High-energy Gamma Photons Research Articles

Improving the efficiency of polymer solar cells based on chitosan@PVA@rGO composites via gamma-irradiated treatment of rGO nanoparticles

Polymer solar cells (PSCs) are growing as attractive contenders for renewable energy technologies given their low cost, adaptability, and environmental sustainability, rendering them valuable in combating climate change. Interestingly, this work investigates the augmentation of photon absorption and overall efficiency in low-cost, effective active layers (ALs) via gamma irradiation treatment, thereby raising the number of active absorption sites. For the first time, novel Chitosan@PVA@rGO (CPG) composite sheets were created as AL materials and treated to varied dosages of in-situ gamma irradiation (0, 10, 20, 30, and 40 KGy) to optimize their microstructural and physicochemical characteristics. The processed ALs were subjected to comprehensive tests, which included J–V variable evaluation as well as evaluations of microstructure, porosity, morphology, contact angle, optical characteristics, and electrochemical impedance spectroscopy (EIS). The findings reveal that the composites' surface properties got better gradually as gamma irradiation dosages grew; peak performance was reached at 30 KGy (75.9 % apparent porosity and roughness parameter Ra = 6.22 μm). Extended gamma irradiation resulted in increased DSSC efficiency, which reached 6.85 % after 10 KGy and 7.63 % after 20 KGy. High-energy gamma photons boosted mobility and decreased resistive limits by reducing carrier recombination and facilitating charge carrier movement inside CPG compounds. This increased the longevity and charge transfer efficiency of the solar cell. After 30 KGy alteration, the CPG AL's optimized efficiency of 8.78 % and Jsc of 20.23 mA/cm2 indicate a 44.3 % improvement in efficacy over the pristine material. The insertion of oxygen-enriched free radicals into the CPG structure is responsible for the improvement in photovoltaic efficiency because it creates continuous pathways for fast electron transport. This work provides an innovative perspective on the use of heteroatom-doped ALs in PSCs by highlighting the benefits of co-doping and regulated heteroatom species.

Cancer radiotherapy with mini neutron/gamma-ray generators

Recent advancements in negative hydrogen (H-) or negative deuterium (D-) ion source technology as well as the commercial availability of high-frequency AC high-voltage power supplies have enabled the development of mini neutron/gamma-ray generators using low-energy nuclear reactions. These generators can provide a useful flux of high-energy neutrons or gamma photons in either pulsed or continuous operations. With the new mini generator, intraoperative radiotherapy as well as treatment of tumors in the brain, skin, breast, salivary gland, pancreas, liver, and kidney can be performed using external or internal neutron/gamma-ray beams. The new radiotherapy system is very compact and requires very low power for operation, enabling its location inside an operation room of a hospital or clinical facility.

A Wide Energy Range and 4π-View Gamma Camera with Interspaced Position-Sensitive Scintillator Array and Embedded Heavy Metal Bars.

(1) Background: Gamma cameras have wide applications in industry, including nuclear power plant monitoring, emergency response, and homeland security. The desirable properties of a gamma camera include small weight, good resolution, large field of view (FOV), and wide imageable source energy range. Compton cameras can have a 4π FOV but have limited sensitivity at low energy. Coded-aperture gamma cameras are operatable at a wide photon energy range but typically have a limited FOV and increased weight due to the thick heavy metal collimators and shielding. In our lab, we previously proposed a 4π-view gamma imaging approach with a 3D position-sensitive detector, with which each detector element acts as the collimator for other detector elements. We presented promising imaging performance for 99mTc, 18F, and 137Cs sources. However, the imaging performance for middle- and high-energy sources requires further improvement. (2) Methods: In this study, we present a new gamma camera design to achieve satisfactory imaging performance in a wide gamma energy range. The proposed gamma camera consists of interspaced bar-shaped GAGG (Ce) crystals and tungsten absorbers. The metal bars enhance collimation for high-energy gamma photons without sacrificing the FOV. We assembled a gamma camera prototype and conducted experiments to evaluate the gamma camera’s performance for imaging 57Co, 137Cs, and 60Co point sources. (3) Results: Results show that the proposed gamma camera achieves a positioning accuracy of <3° for all gamma energies. It can clearly resolve two 137Cs point sources with 10° separation, two 57Co and two 60Co point sources with 20° separation, as well as a 2 × 3 137Cs point-source array with 20° separation. (4) Conclusions: We conclude that the proposed gamma camera design has comprehensive merits, including portability, 4π-view FOV, and good angular resolution across a wide energy range. The presented approach has promising potential in nuclear security applications.

