Tissue Reactions and Dose Relationships in Rats Following Intrapulmonary Beta Radiation

Squamous cell carcinomas of bronchial origin have been produced in lungs of rats exposed to the beta radiation of 106Ru and 32P sources. Utilizing intrabronchial pellets implanted by surgical techniques, the spacial relationships of the emitting pellet to the bronchial origin of tumor has been defined, permitting dose in rads to the target tissue to be directly calculated. Previously reported experiments with electroplated 106Ru sources have shown a rad dose-related incidence of tumor yield. These doses based on time of death with cancer rather than time of initiation of malignant change included some “wasted” radiation. Serial sacrifice experiments with rats exposed to 5 microc 106Ru sources have demonstrated earlier finding of cancer providing for minimum estimates of the period of “wasted” radiation. Spontaneous deaths in the serial sacrifice pool have confirmed the cancer incidences of previous experiments at the 5 microc level. A hollow plastic pellet has been devised for the examination of dose rate effect on tumor induction with the use of isotopes of varying half life. An initial experiment with Phosphorus-32 delivering doses of 103, 104, 105 rads has resulted in a yield of tumors at these levels comparable to the yield from the same dose in rads delivered by 106Ru pellets. Thus, within these limits, there has been no dose-rate dependence for tumor yield.