title: Changes in the effect of dose fractionation during daily fractionated irradiation: studies in mouse oral mucosa.
abstract: OBJECTIVE
  The aim of the present study was to quantify the fractionation effect in mouse oral mucosa during a daily fractionated protocol.
  
  
  METHODS
  Irradiation of the snout of C3H mice was performed with 5 x 3 Gy/week. In the first experiment, graded test doses were applied to the lower tongue on Days 4, 7, 11, 14, or 18. Subsequently, a split-dose experiment was performed on the same days with 1, 2, 3, or 5 fractions (graded doses).
  
  
  RESULTS
  The ED50 (dose expected to induce ulcer in 50% of the mice) for untreated mucosa was 10.7 +/- 1.0 Gy. Fractionated irradiation with 5 x 3 Gy/week yielded an ED50 for top-up irradiation of 6.5 +/- 1.8 Gy, 6.8 +/- 0.9 Gy, 5.3 +/- 2.1 Gy, 7.3 +/- 1.9 Gy, and 7.5 +/- 1.3 Gy on Days 4, 7, 11, 14, and 18. The ED50 values for split-dose irradiation on Day 4 increased from 6.24 +/- 1.48 Gy (1 fraction) to 9.96 +/- 1.47 Gy (5 fractions). Similarly, an increase from 4.04 +/- 1.56 Gy to 10.07 +/- 1.9 Gy was found on Day 11, and from 5.84 +/- 2.37 Gy to 9.81 +/- 2.29 Gy on Day 18. After the weekend breaks, values between 6.22 +/- 1.60 Gy (1 fraction) and 4.7 +/- 1.95 Gy (5 fractions) were observed on Day 7, and between 5.62 +/- 1.36 Gy and 5.98 +/- 2.01 Gy on Day 14.
  
  
  CONCLUSIONS
  These results indicate that the fractionation effect in oral mucosa is consistently lost over the weekends and restored during the treatment weeks.
authors.affiliation: Klinik und Poliklinik für Strahlentherapie und Radioonkologie, Medizinische Fakultät Carl Gustav Carus, Technischen Universität, Fetscherstrasse 74, D-01307 Dresden, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Pabst
authors.forename: Kathrin
authors.initials: K
authors.lastname: Spekl
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Dörr
mesh_terms: D000818:Animals; D002455:Cell Division; D019583:Dose Fractionation, Radiation; D004307:Dose-Response Relationship, Radiation; D005260:Female; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D009061:Mouth Mucosa / Q000528:radiation effects*; D011833:Radiation Injuries, Experimental / Q000150:complications; D011836:Radiation Tolerance; D013280:Stomatitis / Q000209:etiology*; D014059:Tongue / Q000528:radiation effects*