Radiation and Gut

Abstract

Two books with very similar titles have been published recently: Radiation and the Gastrointestinal Tract (edited by A Dubois et al) and Radiation and Gut. Despite their rather similar titles, their content is very different. The former is concerned with acute radiation effects and their avoidance or control in the context of radiation therapy and the possible irradiation of military personnel. It consists essentially of extended papers from the proceedings of a symposium. The latter, while also having chapters contributed by different authors, seeks to cover the field from the basic structure and cell replacement processes in the gut to its response to radiation in terms of cancer induction and tissue injury in experimental animals and human beings. The gut is a remarkable organ. As is commonly understood, it forms a tube from mouth to anus, but less well known is the rate of cell renewal in its epithelial lining, particularly in the small intestine. It is estimated that, for example, a mouse replaces about cells in its small intestine during a 3 year life-span. In human beings, this number of cells may be produced each day, corresponding to a mass of tissue produced and shed during a 70 year life-span of about ten times adult body weight. People have puzzled over the apparent paradox that the small intestine is the most sensitive region of the gut to radiation-induced cell killing and reproductive failure, consistent with its high rate of cell turnover, but has a low susceptibility to cancer induction. Thus, about 40% of the excess cancers among the A-bomb survivors in Japan are attributable to those arising in the gut but with significant increases confined to the stomach and colon. One emerging explanation, based on studies using mice, is that the small intestine may have an efficient mechanism for recognising and removing damaged stem cells. This is thought to involve a process of programmed cell death, termed apoptosis, in which cells commit suicide. Comparisons of apoptotic response to radiation in the small and large intestine show correspondence with the position thought to be occupied by the stem cells in the small intestine but not the large intestine. It may be, therefore, that stem cells in the large intestine are substantially more prone to the accumulation of genetic errors that might ultimately lead to malignant change. Populations differ considerably in their incidence of gut cancer. They account for 15 - 16% of total cancer deaths in England and Wales and in the USA and about 30% in Japan. Colorectal cancer accounts for about 80% of deaths from gut cancer in the USA whereas stomach cancer predominates in Japan. An important uncertainty in current risk estimates for radiation-induced gut cancer, based largely on incidence in Japan, is the lack of knowledge of how risks should be transferred from one population to another. Radiation and Gut provides very readable and detailed accounts of these issues and generally of the effects of radiation on the gut in experimental animals and human beings. Prominent among the contributors for individual chapters are the editors, Chris Potten and Jolyon Hendry, drawing extensively from their own work at the Paterson Institute for Cancer Research. It will be a pity if the high price of the book limits its availability.