Gel Dosimetry Research Articles

Polymer gel dosimetry for experimental verification of conformal small animal irradiation at a preclinical research platform

In translational research, there is a need for preclinical studies of high quality that corresponds to the conformal dose distributions conventionally delivered to humans in the modern radiotherapy clinic. To facilitate this need, novel preclinical systems consist of preclinical radiation platforms and small animal treatment planning systems. However, small-field dosimetry is challenging and requires dosimeters with high spatial resolution. In this study we demonstrate the feasibility of experimentally validating the dose distribution in small fields at a preclinical X-ray research platform using a polymer gel dosimeter and MRI-readout.

CT and CBCT imaging of gel dosimeters: a review of the state of the art

This review covers the main developments in x-ray CT-based polymer gel dosimetry (PGD) and more recently on-board cone-beam CT (CBCT) polymer gel dosimetry. Fundamental work as well as clinically-based applications are described and advantages and disadvantages of approaches highlighted. The body of work present within the literature points towards an overall feasibility of CT PGD and increasingly CBCT PGD as viable tools for the verification of highly complex, high dose radiotherapy treatments.

Pilot scale validation campaign of gel dosimetry for pre-treatment quality assurance in stereotactic radiotherapy

PurposeComplex stereotactic radiotherapy treatment plans require prior verification. A gel dosimetry system was developed and tested to serve as a high-resolution 3D dosimeter for Quality Assurance (QA) purposes. Materials and MethodsA modified version of a polyacrylamide polymer gel dosimeter based on chemical response inhibition was employed. Different sample geometries (cuvettes and phantoms) were manufactured for calibration and QA acquisitions. Irradiations were performed with a Varian Trilogy linac, and analyses of irradiated gel dosimeters were performed via MRI with a 1.5 T Philips Achieva at 1 mm3 or 2 mm3 isotropic spatial resolution. To assess reliability of polymer gel data, 54 stereotactic clinical treatment plans were delivered both on dosimetric gel phantoms and on the Delta4 dosimeter. Results from the two devices were evaluated through a global gamma index over a range of acceptance criteria and compared with each other. ResultsA quantitative and tunable control of dosimetric gel response sensitivity was achieved through chemical inhibition. An optimized MRI analysis protocol allowed to acquire high resolution phantom dose data in timeframes of ≈ 1 h. Conversion of gel dosimeter data into absorbed dose was achieved through internal calibration. Polymer gel dosimeters (2 mm3 resolution) and Delta4 presented an agreement within 4.8 % and 2.7 % at the 3 %/1 mm and 2 %/2 mm gamma criteria, respectively. ConclusionsGel dosimeters appear as promising tools for high resolution 3D QA. Added complexity of the gel dosimetry protocol may be justifiable in case of small target volumes and steep dose gradients.

End-to-end quality assurance for stereotactic radiotherapy with Fricke-Xylenol orange-Gelatin gel dosimeter and dual-wavelength cone-beam optical CT readout

PurposeThe end-to-end (E2E) quality assurance (QA) test is a unique tool for validating the treatment chain undergone by patients in external radiotherapy. It should be conducted in three dimensions (3D) to get accurate results. This study aims to implement these tests with Fricke-Xylenol orange-Gelatin (FXG) gel dosimeter and a newly developed dual-wavelength reading method on the Vista16™ optical Computed Tomography (CT) scanner (ModusQA) for three treatment techniques in stereotactic radiotherapy, on Novalis (Varian) and CyberKnife (Accuray) linear accelerators. MethodsThe tests were performed in head phantoms. Gel measurements were compared with planned dose distributions and measured by film and ion chamber measurements by plotting isodose curves and dose profiles, and by conducting a 3D local gamma-index analysis (2%/2mm criteria). ResultsGamma passing rates were higher than 95 %. Point dose differences between treatment planning and gel and ion chamber measurements at the isocenter were < 2.3 % for both treatments delivered on the Novalis accelerator, while this difference was higher than 4 % for the treatment delivered on the CyberKnife, highlighting a small overdosing of the tumor volume. A good agreement was observed between gel and film dose profiles. ConclusionsThis study presents the successful implementation of 3D E2E QA tests for stereotactic radiotherapy with FXG gel dosimetry and a dual-wavelength reading method on an optical CT scanner. This dosimetric method provides 3D absolute dose distributions in the 0.25 – 10 Gy dose range with a high spatial resolution and a dose uncertainty of around 2 % (k=1).

