Characterization of PTW-31015 PinPoint ionization chambers in photon and proton beams.

In this study, 48 PTW-TM31015 PinPoint-type micro-ionization chambers that are used in the commissioning and patient specific QA of a proton pencil beam scanning (PBS) delivery system have been characterized in proton and high-energy photon beams.
 
 In both beam modalities, the entire set of PinPoint chambers was characterized by imaging them, by evaluating their stability using check source measurements, by experimentally determining the ion recombination, polarity effect and by cross calibrating them in terms of absorbed dose to water against Farmer-type ionization chambers. Beam quality correction factors were theoretically derived for both beam modalities. 
 
 None of the chambers' check source readings drifted by more than 0.5% over a one year period. Beam quality correction factors for the 6 MV photon with reference to<sup> 60</sup>Co were on average 1.0±0.5% lower than the theoretical values calculated according to the data and procedures outlined in IAEA TRS-398. While this difference is within the overall dosimetric uncertainty, it is significant considering only uncorrelated uncertainties indicating inconsistencies in the theoretical data. Beam quality correction factors for the 179.2 MeV proton beam with reference to <sup>60</sup>Co were in good agreement with the theoretical data. Ion recombination and polarity correction factors were very consistent for all chambers with sta...

Source: Physics in Medicine and Biology - August 28, 2018 Category: Physics Authors: Carlino A, Stock M, Zagler N, Marrale M, Osorio J, Vatnitsky S, Palmans H Tags: Phys Med Biol Source Type: research