title: Does the dose fractionation schedule influence local control of adjuvant radiotherapy for early stage breast cancer?
abstract: OBJECTIVE
  To explore the correlation between dose fractionation and local control for the adjuvant radiotherapy of early stage breast cancer.
  
  
  METHODS
  A matched-pair analysis of early stage invasive breast cancer treated adjuvantly with two different dose fractionation schedules, 4000 cGy in 16 fractions (Cohort A) vs. 5000 cGy in 25 fractions (Cohort B) was undertaken to compare local control rates. A systematic review of the published experience in similar patient populations was conducted and the reported dose fractionation schedule was converted to a biologic effect dose (BED) based upon the linear quadratic equation. The BED was then used as a basis for comparing reported local control rates with different dose fractionation schemes.
  
  
  RESULTS
  The 118 patient pairs were matched from Cohort A and Cohort B using known significant prognostic factors including age, histology, surgical margins, receptor status, lymphvascular space invasion, extensive intraductal disease, lymph node status, and systemic therapy. The local recurrence rate at 5 years for those treated with 4000 cGy (BED = 65 cGy4) and 5000 cGy (BED = 75 cGy4) was 12.7% and 6.8%, respectively, and this difference was not statistically significant (p = 0.09). Overall survival was 84% at 5 years for both groups. Comparison of the different dose fractionation schemes reported in the literature revealed a highly statistically significant difference between those treated with less than a BED of 75 Cy4 and those treated with a BED of 75 Gy4 or greater.
  
  
  CONCLUSIONS
  Although not statistically significant, there was a trend in the matched pair analysis which suggests that 4000 cGy in 16 fractions (BED = 65 cGy4) provides inferior local control compared to 5000 cGy in 25 fractions (BED = 75 cGy4). Moreover, the literature review demonstrates that a dose control relationship may exist for local control in the adjuvant setting. A dose fractionation schedule equivalent to 5000 cGy in 25 fractions to the whole breast may represent the optimal dose fractionation schedule for local control.
authors.affiliation: Department of Radiation Oncology, Toronto-Sunnybrook Regional Cancer Centre, University of Toronto, Ontario, Canada.
authors.forename: Y
authors.initials: Y
authors.lastname: Yamada
authors.forename: I
authors.initials: I
authors.lastname: Ackerman
authors.forename: E
authors.initials: E
authors.lastname: Franssen
authors.forename: R G
authors.initials: RG
authors.lastname: MacKenzie
authors.forename: G
authors.initials: G
authors.lastname: Thomas
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D016555:Matched-Pair Analysis; D008875:Middle Aged; D009367:Neoplasm Staging; D018714:Radiotherapy, Adjuvant; D012062:Relative Biological Effectiveness; D016019:Survival Analysis