Laser Driven Electron Acceleration from Near-Critical Density Targets towards the Generation of High Energy γ-Photons

In this paper, we investigate the production of high energy gamma photons at the interaction between an ultra-high intensity laser pulse with an energetic electron beam and with a near-critical density plasma for the laser intensity varying between 1019–1023 W/cm2. In the case of the interaction with an electron beam, and for the highest laser intensities considered, the electrons lose almost all their energy to emit gamma photons. In the interaction with a near-critical density plasma, the electrons are first accelerated by the laser pulse up to GeV energies and further emit high energy radiation. A maximum laser-to-photons conversion coefficient of 30% is obtained. These results can be used for the preparation of experiments at the Apollon and ELI laser facilities for the investigation of the emission of high energy γ-photons and to study the electron-positron pair creation in the laboratory.

RADT-20. REPORT OF THE RESPECT-GBM™ PHASE I/IIA DOSE ESCALATION TRIAL OF RHENIUM-186 NANOLIPOSOME (186RNL) IN RECURRENT GLIOMA VIA CONVECTION ENHANCED DELIVERY (CED) &amp; PLANNED PHASE IIB TRIAL

Abstract A phase I/IIa dose escalation trial was initiated to determine the safety and recommended phase II dose (RP2D) of 186RNL in patients with recurrent glioma. Liposomal rhenium-186 (186RNL) is a source of high energy beta particles and gamma photons with attractive properties for brain CED.Patients with biopsy proven recurrent glioma had computerized treatment planning and placement of up to 4 intracranial catheter(s). Each patient received a single administration of 186RNL by CED. Whole body planar and SPECT/CT imaging from days 1-8 following treatment was performed. Patients were followed for safety, sufficiency of delivery and overall survival. Twenty-one patients across 6 dose escalation cohorts received 1.0-22.3mCi in a volume of 0.6-8.8mL. Mean tumor volume was 8.3mL, patients were heavily pretreated (mean 1.7 recurrences) with poor prognostic factors. There were no CED failures. Mean absorbed radiation dose to the tumor (MARDT) was 271Gy. No dose limiting toxicities were observed. Patients were stratified by MARDT. Those receiving &amp;gt; 100Gy MARDT (n=12) had a median and mean overall survival of 129.9 (95% CI 35.1 to 169.3) and 99.5 ± 19 weeks respectively with 3 patients alive. Patients receiving ≤ 100Gy MARDT (n=9) had a median and mean overall survival of 22.4 (95% CI 6.6 to 45.4) and 24.7 ± 4.8 weeks respectively, none are alive. Kaplan Meier analysis of overall survival for patients receiving MARDT greater than 100Gy vs. those with ≤ 100Gy showed a statistically significant difference in overall survival (p&amp;lt; 0.001).A single administration of 186RNL by CED in recurrent glioma patients is feasible, safe, and potentially effective in increasing overall survival when &amp;gt; 100Gy radiation is delivered to the tumor. A RP2D of 22.3mCi in 8.8mL was selected for patients with tumor size of ≤ 15mL in the planned phase 2b trial. The PIIb trial design and comparative survival data will also be presented.

