A 76×55 X-Ray Energy Binning Dosimeter for Closed-Loop Cancer Radiotherapy

X-ray radiation dose delivered during cancer radiotherapy is nonlinear with biological effect on cancer cells and healthy tissues, necessitating an understanding of X-ray energy deposition at the single photon level. Here we present a single X-ray sensitive, energy binning ASIC to enable closed-loop cancer radiotherapy to personalize patient treatment. We use deep n-well (DNWELL) diodes designed at low capacitive nodes $(\mathrm{C}_{\text{diode}})$, such that the miniscule energy deposition from single X-rays at these nodes generates a voltage signal large enough to be sensed $(\mathrm{V}_{\text {diode }}=\mathrm{Q}_{\text {dep }} / \mathrm{C}_{\text {diode }})$, where $\mathrm{V}_{\text{diode}}\propto$ energy deposited. To enable single photon energy resolution without the significant power and area of high resolution ADCs, we implement an analog voltage supply (AVDDH) -log resistor grid to create a pixel sensitivity gradient for X-ray energy binning. The ASIC is highly linear with radiation dose (10–250 cGy) and accurately tracks dose up to 3 cm deep in tissue.