Minibeam radiation therapy at a conventional irradiator: Dose-calculation engine and first tumor-bearing animals...

Minibeam radiation therapy (MBRT) is a novel therapeutic strategy, whose exploration was hindered due to its restriction to large synchrotrons. Our recent implementation of MBRT in a wide-spread small animal irradiator offers the possibility of performing systematic radiobiological studies. The aim of this research was to develop a set of dosimetric tools to reliably guide biological experiments in the irradiator.

A Monte Carlo (Geant4)-based dose calculation engine was developed. It was then benchmarked against a series of dosimetric measurements performed with gafchromic films. Two voxelized rat phantoms (ROBY, computer tomography) were used to evaluate the treatment plan of F98 tumor-bearing rats. The response of a group of 7 animals receiving a unilateral irradiation of 58 Gy was compared to a group of non-irradiated controls.

The good agreement between calculations and the experimental data allowed the validation of the dose-calculation engine. The latter was first used to compare the dose distributions in computer tomography images of a rat's head and in a digital model of a rat's head (ROBY), obtaining a good general agreement. Finally, with respect to the in vivo experiment, the increase of mean survival time of the treated group with respect to the controls was modest but statistically significant.

The developed dosimetric tools were used to reliably guide the first MBRT treatments of intracranial glioma-bearing rats outside synchrotrons. The significant tumor response obtained with respect to the non-irradiated controls, despite the heterogenous dose coverage of the target, might indicate the participation of non-targeted effects.