Response investigation of a new polymer gel dosimeter based on ammonium salt through MRI technique

Increasing the use of polymer gel dosimetry (PGD) in radiotherapy requires reducing its toxicity. The toxicity of the PGD components causes risks for the users as well as the environment. The aim of this study is to produce a new PGD called PAGBIT (Polymer, Amps ammonium salt, Gelatin, BIs, Thpc) based on the nontoxic monomer of 2-acrylamido-2-methylpropanesulfonic acid ammonium salt. Furthermore, this monomer is ecofriendly. The PAGBIT PGD was prepared in the laboratory in ambient conditions. PGDs were irradiated using a clinical accelerator with a dose range of 0–10 Gy. The incident photon energy and dose rate were 6-MV and 300 cGy/min, respectively. The irradiated PGDs were imaged using a 1.5T MRI scanner 9 times in a time range of 12–720 h post-irradiation. The maximum obtained sensitivity was 0.115 ± 0.005 Gy−1s−1 at 36 h post-irradiation time. The average sensitivity change as a function of post-irradiation time was 0.0017 Gy−1s−1h−1. However, the average sensitivity change as a function of scanning temperature was 0.0006 Gy−1s−1°C−1. Results showed that the differences of effective atomic number and electron density between PAGBIT and soft tissue were 2.3% and 0.3%, respectively. It was concluded that the PAGBIT is a low toxic, water equivalent PGD with noticeable temporal and temperature stabilities.

Evaluation of a novel N-(Hydroxymethyl) acrylamide polymer gel dosimeter formulation with organic glucose additive for radiotherapy

In this study, the first evaluation of organic sensitizer material on N-(Hydroxymethyl) acrylamide (NHMA) polymer gel dosimeter was presented. A novel tissue-equivalent polymer gel formula composed of NHMA containing different concentrations of organic glucose additive (GL-NHMA) was developed and evaluated for its potential use to measure 3D dose distributions to compare with treatment planning system. The new polymers of GL-NHMA were irradiated using a linear accelerator (LINAC) with a megavolt X-ray photon beam over a dose range of 2–20 Gy, energies of 6, 10, and 15 MV, and dose rates of 50, 200, and 500 cGy/min. The samples were evaluated using 0.5 T nuclear magnetic resonance (NMR) technique in terms of spin-spin relaxation rate (R2). Comparing with the conventional NHMA composition (i.e., 0 wt% GL concentration), the sensitivity of the GL-NHAM was improved by 53%, 68%, 89%, and 115% with 10, 15, 20, and 25 wt% GL, respectively, with an excellent linear dose response up to 8 Gy. There were no observable effects on the R2 dose response induced by varying the dose rate, photon energy, and irradiation temperature. The polymerization was stable after irradiation for a period of 10 days. Additionally, the R2 values decreased with increasing the scanning temperature. The dosimeter is water equivalent and is energy-independent from 0.1 to 20 MeV when considering the optimum composition. The gel dosimetry accuracy was evaluated in this study by calculating the overall uncertainty and found to be 4.64% (2σ, 95% confidence level). The GL additive acts as an excellent organic sensitizer in the GL-NHMA system, suggesting that this improved polymer formulation may be a useful tool for measuring dose distributions in radiotherapy at clinically relevant dose levels.

Iterative image reconstruction with polar coordinate discretized system matrix for optical CT radiochromic gel dosimetry.

