Silicon Photomultipliers for Deep Tissue Cerenkov Emission Detection During External Beam Radiotherapy

Abstract

Cerenkov Emission (CE) during external beam radiation therapy (EBRT) from a linear accelerator (Linac) has been demonstrated as a useful tool for radiotherapy quality assurance and potentially other applications for online tracking of tumors during treatment delivery. However, some of the current challenges that are impacting the potential of CE are related to the limited detection sensitivity and the lack of flexible tools to fit into an already complex treatment delivery environment. Silicon photomultiplier (SiPM) solid-state devices are new promising tools for low light detection due to their extreme sensitivity that mirrors photomultiplier tubes and yet have a form factor that is similar to silicon photodiodes, allowing for improved flexibility in device design that may help in the process of wider clinical applicability. In this paper, we assess the feasibility of using SiPMs to detect CE during EBRT from a Linac and contrast their performance with commercially available silicon photodiodes (PDs). We demonstrate the feasibility of the SiPM-based probes for standard dosimetry measurements. We also demonstrate that CE optical signals can be detected from tissue depths about five times greater than that for standard probes based on PDs, making our SiPM probe an enabling technology of CE measurements, particularly for deep tissue applications.

An ionizing radiation acoustic imaging (iRAI) technique for real‐time dosimetric measurements for FLASH radiotherapy

“…For this study, individual linac pulses were used as acquisition trigger signals for iRAI. This was accomplished by measuring the Cerenkov Emission (CE) generated in a water/glycerin solution using a silicon avalanche photodiode (Thorlabs APD101A) during each single pulse 24 . The container holding the solution was wrapped in light‐blocking masking tape (Thorlabs, T743) to prevent photodetector saturation due to ambient lights.…”

“…This was accomplished by measuring the Cerenkov Emission (CE) generated in a water/ glycerin solution using a silicon avalanche photodiode (Thorlabs APD101A) during each single pulse. 24 The container holding the solution was wrapped in light-blocking masking tape (Thorlabs, T743) to prevent photodetector saturation due to ambient lights. This device was placed before the electron beam was collimated and was out of the central axis of the beam, relying off scattered electrons to generate the CE during the time period when the beam was ON.…”

Measuring Tumor Microenvironment pH During Radiotherapy Using a Novel Cerenkov Emission Multispectral Optical Probe Based on Silicon Photomultipliers

“…The work reported here extends the previous work using SiPM based optical probes [33] and introduces a novel Cerenkov Emission Multispectral Imaging (CMSI) optical probe application, based on SiPMs, that can take multiple spectral measurements of CE during external beam radiotherapy (EBRT). Here, we demonstrate that such CMSI probes can measure pH changes in vitro to delineate the treatment response in heterogeneous radiation sensitivity cell lines and has also shown promise in a pilot mouse study for in vivo pH measurements.…”

“…The CMSI optical probe (supplied by Endectra), shown in Figure 2A, consists of four 1 × 1 mm 2 SiPM channels (MicroFC-10035-SMT, ON Semiconductor) mounted on a flexible substrate with integrated transimpedance amplifiers (2200 V/A), as described in greater detail in an earlier publication [33]. The multispectral configuration used for this work is shown schematically in Figure 2B, with two spectral channels, which have integrated optical bandpass filters (chosen based on the spectral features of interest), one channel with no optical filtration (in order to collect the integrated optical intensity), and one channel that is referred to as "Light-Blocked" (LB), which is opaque to incident optical light (measuring only the signal generated from either scattered radiation or CE generated within the filter/SiPM encapsulation material).…”

“…Though the spatial resolution is excellent with these methods, one of the limitations of using a camera imaging at a distance away is that it is limited to superficial measurements of CE for dosimetry and is even more limited for deep tissue spectroscopy, where only a small region of the overall CE spectrum can be measured at any given time. An alternative approach involving on-skin, hypersensitive optical probes, based on solid-state silicon photomultipliers (SiPMs), has been shown to have the ability to measure CE that can result from deep seated regions in tissue with improved signal-to-noise ratio (SNR) [33]. This higher sensitivity is much needed for spectroscopy applications where the molecular signal is much weaker than that for typical irradiation dose measurements.…”