A systematic review of clinical applications of polymer gel dosimeters in radiotherapy

A Preliminary Investigation of Radiation-Sensitive Ultrasound Contrast Agents for Photon Dosimetry

Radiotherapy treatment plans have become highly conformal, posing additional constraints on the accuracy of treatment delivery. Here, we explore the use of radiation-sensitive ultrasound contrast agents (superheated phase-change nanodroplets) as dosimetric radiation sensors. In a series of experiments, we irradiated perfluorobutane nanodroplets dispersed in gel phantoms at various temperatures and assessed the radiation-induced nanodroplet vaporization events using offline or online ultrasound imaging. At 25 °C and 37 °C, the nanodroplet response was only present at higher photon energies (≥10 MV) and limited to <2 vaporization events per cm2 per Gy. A strong response (~2000 vaporizations per cm2 per Gy) was observed at 65 °C, suggesting radiation-induced nucleation of the droplet core at a sufficiently high degree of superheat. These results emphasize the need for alternative nanodroplet formulations, with a more volatile perfluorocarbon core, to enable in vivo photon dosimetry. The current nanodroplet formulation carries potential as an innovative gel dosimeter if an appropriate gel matrix can be found to ensure reproducibility. Eventually, the proposed technology might unlock unprecedented temporal and spatial resolution in image-based dosimetry, thanks to the combination of high-frame-rate ultrasound imaging and the detection of individual vaporization events, thereby addressing some of the burning challenges of new radiotherapy innovations.

Post-Irradiation Behavior of Colored PVA-Based Films Containing Ag Nanoparticles as Radiation Detectors/Exposure Indicators

Ionizing radiation covers a broad spectrum of applications. Since radioactive/radiation pollution is directly related to radiation risk, radiation levels should be strictly controlled. Different detection methods can be applied for radiation registration and monitoring. In this paper, radiation-induced variations in the optical properties of silver-enriched PVA-based hydrogel films with and without azo dye (Toluidine blue O, TBO, and Methyl red, MR) additives were investigated, and the feasibility of these free-standing films to serve as radiation detectors/exposure indicators was assessed. AgNO3 admixed with PVA gel was used as a source for the radiation-induced synthesis of silver nanoparticles (AgNPs) in irradiated gel films. Three types of sensors were prepared: silver-enriched PVA films containing a small amount of glycerol (AgPVAGly); silver-enriched PVA films with toluidine blue adducts (AgPVAGlyTBO); and silver-enriched PVA films with methyl red additives (AgPVAGlyMR). The selection of TBO and MR was based on their sensitivity to irradiation. The irradiation of the samples was performed in TrueBeam2.1 (VARIAN) using 6 MeV photons. Different doses up to 10 Gy were delivered to the films. The sensitivity of the films was assessed by analyzing the characteristic UV-Vis absorbance peaks on the same day as irradiation and 7, 30, 45, 90, and 180 days after irradiation. It was found that the addition of azo dyes led to an enhanced radiation sensitivity of the AgNPs containing films (0.6 Gy-1 for AgPVAGlyTBO and 0.4 Gy-1 for AgPVAGlyMR) irradiated with <2 Gy doses, indicating their applicability as low-dose exposure indicators. The irradiated films were less sensitive to higher doses. Almost no dose fading was detected between the 7th and 45th day after irradiation. Based on the obtained results, competing AgNP formation and color-bleaching effects in the AgPVAGly films with dye additives are discussed.

Validation of complex radiotherapy techniques using polymer gel dosimetry

Modern radiotherapy delivers highly conformal dose distributions to irregularly shaped target volumes while sparing the surrounding normal tissue. Due to the complex planning and delivery techniques, dose verification and validation of the whole treatment workflow by end-to-end tests became much more important and polymer gel dosimeters are one of the few possibilities to capture the delivered dose distribution in 3D. The basic principles and formulations of gel dosimetry and its evaluation methods are described and the available studies validating device-specific geometrical parameters as well as the dose delivery by advanced radiotherapy techniques, such as 3D-CRT/IMRT and stereotactic radiosurgery treatments, the treatment of moving targets, online-adaptive magnetic resonance-guided radiotherapy as well as proton and ion beam treatments, are reviewed. The present status and limitations as well as future challenges of polymer gel dosimetry for the validation of complex radiotherapy techniques are discussed.

