Differences between Bragg curves for an unmodulated 78 MeV proton beam measured with different ionization chambers

Depth dose measurements were performed with several ionization chambers (Capintec/PR-06G, Attix, PTW/Markus and Exradin T1) irradiated in either water or RMI 457 solid water to determine the shape of the depth dose curve for a 78 MeV unmodulated proton beam. Differences in the depth dose curves measured with these chambers can be corrected by a depth scaling factor based on the ratio of the depth of the Bragg peak in water and depth of the Bragg peak in the phantom material (R^wat _peak/R^med_peak). The depth scaling factor for RMI 457 solid water phantom was determined by this method to be 1.024. An effective point of measurement correction for the Capintec/PR-06G ionization chamber proposed by AAPM-TG25 dosimetry protocol for electron beams is also applicable to proton beams