There are essentially two major life-threatening situations. One is the development of pulmonary embolism--blood clots in the lung. The second acute situation is bleeding in the intestinal tract.
It is correct that a lot of patients can be taken care of with a spiral CT. If the patient cannot have a spiral CT scan because of allergy to x-ray dye, etc., the only alternative for them is a lung scan. In my own situation at Brantford General, we had no isotopes to do emergency procedures on two patients. A lung scan...undiagnosed, has a high mortality rate of about 20% to 25%. So in my own experience in the community hospital setting, where you don't have a lot of resources, this had a significant impact and put patients' lives at risk.
On alternate isotope supplies, there is no other alternative supply for doing lung scans. Technetium is the only isotope we can use. As the commission probably knows by now, technetium comes from molybdenum, which is made in the Chalk River reactor.