title: Moderately low alpha/beta ratio for rectal cancer may best explain the outcome of three fractionation schedules of preoperative radiotherapy.
abstract: OBJECTIVE
  To estimate the alpha/beta ratio for rectal cancer according to the outcome of three fractionation schedules of preoperative radiotherapy.
  
  
  METHODS
  Between 1996 and 2002, 168 patients with locally advanced rectal cancer were treated as follows: 53 patients received 25 Gy in 5 Gy per fraction, 45 received 30 Gy in 3.0 Gy per fraction, and 70 were treated with accelerated hyperfractionation (42 Gy, 1.5 Gy per fraction, given twice daily). No patients received concurrent chemotherapy. The clinical characteristics of the groups were comparable. Surgery was performed shortly after radiotherapy. Crude data on locoregional tumor control were fitted directly using a linear-quadratic model, and the actuarial data were analyzed using Cox model.
  
  
  RESULTS
  A linear-quadratic model provided an alpha estimate of 0.339 (SE 0.115) and beta estimate of 0.067 (SE 0.027), which resulted in an alpha/beta ratio of 5.06 Gy (95% confidence interval -0.1 to 10.3). In all three schemes the overall radiation treatment time was short, which limits the rationales for incorporating time effect into the model. If, however, time was incorporated the alpha/beta ratio was 11.1 Gy and the dose increment required to compensate for repopulation was 0.15 Gy/day. The actuarial analysis provided similar alpha/beta estimates.
  
  
  CONCLUSIONS
  Although because of the retrospective character of the study, nonrandomized selection of fractionation schedule, and uncontrolled quality of surgery the present results can be regarded as hypothesis generating only, the control rates obtained in the pelvis are consistent with a moderately low alpha/beta ratio for rectal cancer.
authors.affiliation: Department of Radiation Oncology, Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Gliwice Branch, Gliwice, Poland. rafals@io.gliwice.pl
authors.forename: Rafal
authors.initials: R
authors.lastname: Suwinski
authors.forename: Iwona
authors.initials: I
authors.lastname: Wzietek
authors.forename: Rafal
authors.initials: R
authors.lastname: Tarnawski
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Namysl-Kaletka
authors.forename: Mariusz
authors.initials: M
authors.lastname: Kryj
authors.forename: Andrzej
authors.initials: A
authors.lastname: Chmielarz
authors.forename: Jerzy
authors.initials: J
authors.lastname: Wydmanski
mesh_terms: D000230:Adenocarcinoma / Q000532:radiotherapy* / Q000601:surgery; D000328:Adult; D000368:Aged; D000465:Algorithms; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D011853:Radiobiology; D018714:Radiotherapy, Adjuvant; D012004:Rectal Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D012189:Retrospective Studies