Abstract
A method of measuring the thoron content of the breath of patients who have been injected with colloidal thorium dioxide as a radiological contrast medium, is described. The levels are sufficiently high for the decay of the thoron to be observed using only four litres of breath, being in the range 250 to 2000 μμc per litre, and they can be used to estimate the volumes of colloid injected many years previously. It is also shown that not more than about 10% of the thoron produced in the liver and spleen (the organs containing the major part of the thorium) is exhaled.
The average radiation dose-rates to the lung are estimated to be in the region of 0·3 rem per week (R.B.E. for α-particles assumed to be 10), but the dose-rates to the bronchus and trachea are 10 to 15 times as great. A patient injected with 75 ml colloidal thorium dioxide may thus receive a cumulative dose to the bronchus of about 1000 rads in 16 years.