Spleen cancer. Gross specimen of a spleen showing a large tumour (upper frame) caused by thorotrastosis, a reaction to the radioactive tracer chemical thorotrast. Thorotrast is a solution of thorium-232, which emits alpha particles during radioactive decay. It was formerly used as a tracer in diagnostic radiology. The Th-232 is not expelled from the body, however, and patients who received thorotrast developed malignant tumours due to the alpha radiation in their bodies. There is no treatment for radiation poisoning.