title: Lung tumour induction in mice after uniform and non-uniform external thoracic X-irradiation.
abstract: The aim of this study was to investigate the validity of the ICRP procedure of using average tissue/organ dose in estimating carcinogenic risk. It has been suggested that highly non-uniform exposure ('hot spots') is much more carcinogenic than an equivalent dose delivered uniformly. In a series of experiments, mice were irradiated with X-rays either uniformly to the thorax or non-uniformly with 72 1-mm microbeams which irradiated approximately 20 per cent of the total lung volume. Two experiments involving uniform irradiation showed a peaked tumour incidence curve with a maximum at 5 Gy. The first 'microbeam' study also produced a pronounced peak in the dose response with a maximum tumour incidence at 1 Gy average lung dose or 5 Gy to the irradiated lung tissue. This implied the use of average tissue dose might underestimate the carcinogenic hazard of non-uniform exposure. Later, more extensive, microbeam experiments failed to replicate this finding. The results were nearly similar to those for uniform irradiation, with a slight increase in tumour incidence from 2.5-5.0 Gy average lung dose. These results imply that for these irradiation conditions the ICRP dose averaging procedure remains valid.
mesh_terms: D000818:Animals; D004307:Dose-Response Relationship, Radiation; D004735:Energy Transfer; D005260:Female; D008175:Lung Neoplasms / Q000209:etiology*; D008297:Male; D051379:Mice; D009381:Neoplasms, Radiation-Induced / Q000209:etiology*; D012306:Risk; D013909:Thorax / Q000528:radiation effects*; D014965:X-Rays