Interstitial pneumonitis following total body irradiation for bone marrow transplantation using two different dose rates

A total of 22 patients with leukemia (10 ALL, 11 AML, 1 CML) have undergone allogeneic bone marrow transplantation (BMT) by the Quebec Co-operative Group for Marrow Transplantation from 1980 to 1982. All patients received 900 cGy total body irradiation (TBI), in a single fraction, on the day preceding BMT. The first 11 patients were treated on a cobalt unit at a constant dose rate of 4.7 to 6.3 cGy/min. Six of these patients developed interstitial pneumonitis (IP). The clinical course of three patients, two with idiopathic and one with drug-induced pneumonitis, was mild and recovery was complete in all. The other three patients developed severe infectious IP and two died. The next 11 patients were treated with a sweeping beam technique on a 4 MV linear accelerator delivering a total tumor dose of 900 cGy at an average dose rate of 6.0 to 6.5 cGy/min but an instantaneous dose rate of 21.0 to 23.5 cGy/min. Eight patients developed severe IP. Five of these were idiopathic and four died. Three were infectious and all died. The fatality of interstitial pneumonitis appeared to be greater in the group treated with the sweeping beam technique.