Measurement of the stopping power of water for carbon ions in the energy range of 1 MeV - 6 MeV using the inverted Doppler–shift attenuation method
von Johannes Martin Rahm
Datum der mündl. Prüfung:2016-10-31
Betreuer:Prof. Dr. Hans Christian Hofsäss
Gutachter:Prof. Dr. Hans Christian Hofsäss
Gutachter:Prof. Dr. Tim Salditt
EnglischCancer therapy using carbon ions has gained increasing interest in the last decade due to its advantageous dose distributions. For the dosimetry and treatment planning, the accurate knowledge of the stopping power of water for carbon ions is of crucial importance. In the high energy region, the stopping power can be calculated rather accurately by means of the Bethe–Bloch formula. In the case of projectile velocities comparable to those of the valence electrons of the target, these calculations are subject to large uncertainties. There exist no experimental data for the stopping power of water for projectile energies prevailing in the so–called Bragg peak region. The currently available stopping power data for water are derived from measurements in water vapour or D2O ice and, hence, neglect the dependence on the state of aggregation. The stopping power of water for charged particles is of high interest not only for practical applications but also to consider how physical and chemical state of the target influence the collisional energy transfer. For the measurement of the stopping power of water, the inverted Doppler–shift attenuation method was used in this work. This method has the advantage that the projectile itself is not needed to be detected and can be slowed down entirely in the target. In this method, the stopping power is determined from the Doppler–shift of the gamma–quanta emitted by projectiles during their slow down. This experiment can be performed at atmospheric pressure and consequently, the stopping power of water can be measured in its real physiological condition. In this work, the stopping power of water for carbon ions was measured for the first time in the energy range between 1 MeV and 6 MeV covering the kinetic energies of carbon ions in the Bragg peak region. The experimental method is presented in detail along with the design of the apparatus and of the data acquisition system. A comprehensive analysis of instrumental effects influencing the experimental results was performed. The overall relative uncertainty of the present data amounts to 11.9%. Within the uncertainty, the measured data is consistent with the stopping power predicted by MSTAR , CASP  and the recommendation of the ICRU report 73 errata . The data predicted by SRIM2013  and ICRU report 73  appear to be higher by 13% in average.
Keywords: carbon ions; cancer therapy; inverted Doppler-shift attenuation method; stopping power of water