Speaker
Description
Introduction: Proton therapy makes it possible to achieve coverage levels for target volumes similar to the most advanced gamma radiotherapy techniques, irradiating significantly less healthy tissue. In addition, numerous publications suggest that proton irradiation produces a high biological effect. On the other hand, Monte Carlo (MC) simulation is accepted as the most accurate tool for calculating doses in proton therapy and has been shown in various publications to be superior to commercial tools based on simplified MC. With the aim of improving the efficacy of proton therapy treatments, we have started a funded project to introduce MC planning with biological dose calculation in proton therapy treatments for CUN.
Method: In a first phase, it is necessary to adjust the parameters of the MC simulation to the CUN beam in a similar way to how it is done for the implementation of the Treatment Planning System. In the second phase, the biological effects will be introduced in the MC planning of the treatments, using the latest LEM and MKM mechanistic models, which are already in use in carbon ion therapy and will be adapted to proton therapy. In parallel, a Graphical User Interface (GUI) will be developed to allow easy use by CUN staff. The last stage will consist of a retrospective study of patients with the objective of analyzing the predictions of an increase in the Relative Biological Effect by MC, comparing them with the clinical effects in the medium and long term in patients, to identify those cases where the dose calculation biological is more necessary.
Results: Using a double Gaussian Twiss model for the spatial and angular description of the beam, we have developed a quasi-automatic method to fit the 16 model parameters for each of the 98 possible energies of the CUN beam. The adjustment with the experimental results offers values of the gamma index 1%/1mm below 0.5. Likewise, by tuning the energy and the ionization potential in water, we have adjusted the positions of the Bragg peak, achieving an agreement with the IDD measurements with values below 0.5 of the 1%/1mm gamma index. Finally, after adjusting the absolute dose and verifying the dose with various water and heterogeneous phantoms, we achieved a good agreement for complete treatments. The differences observed with the TPS are as expected given the higher precision of the MC simulation calculations.
Conclusion: We have adjusted the parameters of the MC simulation to the CUN proton therapy beam, obtaining very good agreement with the experimental data and the TPS. After introducing the prediction of biological effects, we will be able to begin the retrospective study of patients of the effect of the increase in RBE predicted by the MC calculations. In parallel, a GUI will be developed to allow its daily use in treatment planning at the CUN.
