Clinical CBCT-Based Dose Simulation for 80 kVp X-PACT Treatment Using FLUKA Monte Carlo Package

X-PACT as a novel cancer therapy utilizes kilovoltage x-ray beam, phosphor and psoralen to treat solid tumors. Since x-ray beam is not commonly used for radiation therapy treatment purposes, a lack of treatment planning tool and plan based dose calculation is hindering the development of X-PACT. In this study, we try to approach the challenge by creating a Monte Carlo model that is an accurate representation of the actual treatment. The Monte Carlo model will be validated with commissioning measurements and is applicable to clinical data.

FLUKA is used as the Monte Carlo package for our simulations. The Monte Carlo model is created based on the Variantm OBI system. The geometry is created and optimized in Flair. To improve simulation efficiency, we collected the filtered simulated 80 kVp x-ray spectrum and used that as the source file for photon simulation. This way, the x-ray tube is bypassed, and 80 kVp photon can be simulated directly.

The validation process consists of two qualities: the back-scatter factor and the percentage depth dose. The commissioning was done separately from this study [1], and the commissioning data was used to compare with simulation results. The Model shows good overall matching to the commissioning PDD data. At small or large field size, a discrepancy between the simulation PDD data and commissioning PDD data can be observed at the surface, the differences are with 3-4%.

The final step is to apply the model to the Phase I canine trial. The clinical trial includes six dog study cases. In this thesis, Monte Carlo dose calculation based on the CBCT images of each dog study was performed for all six dog studies. The result is a 3D dose matrix for the CBCT images. According to the prescription dose for each dog study, the simulated dose was normalized, and the dose distribution for each dog was generated..