Monte Carlo approach to comparison of parallel-hole collimators of clinical scintillation camera system for imaging astatine-211 (At-211)

Astatine-211 (At-211) is a promising alpha particle emitter for targeted radionuclide therapy. Since its daughter isotope (polonium-211(Po-211)) emits characteristic X-rays of about 80 keV, the distribution of At-211 in the body can be imaged by detecting the X-rays with a scintillation camera. However, the isotopes also emit high-energy gamma photons that are collimated with difficulty for a parallel-hole collimator of a clinical scintillation camera system, and thus the selection of a collimator is important. In this study, we compared the performances of low-energy high-resolution (LEHR), low-energy all-purpose (LEAP), medium-energy (ME), and high-energy (HE) parallel-hole collimators for At-211 using Monte Carlo simulation. We simulated a clinical scintillation camera system with the collimators using the Geant4 toolkit. The energy spectra, sensitivities, and spatial resolutions for the point source of At-211 were evaluated. Moreover, we simulated imaging of six sphere sources of At-211 in a 1-cm-thick cylindrical phantom filled with At-211 solution to evaluate image contrast. All of the results in this study are simulation data. The spatial resolution with LEHR was 7.6 mm full width at half maximum (FWHM) and the highest between collimators, while the sensitivity with LEAP was 85 cps/MBq and the highest. The image contrast acquired with the ME collimator was superior to those with the other collimators. We concluded that the LEHR, LEAP, and ME collimators had their advantages, so an optimum collimator should be selected depending on the purpose of imaging of At-211, although there was no advantage in using the HE collimator for the imaging of At-211.

Technical note: Short-time sequential high-energy gamma photon imaging using list-mode data acquisition system for high-dose-rate brachytherapy.

Measurement of the dwell time and moving speed of a high-activity iridium-192 (Ir-192) source used for high-dose-rate (HDR) brachytherapy is important for estimating the precise dose delivery to a tumor. For this purpose, we used a cerium-doped yttrium aluminum perovskite (YA1O3 :YAP(Ce)) gamma camera system, combined with a list-mode data acquisition system that can acquire short-time sequential images, and measured the dwell times and moving speeds of the Ir-192 source. Gamma photon imaging was conducted using the gamma camera in list mode for the Ir-192 source of HDR brachytherapy with fixed dwell times and positions. The acquired list-mode images were sorted to millisecond-order interval time sequential images to evaluate the dwell time at each position. Time count rate curves were derived to calculate the dwell time at each source position and moving speed of the source. We could measure the millisecond-order time sequential images for the Ir-192 source. The measured times for the preset dwell times of 2 s and 10 s were 1.98 to 2.00 s full width at half maximum (FWHM) and 10.0 s FWHM, respectively. The dwell times at the first dwell position were larger than those at other positions. We also measured the moving speeds of the source after the dwells while moving back to the afterloader and found the speed increased with the distance from the edge of the field of view to the last dwell position. We conclude that millisecond-order time sequential imaging of the Ir-192 source is possible by using a gamma camera and is useful for evaluating the dwell times and moving speeds of the Ir-192 source.

Trials of transmission imaging using clinically used Ir-192 source for high-dose-rate brachytherapy

In high-dose-rate (HDR) brachytherapy, verification of an Ir-192 source's position during treatment is required. One of the methods for this used a high-energy pinhole gamma camera to image the position of the source, but the absolute position of the source cannot be measured. To confirm the absolute position, it will be useful to acquire the transmission image of a subject in addition to the gamma photon image at the same time without using an additional X-ray system. To measure the transmission images, we tried to use the high-energy gamma photons emitted from the Ir-192 source used for the therapy. We developed a high-energy gamma photon imaging system composed of 1-mm-thick Pr doped Gd2O2S (GOS), a surface mirror, and a cooled charge-coupled device (CCD) camera. The developed imaging system achieved transmission imaging of high-energy gamma photons by transporting the Ir-192 source in front of the imaging system. The spatial resolution of the imaging system was better than 2.4 mm FWHM with and without a 10-cm-thick acrylic block set between the imaging system and the source. Moderate spatial resolution and contrast images of phantoms were obtained with the system. For the dynamic imaging mode, continuous images of the phantoms were measured with 1-sec intervals. There was no observable difference in the transmission images by the movement of the Ir-192 source. Transmission imaging of subjects using an Ir-192 source for HDR brachytherapy could be achieved using our developed imaging system. The system offers a new method to measure the real-time transmission images of the subject during HDR brachytherapy.

