414. Int J Radiat Biol. 1990 Aug;58(2):351-60.
Dose and dose-splitting effects of X-rays on lung tumour induction in mice.
Hashimoto N(1), Endoh D, Kuwabara M, Satoh H, Sato F.
Author information:
(1)Department of Radiation Biology, Faculty of Veterinary Medicine, Hokkaido
University, Sapporo, Japan.
This paper reports lung-tumour induction 12 months after single or split doses of
X-rays in C3H/He male mice. The early proliferative response of lung cells after
doses which induced lung tumours was also examined after single X-irradiation.
The lung-tumour incidence tended to increase with increasing dose after a single
irradiation and peaked at 5 Gy. At more than 10 Gy it decreased sharply to the
control level. The mean tumour diameters tended to increase with doses up to 7.5
Gy and then decreased beyond 10 Gy. These results suggested that suppression of
tumour growth reduced the tumour incidence at doses of over 10 Gy. The
lung-tumour incidence decreased with increasing intervals between two equal doses
of 2.5 or 5 Gy. The decrease was thought to be caused by the repair of the
tumorigenic injury. However, the tumour incidence after two 2.5 Gy irradiations
at 1 day intervals or two 5 Gy irradiations at 6 h intervals was higher than that
observed after a single dose. This phenomenon was regarded as a progression of
the tumorigenic injury. The labelling indices of the lung cells, determined using
tritiated thymidine after a single irradiation, were higher than those of
non-irradiated control cells. This response was delayed as the dose increased.
The responses versus days after irradiation could be classified into three
patterns on the basis of their peaks. The possibility that the larger delay after
higher doses had some relation to the reduction of target cells for tumour
incidence is suggested.
PMID: 1974581 [PubMed - indexed for MEDLINE]