Evaluation of density correction algorithms for photon-beam dose calculations

The authors questioned whether more sophisticated density correction algorithms than those presently used for photon-beam dose calculations are necessary to take full advantage of CT in treatment planning. Predictions obtained with correction equations based on the radiological thickness (effective SSD) and generalized power-law TAR methods, as well as on the more complex equivalent-TAR method, are compared with ionization-chamber measurements in phantoms containing simulated lung and soft tissues. Various geometric configurations were investigated for 60Co and 8-MV radiations. While the equivalent-TAR method gave the best general agreement, the power-law method appears to be accurate enough for regular treatment-planning purposes. The effective SSD method has a limited range of validity. At present, complicated methods of density correction do not seem to be justified