Evaluation of density correction algorithms for photon-beam dose calculations.

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Abstract
Whether density correction algorithms more sophisticated than those presently used for photon-beam dose calculations are necessary in order to take full advantage of computed tomography in treatment planning was questioned. Predictions obtained with correction equations based on the radiological thickness (effective SSD [source skin distance]) and generalized power-law TAR [tissue air ratio] 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.