Radium retention and dosimetry in the St. Bernard

The percentage total-body retention (R) of 226Ra was determined in 14 young adult St. Bernards for the first 4 years after injection to be represented by the equation, R = 34.8 e-0.165t + 24.6 e-0.00537t + 40.6 e-0.000503t, where t is the time after injection in days. It was found that the 222Rn/226Ra ratio in the skeleton was similar to that measured previously for young adult beagles given 226Ra. Excretion of injected 226Ra averaged about 32% in the first 2 weeks, with about 2/3 of the total appearing in the feces. St. Bernards appear to retain more 226Ra than do beagles injected at the same age. The last two terms of the retention equation were used to calculate the average skeletal radiation dose rate and cumulative radiation dose normalized to each dog's individual retention measurements. Allowance was made in the calculations for the changing skeletal retention of 222Rn and its radioactive daughters as a function of time.