Gel dosimeters are a potential tool for measuring the complex dose distributions that characterize modern radiotherapy. A prototype tabletop solid-tank fan-beam optical CT scanner for readout of gel dosimeters was recently developed. This scanner does not have a straight raypath from source to detector, thus images cannot be reconstructed using filtered backprojection (FBP) and iterative techniques are required. Iterative image reconstruction requires a system matrix that describes the geometry of the imaging system. Stored system matrices can become immensely large, making them impractical for storage on a typical desktopcomputer. Here we develop a method to reduce the storage size of optical CT system matrices through use of polar coordinate discretization while accounting for the refraction in optical CTsystems. A ray tracing simulator was developed to track the path of light rays as they traverse the different mediums of the optical CT scanner. Cartesian coordinate discretized system matrices (CCDSMs) and polar coordinate discretized system matrices (PCDSMs) were generated by discretizing the reconstruction area of the optical CT scanner into a Cartesian pixel grid and a polar coordinate pixel grid, respectively. The length of each ray through each pixel was calculated and used to populate the system matrices. To ensure equal weighting during iterative reconstruction, the radial rings of PCDSMs were asymmetrically spaced such that the area of each polar pixel was constant. Two clinical phantoms and several synthetic phantoms were produced and used to evaluate the reconstruction techniques under known conditions. Reconstructed images were analyzed in terms of spatial resolution, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), signal nonuniformity (SNU), and Gamma map passpercentage. A storage size reduction of 99.72% was found when comparing a PCDSM to a CCDSM with the same total number of pixels. Images reconstructed with a PCDSM were found to have superior SNR, CNR, SNU, and Gamma (1mm, 1%) pass percentage compared to those reconstructed with a CCDSM. Increasing spatial resolution in the radial direction with increasing radial distance was found in both PCDSM and CCDSM reconstructions due to the outer regions refracting light more severely. Images reconstructed with a PCDSM showed a decrease in spatial resolution in the azimuthal directions as radial distance increases, due to the widening of the polar pixels. However, this can be mitigated with only a slight increase in storage size by increasing the number of projections. A loss of spatial resolution in the radial direction within 5mm radially from center was found when reconstructing with a PCDSM, due to the large innermost pixels. However, this was remedied by increasing the number of radial rings within the PCDSM, yielding radial spatial resolution on par with images reconstructed with a CCDSM and a storage size reduction of 99.26%. Discretizing the image pixel elements in polar coordinates achieved a system matrix storage size reduction of 99.26% with only minimal reduction in the imagequality.

A real-world assessment of the robustness of gel dosimetry

The purpose of this multi-institutional study was to evaluate the robustness of a transported gel dosimeter. Six vials were filled with a normoxic N-vinylpyrrolidone-based polymer gel dosimeter containing inorganic salt as a sensitizer (iVIPET), manufactured by Triangle Products (Kashiwa, Japan). Three vials were sent to the home institution (National Cancer Center Hospital East, Chiba, Japan) and three to an external institution. At each institution, vials received a dose of 0, 5, or 10 Gy using a 10 MV X-ray beam. After irradiation, the gel in the vial was imaged using a 3 T MRI scanner, and an R2 (spin–spin relaxation rate) map was created. The dose–R2 relationship was then analyzed using linear regression and the dose uncertainty computed. Thirty-four institutions participated in the study from July 2020 to July 2021. At the home institution, dose uncertainties were constant throughout the year (95% confidence interval [mean ± 1.96σ]: 3.3 ± 2.1% at 5 Gy and 4.0 ± 2.5% at 10 Gy). The ratio of the dose uncertainties measured at the external institutions and home institution was 1.1 ± 0.4 at 5 Gy (r = 0.88) and 1.0 ± 0.3 at 10 Gy (r = 0.81). Dose uncertainties were approximately 4% within 4 d of transportation but exceeded 10% when the gels were irradiated 7 d after fabrication. Temperature variations during transportation resulted in negligible uncertainties in absorbed dose; however, extended transportation times may increase dose uncertainty. Thus, polymer gel dosimeters should be used within 2–4 d of fabrication.

Dual application of Polyvinyl Alcohol Glutaraldehyde Methylthymol Blue Fricke hydrogel in clinical practice: Surface dosimeter and bolus

An essential issue is an accurate evaluation of surface dose distribution for such sensitive treatments. This work aimed to feasibility of the dual application of the Ferrous Polyvinyl Alcohol Glutaraldehyde Methylthymol Blue (PVA-GTA-MTB) gel as a bolus compensator and surface dosimeter in breast radiotherapy. The differences between the surface dose measured using PVA-GTA-MTB gel and film dosimetry in the medial and lateral parts of the breast were 3.74% and 4.18%, respectively. A qualitative comparison of the isodose curves showed that the PVA-GTA-MTB bolus creates a uniform dose distribution similar to the superflab bolus in the target volume.

