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