Abstract
Purpose: To perform dosimetric characterization of a minibeam collimator in both carbon and
oxygen ion beams to guide optimal set up geometry and irradiation for future radiobiological studies
using these beams.
Methods: Carbon and oxygen minibeams were generated using a prototype tungsten multislit
collimator presenting line apertures 700 μm wide, which are spaced 3500 μm centre-to-centre
distance apart. Several radiation beam spots generated the desired field size of 15×15 mm2 and
production of a 50 mm long spread out Bragg peak (SOBP) centered at 80 mm-depth in water. Dose
evaluations were performed with two different detectors: a PTW microDiamond R© single crystal
diamond detector and radiochromic films (EBT3). Peak-to-valley dose ratio (PVDR) values, output
factors (OF), penumbras and full width at half maximum (FWHM) were measured.
Results: Measured lateral dose profiles exhibited spatial fractionation of dose at depth in a water
phantom in the expected form of peaks and valleys for both carbon and oxygen radiation fields.
The diamond detector and radiochromic film provided measurements of PVDR in good agreement.
PVDR values at shallow depth were about 60 and decreased to about 10 at 80 mm-depth in water.
OF in the center of the SOBP was about 0.4; this value is larger than the corresponding one in
proton minibeam radiation therapy measured using comparable collimator due to a reduced lateral
scattering for carbon and oxygen minibeams.
Conclusions: Carbon and oxygen minibeams may be produced by a mechanical collimator.
PVDR values and output factors measured in this first study of these minibeam radiation types
indicate there is potential for their therapeutic use. Optimization of minibeam collimator design
and the number and size of focal spots for irradiation are advocated to improve PDVR values and
dose distributions for each specific applied use.