Preparation of polymer gel dosimeters for low gamma irradiation dose

Abstract In this study, two separate hydrogel dosimeters were prepared for low-dose measurement. The first system is based on Congo Red (CR) dye and a blend of natural polymers (gelatin/CMC) while the second system is based on 2,6-dichlorophenol indophenol (DCP) blue dye and a hybrid polymer blend (PVA/gelatin/CMC). The sensitivity of Congo red (CR)–(gelatin/CMC) gel dosimeter and 2, 6 – di choro phenol indophenols(DCP)-(PVA/gelatin/CMC) gel dosimetry systems were examined by studying the comparative results between the two different systems through the change in optical properties upon exposure to different gamma radiation doses, which showed the sensitivity of the second system (DCP)-(PVA/gelatin/CMC) to radiation is more than the first system(CR)–(gelatin/CMC) (CR) and (DCP)dyes have absorbance crest at 492 and 622 nm respectively. With the increase of the radiation dose, the decomposition of the dyes increases, and thus the color of the prepared hydrogel changes from orange to colorless in the case of (CR) dye at the dose (0–3.5 kGy) and from blue to colorless in the case (DCP) dye at the absorbed doses ranged from (0–1000 Gy). Dose-response curves, sensitivity, FTIR analysis, and the relative stability of the prepared hydrogel before and after irradiation were studied.

Radio-fluorogenic nanoclay gel dosimeters with reduced linear energy transfer dependence for carbon-ion beam radiotherapy.

The precise assessment of the dose distribution of high linear energy transfer (LET) radiation remains a challenge, because the signal of most dosimeters will be saturated due to the high ionization density. Such measurements are particularly important for heavy-ion beam cancer therapy. On this basis, the present work examined the high LET effect associated with three-dimensional gel dosimetry based on radiation-induced chemical reactions. The purpose of this study was to create an ion beam radio-fluorogenic gel dosimeter with a reduced effect of LET. Nanoclay radio-fluorogenic gel (NC-RFG) dosimeters were prepared, typically containing 100μM dihydrorhodamine 123 (DHR123) and 2.0wt% nanoclay together with catalytic additives promoting Fenton or Fenton-like reactions. The radiological properties of NC-RFG dosimeters having different compositions in response to a carbon-ion beam were investigated using a fluorescence gel scanner. An NC-RFG dosimeter capable of generating a fluorescence intensity distribution reflecting the carbon-ion beam dose profile was obtained. It was clarified that the reduction of the unfavorable LET dependence results from an acceleration of the reactions between DHR123 and H2 O2 , which is a molecular radiolysis product. The effects of varying the preparation conditions on the radiological properties of these gels were also examined. The optimum H2 O2 catalyst was determined to include 1mM Fe3+ ions, and the addition of 100mM pyridine was also found to increase the sensitivity. This technique allows the first-ever evaluation of the depth-dose profile of a carbon-ion beam at typical therapeutic levels of several Gy without LET effect.

Carbon-Ion Therapy Patient-Specific QA: Preliminary Results Derived Using 3D Polymer Gel Dosimetry in Anthropomorphic Inhomogeneous Geometry

