Acute changes in pulmonary arterial perfusion following irradiation

Computerized tomography versus perfusion lung scanning in canine radiation lung injury

Computerized tomographic (CT) measurements of lung density were obtained before and serially after thoracic irradiation in dogs to detect the alterations caused by radiation therapy. Fourteen mongrel dogs were given either 2000 cGy (Group A, 10 dogs, right lower zone irradiation), 1000 cGy (Group B, 2 dogs, right lower zone irradiation), or 500 cGy (Group C, 2 dogs, right lung irradiation) in one fraction. Once before and bi-weekly after irradiation, the anesthetized dogs had thoracic CT scans. CT numbers for the irradiated area were compared to their preirradiation control values. Macro-aggregated albumin (MAA) perfusion lung scans were also obtained before and at weekly intervals after irradiation and were evaluated visually and quantitatively for abnormalities. When both these tests were abnormal, or at the end of the scheduled study, the dogs were sacrificed to confirm radiation lung injury histologically. Our results showed that CT numbers (as a measure of tissue density) were higher with higher doses of radiation. Among all the techniques used, only the quantitative assessment of macro-aggregated albumin perfusion scan detected abnormalities in all the dogs given 2000 cGy. Their abnormalities correlated well with the presence of radiation lung damage histologically, however, the applicability of these methods in the detection of early injury has to be further evaluated.

N-isopropyl-p[123I]iodoamphetamine, a new agent for lung imaging studies

N-isopropyl-p[123I]iodoamphetamine, originally designed for brain scintigraphy, has been found to be retained by the normal lung and to produce excellent camera images. Ten patients with gross abnormalities on their chest radiographs due to lung cancer have been studied with this drug. The diseased parts of the lung consistently showed less uptake and these defects matched those obtained with microspheres labelled with technetium-99m, indicating that 123I-iodoamphetamine has the characteristics of a perfusion tracer. In five out of the 10 patients studied sequential studies showed that improved iodoamphetamine uptake was encountered shortly after a favourable response to radiotherapy and reduced uptake was seen in congruence with the radiation field at a later stage. This first clinical demonstration indicates that the retention of 123I-iodoamphetamine could be a sensitive marker for pulmonary vascular integrity and a useful new tool to identify the extent of disease where the pulmonary circulation is the initial site of the disorder.