Assessment of Silicon Drift Detector Timing Performance for Proton Therapy Application

Proton therapy is a growing modality for cancer treatment, thanks to the finite penetration range of protons with a localized dose deposition maximum. However, range uncertainties prevent full exploitation of these advantages in clinical practice, leading to the need of range monitoring during treatment. One approach is to take advantage of high-energy (2 – 8 MeV) prompt-gamma (PG) rays, naturally produced in nuclear reactions between protons and target nuclei. In this paper, we study the timing performances of the Silicon Drift Detector (SDD) as a photodetector candidate to be used for the scintillator readout for high-energy gamma detection in this application. The peculiar drift mechanism of the charge created inside the SDD volume is responsible for a non-negligible rise time of the signal at the output of the device. In this work, the effect of the drift mechanism on the timing performances of SDDs is first theoretically assessed in a device-level simulation. Next, experimental evaluation of the timing resolution is performed by directly irradiating the sensor with laser light.