[en] This study has indicated that CT scanning is an extremely useful technique for non-invasively monitoring the increase in lung density caused by irradiation. However, careful consideration needs to be given to artifacts and variations associated with lung cross-sectional area and breathing rate (Nicholas and Down, 1985). CT scanning of mice subjected to whole thorax irradiation yields lung density measurements which compare well with breathing rate measurements and also indicate the type of injury sustained. Furthermore, compensatory hypertrophy of shielded lung tissue following hemithorax irradiation can also be visualised and quantified with CT. These results emphasise the potential value of X-ray CT for quantifying lung density changes in patients receiving radiotherapy to the thorax. Clinical studies are already being conducted at the Royal Marsden Hospital. (UK)