title: Modeling of alpha/beta for late rectal toxicity from a randomized phase II study: conventional versus hypofractionated scheme for localized prostate cancer.
abstract: BACKGROUND
  Recently, the use of hypo-fractionated treatment schemes for the prostate cancer has been encouraged due to the fact that alpha/beta ratio for prostate cancer should be low. However a major concern on the use of hypofractionation is the late rectal toxicity, it is important to be able to predict the risk of toxicity for alternative treatment schemes, with the best accuracy. The main purpose of this study is to evaluate the response of rectum wall to changes in fractionation and to quantify the alpha/beta ratio for late rectal toxicity
  
  
  METHODS
  162 patients with localized prostate cancer, treated with conformal radiotherapy, were enrolled in a phase II randomized trial. The patients were randomly assigned to 80 Gy in 40 fractions over 8 weeks (arm A) or 62 Gy in 20 fractions over 5 weeks (arm B). The median follow-up was 30 months. The late rectal toxicity was evaluated using the Radiation Therapy Oncology Group (RTOG) scale. It was assumed >or= Grade 2 (G2) toxicity incidence as primary end point. Fit of toxicity incidence by the Lyman-Burman-Kutcher (LKB) model was performed.
  
  
  RESULTS
  The crude incidence of late rectal toxicity >or= G2 was 14% and 12% for the standard arm and the hypofractionated arm, respectively. The crude incidence of late rectal toxicity >or= G2 was 14.0% and 12.3% for the arm A and B, respectively. For the arm A, volumes receiving >or= 50 Gy (V50) and 70 Gy (V70) were 38.3 +/- 7.5% and 23.4 +/- 5.5%; for arm B, V38 and V54 were 40.9 +/- 6.8% and 24.5 +/- 4.4%. An alpha/beta ratio for late rectal toxicity very close to 3 Gy was found.
  
  
  CONCLUSIONS
  The >or= G2 late toxicities in both arms were comparable, indicating the feasibility of hypofractionated regimes in prostate cancer. An alpha/beta ratio for late rectal toxicity very close to 3 Gy was found.
authors.affiliation: Laboratorio di Fisica Medica e Sistemi Esperti, Istituto Regina Elena, Rome, Italy. marzi@ifo.it
authors.forename: Simona
authors.initials: S
authors.lastname: Marzi
authors.forename: Biancamaria
authors.initials: B
authors.lastname: Saracino
authors.forename: Maria G
authors.initials: MG
authors.lastname: Petrongari
authors.forename: Stefano
authors.initials: S
authors.lastname: Arcangeli
authors.forename: Sara
authors.initials: S
authors.lastname: Gomellini
authors.forename: Giorgio
authors.initials: G
authors.lastname: Arcangeli
authors.forename: Marcello
authors.initials: M
authors.lastname: Benassi
authors.forename: Valeria
authors.initials: V
authors.lastname: Landoni
mesh_terms: D000368:Aged; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000009:adverse effects; D012007:Rectum / Q000473:pathology / Q000528:radiation effects*
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