Towards neuro-oncologic clinical trials of high dose rate synchrotron Microbeam Radiation Therapy: first treatment of a spontaneous canine brain tumor.: First microbeam treatment of canine brain tumor.

INTRODUCTION

The high potential of Microbeam Radiation Therapy (MRT) in improving tumor control whilst reducing side effects has been shown by numerous preclinical studies. MRT offers a widened therapeutic window by using the periodical spatial fractionation of synchrotron generated x-rays into an array of intense parallel microbeams. MRT now enters a clinical transfer phase. As proof of principle and cornerstone for the safe clinical transfer of MRT, we conducted a "first in dog" trial under clinical conditions. In this report, we evaluated whether a 3D conformal MRT can be safely delivered as exclusive radiosurgical treatment in animal patients.

METHODS

We irradiated a 17.5 kg French Bulldog for a spontaneous brain tumor (glioma suspected on MRI) with conformal high dose rate microbeam arrays (50µm-wide microbeams, replicated with a pitch of 400μm) of synchrotron-generated x-rays. The dose prescription adjusted a minimal cumulated valley dose of 2.8Gy to the PTV (CTV+1mm). Thus, each beam delivered 20-25Gy to the target as peak doses, and ∼1Gy as valley doses.

RESULTS

The treatment was successfully delivered. Clinical follow-up over 3 months showed a significant improvement of the dog's quality of life: the symptoms disappeared. MRI, performed 3 months post irradiation, revealed reduction in tumor size (-87.4%) and mass effect with normalization of the left lateral ventricle.

CONCLUSION

To our knowledge, this neuro-oncologic veterinary trial is the first 3D conformal synchrotron x-ray MRT treatment of a spontaneous intracranial tumor in a large animal. It is an essential last step towards the clinical transfer of MRT in the near future, to demonstrate the feasibility and safety of treating deep seated tumors using synchrotron-generated microbeams.