Estimation of tumor dose in conformation radiotherapy.

Dosage estimation for conformation radiotherapy applied to cervical cancer was discussed. Field size and shape in conformation therapy was freely change able according to the shape and size of tumor. When the same size and shape of the field for therapy by Co 60 gamma ray was applied to each case, tissue-air ratio TAR was given by an equation, T=-0.00326d+1.035, where T is TAR and d an average depth. The concept of tissue-air ratio could not be applied to dose calculation in moving field radiotherapy by 6MV x-rays, because the quality of x-rays emitted from a linear accelerator is rather different from that of ƒÁ-rays of the telecobalt unit. Therefore, the tissue-reference output ratio was defined instead of tissue-air ratio in the form of: