The Role of radiobiological parameters on Tumor control probability (TCP) in prostate cancer

Introduction: The aim of this study was to evaluation radiobiological modeling parameters on tumor control probability (TCP) for prostate cancer in three different models. These parameters included α⁄β ratios and cell surviving fraction at 2 Gy (SF2). Materials and Methods: The Poisson, equivalent uniform dose (EUD) and linear quadratic (LQ) models was used as the radiobiological models. TCP was calculated in 10 prostate cancer patients as a function of α⁄β ratios (1.5-20) for all radiobiological models and SF2 (0.3-0.7) for LQ model. For each patient, 3D-CRT and IMRT plans were designed to deliver, on average 76 Gy and 82 Gy to planning target volume, respectively. Results: The TCPs calculated by Poisson model were dependent on α/β, results demonstrated that dose escalation from 76 Gy in 3D-CRT to 82 Gy for IMRT caused 5% improvement in TCP for prostate cancer considering the α/β of 10 and higher TCP for IMRT relative to 3D-CRT was seen for α/β higher than 5. According to our results for EUD model the TCPs were independent on α/β. In the LQ model with increase in α/β in specific SF2, TCP will not change remarkable. but with the change of SF2 from 0.7 to 0.3, TCP values change from 0 to 100 % at the prescribed doses in both treatment planning’s. Conclusion: Different mathematical models provided different quantitative outcome for TCP of prostate cancer plans. The IMRT plans were significantly advantageous over the 3DCRT plans with some small variations in each patient. more studies are needed for the optimization of radiobiological models for the prediction of the treatment outcomes in radiation therapy.