Confirmation of a Low {alpha}/{beta} Ratio for Prostate Cancer Treated by External Beam Radiation Therapy Alone Using a Post-Treatment Repeated-Measures Model for PSA Dynamics
Journal Article
·
· International Journal of Radiation Oncology, Biology and Physics
- INSERM, U897, Epidemiology and Biostatistics Research Center, Bordeaux (France)
- Department of Biostatistics, University of Michigan, Ann Arbor, MI (United States)
- Department of Radiation Oncology, Cedars-Sinai Medical Center, Los Angeles, CA (United States)
- Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI (United States)
- British Columbia Cancer Agency, Vancouver, British Columbia (Canada)
- Radiation Therapy Oncology Group, Philadelphia, PA (United States)
- Division of Oncology, Royal Brisbane and Women's Hospital, Brisbane (Australia)
- Division of Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne (Australia)
Purpose: To estimate the {alpha}/{beta} ratio of prostate cancer treated with external beam radiation only by use of a model of long-term prostate-specific antigen (PSA) dynamics. Methods and Materials: Repeated measures of PSA from 5,093 patients from 6 institutions treated for localized prostate cancer by external beam radiation therapy (EBRT) without planned androgen deprivation were analyzed. A biphasic linear mixed model described the post-treatment evolution of PSA, rather than a conventional model of time to biochemical recurrence. The model was adjusted for standard prognostic factors (T stage, initial PSA level, and Gleason score) and cohort-specific effects. The radiation dose fractionation effect was estimated from the long-term rate of rise of PSA level. Results: Adjusted for other factors, total dose of EBRT and sum of squared doses per fraction were associated with long-term rate of change of PSA level (p = 0.0017 and p = 0.0003, respectively), an increase of each being associated with a lower rate of rise. The {alpha}/{beta} ratio was estimated at 1.55 Gy (95% confidence band, 0.46-4.52 Gy). This estimate was robust to adjustment of the linear mixed model. Conclusions: By analysis of a large EBRT-only cohort along with a method that uses all the repeated measures of PSA after the end of treatment, a low and precise {alpha}/{beta} was estimated. These data support the use of hypofractionation at fractional doses up to 2.8 Gy but cannot presently be assumed to accurately represent higher doses per fraction.
- OSTI ID:
- 21491554
- Journal Information:
- International Journal of Radiation Oncology, Biology and Physics, Journal Name: International Journal of Radiation Oncology, Biology and Physics Journal Issue: 1 Vol. 79; ISSN IOBPD3; ISSN 0360-3016
- Country of Publication:
- United States
- Language:
- English
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