title: Alpha/beta (α/β) ratio for prostate cancer derived from external beam radiotherapy and brachytherapy boost.
abstract: OBJECTIVE
  There is disagreement regarding the value of the α/β ratio for prostate cancer. Androgen deprivation therapy (ADT) may dominate the effects of dose fractionation on prostate-specific antigen (PSA) response and confound estimates of the α/β ratio. We estimate this ratio from combined data on external beam radiation therapy (EBRT) and brachytherapy (BT)-treated patients, providing a range of doses per fraction, while accounting for the effects of ADT.
  
  
  METHODS
  We analyse data on 289 patients with local prostate cancer treated with EBRT (2 Gy per fraction) or EBRT plus one or two BT boosts of 10 Gy each. The timing of ADT was heterogeneous. We develop statistical models to estimate the α/β ratio based upon PSA measurements at 1 year as a surrogate for the surviving fraction of cancer cells as well as combined biochemical + clinical recurrence-free survival (bcRFS), controlling for ADT.
  
  
  RESULTS
  For the PSA-based end point, the α/β ratio estimate is 7.7 Gy [95% confidence interval (CI): 4.1 to 12.5]. Based on the bcRFS end point, the estimate is 18.0 Gy (95% CI: 8.2 to ∞).
  
  
  CONCLUSIONS
  Our model-based estimates of the α/β ratio, which account for the effects of ADT and other important confounders, are higher than some previous estimates.
  
  
  CONCLUSIONS
  Although dose inhomogeneities and other limitations may limit the scope of our findings, the data suggest caution regarding the assumptions of the α/β ratio for prostate cancer in some clinical environments.
authors.affiliation: 1 Department of Biostatistics, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Philip S
authors.initials: PS
authors.lastname: Boonstra
authors.affiliation: 1 Department of Biostatistics, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Jeremy M G
authors.initials: JM
authors.lastname: Taylor
authors.affiliation: 2 Radiotherapy Clinic and Teaching Hospital, M. Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Gliwice Branch, Poland.
authors.forename: Beata
authors.initials: B
authors.lastname: Smolska-Ciszewska
authors.affiliation: 2 Radiotherapy Clinic and Teaching Hospital, M. Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Gliwice Branch, Poland.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Behrendt
authors.affiliation: 2 Radiotherapy Clinic and Teaching Hospital, M. Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Gliwice Branch, Poland.
authors.forename: Tomasz
authors.initials: T
authors.lastname: Dworzecki
authors.affiliation: 2 Radiotherapy Clinic and Teaching Hospital, M. Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Gliwice Branch, Poland.
authors.forename: Marzena
authors.initials: M
authors.lastname: Gawkowska-Suwinska
authors.affiliation: 3 Department of Brachytherapy, M. Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Gliwice Branch, Poland.
authors.forename: Brygida
authors.initials: B
authors.lastname: Bialas
authors.affiliation: 2 Radiotherapy Clinic and Teaching Hospital, M. Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Gliwice Branch, Poland.
authors.forename: Rafal
authors.initials: R
authors.lastname: Suwinski
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000726:Androgen Antagonists / Q000008:administration & dosage; D001918:Brachytherapy; D003131:Combined Modality Therapy; D019583:Dose Fractionation, Radiation; D006801:Humans; D008297:Male; D008875:Middle Aged; D017430:Prostate-Specific Antigen / Q000097:blood; D011471:Prostatic Neoplasms / Q000097:blood / Q000532:radiotherapy*; D020266:Radiotherapy, Conformal; D012189:Retrospective Studies
chemical_list: D000726:Androgen Antagonists; D017430:Prostate-Specific Antigen