Monte Carlo simulation of novel procedures for highly conformal percutaneous radiation with keV-photons for tumor treatment in skin proximity

摘要

Photon beams in the energy range of keV are more cost effective and require less shielding efforts compared to MeV-photons or particle beams. The absent build-up effect for low-energetic X-rays however is challenging for percutane-ous radiotherapy. In this work, we study a possible improve-ment of the TCP-NTCP ratio (tumor control vs. normal tissue complication) by geometrically superimposing different colli-mated beamlets. Furthermore, inducing gold (Au) particles into the cancerous tissue leads to a local dose enhancement by additional emission of low-energetic electrons. We analyze this setup with regards to its suitability for clinical use. The study is based on the example of the X-ray source Axxent S700 from Xoft Inc., which is sampled in a Monte Carlo calculation (Ge-ant4). After developing a source model, irradiation with single beams from different directions and distances is simulated and the resulting dose kernels are stored. The weighting factors of the superposition are optimized using linear programming. These simulations are repeated for a tumor volume containing different dosages of gold. The results show that keV-photon irradiation alone does not seem to be suitable for external radiotherapy below the skin. In combination with dose enhancement, however, a two times higher dose to the tumor, compared to skin dose can be achieved. With narrow colli-mation, a dose ratio of five is generated, though only in a very small focal volume. Since primarily the analysis of the local dose enhancement is promising, we suggest to further explore this method including a combination with intracavitary electronic Brachytherapy.