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.

Smart material based on boron crosslinked polymers with potential applications in cancer radiation therapy.

Organoboron compounds have been playing an increasingly important role in analytical chemistry, material science, health applications, and particularly as functional polymers like boron carriers for cancer therapy. There are two main applications of boron isotopes in radiation cancer therapy, Boron Neutron Capture Therapy and Proton Boron Fusion Therapy. In this study, a novel and original material consisting of a three-dimensional polymer network crosslinked with [Formula: see text]B enriched boric acid molecules is proposed and synthesized. The effects of the exposition to thermal neutrons were studied analyzing changes in the mechanical properties of the proposed material. Dedicated Monte Carlo simulations, based on MCNP and FLUKA main codes, were performed to characterize interactions of the proposed material with neutrons, photons, and charged particles typically present in mixed fields in nuclear reactor irradiations. Experimental results and Monte Carlo simulations were in agreement, thus justifying further studies of this promising material.

Dose-response of Fricke- and PAGAT-dosimetry gels in kilovoltage and megavoltage photon beams: Impact of LET on sensitivity.

PURPOSE: Dosimetry of ionizing radiation quantifies the energy deposited by an incident beam to the medium. This study presents the relative response of two types of gel dosimeters describing their differences by estimating radiation chemical yields produced in water radiolysis. METHODS: Two types of gel dosimeter were used, namely an acid ferrous ion solution infused with xylenol orange known as Fricke gel and a polymer gel based on acrylamide and N,N'-methylenebis(acrylamide) known as PAGAT. Samples were irradiated using two photon beam energies, one from a conventional X-ray tube operated at 44 kV and the other one from a LINAC operated at 6 MV. The dosimeters were analyzed by optical absorbance and magnetic resonance imaging. Additionally, the linear energy transfer of each beam was calculated using Monte Carlo simulations for further estimation of the radiation chemical yields produced during water radiolysis. RESULTS: Obtained results for both gel dosimeters indicate that their response at 44 kV and 6 MV are different, regardless of the read-out technique. On average, the sensitivity at 44 kV was found to be 65 % of the response at 6 MV. The calculated radiation chemical yields are in agreement with the observed experimental results. CONCLUSIONS: The main reason for the difference in the response of the dosimeters may be related to the linear energy transfer of each photon beam, which varies the production of primary chemical species during water radiolysis.

Obturación endodóntica de las raíces mesiales de molares inferiores con sellador Bio-C Sealer y AHPlus / Endodontic obturation of mesial roots of mandibular molars with Bio-C Sealer and AHPlus

La obturación del conducto radicular se realiza con conos de gutapercha y un sellador endodóntico, el cual rellena los espacios entre la pared dentinaria y el material obturador; y las irregularidades del conducto radicular. El sellador Bio-C Sealer es un cemento biocerámico con propiedades bioactivas, mientras que el sellador AH Plus es un cemento a base de resina. La hipótesis del presente estudio fue que el sellador BioC Sealer ocupa mayor volumen y superficie, respecto del sellador AH Plus. OBJETIVO: Comparar el uso del sellador Bio-C Sealer con el sellador AH Plus en la obturación de conductos mesiales de molares inferiores. MATERIALES Y MÉTODOS: Se seleccionaron 40 conductos (20 mesio-vestibulares y 20 mesiolinguales) de 20 raíces mesiales de molares inferiores permanentes. Los conductos fueron instrumentados con limas Wave One Gold Small (Dentsply, Maillefer) y WaneOne Gold Primary e irrigados con hipoclorito de sodio. Para la obturación, la muestra se dividió en dos grupos de 20 conductos cada uno, de acuerdo al sellador endodóntico utilizado. Grupo A: sellador AH Plus (Dentsply, Maillefer) y Grupo B: sellador Bio-C Sealer (Angelus). Finalizada la obturación, se utilizó la microtomografía computada (microCT) de alta resolución con un detector tipo flat-panel certificado de la compañía Varian R (USA) modelo PaxScan 2020+ para obtener 180 proyecciones tomográficas de cada muestra. Luego se reconstruyó la imagen 3D de la muestra utilizando algoritmos específicos dedicados en el software MatLab (MathWorks, USA), y con desarrollos propios del equipo de investigación en lenguaje Python en las instalaciones del LIIFAMIRx de la Universidad Nacional de Córdoba. Los datos obtenidos fueron analizados estadísticamente mediante el test de Mann Whitney. RESULTADOS: No se encontraron diferencias significativas en el volumen de obturación entre las muestras tratadas con sellador AH Plus y sellador Bio C- Sealer (p>0,05). Respecto al volumen de espacios vacíos, la frecuencia de casos en los cuales pudieron detectarse volúmenes de vacíos mensurables (≥ 0,01 mm3) fue del 15%; registrándose 2 en el grupo BIO-C sealer (5%) y 4 en AH Plus (10%). CONCLUSIÓN: Bajo las condiciones de este estudio, puede concluirse que ambos selladores AH Plus y Bio-C Sealer resultaron adecuados para la obturación de los conductos mesio-vestibulares y mesiolinguales de molares inferiores. Sin embargo, el volumen de espacios vacíos fue menor cuando se usó el sellador biocerámico Bio-C Sealer

Assessment of FLUKA, PENELOPE and MCNP6 Monte Carlo codes for estimating gold fluorescence applied to the detection of gold-infused tumoral volumes.

