Purpose: Cherenkov imaging is applied to TSET as a non-invasive and real-time remote monitoring technique. Monte Carlo (MC) simulations of TSET with TOPAS are capable of generating and propagating Cherenkov photons as well as transporting radiation. This study compares doses that are simulated using both TOPAS and EGSnrc, and are benchmarked with data in order to validate the accuracy of simulations of realistic incidents in a real clinical treatment geometry.
Methods: The complete physical processes of all particles from a clinical electron beam interacting with different materials of phantoms are simulated by using TOPAS. A treatment head model, patient phantom model, and TSET clinical treatment setting including geometry, chemical compositions, and optical properties of materials, especially of human tissues, are all studied and simulated with TOPAS. The 6 MeV electron beam phase space files scored before incidence on the JAWS are provided by Varian. Realistic clinical incident beams used in TSET including the setup geometry are simulated with both TOPAS and EGSnrc. The results are compared and benchmarked with experiments.
Results: MC simulations of TSET are validated by comparing with measurements, such as PDD in water at 100 cm SSD, PDD in solid water at 500 cm SSD with a 3 mm beam spoiler, and vertical profiles at 500 cm SSD in a PVC board with the spoiler in single and dual fields. The calculated dose distributions from TOPAS agree with those from EGSnrc. Simulations with TOPAS also show the relationship between dose distributions and distributions of Cherenkov photons emitted from phantom surfaces.
Conclusion: The agreement between TOPAS, EGSnrc, and data establishes the accuracy of the simulated incident beams and dose distributions. By using the relationship between dose distribution and Cherenkov photon distribution we are able to monitor the patient skin dose during the radiation delivery of TSET.