Impact of cardiosynchronous brain pulsations on Monte Carlo calculated doses for synchrotron micro‐ and minibeam radiation therapy

Abstract

Optimal setups for brain treatments with synchrotron radiation micro- and minibeam combs depend on the brain displacement due to cardiosynchronous pulsation. Peak-to-valley dose ratios larger than 90% of the maximum values obtained in the static case occur only for minibeams and relatively large dose rates.

High resolution radiochromic film dosimetry: Comparison of a microdensitometer and an optical microscope

“…In addition, medium-energy X-ray photons (mean energy around 100 keV) are used instead of MeV photons to reduce the travel range of secondary electrons in the tissues, and the divergence of the beam must be small to preserve the microbeams shape throughout the target. The extremely high dose rates achievable with synchrotron X-rays [7][8][9] allow reducing the exposure time and avoiding the blur of the microbeams traces due to tissue motion that in the human brain has a motion range up to hundreds of micrometres with a maximum motion velocity of 2 mm/s [10][11][12].…”

Spatially fractionated proton minibeams

“…[34][35][36][37][38][39][40] The need for ultra-high dose rates (>100 Gy s -1 ) to prevent blurring by cardiosynchronous pulsations 41 of the peak and valleys patterns, the need for low-kilovoltage energies (<200 keV), 42 and the technical challenges related to positioning and dosimetry triggered the exploration of minibeam radiation therapy (MBRT) 29,43 with slightly larger but still submillimetre beams. MBRT is less vulnerable to beam smearing than MRT, 44,45 technically easier to implement and feasible with higher energies. 42 MBRT has also been shown to significantly increase the normal tissue resistance in animal experiments with respect to uniform irradiation, [46][47][48][49][50] while delaying tumour growth.…”

Combining FLASH and spatially fractionated radiation therapy: The best of both worlds

“…Instead, the most important conditions for tissue sparing in SFRT are (i) a significant spatial modulation of the dose (meaning a high peak-to-valley dose ratio and low valley doses (4,40)) and (ii) the beam size (the smaller the beam size, the higher the doses tolerated by the tissue (41)). Additionally, the micrometer-scale beam sizes used in MRT (20-100 µm) require UHDR to prevent the distortion of microbeam patterns due to cardiosynchronous motion (42,43). Similar to FLASH-RT, the sparing effects of SFRT have been demonstrated with different types of particles, namely photons, protons and even neon ions (4).…”

“…While megavoltage photons are a good candidate for GRID-RT and LRT, energies in the range of ∼ 50-400 keV are preferred for MRT and MBRT (86,88) to maintain a satisfactory spatial modulation. As mentioned in section 2, because of their small dimensions, microbeams must be delivered at UHDR to prevent smearing of peak-and-valley patterns caused by cardiosynchronous pulsations (42). Therefore, almost all MRT experiments to date have been performed at synchrotron X-ray sources (86), which can deliver extremely high dose rates of up to 16,000 Gy/s (14,40).…”