Use of Radiobiological Modeling in Treatment Plan Evaluation and Optimization of Prostate Cancer Radiotherapy

There are many tools available that are used to evaluate a radiotherapy treatment plan, such as isodose distribution charts, dose volume histograms (DVH), maximum, minimum and mean doses of the dose distributions as well as DVH point dose constraints. All the already mentioned evaluation tools are dosimetric only without taking into account the radiobiological characteristics of tumors or OARs. It has been demonstrated that although competing treatment plans might have similar mean, maximum or minimum doses they may have significantly different clinical outcomes (Mavroidis et al. 2001). For performing a more complete treatment plan evaluation and comparison the complication-free tumor control probability (P+) and the biologically effective uniform dose ( D ) have been proposed (Källman et al. 1992a, Mavroidis et al. 2000). The D concept denotes that any two dose distributions within a target or OAR are equivalent if they produce the same probability for tumor control or normal tissue complication, respectively (Mavroidis et al. 2001). In this chapter, the importance of the P D  diagrams is illustrated. These diagrams provide important information by combining the radiobiological data of the organs involved with the dosimetric information of the delivered dose distribution (Mavroidis et al. 2010). It would increase the flexibility and clinical application of the P+ index if in its original definition the different terms related to the tumor control and normal tissue complication probabilities were accompanied by some weighting factors, which could be adjustable by the clinicians depending on the important of the different clinical endpoints used (Mavroidis et al. 2011). In practice the P+ index finds the pure benefit from the treatment by subtracting the normal tissue complication probabilities from the tumor control probability.