Optimization of the dose level for a given treatment plan to maximize the complication-free tumor cure

During the past decade, tumor and normal tissue reactions after radiotherap y have been increasingly quantified in radiobiological terms. For this purp ose, response models describing the dependence of tumor and normal tissue r eactions on the irradiated volume: heterogeneity of the delivered dose dist ribution and cell sensitivity variations can be taken into account. The pro bability of achieving a good treatment outcome can be increased by using an objective function such as P-divided by, the probability of complication-f ree tumor control. A new procedure is presented, which quantifies P-divided by from the dose delivery on 2D surfaces and 3D volumes and helps the user of any treatment planning system (TPS) to select the best beam orientation s, the best beam modalities and the most suitable beam energies. The final step of selecting the prescribed dose level is made by a renormalization of the entire dose plan until the value of P-divided by is maximized. The ind ex P-divided by makes use of clinically established dose-response parameter s, for tumors and normal tissues of interest, in order to improve its clini cal relevance. The results, using P-divided by, are compared against the as sessments of experienced medical physicists and radiation oncologists for t wo clinical cases. It is observed that when the absorbed dose level for a g iven treatment plan is increased, the treatment outcome first improves rapi dly. As the dose approaches the tolerance of normal tissues the complicatio n-free cure begins to drop. The optimal dose level is often just below this point and it depends on the geometry of each patient and target volume. Fu rthermore, a more conformal dose delivery to the target results in a higher control rate for the same complication level. This effect can be quantifie d by the increased value of the P-divided by parameter.