Modelization of the ophthalmic treatment set up beam line of the INSTITUT CURIE – CENTRE DE PROTONTHÉRAPIE D'ORSAY

Abstract

Introduction In order to simulate the dose measurement of ophthalmic treatments by Monte Carlo at the ICCPO, the modeling of the geometrical elements of the set up beam line was achieved. However, a problem has been identified about the position and the characterisation of the virtual proton beam source. Until now, we could only model a divergent source after the modulator preventing the creation of spread-out Bragg peaks (SOBP). Thus, it was necessary to modelize a convergence source to validate the beam line. Material and methods Monte Carlo calculations are performed using the codeMCNPX2.6e Los AlamosNational Laboratory (LANL). To create our source we used a spherical volumesource delimited by a plane. For the experimental measurements, we used a water tank, an ionization chamber IBA PPC05 for the acquisition of Bragg peaks, radiochromic films and a 2D detector Lynx Fimel for transverse dose profiles. The code was then compared to the measurments for validation. Results According to EBT2 films, we observed the convergence of the source after the modulator wheel. Therefore, we have succeeded in modeling of the MCNPX source respecting the actual parameters and having the ability to create SOBP. With this source we were able to validate all the elements of the optical bench. The comparison between measured Bragg peaks and profiles and calculated ones showed a good agreement with a precision of 3% on dose deposition. Conclusion The validation of the beam line and the integration of CT scan to modelize Monte Carlo allows us to get more accurate treatment simulations than we had with Eyeplan. Phase space can be generated to make the calculation faster using voxellised imaging and facilitate quality assurances. In order to simulate the dose measurement of ophthalmic treatments by Monte Carlo at the ICCPO, the modeling of the geometrical elements of the set up beam line was achieved. However, a problem has been identified about the position and the characterisation of the virtual proton beam source. Until now, we could only model a divergent source after the modulator preventing the creation of spread-out Bragg peaks (SOBP). Thus, it was necessary to modelize a convergence source to validate the beam line. Monte Carlo calculations are performed using the codeMCNPX2.6e Los AlamosNational Laboratory (LANL). To create our source we used a spherical volumesource delimited by a plane. For the experimental measurements, we used a water tank, an ionization chamber IBA PPC05 for the acquisition of Bragg peaks, radiochromic films and a 2D detector Lynx Fimel for transverse dose profiles. The code was then compared to the measurments for validation. According to EBT2 films, we observed the convergence of the source after the modulator wheel. Therefore, we have succeeded in modeling of the MCNPX source respecting the actual parameters and having the ability to create SOBP. With this source we were able to validate all the elements of the optical bench. The comparison between measured Bragg peaks and profiles and calculated ones showed a good agreement with a precision of 3% on dose deposition. The validation of the beam line and the integration of CT scan to modelize Monte Carlo allows us to get more accurate treatment simulations than we had with Eyeplan. Phase space can be generated to make the calculation faster using voxellised imaging and facilitate quality assurances.