The Hazards of Dose Escalation in Prostate Cancer Radiation
Reviewer: William Levin, MD
Last Modified: October 11, 2002
Presenter: D.A. Kuban
Presenter's Affiliation: Department of Radiation Oncology, UT MD Anderson Cancer Center, Houston, TX, USA
Type of Session: Scientific
- Numerous previous studies have suggested that there is a dose-response relationship with radiation therapy (RT) used in the treatment of prostate cancer.
- The current study analyzes the benefit of dose escalation, versus the increase in treatment-related morbidity.
Materials and Methods
- This is a retrospective study of 1087 patients who received definitive RT for treatment of adenocarcinoma of the prostate.
- No hormonal therapy was given unless the patient relapsed.
- Doses ranged from 64 Gy in earlier years, to 78 Gy more recently.
- Median follow-up was 65 months.
- PSA failure was by the ASTRO definition
- Pts were assigned to risk groups based on stage, grade, and PSA.
- A modified RTOG morbidity scale was used.
- Tumor stage, grade, and pre-treatment PSA (PT-PSA) were all predictive of PSA failure.
- The hazard ratio for PSA failure peaked at 1.5-2.5 years.
- For patients with PT-PSA of = 10ng/ml, there was a difference in disease-free survival between those patients treated with 64-66 Gy, versus those who received 68-70 Gy, with 8-y DFS of 64% vs. 81% (p<.0001)
- In pts with a PT-PSA >10, there was a significant benefit to increasing the total dose up to the 78 Gy level.
- Rectal morbidity was both dose and volume related.
- At 5 years, 24% of pts treated with 78 Gy developed grade ¾ rectal toxicity, vs. only 12% of pts. Who received 70 Gy.
- 75% of complications were grade 2 and had developed by 2 years after therapy.
- At 5 years post-RT, Grade 2/3 rectal morbidity was 13% for pts with < 26% of rectum irradiated to 70 Gy, vs. 54% for when larger amounts were irradiated.
- Bladder toxicity did not increase with dose.
- While dose escalation may be beneficial for intermediate and high-risk patients, in terms of DFS, these pts seem to pay a price in regards to toxicity.
- Advances in treatment planning techniques may aid in reducing this treatment-related morbidity.
- Follow-up is relatively short, so it is hard to draw strong conclusions regarding late-effects, and survival.
- But, this is a large retrospective study from a premiere cancer facility, so we can at least get a glimpse of what current benchmarks might be regarding the cost/benefit ratio in those pts. treated with increased radiation doses for localized prostate cancer.
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