Microbeam-irradiated tumour tissue possesses a different infrared absorbance profile compared to broad beam and sham-irradiated tissue.

PURPOSE

To investigate biochemical changes in mouse tumour tissue following Microbeam Radiation Therapy (MRT) and Broad Beam (BB) irradiation using synchrotron Fourier-Transform Infrared (FTIR) microspectroscopy.

MATERIALS AND METHODS

Synchrotron FTIR microspectroscopy was carried out on mouse tumour sections previously irradiated with BB (11, 22 or 44 Gy), MRT (560 Gy in-beam, 25 μm wide, 200 μm peak separation) or sham-irradiation (0 Gy) from mice culled 4 hours post-irradiation.

RESULTS

MRT and BB-irradiated tumour sections showed clear chemical shifts in spectral bands corresponding to functional group vibrations in protein (1654-1630 cm(-1)), lipid (~1470, 1463 cm(-1)) and nucleic acid (1130-1050 cm(-1)). MRT peak and valley regions showed virtually identical absorbance patterns in protein and lipid regions. However, we observed chemical shifts corresponding to the nucleic acid region (1120-1050 cm(-1)) between the peak and valley dose regions. Chemical maps produced from integrating absorbance bands of interest over the scanned tumour area did not reveal any microbeam paths.

CONCLUSIONS

The lack of difference between MRT peak and valley irradiated areas suggests a holistic tissue response to MRT that occurs within 4 h, and might be the first evidence for a mechanism by which MRT kills the whole tumour despite only a small percentage receiving peak irradiation.