Biological effect of intermittent radiation exposure in vivo: recovery from sublethal damage versus reoxygenation.
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.
Tomita
Natsuo
N
Department of Radiology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan. ntomita@med.nagoya-cu.ac.jp
Shibamoto
Yuta
Y
Ito
Masato
M
Ogino
Hiroyuki
H
Sugie
Chikao
C
Ayakawa
Shiho
S
Iwata
Hiromitsu
H
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