Speaker
Description
Proton minibeam radiation therapy (pMBT) and FLASH radiotherapy (FLASH-RT) have attracted the interest of scientists due to the better sparing of healthy tissue compared to conventional modalities. Combining these methods may lead to further reduction of the induced side effects. In this proof-of-principle study, the feasibility of designing a ridge filter (RF) for the FLASH application of pMBT has been investigated. The simulations were performed in TOPAS using a 68.5 MeV magnetically focused planar proton minibeam. An RF was designed to create a spread-out Bragg peak (SOBP) in a water phantom with a tumor at 2.88 - 3.88 cm depth. It is made by an asymmetrical carbon unit with 10 steps of equal thicknesses and different widths, which is repeated in space vertically to the axis of the incoming beam. The distance from the middle of one unit to the other is equal to twice the sigma (σ) of the non-degraded beam at the position of the RF. The dose fluctuation in the SOBP region, the dose homogeneity of the tumor, and the beam size at the phantom entrance were evaluated and a robustness analysis related to the RF positioning has been done. The dose fluctuation in the tumor region is almost ±2% and also the application of 10 beams with a center-to-center distance (ctc) of 1.4 mm, creates a dose distribution in the tumor meeting the ICRU criteria. The preservation of small beam sizes at the entrance, with a high peak-to-value dose ratio (PVDR) is possible. The robustness analysis revealed the sensitivity in movements and that precise positioning is needed to always fulfill the homogeneity standards. The simulation study has shown that the designed RF enables the generation of a SOBP in pMBT. In future research, the fabrication method and an accurate positioning system should be investigated.
