Towards a novel small animal proton irradiation platform: the SIRMIO project

Background: Precision small animal radiotherapy research is a young emerging field aiming to provide new experimental insights into tumor and normal tissue models in different microenvironments, to unravel complex mechanisms of radiation damage in target and non-target tissues and assess efficacy of novel therapeutic strategies. For photon therapy, modern small animal radiotherapy research platforms have been developed over the last years and are meanwhile commercially available. Conversely, for proton therapy, which holds potential for an even superior outcome than photon therapy, no commercial system exists yet. Material and methods: The project SIRMIO (Small Animal Proton Irradiator for Research in Molecular Image-guided Radiation-Oncology) aims at realizing and demonstrating an innovative portable prototype system for precision image-guided small animal proton irradiation, suitable for installation at existing clinical treatment facilities. The proposed design combines precise dose application with in-situ multi-modal anatomical image guidance and in-vivo verification of the actual treatment delivery. Results and conclusions: This manuscript describes the status of the different components under development, featuring a dedicated beamline for degradation and focusing of clinical proton beams, along with novel detector systems for in-situ imaging and range verification. The foreseen workflow includes pre-treatment proton transmission imaging, complemented by ultrasonic tumor localization, for treatment planning and position verification, followed by image-guided delivery with on-site range verification by means of ionoacoustics (for pulsed beams) and positron-emission-tomography (PET, for continuous beams). The proposed compact and cost-effective system promises to open a new era in small animal proton therapy research, contributing to the basic understanding of in-vivo radiation action to identify areas of potential breakthroughs for future translation into innovative clinical strategies

Performance evaluation of a staggered three-layer DOI PET detector using a 1 mm LYSO pitch with PETsys TOFPET2 ASIC: comparison of HAMAMATSU and KETEK SiPMs

In this study, we propose a staggered three-layer depth-of-interaction (DOI) detector with a 1 mm crystal pitch and 19.8 mm total crystal thickness for a high-resolution and high-sensitivity small animal in-beam PET scanner. A three-layered stacked LYSO scintillation array (0.9~×~0.9~×~6.6 mm3crystals, 23~×~22 mm2surface area) read out by a SiPM array (8~×~8 channels, 3~×~3 mm2active area/channel and 50μm microcell size) with data acquisition, signal processing and digitization performed using the PETsys Electronics Evaluations kit (based on the TOFPET v2c ASIC) builds a DOI LYSO detector block. The performance of the DOI detector was evaluated in terms of crystal resolvability, energy resolution, and coincidence resolving time (CRT). A comparative performance evaluation of the staggered three-layer LYSO block was conducted with two different SiPM arrays from KETEK and HAMAMATSU. 100% (KETEK) and 99.8% (HAMAMATSU) of the crystals were identified, by using a flood irradiation the front- and back-side. The average energy resolutions for the 1st, 2nd, and 3rd layers were 16.5 (±2.3)%, 20.9(±4.0)%, and 32.7 (±21.0)% (KETEK) and 19.3 (±3.5)%, 21.2 (±4.1)%, and 26.6 (±10.3)% (HAMAMATSU) for the used SiPM arrays. The measured CRTs (FWHM) for the 1st, 2nd, and 3rd layers were 532 (±111) ps, 463 (±108) ps, and 447 (±111) ps (KETEK) and 402 (±46) ps, 392 (±54) ps, and 408 (±196) ps (HAMAMATSU). In conclusion, the performance of the staggered three-layer DOI detector with 1 mm LYSO pitch and 19.8 mm total crystal thickness was fully characterized. The feasibility of a highly performing readout of a high resolution DOI PET detector via SiPM arrays from KETEK and HAMAMATSU employing the PETsys TOFPET v2c ASIC could be demonstrated

Induced radioactivity of a GSO scintillator by secondary fragments in carbon ion therapy and its effects on in-beam OpenPET imaging

The accumulation of induced radioactivity within in-beam PET scannerscintillators is of concern for its long-term clinical usage in particle therapy.To estimate the effects on OpenPET which we are developing for in-beam PETbased on GSOZ (Zi doped Gd2SiO5), we measured the induced radioactivityof GSO activated by secondary fragments in a water phantom irradiation by a12C beam with an energy of 290 MeV u−1. Radioisotopes of Na, Ce, Eu, Gd,Nd, Pm and Tb including positron emitters were observed in the gamma rayspectra of the activated GSO with a high purity Ge detector and their absoluteradioactivities were calculated. We used the Monte Carlo simulation platform,Geant4 in which the observed radioactivity was assigned to the scintillatorsof a precisely reproduced OpenPET and the single and coincidence ratesimmediately after one treatment and after one-year usage were estimated forthe most severe conditions. Comparing the highest coincidence rate originatingfrom the activated scintillators (background) and the expected coincidencerate from an imaging object (signal), we determined the expected signal-tonoiseratio to be more than 7 within 3 min and more than 10 within 1 min fromthe scan start time. We concluded the effects of scintillator activation and theiraccumulation on the OpenPET imaging were small and clinical long-termusage of the OpenPET was feasible.Keywords: in-beam PET, GSO scintillator, particle therapy, openPET,induced radioactivity, secondary fragments(Some figures may appear in colour only in the online journal

Radiation hardness of organic photodiode detectors for carbon beam irradiation

Recently, many groups have been developing organic devices such as photodiodes, electroluminescence cells, photovoltaic cells, and transistors as various detection devices. These organic devices are thin, flexible, printable and inexpensive to manufacture. If they can be used in radiation measurements, it is expected that many innovative radiation detectors can be fabricated because of these desirable characteristics. Especially interesting are organic photodiodes (OPDs) that work like conventional Si semiconductor photodiodes. Based on these points, the OPDs are suitable for application as carbon therapy dosimeters. Therefore, we are investigating the OPDs as radiation detectors for heavy ion beam irradiation. In this presentation, we evaluate the radiation hardness of the OPD detectors to the carbon beam irradiation and report our results.\nThe OPD detector structure consisted of layers of IZO/ PEDOT: PSS / PCBM: P3HT / Al. The OPDs were fabricated on 10 mm × 10 mm black ABS boards by spin coating; fabrication was done 3 days before an experiment. Various sizes of the OPD were used in the experiment. We performed the experiment in the PH2 course of the HIMAC at NIRS. The energy of the 12C beam was 290 MeV/u which is typically used in actual carbon therapy. The OPDs were irradiated by the 12C beam that passed through an ion chamber to monitor the number of irradiated particles. The beam intensity was 1.8×109 particles per second. The diameter of the 12C beam was 1 cm. The induced charges of the OPDs by the carbon beam irradiation and dark current components were measured in the experiment. Experimental results showed that the performance degradations of the OPDs by carbon beam irradiation were negligible for irradiation times in this experiment. Finally, we concluded that the radiation hardness of the OPD detector is sufficient for application as dosimeters for carbon beams.IEEE NSS-MIC201