LQ-based model for biological radiotherapy planning.

Despite the increasing accumulation of radiobiological data, radiotherapy planning does not take into account the alpha/beta values of normal irradiated tissues. The importance of the fact that the dose per fraction outside the 100% isodose area is not at all identical to the one inside the tumor area is also underestimated. Altered fractionation regimens further complicate the reliability of the conventional radiotherapy plans. In this study we report a theoretical application of the Macejewski's concept of "normalised total dose" that could make feasible the integration of alpha/beta and dose per fraction values in everyday radiotherapy practice. The concept of cumulative normalised total dose permits the preparing of radiotherapy plans with normalised isodose areas (the cumulative isodose area maps) for chosen ranges of radiation normalised doses. The effect of overall treatment time and interfraction interval is also taken into account. The present study suggests some guidelines that could be of value for the elaboration of a computer program for biological radiotherapy planning.