Microbeam radiation therapy - grid therapy and beyond: a clinical perspective

Abstract

Microbeam irradiation is spatially fractionated radiation on a micrometer scale. Microbeam irradiation with therapeutic intent has become known as microbeam radiation therapy (MRT). The basic concept of MRT was developed in the 1980s, but it has not yet been tested in any human clinical trial, even though there is now a large number of animal studies demonstrating its marked therapeutic potential with an exceptional normal tissue sparing effect. Furthermore, MRT is conceptually similar to macroscopic grid based radiation therapy which has been used in clinical practice for decades. In this review, the potential clinical applications of MRT are analysed for both malignant and non-malignant diseases.

Figure 1.

The primary X-ray beam is split by insertion of a collimator into an array of quasi-parallel microbeams. As a result, peak-dose, valley-dose and transitional zones are generated in the tissue (modified after).

Figure 2.

(a) Immunostain (H2AX) of adult mouse cerebral cortex, illustrating the characteristic pattern of DNA double strand breaks (bright green dots) caused by irradiation with an array of quasi-parallel microbeams (≈50 µm wide, white arrow), spaced ≈400 µm from centre to centre (red arrow), two hours after exposure (C. Fernandez-Palomo and E. Schültke, unpublished). (b) DAPI stain to demonstrate the presence of nuclei (blue dots) in the same section as in a.

Figure 3.

Distribution of publications in the field of MRT according to field of specialization, also illustrating the trend from exclusively cancer-oriented work to the inclusion of non-malignant diseases as therapy targets. Abscissa: number of publications.

Figure 4.

Rabbit, maxilla, 411 days post irradiation. H&E stain of cartilage traversed by a quasi-parallel array of microbeams; valley dose ≈10 Gy; the general tissue structure appears unchanged (Laissue et al unpublished).