Design of a high dynamic range integrated charge to digital converter for online dosimetry in radiotherapy

The Intensity Modulated Radiotherapy allows a more efficient dose delivery in the tumour leading to a reduction of the dose deposited in the nearby healthy organs. However, this technique requires additional resources to perform on line dosimetry and insure patient safety. A quasi transparent 2D transmission detector for monitoring the treatment X-ray beam has been developed. It includes a high performance embedded electronics relying on a Charge to Digital Converter designed in a CMOS 0.35 μm process. The Charge Balancing Integration technique coupled to an internal 6-bit Analog to Digital Converter allows high resolution and high dynamic range to be reached. This 16-channel, 16-bit converter exhibits a 6 fC LSB value, a nonlinearity better than 0.1 LSB and a RMS noise lower than 0.5 LSB.