Monte Carlo simulation studies for spatially fractionated radiation therapy techniques

The purpose of this work was to evaluate the possible gain in tissue sparing in hadrontherapy when a spatial fractionation of the dose is used. Monte Carlo simulations (GATE v.6) have been used as a method to assess the dose distributions in a cylindrical water phantom (16 cm height and 16 cm of diameter). The phantom was irradiated with carbon and oxygen minibeams of 0.7 mm of beam width, and with protons in a grid geometry configuration. Several centre-to-centre distances, covering a 2 x 2 cm2 area, have been taken into account. The ratio of the peak-to-valley doses (PVDR) and the penumbrae was used as evaluation parameter, since PVDR is considered to be a very relevant dosimetric parameter for tissue sparing. Extremely high PVDRs values and very narrow penumbrae were obtained in all depths. This means that this new way of dose delivery might allow the use of higher and potentially curative doses in clinical cases where tissue tolerances are a limit to achieve a curative treatment. The high PVDR obtained and the small penumbrae in comparison with existing radiosurgery techniques, suggest a potential gain in healthy tissue sparing in those new techniques.