Intercalibration of a polycrystalline 3D diamond detector for small field dosimetry

In medical radiation dosimetry, the use of small photon fields is almost a prerequisite for high precision localized dose delivery to delineated target volumes. The accurate measurement of standard dosimetric quantities in such situations depends on the size of the detector with respect to the field dimensions. Polycrystalline diamond devices with 3-dimensional structures are produced by using laser pulses to create graphitic paths in the diamond bulk. By fabricating very narrow and close-by columnar electrodes perpendicular to the detector surface, it is possible to create arrays of 3-D cells (pixels) with a very small sensitive volume. In order to present a solution to the problem of the detector size for small field dosimetry the 3-D technology aims to a new highly segmented larger polycrystalline diamond dosimeter to obtain field profiles in a single measurement, reducing the uncertainty of the delivered dose. To this purpose a 3D all carbon detector with an array of 9 3-D pixels has been produced. Due to the heterogeneous structure of the polycrystalline diamond substrate, it was necessary to study the response of each pixel under a standard field photon beam (10 x 10 cm2). For 6 pixels of the array was demonstrated that they present different sensitivities to the radiation beam, but the response is linear and stable hence different calibration factors can be applied to obtain an overall detector response and reduce the uncertainty of the delivered dose.