<h3>Purpose/Objective(s)</h3> Improved conformity in carbon-ion radiation therapy (CIRT) with respect to photon RT comes at the cost of a potential reduced delivery robustness due to patient setup uncertainties, approximations in dose calculations and carbon-ion range uncertainties. This work presents preliminary results of a study aiming to address these challenges using 3D polymer gel dosimetry in anthropomorphic and inhomogeneous geometry. <h3>Materials/Methods</h3> All irradiations were performed at a synchrotron facility, in one of the treatment rooms equipped with a horizontal fixed beam line and pencil beam scanning (PBS) modality. For basic dosimetric characterization, carbon pristine Bragg peaks (BP) (ranges 30, 70, 90 mm in water) and a spread-out BP (SOBP) (range 115 mm and modulation 40 mm) were delivered on a cylindrical PMMA container filled with VIPAR polymer gel. An anthropomorphic phantom equipped with a cylindrical polymer gel insert was used for the irradiation of a pseudo-clinical CIRT plan, following all the steps of the standard clinical workflow, from simulation CT to irradiation. Two contralateral beams were optimized with a TPS (v.8b) to deliver 15 Gy (RBE) on a target located approximately at the center of the brain, in proximity of critical OARs such as brainstem and optical pathways. The phantom was then MRI scanned post-irradiation to retrieve the irradiated brain volume in 3D. The measured irradiated volume was compared against corresponding TPS derived data. <h3>Results</h3> Carbon-ion range was spatially verified with an accuracy of < 1 mm. For both the pristine BP and the SOBP irradiations. A significant deviation of the polymer gels' response on high-LET has been observed, as expected from previous studies with proton irradiations. For the pseudo-clinical treatment plan, a qualitative comparison between doses measured in polymer gels, against the corresponding TPS calculations, revealed a satisfying geometric accuracy of dose delivery in 3D, thus showing a high 3D geometrical accuracy of dose delivery in a typical standard clinical workflow. <h3>Conclusion</h3> In this work, we showed that patient-specific 3D polymer gel dosimetry is applicable to CIRT, as a valid tool to evaluate dosimetric and spatial plan accuracy in the clinical environment. As expected, the LET dependence of polymer gel's response, especially in the high-LET region, poses severe limitations for accurate dose measurements. Nevertheless, the proposed methodology is a promising efficient and safe clinical way for verifying such a complex RT technique.

Chemical Overview of Gel Dosimetry Systems: A Comprehensive Review.

Advances in radiotherapy technology during the last 25 years have significantly improved both dose conformation to tumors and the preservation of healthy tissues, achieving almost real-time feedback by means of high-precision treatments and theranostics. Owing to this, developing high-performance systems capable of coping with the challenging requirements of modern ionizing radiation is a key issue to overcome the limitations of traditional dosimeters. In this regard, a deep understanding of the physicochemical basis of gel dosimetry, as one of the most promising tools for the evaluation of 3D high-spatial-resolution dose distributions, represents the starting point for developing new and innovative systems. This review aims to contribute thorough descriptions of the chemical processes and interactions that condition gel dosimetry outputs, often phenomenologically addressed, and particularly formulations reported since 2017.

Fast Isocenter Determination Using 3D Polymer Gel Dosimetry with Kilovoltage Cone-Beam CT Reading and the PolyGeVero-CT Software Package for Linac Quality Assurance in Radiotherapy.

This work presents an approach to the fast determination of a medical accelerator irradiation isocenter as a quality assurance (QA) procedure in radiotherapy. The isocenter determination tool is the tissue equivalent high-resolution 3D polymer gel dosimeter (PABIGnx) in a dedicated container combined with kilovoltage imaging systems and the polyGeVero-CT software package (v. 1.2, GeVero Co., Poland). Two accelerators were employed: Halcyon and TrueBeam (Varian, USA), both equipped with cone beam computed tomography (CBCT) and iterative reconstruction CBCT (iCBCT) algorithms. The scope of this work includes: (i) the examination of factors influencing image quality (reconstruction algorithms and modes), radiation field parameters (dose and multi-leaf collimator (MLC) gaps), fiducial markers, signal averaging for reconstruction algorithms and the scanning time interval between consecutive scans, (ii) the examination of factors influencing the isocenter determination, image processing (signal averaging, background subtraction, image filtering) and (iii) an isocenter determination report using a 2D and 3D approach. An optimized protocol and isocenter determination conditions were found. The time and effort required to determine the isocenter are discussed.

Radiation Dosimetry by Use of Radiosensitive Hydrogels and Polymers: Mechanisms, State-of-the-Art and Perspective from 3D to 4D.