Compressing magnetic field into a high-intensity electromagnetic field with a relativistic flying mirror

Ultrahigh electromagnetic fields (≥~1023 W cm−2) are necessary for the study of strong-field quantum electrodynamics (QED). In this study, for the first time, we propose the compression of a pre-seeding static magnetic field with a relativistic flying mirror to generate a high electromagnetic field. The produced field intensity can be further amplified to be 5 × 1023 W cm−2 owing to the multiple reflections between the flying mirror and a stationary solid target; this produced field intensity is approximately four orders of magnitude larger than that of the seeding field and far exceeds that of the driver laser field (9.6 × 1022 W cm−2). Therefore, the ultrahigh electromagnetic field can significantly facilitate strong-field QED effects such as high-energy gamma photon emission. An analytical theory is developed to self-consistently describe the motion of the flying mirror and the field amplification. The predications from the theory are well demonstrated by numerical simulations. The scheme of producing high-intensity electromagnetic fields proposed in this letter provides a new, powerful means to study strong-field QED with a relatively low laser intensity.

Comparative study of gamma-ray attenuation for poly (imide siloxane) block copolymer in biocompatible flexible sheet and pelletize forms

The poly (imide siloxane) block copolymer were synthesized at different forms with resistance to dissolve in several corrosive environments. The optimum gamma shielding of the poly (imide siloxane) block copolymer was obtained with the comparison of flexible sheet and pelletized forms to be tolerant at harsh environment. The comparison in the improvement of thermal performance was performed in two different forms of the poly (imide siloxane) block copolymer (such as the flexible sheet and the pelletized form). The shielding tolerance against gamma radiation was specified to identify their gamma shielding capacity with low-energy (<1 MeV) gamma photons by using Cs-137 radioisotope and with high energy (>1 MeV) gamma photons by using Co-60 radioisotope. The variations in the flexible sheet and the pelletized form were significant that the linear attenuation coefficient of flexible sheet form has presented the highest gamma shielding capacity. The flexible shield form of the poly(imide siloxane) block copolymer has exhibited optimum radiation shielding with the resistance against gamma radiation in extreme environment with high temperature and corrosive ambient.

High-energy γ -photon polarization in nonlinear Breit-Wheeler pair production and γ polarimetry

The interaction of an unpolarized electron beam with a counterpropagating ultraintense linearly polarized laser pulse is investigated in the quantum radiation-dominated regime. We employ a semiclassical Monte Carlo method to describe spin-resolved electron dynamics, photon emissions and polarization, and pair production. Abundant high-energy linearly polarized gamma photons are generated intermediately during this interaction via nonlinear Compton scattering, with an average polarization degree of more than 50%, which further interacting with the laser fields produce electron-positron pairs due to nonlinear Breit-Wheeler process. The photon polarization is shown to significantly affect the pair yield by a factor beyond 10%. The considered signature of the photon polarization in the pair's yield can be experimentally identified in a prospective two-stage setup. Moreover, the signature can serve also for the polarimetry of high-energy high-flux gamma photons with a resolution well below 1% with currently achievable laser facilities.

Primary, scatter, and penetration characterizations of parallel-hole and pinhole collimators for I-123 SPECT

