title: Biological effect of intermittent radiation exposure in vivo: recovery from sublethal damage versus reoxygenation.
abstract: OBJECTIVE
  In vivo effects of intermittent irradiation are influenced by recovery from sublethal damage (SLDR) and reoxygenation, so contribution of the two factors were investigated using murine tumors.
  
  
  METHODS
  1-cm-diameter SCCVII tumors growing in the legs of C3H/HeN mice were used. First, effects of 5 fractions of 6 Gy given at intervals of 2.5-15 min were compared using an in vivo-in vitro assay, by clamping the tumor-bearing legs to exclude the influence of reoxygenation. In the second and third experiments, changes in the hypoxic fraction at 0-15 min after 13 or 5 Gy were assessed by a paired cell survival method. Fourth, effects of 5 fractions of 5 Gy given at intervals of 3-10 min under conditions of limited reoxygenation were compared using a growth delay assay.
  
  
  RESULTS
  Cell survival from clamped tumors tended to increase with elongation of the intervals, but not significantly. The hypoxic fraction tended to decrease at 5-15 min from the level immediately after irradiation. Effects on tumor growth tended to decrease with elongation of the intervals.
  
  
  CONCLUSIONS
  Reoxygenation occurring within 5-15 min appeared to compensate for SLDR in SCCVII tumors. When reoxygenation was limited, the decrease of radiation effect occurred due to SLDR.
authors: Department of Radiology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan. ntomita@med.nagoya-cu.ac.jp
authors: Natsuo
authors: N
authors: Tomita
authors: Yuta
authors: Y
authors: Shibamoto
authors: Masato
authors: M
authors: Ito
authors: Hiroyuki
authors: H
authors: Ogino
authors: Chikao
authors: C
authors: Sugie
authors: Shiho
authors: S
authors: Ayakawa
authors: Hiromitsu
authors: H
authors: Iwata
mesh_terms: D000818:Animals; D002294:Carcinoma, Squamous Cell / Q000378:metabolism / Q000532:radiotherapy*; D002470:Cell Survival / Q000528:radiation effects*; D019583:Dose Fractionation, Radiation; D005260:Female; D000860:Hypoxia; D051379:Mice; D008809:Mice, Inbred C3H; D009368:Neoplasm Transplantation; D009374:Neoplasms, Experimental / Q000378:metabolism / Q000532:radiotherapy*; D011829:Radiation Dosage; D013997:Time Factors