A small electronics prototyping business has agreed to assist in the development of a second generation detector interface. Delivery of this device is scheduled for mid-September, 2010 due to problems with the high voltage circuits of the photon counting modules. It will be a self-gated system with 4 detection channels and all signal processing will be performed completely via hardware. Additionally, new fibers are being developed by NRL that will be more uniform in dose response and will be based on a 100 micron optical fiber rather than the current 400 micron model. The resulting system will undergo validation as a radiation dosimetry system and will be employed for non-routine clinical and research measurements involving small field and micro-field dosimetry for both megavoltage and kilovoltage x-ray and electron beams. The prototype dosimeter electronics have been delivered. Preliminary experiments have detected small calibration shifts between measurement sets. Currently the measurement uncertainty is +/-4%. If the shift can be eliminated, it will reduce to +/-0.5%. We are currently working with the company to determine the source of the uncertainty and to correct it. Once this is completed, we will fully certify the system for clinical measurements. Additionally, modification to the software will permit operation of the device in continuous acquisition as well as pulsed mode. This will permit use of the device for dosimetry with lower energy x-ray energies (orthovoltage x-rays and most brachytherapy sources). This is important for the measurement of very small field size dose distributions and output factors associated with the newly acquired small animal imaging irradiator.
