Radiation 2006. In association with the Polymer Division, Royal Australian Chemical Institute. Incorporating the 21st AINSE Radiation Chemistry Conference and the 18th Radiation Biology Conference, conference handbook

Full text: For Quality Assurance (QA) in Fast Neutron Therapy (FNT), separate verification of neutron and gamma absorbed dose in a water phantom or in vivo is essential due to the different RBEs of each component of the radiation. Currently the paired detector method is used for measurements of neutron and gamma doses which is based on tissue equivalent ionization chambers (TEIC) and Geiger- Muller (G-M) counters. This approach essentially has an uncertainty within 8% due to unknown accuracy sensitivity of G-M counter to fast neutron radiation and possible pile up effect. Poor spatial resolution of TEIC and temporal inefficiencies related to two independent scans with different types of detectors is another drawback of this method. A new passive single Si sensor based on a combination of a planar and bulk p-i-n Si detector has been developed. This device is capable of measuring neutron and gamma doses concurrently. This is achieved by simultaneous measurements of neutron displacement KERMA (change of the forward voltage of the planar p-i-n diode) and ionization charge induced in the same silicon sensor. A reader and software for scanning mode applications and presentation in real time has also been developed. The dosimetry system was tested in a water phantom on a mixed gamma-neutron beam at a Fast Neutron Therapy (FNT) facility with an average neutron energy of 20 MeV and maximum energy 48.5MeV and also at a Co-60 facility for calibration in charge mode. It was demonstrated that neutron and gamma doses were in good agreement with dose derived from the paired detector method. In 'edge on' mode, the Si planar sensors had much better spatial resolution in deriving of penumbra of the beam in the water phantom, and this was found to be 0.35mm (limited by sensor thickness) in comparison with the TEIC's spatial resolution of approximately 6-10mm. The depth dose distribution of neutron doses in the water and the total doses were within 3-5% of the dual detector method. Therefore, a system has been implemented for QA and real time dosimetry in FNT