Study on dosimetry for therapeutic carbon beams (in Japanese)

Abstract

The main objective of this study is to establish reliable dosimetry for high-energy carbon beams used for cancer treatment. The thesis describes and compares the absolute dosimetry using an ionization chamber, a calorimeter, and a fluence detector. The doses obtained with the three methods were in agreement within experimental errors. The discrepancy between the ionization chamber and calorimeter methods was less than 1%, making the ionization chamber method appropriate for carbon beam dosimetry. Good agreement, within 0.5%, was obtained in a dosimetry intercomparison between two different carbon beam facilities, NIRS and GSI-DKFZ in Germany. Miniature p-type silicon diodes were investigated as relative dosimeters. They were used in a head phantom for the verification of the treatment planning. A simple method using visible light emitted from a bare plastic scintillator allowed real-time range measurements with spatial resolution better than 0.5 mm. Fragmentation of carbon nuclei in an energy absorber may possibly change the fluence of carbon beams to be used for patient irradiation. Survival of primary carbon beams after passing through an absorber was measured with ΔE plastic scinitillator. The results showed that polyethylene and PMMA were water equivalent in terms of the nuclear reactions and appropriate as energy absorbers to shift the range of the primary beams. The total charge-changing cross sections of several materials for carbon beams were deduced from the slope of the attenuation. Dosimetry is essential to compare and/or to discuss biological effects and clinical results. This study contributed significantly to the NIRS carbon beam therapy trials. © 2000, American Association of Physicists in Medicine. All rights reserved.