Multi-pinhole (MPH) collimators are known to provide better trade-off between sensitivity and resolution for preclinical, as well as for smaller regions in clinical SPECT imaging compared to conventional collimators. In addition to this geometric advantage, MPH plates typically offer better stopping power for penetration than the conventional collimators, which is especially relevant for I-123 imaging. The I-123 emits a series of high-energy (>300 keV, ~2.5% abundance) gamma photons in addition to the primary emission (159 keV, 83% abundance). Despite their low abundance, high-energy photons penetrate through a low-energy parallel-hole (LEHR) collimator much more readily than the 159 keV photons, resulting in large downscatter in the photopeak window. In this work, we investigate the primary, scatter, and penetration characteristics of a single pinhole collimator that is commonly used for I-123 thyroid imaging and our two MPH collimators designed for I-123 DaTscan imaging for Parkinson’s Disease, in comparison to three different parallel-hole collimators through a series of experiments and Monte Carlo simulations. The simulations of a point source and a digital human phantom with DaTscan activity distribution showed that our MPH collimators provide superior count performance in terms of high primary counts, low penetration, and low scatter counts compared to the parallel-hole and single pinhole collimators. For example, total scatter, multiple scatter, and collimator penetration events for the LEHR were 2.5, 7.6 and 14 times more than that of MPH within the 15% photopeak window. The total scatter fraction for LEHR was 56% where the largest contribution came from the high-energy scatter from the back compartments (31%). For the same energy window, the total scatter for MPH was 21% with only 1% scatter from the back compartments. We therefore anticipate that using MPH collimators, higher quality reconstructions can be obtained in a substantially shorter acquisition time for I-123 DaTscan and thyroid imaging.

The emission of \u03b3-Ray beams with orbital angular momentum in laser-driven micro-channel plasma target

We investigated the emission of multi-MeV γ-Ray beams with orbital angular momentum (OAM) from the interaction of an intense circularly polarized (CP) laser with a micro-channel plasma target. The driving laser can generate high energy electrons via direct laser acceleration within the channel. By attaching a plasma foil as the reflecting mirror, the CP laser is reflected and automatically colliding with the electrons. High energy gamma-photons are emitted through inverse Compton scattering (ICS) during collision. Three-dimensional particle-in-cell simulations reveal that the spin angular momentum (SAM) of the CP laser can be transferred to the OAM of accelerated electrons and further to the emitted gamma-ray beam. These results may guide future experiments in laser-driven gamma-ray sources using micro-structures.

Timepix3 detector and Geant4-based simulations for gamma energy detection in Laser Produced Plasmas

The particular physics of Laser Produced Plasmas (LPP) needs some diagnostic requirements. Specifically, the X-ray monitoring of the plasma is known to be difficult since typically X-ray emissions are concentrated in bursts from a few tens of ps to few ns, based on the power and pulse time width of the laser. Therefore, the energy measurement of the radiation coming from a single experimental run is basically unfeasible using conventional techniques. Additional particles can be produced from LPP experiments, especially high energy gamma photons and electrons. As a case study in recent experiments, carried out on VEGA-2 laser facility (CLPU, Salamanca, Spain), the aim was to produce neutrons through photonuclear reactions on different types of solid targets. We have used the Timepix3 chip, in a “side-on” configuration, in order to produce a quick estimate of the gamma photons energy involved in the reactions. This detector, based on silicon, is realized with a single chip of 256 × 256 pixels bump-bonded with a 14 mm × 14 mm × 300 μm silicon layer. Interaction of gammas with the detector in this configuration produces some characteristic clusters of pixels and, for each cluster, a variety of physical and morphological parameters can be defined. Based on some of these parameters, we have characterized the detector response using some known laboratory gamma sources and the related Geant4 simulations. This allows quick energy discrimination for the gamma photons coming from different experimental runs.

First Cerenkov charge-induction (CCI) TlBr detector for TOF-PET and proton range verification

