Radiobiological robustness and its influence in pretreatment verification of IMRT plans

Abstract

Recently, a radiobiological robustness index has been proposed with the aim to characterize treatment plans. This robustness index is based on tumor control probability (TCP) and normal tissue complications probability (NTCP) curves. The purpose of this paper is to further investigate the relation of this index with the rejection probability of an IMRT plan under different metrics at the pretreatment verification. The metrics under consideration are based on a γ analysis, based on dose differences or based on radiobiological features. To this purpose, we had at our disposal 113 step & shoot IMRT plans. We have computed the robustness index for these plans and, according to this index, the corresponding rejection probability under the aforementioned metrics. As a conclusion, we have been able to set a cutoff value for the robustness index, so that a plan with a robustness index under this value has a greater rejection probability for all the considered metrics. This shows that this index can be of great utility, since it adds valuable information about the plan quality and its stability at the verification.