancer, permanent prostate seed implantation (PPI) appears to be as effective as high-dose conformal proton beam radiotherapy (CPBRT) in terms of biochemical control and reduction of PSA levels, according to findings from a new study.

The results may reassure patients that brachytherapy is a good treatment choice, according to the authors, from the University of California, San Francisco, Comprehensive Cancer Center. The findings were presented at the 2005 American Society of Clinical Oncology annual meeting here.

The UCSF group, led by Mack Roach, III, MD, retrospectively compared outcomes between men with early-stage prostate cancer treated with high-dose (79 GyE) conformal beam radiotherapy (196 patients) or permanent seed implants (218 patients). Among those receiving seeds, 28% also received short-term neoadjuvant hormonal therapy, 12% received external beam radiotherapy, and 14% received both.

The study found that patients treated with seed implants achieved lower PSA nadirs after treatment than those treated with conformal beam radiotherapy, with 89% of seed implant patients achieving a nadir PSA <0.5 ng/mL, compared with 50% of conformal beam patients, reported Dr. Roach, professor of radiation oncology and urology at UCSF.

Biochemical control similar Because of the retrospective nature of this study, no formal statistical comparison was performed between these groups. Of note, however, the estimated 5-year biochemical control among patients treated by seed implants and those undergoing conformal beam radiotherapy were 96% and 81%, respectively, at a median follow-up of 63 months and 48 months. For the permanent seed patients who also received neoadjuvant hormones, the 5-year biochemical control rose to 98%, compared with 94% in those who did not receive neoadjuvant hormones.

"Patients do really well with permanent seeds, both in terms of biochemical control and effect on PSA," said Vivian Weinberg, PhD, a biostatistician at USC. "They do at least as well with PPI as with CPBRT."

The authors suggest that the more dramatic reductions in PSA and high biochemical control at 5 years in the seed implant group may be due to the substantially higher doses given to these patients. When given alone, the minimum irradiation dose was 144 Gy in seed implant therapy, with nearly half of the prostate receiving a dose of more than 200 Gy. In patients who also received external beam therapy, a total dose of more than 145 Gy was used. In contrast, the total dose of radiation delivered by conformal beam radiotherapy was 79 Gy.

Given the cost and limited availability of conformal beam therapy, the results suggest that permanent seed implantation remains the better treatment option for early stage prostate cancer, according to the researchers.

"PPI is readily available around the country and is relatively inexpensive, but a proton machine costs more than $100 million and is only available in a handful of places," Dr. Roach said.