Thallium bromide (TlBr) is a semiconductor material and, simultaneously, a good Cerenkov radiator. The performance of a TlBr detector that integrates two different readouts, the charge induction readout and the detection of Cerenkov light, was evaluated. A TlBr detector with dimensions of 4 × 4 × 5 mm3, with a monolithic cathode and an anode segmented into strips, was manufactured. One of the bare and polished 4 × 4 mm2 faces of the detector was coupled to a silicon photomultiplier (SiPM) to read out the Cerenkov light. Simultaneous timing and energy resolutions of <400 ps full width at half maximum (FWHM) and ~8.5% at 511 keV were measured using the Cerenkov detection and charge induction readouts, respectively. A coincidence time resolution of 330 ps was obtained when selecting Cerenkov events with amplitudes above 70 mV. The combination of both readouts showed the potential to resolve the depth-of-interaction (DOI) positioning, based on the improvement of energy resolution when selecting events with similar electron drift times. This manuscript sets the stage for a new family of semiconductor detectors that combine charge induction readout with the Cerenkov light detection. Such detectors can provide, simultaneously, outstanding timing, energy, and spatial resolution, and will be an excellent fit for applications that require the detection of high-energy gamma photons with high timing accuracy, such as time-of-flight positron emission tomography (TOF-PET) and prompt gamma imaging (PGI) to assess the particle range in hadron therapy.

Estimation of the fractions of luminescence of water at higher energy than Cerenkov-light threshold for various types of radiation.

.Although the luminescence of water at a lower energy than the Cerenkov-light (CL) threshold has been found for various types of radiation, the fractions of the luminescence of water to the total produced light have not been obvious for radiations at a higher energy than the CL threshold because it is difficult to separate these two types of light. Thus, we used a Monte Carlo simulation to estimate the fractions of the luminescence of water for various types of radiation at a higher energy than the CL threshold to confirm the major component of the produced light. After we confirmed that the estimated light production of the luminescence of water could adequately simulate the experimental results, we calculated the produced light photons of this luminescence and the CL from water for protons (170 MeV), carbon ions (330 MeV/n), high-energy x-ray (6 MV) from a linear accelerator (LINAC), high-energy electrons (9 MeV) from LINAC, positrons (F-18, C-11, O-15, and N-13), and high-energy gamma photon radionuclides (Co-60). For protons, the major fraction of the produced light was the luminescence of water in addition to the CL from the prompt gamma photons produced by the nuclear interactions. For carbon ions, the major fraction of the produced light was the luminescence of water and the CL produced by the secondary electrons in addition to the prompt gamma photons produced by the nuclear interactions. For high-energy x-ray and electrons from LINAC, the fractions of luminescence of water were to 0.2%. The fractions of luminescence of water for positrons were 0.2% to 1.5% and that for Co-60 was 0.4%. We conclude that the major fractions of light produced from x-ray and electrons from LINAC, positron radionuclides, and the Co-60 source are CL, with fractions of the luminescence of water from to 1.5%.

A Monte Carlo Study on the Shielding Properties of a Novel Polyvinyl Alcohol (PVA)/WO3 Composite, Against Gamma Rays, Using the MCNPX Code.

Background:In recent years, there has been an increased interest toward non-lead radiation shields consisting of small-sized filler particles doped into polymer matrices. In this paper, we study a new polyvinyl alcohol (PVA)/WO3 composite in the presence of high-energy gamma photons through simulation via the Monte Carlo N-Particle (MCNP) simulation code. Material and Methods: An MCNP geometry was first designed in the software based on real-life conditions, and the generated geometry was validated by calculating the mass attenuation coefficient and making relative comparisons with standard tables. Using the lattice card in the MCNP input file, WO3 was considered as a filler dispersed in a PVA polymer at sizes of 10 µm and 30 nm with a weight concentration of 50 wt%. By defining 106-photons emitted from point sources corresponding to 662, 778, 964, 1112, 1170, 1130 and 1407 keV energy levels, and the F4 tally used to estimate the cell average flux, the values for mass attenuation coefficient and half-value layer (HVL) were calculated. Results:The results show that PVA/WO3 composite can be considered to shield X and γ-rays in the mentioned energies. However, nano-WO3 has a better ability to shield in comparison with the micro-WO3 fillers. The differences in attenuation changed at different energy levels, ascribed to the dominance of pair production occurrence and photon interactions in the composite, which was in good agreement with previous studies. Conclusion: Our finding showed that the composite can be considered as a lead-free shielding material.