Gel dosimetry was developed in the 1990s in response to a growing need for methods to validate the radiation dose distribution delivered to cancer patients receiving high-precision radiotherapy. Three different classes of gel dosimeters were developed and extensively studied. The first class of gel dosimeters is the Fricke gel dosimeters, which consist of a hydrogel with dissolved ferrous ions that oxidize upon exposure to ionizing radiation. The oxidation results in a change in the nuclear magnetic resonance (NMR) relaxation, which makes it possible to read out Fricke gel dosimeters by use of quantitative magnetic resonance imaging (MRI). The radiation-induced oxidation in Fricke gel dosimeters can also be visualized by adding an indicator such as xylenol orange. The second class of gel dosimeters is the radiochromic gel dosimeters, which also exhibit a color change upon irradiation but do not use a metal ion. These radiochromic gel dosimeters do not demonstrate a significant radiation-induced change in NMR properties. The third class is the polymer gel dosimeters, which contain vinyl monomers that polymerize upon irradiation. Polymer gel dosimeters are predominantly read out by quantitative MRI or X-ray CT. The accuracy of the dosimeters depends on both the physico-chemical properties of the gel dosimeters and on the readout technique. Many different gel formulations have been proposed and discussed in the scientific literature in the last three decades, and scanning methods have been optimized to achieve an acceptable accuracy for clinical dosimetry. More recently, with the introduction of the MR-Linac, which combines an MRI-scanner and a clinical linear accelerator in one, it was shown possible to acquire dose maps during radiation, but new challenges arise.

Global and spatial dosimetric characteristics of N-vinylpyrrolidone-based polymer gel dosimeters as a function of medium-term post-preparation and post-irradiation time

It is useful in practice to know the best time intervals between gel preparation, irradiation and imaging for optimal dosimetric response. Knowing how long after preparation and/or irradiation a gel dosimeter can still produce reliable results is also practically helpful. This study aimed to answer these two important but little-investigated questions for normoxic N-vinylpyrrolidone-based polymer gel dosimeters (VIPET) during a nine-day time period. We evaluated the global dose response, reproducibility and high-dose-gradient spatial integrity of this gel dosimetry system for up to 6 Gy dose and assessed the medium-term post-preparation and post-irradiation stability of these key properties with relatively short time intervals of 3 days. After synthesis, several batches of VIPET vials were irradiated with 6 MV photon beams and imaged on a 3 T magnetic resonance imaging (MRI) scanner in different time and dose schemes and were subsequently analysed. Statistical analysis of the experimental data showed acceptable relative dosimetric characteristics in terms of dose sensitivity, offset (R0) values, and linearity of synthesized gel over the course of a nine-day post-preparation and post-irradiation time. The results showed reasonably good reproducibility of dose sensitivity (standard error of measurement, SEM: 0.009) and R0 value (SEM: 0.023). Further, the measurements indicated satisfactory spatial stability of relative dose distribution in high-dose-gradient regions throughout the nine-day studied period (variations in beam penumbra widths and off-axis positions being typically less than 1 mm). These findings provide further evidence to the suitability of the VIPET gel for practical three-dimensional dosimetry in clinical settings such as modern radiotherapy.

Pilot Study of Polymerization Dynamics in nMAG Dose Gel.

The essential component of modern radiation therapy is the application of steep dose gradients during patient treatment in order to maximize the radiation dose to the target volume and protect neighboring heathy tissues. However, volumetric dose distribution in an irradiated target is still a bottleneck of dose verification in modern radiotherapy. Dose gels are almost the only known dosimetry tool which allows for the evaluation of dose distribution in the irradiated volume due to gel’s polymerization upon irradiation. The accuracy of dose gel dosimetry has its own obstacle, which is related to the continuation of the gel’s polymerization after the radiation treatment procedure is finished. In this article, a method to monitor the polymerization dynamics of dose gels in real-time is proposed using a modified optical spectrometry system. Using the proposed method, the changes of the optical characteristics of irradiated nMAG dose gels in situ were assessed. The investigation revealed that the detectable polymerization in dose gel proceeds up to 6 h after irradiation. This time is significantly shorter compared with a commonly recommended 24 h waiting time allocated for polymer gel to settle. It was also found that dose rate significantly influences the temporal response of the nMAG dosimeter. By increasing the irradiation dose rate by a factor of 2, the time needed for the polymerization process to settle was increased by 22%. Identification of the gel’s post-irradiation polymerization time interval and its dependence on irradiation parameters will contribute to more accurate dose verification using dose gel dosimetry.

