Characterization of the IBA StingRay plane-parallel ionization chamber for proton and carbon dosimetry

Abstract

The vendor IBA (IBA Dosimetry GmbH, Schwarzenbruck, Deutschland) has developed a new large area plan-parallel ionisation chamber, the so called IBA StingRay chamber, with an outer diameter of 156 mm and a nominal diameter of the active area of 120 mm. Different methods to measure a lateral dose response profile of a plane-parallel ionisation chamber were executed with the IBA StingRay chamber and compared within this thesis. Horizontal and vertical profile measurements with photon and proton beams as well as a diagonal profile measurement with photon beam were performed. The horizontal response of both IBA StingRay chambers (SN91 and SN93) with XRay beam showed an increase of the chamber charge of 5% from chamber radius ±25 to ±60 in comparison to the charge at the center. The vertical profile of IBA StingRay chambers in the X-ray beam had no increase towards the edges like that one of the horizontal axis. The results of vertical and horizontal axis of IBA StingRay SN91 with proton beam were similar to the measurements with X-ray beam, except for the increase at the horizontal axis, which occurred for X-ray beam. Moreover a field of 70 mm x 70 mm was measured with a photon beam. The results of this measurements showed that the chamber dose profile of IBA StingRay SN91 and SN93 were similar, but the chamber response of IBA StingRay SN93 was over all measurement points about 2% higher. Furthermore the polarity, dose stability, dose rate stability and voltage stability of IBA StingRay were measured with X-ray beam. The ion recombination effect of the IBA StingRay were measured with a carbon ion beam. The polarity of IBA StingRay chamber SN91 had a maximum of 1.12%, the relationships of dose stability as well as dose rate stability were linear and the voltage stability was quadratic. The ion recombination effect was measured with different carbon ion beam key energies at the plateau, in peak and fall off. Moreover different chamber voltages from -150 V up to 150 V were applied to the IBA StingRay chamber and its corresponding response measured. Measurements with and without ripple filter and different degrader settings were gathered and analyzed. Last but not least also lateral offsets (±30 mm) were applied to the chamber location. The initial recombination had a maximum of 1.5% and the volume recombination was maximal 0.2% at the bragg peak. In summary was the behaviour of IBA StingRay chamber SN91 and SN93 very similar. If the IBA StingRay chamber is compared with PTW 34089, it showed that the Ionization chamber charge of IBA StingRay was lower than the Ionization chamber charge of PTW 34089.