Pathologic Evidence of Dose-Response and Dose-Volume Relationships for Prostate Cancer Treated with Combined External Beam Radiotherapy and High-Dose-Rate Brachytherapy

Reviewer: William Levin, MD
OncoLink
Last Modified: October 8, 2002

Presenter: L. Kestin
Presenter's Affiliation: Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI, USA
Type of Session: Scientific

Background

There has been a long-running debate as to if prostate biopsies should be obtained following radiation therapy.
In this study, investigators performed a detailed pathologic review of post-irradiation prostate biopsies. They then attempted to correlate these findings with radiation dose and clinical outcome.

Materials and Methods

78 patients with locally advanced prostate cancer were prospectively treated with external beam radiation therapy (EBRT) in combination with high dose rate brachytherapy (HDRB) and had post-radiation biopsies available for review.
EBRT (46 Gy) was followed by either 2 or 3 iridium-192 HDR implants.
HDRB dose was escalated from 5.50 to 10.50 Gy per implant.
Post-irradiation biopsies were obtained at a median interval of 1.5 years after completion of treatment.
All pre- and post-irradiation biopsies were reviewed by a single pathologist.
Median follow-up was 5.7 years.
The ASTRO definition for PSA failure was used.

Results

40 patients(51%) had residual tumor in post-radiation biopsies.
7-year biochemical control(BC) was 79% for patients with negative biopsies, versus 33% for positive biopsies.
By regression analysis, biochemical failure was associated with a higher percentage of positive pre-irradiation biopsies, lower radiation dose, lower dose per implant, and a higher percentage of positive post-irradiation biopsies.
For patients with less than 25% pre-RT biopsies, positive 7-y BC was 81%, versus 32% for those with 50% or more positive biopsies (p=0.01)
Only pre-treatment cancer volume and lower RT dose were significantly associated with residual cancer.
For patients who received less than 80 Gy, 73% had positive post-RT biopsies, versus a 56% positve biopsy rate for 84-90 Gy, and only 39% for those who received 92 Gy or greater.

Author's Conclusions

Patients with positive-post RT biopsies are more likely to experience biochemical failure.
Patients with greater tumor volume, or those who receive a lower RT dose are more likely to have positive post-treatment biopsies and to experience biochemical failure.

Clinical/Scientific Implications

This study shows a correlation between a pathologic finding and the clinical course of disease.
It also shows that patients with a high volume of disease are at high risk for biochemical failure, even with high total radiation doses. Thus, other treatment stratagies should be investigated for these patients.
One issue that was not addressed by this study is the optimal timing for post-irradiation biopsy.

Oncolink's ASTRO Coverage made possible by an unrestricted Educational Grant from Ortho Biotech.