Evaluation of Fused Deposition Modeling Materials for 3D-Printed Container of Dosimetric Polymer Gel

Accurate dosimetric verification is becoming increasingly important in radiotherapy. Although polymer gel dosimetry may be useful for verifying complex 3D dose distributions, it has limitations for clinical application due to its strong reactivity with oxygen and other contaminants. Therefore, it is important that the material of the gel storage container blocks reaction with external contaminants. In this study, we tested the effect of air and the chemical permeability of various polymer-based 3D printing materials that can be used as gel containers. A methacrylic acid, gelatin, and tetrakis (hydroxymethyl) phosphonium chloride gel was used. Five types of printing materials that can be applied to the fused deposition modeling (FDM)-type 3D printer were compared: acrylonitrile butadiene styrene (ABS), co-polyester (CPE), polycarbonate (PC), polylactic acid (PLA), and polypropylene (PP) (reference: glass vial). The map of R2 (1/T2) relaxation rates for each material, obtained from magnetic resonance imaging scans, was analyzed. Additionally, response histograms and dose calibration curves from the R2 map were evaluated. The R2 distribution showed that CPE had sharper boundaries than the other materials, and the profile gradient of CPE was also closest to the reference vial. Histograms and dose calibration showed that CPE provided the most homogeneous and the highest relative response of 83.5%, with 8.6% root mean square error, compared with the reference vial. These results indicate that CPE is a reasonable material for the FDM-type 3D printing gel container.

Patient specific quality assurance in SBRT: a systematic review of measurement-based methods

This topical review focuses on Patient-Specific Quality Assurance (PSQA) approaches to stereotactic body radiation therapy (SBRT). SBRT requires stricter accuracy than standard radiation therapy due to the high dose per fraction and the limited number of fractions. The review considered various PSQA methods reported in 36 articles between 01/2010 and 07/2022 for SBRT treatment. In particular comparison among devices and devices designed for SBRT, sensitivity and resolution, verification methodology, gamma analysis were specifically considered. The review identified a list of essential data needed to reproduce the results in other clinics, highlighted the partial miss of data reported in scientific papers, and formulated recommendations for successful implementation of a PSQA protocol.

Development of a silicone-based radio-fluorogenic dosimeter using dihydrorhodamine 6G

A silicon-based three-dimensional dosimeter can be formed in a free shape without a container and deformed because of its flexibility. Several studies have focused on enhancing its radiological characteristics and assessing its applicability as a quality assurance tool for image-guided and adaptive radiation therapy, considering motion and deformation. Here, we applied a fluorescence probe (dihydrorhodamine 6G, DHR6G) to a silicon elastomer as a new radiosensitive compound that converts nonfluorescent into fluorescent dyes using irradiation, and its fluorescence intensity increases linearly with the absorbed dose. In this study, we demonstrated a cost-effective synthesis method and optimized the composition conditions. The results showed that the DHR6G-SE prepared from 2.2 × 10-3 wt% DHR6G, 0.024 wt% pyridine, and a silicone elastomer (SE) (SILPOT TM 184, base/curing agent = 10/1) exhibited a linear increase in fluorescence with radiation exposure within a dose range of 0-8 Gy and a highly stable sensitivity for as long as 64 h. To demonstrate its container-less characteristics, the possibility of dosimetry for low-energy X-rays using DHR6G-SE was investigated.

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.

A Systematic Review of the Chemo/Radioprotective Effects of Melatonin against Ototoxic Adverse Effects Induced by Chemotherapy and Radiotherapy

BACKGROUND

Although chemotherapy and radiotherapy are effective in cancer treatment, different adverse effects induced by these therapeutic modalities (such as ototoxicity) restrict their clinical use. Co-treatment of melatonin may alleviate the chemotherapy/radiotherapy-induced ototoxicity.

OBJECTIVE

In the present study, the otoprotective potentials of melatonin against the ototoxicity induced by chemotherapy and radiotherapy were reviewed.

METHODS

According to the PRISMA guideline, a systematic search was carried out to identify all relevant studies on "the role of melatonin against ototoxic damage associated with chemotherapy and radiotherapy" in the different electronic databases up to September 2022. Sixty-seven articles were screened based on a predefined set of inclusion and exclusion criteria. Seven eligible studies were finally included in this review.

RESULTS

The in vitro findings showed that cisplatin chemotherapy significantly decreased the auditory cell viability compared to the control group; in contrast, the melatonin co-administration increased the cell viability of cisplatin-treated cells. The results obtained from the distortion product otoacoustic emission (DPOAE) and auditory brainstem response (ABR) tests demonstrated a decreased amplitude of DPOAE and increased values of ABR I-IV interval and ABR threshold in mice/rats receiving radiotherapy and cisplatin; nevertheless, melatonin co-treatment indicated an opposite pattern on these evaluated parameters. It was also found that cisplatin and radiotherapy could significantly induce the histological and biochemical changes in the auditory cells/tissue. However, melatonin co-treatment resulted in alleviating the cisplatin/radiotherapy-induced biochemical and histological changes.