MO-0051 Machine learning prediction of calibration curves in gel dosimetry

MO-0051 Machine learning prediction of calibration curves in gel dosimetry

Polymer-Gel Radiation Dosimetry of Laser-Based Relativistic Electron Sources for Biomedical Applications: First Qualitative Results and Experimental Challenges

The generation of laser based relativistic electron sources involves impressive basic science as well as innovative applications. This study reports first novel qualitative results on polymer-gel radiation dosimetry of ultrafast laser-based relativistic electron beams. The fabricated polymer-gels are irradiated by the ultra-high dose rate (FLASH) laser-generated electron beams and then are analysed using magnetic resonance imaging. The reading of the irradiated dosimeters is performed using a clinical 1.5 T Magnetic Resonance Imaging system. Three-dimensional colour parametric T2 maps are then constructed from the original PD-T2 weighted images obtained from the clinical MRI scanner. For comparison, the gels are also irradiated with standard electron beams of various energies utilizing a radiotherapy clinical linear accelerator system. For the calibration measurements of the gel dosimetry method, special calibrated dosimetric films are also implemented. The preliminary results demonstrate the potential of polymer gel dosimetry for 3D-dose-distribution of FLASH type irradiation of laser generated electron beams. Furthermore, they illustrate potential issues related to the polymer gel based dosimetry in challenging irradiation arrangements, such as the oxygen sensitivity and necessity for oxygen impermeable container material.

Preface

ESCUELA POLITÉCNICA NACIONAL Departamento de Física XVII Encuentro de Física October 2021Dear Participants,On behalf of the organizing committee, I would like to express our gratitude for sharing and discussing the results of your research in the framework of the XVII Encuentro de Física.October 2021 was an exciting month, in which we organized five practical workshops prior to the conference. The topics for each of these workshops were mechanics, electromagnetism, optics, biophysics, scientific programming, and the teaching of physics. All in all, more than 170 students took part in these.During the conference, we had 13 truly outstanding keynote speakers, 52 oral presentations, and 26 poster contributions. In this edition of the XVII Encuentro de Física we decided to accept works from all the major topics of physics reflecting the interests of our Physics Department. In Fig. 1, the topics distributions of the presented works as oral contributions and posters are shown.List of titles WELCOME TO THE XVII ENCUENTRO DE FíSICA, HISTORY OF THE ENCUENTRO DE FíSICA, COMMITTEE, KEYNOTES, ASTRONOMY, HIGH ENERGY PHYSICS, DARK MATTER AND STANDARD MODEL, ELECTROWEAK INTERACTIONS: FROM DISCOVERYTO PRECISION TESTS OF THE STANDARD MODEL, MACHINE LEARNING / COMPLEX SYSTEMS ARTIFICIAL INTELLIGENCE FROM PHYSICS, COMPLEX NETWORKS AND THEIR APPLICATIONS, ARTIFICIAL INTELLIGENCE IN MULTIMODALITY MEDICAL IMAGING: PAST, PRESENT, ANY FUTURE?, GEL DOSIMETRY, APPLICATIONS OF MACHINE LEARNING IN RADIOTHERAPY, LOW-COST METHODS AND INSTRUMENTS FOR ADVANCED HOLOGRAPHIC MICROSCOPY, TEACHING OF PHYSICS, TEACHING OF PHYSICS, LOW-COST EXPERIMENTAL RESOURCES IN THE TEACHING OF PHYSICS TO SHARE WITH TEACHERS, PEROVSKITE SOLAR CELLS, A BRIEF LOOK INTO ELECTRON MICROSCOPY: UNVEILING MATERIALS PROPERTIES AT THE ATOMIC AND NANOMETER LEVEL, A VIRTUAL TOUR OF THE GALAPAGOS ISLANDS, ORAL CONTRIBUTIONS, Complex systems, Condensed matter physics, High-energy physics, Medical physics, Optics, Teaching of physics, Other, POSTERS, Complex systems, Condensed matter physics, High-energy physics, Optics, Other are available in this Pdf.