An LED PLD based controller for experimental characterization of an optical fibre sensor system for measurement of x-ray radiation in clinical linacs

A novel robust compact light emitting diode (LED) based laboratory simulator system for mimicking the output from an optical fibre sensor used to detect therapeutic X-ray pulses from a clinical linear accelerator (linac) is described and performance characterised with reference to real clinical data. The purpose of configuring the LED system is to facilitate accurate assessment of the operating characteristics of the optical fibre based measurement system without having to deploy it in the clinic, thus minimising the need for expensive repeated clinical testing. The output signal from the scintillation material based optical fibre sensor is known to be pulsatile in response to the pulsed X-ray output of the linac. An in-depth knowledge of the characteristics of the X-ray pulsed waveform arising from a series of previous clinical based measurements has facilitated the design and construction of the dedicated LED source described in this article. Results are presented using a field programmable gate array (FPGA) LED simulator source system that replicates a wide range of the linac's pulsed output waveforms including being able to vary the amplitude, pulse width and frequency (repetition rate) of the source. These results are compared to recent results captured using a multi-pixel photon counting (MPPC) detector in the clinic for proving efficacy.