A measuring system with a recombination chamber for neutron dosimetry around medical accelerators

A measuring system for dosimetry of neutrons generated around medical electron accelerators is proposed. The system consists of an in-phantom tissue-equivalent recombination chamber and associated electronics for automated control and data acquisition. A second ionization chamber serves as a monitor of photon radiation. Two quantities are determined by the recombination chamber-the total absorbed dose and the recombination index of radiation quality. The ambient dose equivalent, H*(10), or neutron absorbed dose in an appropriate phantom, can be then derived from the measured values. Tests of the system showed that a 0.5% dose contribution of neutrons to the absorbed dose of photons could be detected and estimated under laboratory conditions. Preliminary tests at the 15 MV Varian Clinac 2300C/D medical accelerator confirmed that the measuring system could be used under clinical conditions. The H*(10) of the mixed radiation was determined with an accuracy of ∼10%.