CONCLUSION

According to the findings, it was shown that melatonin co-treatment alleviates the ototoxic damage induced by chemotherapy and radiotherapy. Mechanically, melatonin may exert its otoprotective effects via its anti-oxidant, anti-apoptotic, and anti-inflammatory activities and other mechanisms.

Dosimetric properties of PASSAG polymer gel dosimeter in electron beam radiotherapy using magnetic resonance imaging

BACKGROUND

Several physical factors such as photon beam energy, electron beam energy, and dose rate may affect the dosimetric properties of polymer gel dosimeters. The photon beam energy and dose rate dependence of PASSAG gel dosimeter were previously evaluated.

OBJECTIVE

This study aims to assess the dosimetric properties of the optimized PASSAG gel samples in various electron beam energies.

METHODS

The optimized PASSAG gel samples are first fabricated and irradiated to various electron energies (5, 7, 10 and 12 MeV). Then, the response (R2) and sensitivity of gel samples are analyzed by magnetic resonance imaging technique at a dose range of 0 to 10 Gy, scanning room temperature range of 15 to 22 °C, and post-irradiation time range of 1 to 30 days.

RESULTS

The R2-dose response and sensitivity of gel samples do not change under the evaluated electron beam energies (the differences are less than 5%). Furthermore, a dose resolution range of 11 to 38 cGy is obtained for the gel samples irradiated to different electron beam energies. Moreover, the findings show that the R2-dose response and sensitivity dependence of gel samples on electron beam energy varies over different scanning room temperatures and post-irradiation times.

CONCLUSION

The dosimetric assessment of the optimized PASSAG gel samples provides the promising data for this dosimeter during electron beam radiotherapy.

Gel Dosimetry

The purpose of radiation therapy (RT) is to cover tumor tissue homogeneously with a planned dose while minimizing the dose to the surrounding healthy tissue [...].

Protective Potentials of Alpha-Lipoic Acid against Ionizing Radiation-Induced Brain Damage in Rats

Background

This study was aimed at determining the effects of alpha-lipoic acid on ionizing irradiation-induced oxidative damage and apoptosis in the brain of rats.

Methods

The animals were exposed to whole-brain X-radiation with a 15 Gy single dose in the absence or presence of alpha-lipoic acid (200 mg/kg body weight) pretreatment for one week. The rats were divided into four groups (5 rats in each group): vehicle control, alpha-lipoic acid alone (ALA), radiation alone (RAD), and radiation plus alpha-lipoic acid (RAD+ALA). In the next stage, malondialdehyde (MDA), nitric oxide, catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) in the brain tissue of the rats were measured. Furthermore, the Western blot analysis technique was performed to assess the NOX2, NOX4, and caspase-3 protein expression levels.

Results

Twenty-four hours after the irradiation, MDA and nitric oxide levels in the irradiated rats were significantly higher than those in the control group (p < 0.001); however, the pretreatment with alpha-lipoic acid resulted in a significant reduction in these stress oxidative markers (p < 0.05). Moreover, a significant decrease in CAT, SOD, and GPx levels was observed in the radiation group alone compared to the control group (p < 0.01); in contrast, the activities of these antioxidant enzymes significantly increased in the radiation plus alpha-lipoic acid group in comparison to the radiation group alone (p < 0.05). The results of Western blot analysis revealed that NOX2, NOX4, and caspase-3 protein expressions significantly elevated in the irradiated rats compared to the control group (p < 0.001). The pretreatment with alpha-lipoic acid could significantly decrease the expression levels of NOX2, NOX4, and caspase-3 in comparison with the radiation group alone (p < 0.05).

Conclusion

According to the obtained findings, it can be mentioned that the alpha-lipoic acid pretreatment could mitigate the ionizing irradiation-induced oxidative damage and apoptosis in the brain of the rats.

An investigation into the dose rate and photon energy dependence of the GENA gel dosimeter in the MeV range

PURPOSE

In the current study, the energy and dose rate dependence of a new genipin-based gel dosimeter, named GENA gel dosimeter, were investigated.

METHODS

Prepared gel dosimeters exposed using a Varian clinical linac. Beam qualities of 6 and 18 MV were applied to investigate the GENA gel dosimeter's energy dependence. Furthermore, the gel dosimeters were exposed to 50, 100, 200, and 350 cGy/min dose rates, ranging from 0 to 8 Gy. The irradiated gel dosimeters were read out using a double beam UV-Visible spectrophotometer. The absorbance peak (AP) and area under spectrum (AUS) were evaluated.

