The utility of computed tomography in radiation therapy: an estimate of outcome

Several studies have shown that computed tomography (CT) scanning leads to changes in planned therapy for some 40 to 60 % of patients studied. An empirical model has been developed to estimate the improvement in local control and long term survival attributable to CT. The model is based upon an average dose-response relationship for the tumors and involves a technique for estimating the change in tumor control probability when part of the tumor is underdosed. Using this model, it was estimated that, in one series of patients, CT scanning improved the local tumor control probability by an average of 6 %, and improved the chance of 5-year survival by an average of 3.5 %.