Comparison of Different Model Predictions on RBE in the Proton Therapy Technique Using the GATE Code

Recently, proton therapy is used as one of the effective methods for treating various types of cancer in clinical treatment. An appropriate formalism to obtain relative biological effectiveness values for treatment planning studies is needed in this hadrontherapy technique. Hereby, the quantity of biological dose, instead of using the physical doses, is introduced to evaluate the biological effect of radiation in tissue. In proton therapy, a constant RBE of 1.1 is usually applied clinically as recommended by ICRU. However, different studies including data from irradiation experiments propose that a variable RBE factor is more appropriate. The primary objective of this project was to calculate and compare the dose-to-patient results of constant RBE versus variable RBE calculated by different models for hadron therapy. The irradiation experiments show the RBE parameter depends on different parameters such as deposited dose, LET, radiation energy and tissue sensitivity. In the present study, Wilkens, Wedenberg, Carabe and McNamara models were used to calculate RBE and biological dose in different models by using GATE Monte Carlo code. The results of the different models were compared with constant RBE of 1.1. On the other hand, bringing further simulations closer to the real situation, proton beam modulation has been used to create Spread-Out Bragg Peak (SOBP) region, and different models of RBE have been used to calculate the biological doses. Results show that the four different models predicted an equal or lower dose in the proton beam-entrance region compared to predictions for constant RBE, while greatly exceeding the predicted constant RBE dose in the distal part of the region target.