ABSTRACT
Adaptive radiation therapy (ART) and treatment individualization requires the identi£cation of suitable biological objectives to facilitate the design, comparison, and ranking of alternate and re£ned treatments. Ÿe main biological objective of curative radiation therapy is to maximize the probability of local tumor control, while simultaneously minimizing normal tissue damage. Because parameters in dose-response models are o«en inaccurate or highly uncertain and because biological mechanisms are not fully understood, isoe¢ect calculations based on concepts such as biologically e¢ective dose (BED; Withers, Ÿames Jr., and Peters 1983) or equivalent uniform dose (EUD; Niemierko 1997) are o«en more useful for comparing and ranking alternate and re£ned treatments, rather than comparing clinical outcomes that are estimated using tumor control probability (TCP) and normal tissue complication probability (NTCP) models. In this chapter, we review the key concepts motivating such biological indices and provide examples of how these concepts might be used to address clinically relevant issues and, ultimately, aid in the clinical implementation of ART and treatment individualization.