Using gold nanoparticles with high energy gamma photons (12MeV)to treat brain cancer

This paper deals with one of the interesting topic in medical application where Gold nanoparticles (GNPs) are good choice due to characterize ability of synthesis as colloidal solution as well as did not interact with healthy tissue, less toxicity, ease of detection and thermal stability. The brain cancer can be treatment by high energy photons of gamma ray about (12 MeV) and gold nanoparticles while preserving the brain and prevents the risk of recurrence of brain cancer. This occur in a minimum dose given for patient i.e. enhancing the radiotherapy that is used in brain cancer treatment by depending on pair production phenomena. Our results showed that GNPs have significantly enhancing the radiotherapy for brain cancer treatment with high energy of gamma photons (12MeV).

Development of ultrahigh resolution radiation imaging detector using 1 mm channel size Si-PM array combined with 0.2 mm × 0.2 mm pixelated GAGG plate

For precise distribution measurements of gamma photons or beta particles, high resolution radiation imaging detectors are required. Reducing the size of the photodetectors combined with small pixel scintillators is a possible method to improve the spatial resolution of the scintillator based radiation imaging detectors. In this paper, we used a 1mm channel size silicon photomultiplier (Si-PM) array combined with a small pixel scintillator array and evaluated the performance for gamma photons and beta particles. For the radiation imaging detector, a Si-PM array with 1mm × 1mm channel size arranged in 8 × 8 (Hamamatsu, S13615-1025N-08) was optically coupled to a 0.2 mm × 0.2 mm pixelated GAGG plate. For 662 keV high energy gamma photons, 0.2mm GAGG pixels were clearly resolved in the position histogram. The peak to valley ratio (P/V) of the position histogram was not improved when only photo-peak events were used while it was improved when the events lower energy than the Compton edge was used. We could also resolve the position histograms for both 122 keV and 60 keV gamma photons. For beta particles, although the position histogram showed good separation for relatively low energy beta particles of Ca-45 (245 keV max), separation became worse for higher energy beta particles from Sr-Y-90 (545keV and 2280keV max). The separation of the position histogram for Sr-Y-90 improved when only lower energy events were used. Using 1mm size Si-PM array, high resolution detectors was realized for low energy gamma photons and beta particle but the spatial resolution was decreased for high energy beta particles from Sr-Y-90.

First approach to ionizing radiation based 3D printing: fabrication of free standing dose gels using high energy gamma photons

3D printing technique is used for the fabrication of differently shaped objects for industrial, research, medical and societal applications. The technique explores scanning laser beam which interacts with a printing material according to the printing algorithm thus fabricating the required 3D object. In medical field 3D printing is successfully used for fabrication of anatomic bone structures, the first attempts are made to print out artificial skin however there are some limits due to the non-equivalency of printing materials to soft tissue. 3D printing concept might have a big potential in radiotherapy for fabrication of tumor imitators – phantoms for quality control of individual patient treatment.Well known radiation induced polymerization of near tissue equivalent dose gels that are used for dose assessment in radiotherapy is a key issue for the development of the ionizing radiation based 3D printing. However it is to point out, that according to irradiation scenario differently shaped polymerized gel parts usually are being produced inside the gel matrix and cannot be removed from the gel.The aim of this work was to develop high energy photon irradiation based 3D printing method for fabrication of nearly tissue equivalent free-standing 3D dose gel shapes. The first approach for method’s application was fabrication of tumor imitators for brachytherapy treatment.Free standing dose gel shapes that are produced using radiotherapy equipment might serve as medical phantoms (tumour imitators) having the size and shape of a real irradiated volume with dose distribution assessment option within this volume. Concept of this method was firstly proposed in our previous publication (Adlienė et al., 2015).Special dose gels were used as “3D printing material” for the processing of free standing dose gel shapes. Varying dose gel content and adjusting high energy photon irradiation parameters with a pre-planned cancer patient treatment procedure, 3D polymerized gel shapes as the separate free-standing objects were fabricated (3D printing). Comparison of the size and shape of produced 3D objects with the irradiation volumes pre-planned by using standard treatment dose planning system of radiotherapy was performed and the obtained results were analyzed and discussed.