Wearable Full-Organic Radiation Detector for Real-Time Dose Monitoring During Radiation Therapy

Mechanical flexibility, portability, low cost of fabrication, scalability onto large areas and human tissue equivalence are crucial properties which make organic and hybrid semiconductors excellent candidates for the development of wearable personal dosimeters. Among others, their employment in the medical field (i.e. during proton therapy treatments) to monitor in real-time and in-situ the dose delivered to the patients during radiotherapy is extremely promising.<br/>Here, we present the results achieved with an innovative fully-organic detector, where a flexible phototransistor (OPT) based on dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) is coupled with a plastic scintillator based on polysiloxane (i.e. homopolymer polymethylphenylsiloxane and polyvinylphenyl-co-phenylmethyl). The ion beam induced luminescence spectra of the scintillators under irradiation with 2 MeV protons and the UV–vis absorbance spectrum of the DNTT film show a significative overlapping, assuring spectral matching between the light emitting sensor (siloxane scintillator) and the photoconverter (DNTT sensitized OPT). Besides, the coupling between the two components of the detector perfectly preserve the mechanical flexibility and conformability of the device. In fact, this detector demonstrated mechanical flexibility down to a curvature radius of RC = 0.5 cm and low power operation (VDS = VGS = -1 V), assessing its potential employment as a personal dosimeter with high comfort and low risk for the patient.<br/>The detector has been firstly tested under 5 MeV proton beam to reproduce the end-of-range conditions typically present at the border of the target during the prostate cancer treatment. We carried out these tests at LABEC ion beam center (Firenze, Italy). We irradiated the devices with subsequent 10 s cycles of irradiation varying the fluxes of particles in the range of (10⁶ ÷ 10¹⁰) H⁺s⁻¹cm⁻². The photocurrent leads to a steep increase upon irradiation which is proportional to the proton flux.<br/>We present a kinetic model able to precisely reproduce the dynamic response of the device under irradiation and to provide further insight into the physical processes controlling it. By this model, the response of the detector, the rise and fall dynamic, and the progressive build-up of a persistent photocurrent are correctly reproduced. The two components identified in the response under proton flux (a swift and a persistent one) were attributed to two kinds of photo-induced defects with different mean values of the distribution of the recovery activation energies. It was demonstrated experimentally and confirmed by the computational analysis that the fast response is recurring, independently from the persistent current drift, thus assessing the suitability of the here proposed devices as a real-time proton detector.<br/>Then, to assess the use of this technology as personal dosimeter, the detecting system has been tested in actual clinical conditions employing an anthropomorphic phantom mimicking the human pelvis, and a therapeutic proton beams provided by the TIFPA proton therapy center (Trento, Italy) typically employed for prostate cancer treatment (energy in the range [70-200] MeV). The wearable detector has been placed in two different positions: (i) centered on the target of the beam (i.e. in the prostate position) and decentered from it, in the region surrounding the tumor (i.e. the rectum which is one of the organs at risk that would benefit from a real-time monitoring of the impinging radiation). The dynamic curve shows that this device is able to monitor in-situ and in real-time the presence/absence of radiation for the accurate recording and mapping of the dose delivered during a treatment plan. Finally, the detector has been characterized as dosimeter when placed centered in the target position demonstrating dose linearity and providing a stable response even after hard and long-lasting proton irradiation (up to 2 x 10¹⁰ protons, 30 min of operation).