Dynamic CT measurement of contrast medium washin kinetics in canine nasal tumors

Tumor oxygenation affects the biologic behavior of a tumor and also its rad iation response. Decreased tumor oxygenation has been associated with an ag gressive phenotype and with decreased local tumor control following irradia tion. Thus, measurement of oxygenation may be useful for pretreatment evalu ation of a tumor. Many methods for assessing tumor oxygenation are availabl e but most are invasive. There is a need for a non-invasive measure of oxyg enation, or a surrogate for oxygenation. Measurement of perfusion has been suggested as a substitute for measurement of oxygenation. The use of washin kinetics of iodinated contrast medium to estimate perfusion has been shown to be related to radiation response of human carcinomas. We quantified the washin kinetics of iodinated contrast medium using dynamic CT in 9 dogs. A ll dogs had a malignant nasal tumor and perfusion was quantified at two sit es in each tumor to evaluate intratumoral variation in perfusion. Dogs were given an intravenous bolus injection of contrast medium and arterial and t umor washin kinetics quantified using a helical CT scanner. Perfusion was e stimated from these data using previously validated methods. Eight of the 9 dogs received definitive radiation therapy and perfusion was quantified a second time in these 8 dogs midway through irradiation, Pretreatment perfus ion varied between dogs by a factor of 16.9, Between dog variation in perfu sion was subjectively greater than within tumor variation based on comparis on of two intratumoral regions. Changes in perfusion in individual dogs dur ing irradiation were observed, but no identifiable pattern of perfusion alt eration was detected. Measurement of perfusion in canine nasal tumors using dynamic CT is possible and further study of this parameter as it relates t o radiation response is reasonable.