An Update on the Depth-Dose Curve of Antiprotons

TY - CONF

T1 - An Update on the Depth-Dose Curve of Antiprotons

AU - Taasti, Vicki Trier

AU - Holzscheiter, Michael H.

AU - Knudsen, Helge

AU - Bassler, Niels

PY - 2014

Y1 - 2014

N2 - Purpose:The CERN AD-4/ACE project aims to measure the relative biological effectiveness of antiprotons. We have revisited previously published data for the antiproton depth-dose curve [1], where the relative dose deposition normalized to a point in the plateau region was plotted. In this revision we refine the experimental set-up to obtain absolute dose per primary particle, and compare these with simulations.Materials and Methods:Scrutinizing the geometrical setup, we could calculate beam scattering along the antiproton beam, which enables replotting the depth-dose curve as absolute dose in water. The experimental results are compared with the Monte Carlo particle transport code SHIELD-HIT12A.Contrary to [1], here the full ionization chamber is simulated and the dose is scored in the ionization chamber air gap. Stopping power ratios are determined as well in order to translate the simulated dose to dose-to-water formalism.Results: Generally, the experimental data are in good agreement with the simulated dose on an absolute scale in the plateau region. However some deviations are found near the annihilation peak. A full geometric description of the ionization chamber simulation improves the situation, in particular on the upstream side of the Bragg-peak. This is attributed to a different spectrum of annihilation products created in the entrance window of the ionization chamber in comparison to the case of simply simulating annihilation taking place on water.Yet, a large portion of dose still is missing in the Bragg-peak. This effect is also visible in the tail where the dose is underestimated in both types of simulations because of the missing annihilation energy/products. Conclusions:The shape of the Bragg-peak has some dependence on what material the antiprotons is annihilating on. Precise modelling of the detector is therefore inevitable. The missing energy in the annihilation peak remains to be explained, but may be related to an overestimation of inelastic cross sections of the antiprotons.[1] Bassler, N., et al., The antiproton depth-dose curve in water, Phys. Med. Biol. 53 (2008), 793.

AB - Purpose:The CERN AD-4/ACE project aims to measure the relative biological effectiveness of antiprotons. We have revisited previously published data for the antiproton depth-dose curve [1], where the relative dose deposition normalized to a point in the plateau region was plotted. In this revision we refine the experimental set-up to obtain absolute dose per primary particle, and compare these with simulations.Materials and Methods:Scrutinizing the geometrical setup, we could calculate beam scattering along the antiproton beam, which enables replotting the depth-dose curve as absolute dose in water. The experimental results are compared with the Monte Carlo particle transport code SHIELD-HIT12A.Contrary to [1], here the full ionization chamber is simulated and the dose is scored in the ionization chamber air gap. Stopping power ratios are determined as well in order to translate the simulated dose to dose-to-water formalism.Results: Generally, the experimental data are in good agreement with the simulated dose on an absolute scale in the plateau region. However some deviations are found near the annihilation peak. A full geometric description of the ionization chamber simulation improves the situation, in particular on the upstream side of the Bragg-peak. This is attributed to a different spectrum of annihilation products created in the entrance window of the ionization chamber in comparison to the case of simply simulating annihilation taking place on water.Yet, a large portion of dose still is missing in the Bragg-peak. This effect is also visible in the tail where the dose is underestimated in both types of simulations because of the missing annihilation energy/products. Conclusions:The shape of the Bragg-peak has some dependence on what material the antiprotons is annihilating on. Precise modelling of the detector is therefore inevitable. The missing energy in the annihilation peak remains to be explained, but may be related to an overestimation of inelastic cross sections of the antiprotons.[1] Bassler, N., et al., The antiproton depth-dose curve in water, Phys. Med. Biol. 53 (2008), 793.

M3 - Poster

T2 - ENLIGHT Annual Meetings 2014

Y2 - 10 July 2014 through 12 July 2014

ER -