A new method of creating minibeam patterns for synchrotron radiation therapy: a feasibility study.

Several synchrotrons around the world are currently developing innovative radiotherapy techniques with the aim of palliating and possibly curing human brain tumors. Amongst them, microbeam radiation therapy (MRT) and, more recently, minibeam radiation therapy (MBRT) have shown promising results. In MBRT the beam thickness ranges from 500 to 700 microm with a separation between two adjacent minibeams of the same value, whilst in MRT the thickness is of the order of 25-50 microm with a distance between adjacent microbeams of the order of 200 microm. An original method has been developed and tested at the ESRF ID17 biomedical beamline to produce the minibeam patterns. It utilizes a specially developed high-energy white-beam chopper whose action is synchronized with the vertical motion of the target moving at constant speed. Each opening of the chopper generates a horizontal beam print. The method described here has the advantage of being simple and reliable, and it allows for an easy control of the patient safety in future clinical trials. To study the feasibility of the method, dosimetric measurements have been performed using Gafchromic HD-810 films and compared with Monte Carlo simulations. The results of this comparison are discussed.