Different kinds of nanoparticles have been widely studied for biomedical purposes, including applications like dose enhancement in radiotherapy treatments and contrast agent in radiological studies. Recent work suggests that gold nanoparticles can be used as contrast agents in K-edge imaging and X-ray Fluorescence Computed Tomography, mainly due to their high K-edge energy value and good biocompatibility. However, the gold X-ray fluorescence (XRF) signal obtained in these procedures is relatively week when compared with Compton or bremsstrahlung radiation emitted in the surrounding tissues, mainly because it is not possible to achieve large gold nanoparticles concentrations within biological tissues added to the XRF is attenuated by other tissues when leaving the patient body. This work presents a feasibility study on implementation of FLUKA, PENELOPE and MCNP6 Monte Carlo codes to model the detection of gold XRF emitted by a small volume containing different gold concentrations and located at different depths in a tissue-equivalent phantom. Results indicate that there is good agreement between PENELOPE and FLUKA for gold Kα and Kß lines estimations when highly symmetric simulation scenario and kilovoltage X-ray beam were used, achieving differences lower than 2%; however, differences up to 6 times were observed between FLUKA and MCNP6 under the same conditions. In addition, remarkable differences were obtained when megavoltage X-ray beam was used, being up to 11 times between PENELOPE and FLUKA and up to 4 times between FLUKA and MCNP6 for gold Kα and Kß lines estimations. In this regard, a suitable normalization method was proposed and implemented to perform cross-comparisons of XRF estimations obtained from the Monte Carlo codes. By means of the proposed method, FLUKA, PENELOPE and MCNP6 can be successfully implemented to assess which configuration (gold concentration and target volume depth) leads to a better detection of gold XRF, despite differences in XRF estimation between the codes.

Parameter estimation and mathematical modeling of the diffusion process of a benzoic acid infused Fricke gel dosimeter.

This work presents a mathematical model implementation for studying the diffusion process of ferric ions in post-irradiated Fricke gel dosimeters. Fricke gel samples were manufactured in layers for their analysis by optical transmission imaging and benzoic acid was incorporated to improve their radiosensitivity. The developed method consists on designing the dosimeters with a suitable composition for their optical analysis which allows accurate measurements in a wide dose range with noticeable linear responses with an average linear correlation coefficient of r2=0.993. The developed algorithm calculates the diffusion coefficient by means of an inverse problem formulation. Moreover, the proposed method is capable of modeling time-dependent physical properties and evolution over time of the irradiated dosimeters accurately and comparable with experimentally measured data. The obtained results evince the complexity of the diffusion phenomena in this type of materials and the capacity of the proposed method to provide a reliable quantification of the diffusion coefficient as a scalar approximation of the diffusion tensor. The obtained diffusion coefficient varies from 1.21 to 1.61 mm2/h with uncertainties lower than 2%. The model is also transferable to other diffusion driven systems and the numerical solving method can also be adapted to solve diffusion calculation based on other theoretical approaches.

Polymer gel dosimeter based on itaconic acid.

A new polymeric dosimeter based on itaconic acid and N, N'-methylenebisacrylamide was studied. The preparation method, compositions of monomer and crosslinking agent and the presence of oxygen in the dosimetric system were analyzed. The resulting materials were irradiated with an X-ray tube at 158cGy/min, 226cGymin and 298cGy/min with doses up to 1000Gy. The dosimeters presented a linear response in the dose range 75-1000Gy, sensitivities of 0.037 1/Gyat 298cGy/min and an increase in the sensitivity with lower dose rates. One of the most relevant outcomes in this study was obtaining different monomer to crosslinker inclusion in the formed gel for the dosimeters where oxygen was purged during the preparation method. This effect has not been reported in other typical dosimeters and could be attributed to the large differences in the reactivity among these species.

Molecular structure effects on the post irradiation diffusion in polymer gel dosimeters.

Polymer gel dosimeters have specific advantages for recording 3D radiation dose distribution in diagnostic and therapeutic medical applications. But, even in systems where the 3D structure is usually maintained for long periods of time after irradiation, it is still not possible to eliminate the diffusion of the different species in the regions of dose gradients within the gel. As a consequence, information of the dose loses quality over time. In the pursuit of a solution and to improve the understanding of this phenomenon a novel system based on itaconic acid and N-N'-methylene-bisacrylamide (BIS) is hereby proposed. Effects of changes in the chemical structure of the monomers over the dosimetric sensitivity and over the post-irradiation diffusion of species was studied. In this study, one of the carboxylic groups of the itaconic acid molecule was modified with aniline to obtain molecules with similar reactivity but different molecular sizes. Then, dosimeters based on these modified species and on the original ITA molecules were irradiated in an X-ray tomography apparatus at different doses up to 173Gy. Afterwards, the resulting dosimeters were characterized by Raman spectroscopy and optical absorbance in order to study their feasibility and capabilities as dosimetric systems, and by optical-CT to analyze the post irradiation diffusion.