Technical advances in x-ray microbeam radiation therapy

Abstract

In MRT, spatial dose-fractionation is achieved on a microscopic scale. Fields are characterised by an array of 25 to 100 µm wide, quasi-parallel, micro-planar beams that have a centre-to-centre spacing of 100 to 400 µm [31] . This kind of array creates an inhomogeneous, periodically alternating dose profile of 'peaks'

The future of radiotherapy is molecular

“…Understanding the full biological impact and mechanisms of RT at the molecular level will form part of the way forward, however even if there is a push towards highly modulated techniques, e.g. micro-beam RT [10], this will not be the full answer. Expense and the immature theoretical/mechanistic basis for the impacts on non-irradiated tissue (with long researched, but still little understood mechanism-wise, bystander and adaptive responses [11]) will impact translation.…”

Clinical microbeam radiation therapy with a compact source: specifications of the line-focus X-ray tube

“…The radiation source needs low divergence and a focal spot smaller than an individual microbeam to maintain the dose pattern and sharp beam penumbras in larger depth in the tissue [11]. A high dose rate, up to kilograys per second, prevents blurring of the microbeam pattern caused by organ motion [7]. These requirements are fulfilled at some third-generation synchrotrons [7].…”

“…A high dose rate, up to kilograys per second, prevents blurring of the microbeam pattern caused by organ motion [7]. These requirements are fulfilled at some third-generation synchrotrons [7]. However, the limited availability, enormous size, and high costs render synchrotrons unfeasible for routine clinical radiotherapy.…”

“…The biological effects of MRT are not fully understood yet [5] , and it is still unclear if a spatially fractionated target dose is more efficient than a homogeneous target dose [2] . Nevertheless, authors agree that a low valley dose, a high peak-to-valley dose ratio (PVDR), and steep lateral penumbras from the peaks to the valleys are crucial for sparing healthy tissue [5] , [6] , [7] .…”

“…Mean photon energies of 100–150 keV give the best compromise between short ranges of secondary electrons, allowing steep lateral penumbras, and shallow depth doses for reaching deep-seated tumors [7] , [8] , [9] , [10] . The radiation source needs low divergence and a focal spot smaller than an individual microbeam to maintain the dose pattern and sharp beam penumbras in larger depth in the tissue [11] .…”