Application of a small ionization chamber to the measurement of pulsed proton beams

The 0.01 ml micro ionization chamber has been re-calibrated in the clinical proton beam by the comparison with the 0.6 ml JARP chambers on the basis of the protocol of ICRU report 59. As the result, if we faithfully obey the protocol, the value of Awall for 60Co beams can be estimated to be 1.005. This may be related to an influence of secondary electrons generated at stem part of the micro ionization chamber by 60Co beams. But, it should be noted that the present protocol does not include any perturbation effects for proton beams. It has turned out that Boag's formulation is no longer available for the 0.01 ml micro chamber. The excellent spatial resolution of the micro chamber is suitable for profile measurements and also applicable to the dosimetry for small size fields. (author)