RESULTS

Absorbance-dose sensitivities of (8.0 ± 0.18) × 10^-3 cm^-1Gy^-1 and (7.8 ± 0.15) × 10^-3 cm^-1Gy^-1 were obtained for GENA gel dosimeter for 6 and 18 MV beam qualities, respectively. Results specified no significant difference (p > 0.05) between the GENA gel dosimeter's sensitivities irradiated using the two energies mentioned above. For the mentioned dose rates, AP-dose sensitivities of (8.2 ± 0.22) × 10^-3, (8.1 ± 0.21) × 10^-3, (8.1 ± 0.2) × 10^-3 and (8.0 ± 0.18) × 10^-3 cm^-1Gy^-1 were obtained, respectively. Results showed no significant difference (p > 0.05) between the GENA gel dosimeter's sensitivities for the investigated dose rates and energies. In addition, results revealed that when the incident photon energy and dose rate changed, there were no significant differences (p > 0.05) between the GENA gel dosimeter's dose resolution values.

CONCLUSIONS

It is concluded that the response of the GENA gel dosimeter is not dependent on the energy and dose rate (p > 0.05) within the studied energy and dose rate ranges.

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.

HyperArcTM Dosimetric Validation for Multiple Targets Using Ionization Chamber and RT-100 Polymer Gel

Multiple brain metastases single-isocenter stereotactic radiosurgery (SRS) treatment is increasingly employed in radiotherapy department. Before its use in clinical routine, it is recommended to perform end-to-end tests. In this work, we report the results of five HyperArcTM treatment plans obtained by both ionization chamber (IC) and polymer gel. The end-to-end tests were performed using a water equivalent Mobius Verification PhantomTM (MVP) and a 3D-printed anthropomorphic head phantom PseudoPatient® (PP) (RTsafe P.C., Athens, Greece); 2D and 3D dose distributions were evaluated on the PP phantom using polymer gel (RTsafe). Gels were read by 1.5T magnetic resonance imaging (MRI). Comparison between calculated and measured distributions was performed using gamma index passing rate evaluation by different criteria (5% 2 mm, 3% 2 mm, 5% 1 mm). Mean point dose differences of 1.01% [min −0.77%−max 2.89%] and 0.23% [min 0.01%−max 2.81%] were found in MVP and PP phantoms, respectively. For each target volume, the obtained results in terms of gamma index passing rate show an agreement >95% with 5% 2 mm and 3% 2 mm criteria for both 2D and 3D distributions. The obtained results confirmed that the use of a single isocenter for multiple lesions reduces the treatment time without compromising accuracy, even in the case of target volumes that are quite distant from the isocenter.

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.

Recent Advances in Hydrogel-Based Sensors Responding to Ionizing Radiation

Ionizing radiation and its applications are widely spread throughout life. Similar to many other things, both the positive and negative aspects of ionizing radiation should always be kept in mind. For example, a proper radiation dose can be delivered to tumor tissue to kill malignant cells in radiotherapy. On the other hand, exceeding this dose can damage the normal tissues of a human organism. Therefore, the application of sensors for measuring ionizing radiation doses is of utmost importance in many fields, especially in cancer therapy. Traditional dosimeters, such as ionization chambers, silicon diodes and thermoluminescence dosimeters, are widely used. However, they have limitations in certain aspects. Hydrogel-based sensors (or dosimeters) for measuring ionizing radiation doses attract extensive attention for decades due to their equivalence to living tissue and biocompatibility. In this review, we catalog hydrogel-based dosimeters such as polymer, Fricke, radio-chromic, radio-fluorescence and NPs-embedded dosimeters. Most of them demonstrate desirable linear response and sensitivity regardless of energy and dose rate of ionizing radiation. We aim to review these dosimeters and their potential applications in radiotherapy as well as to stimulate a joint work of the experts from different fields such as materials science, chemistry, cancer therapy, radiobiology and nuclear science.

Application of 3D Gel Dosimetry as a Quality Assurance Tool in Functional Leksell Gamma Knife Radiosurgery

Highly precise dose delivery to the target (tumor or cancerous tissue) is a key point when brain diseases are treated applying recent stereotactic techniques: intensity-modulated, image-guided radiotherapy, volumetric modulated arc therapy, Gamma knife radiosurgery. The doses in one single shot may vary between tens and hundreds of Gy and cause significant cell/tissue/organ damages. This indicates the need for implementation of quality assurance (QA) measures which are realized performing treatment dose verification with more than one calibrated quality assurance method or tool, especially when functional radiosurgery with a high dose (up to 40 Gy in our case) shall be delivered to the target using small 4 mm collimator. Application of two dosimetry methods: radiochromic film dosimetry using RTQA2 and EBT3 films and dose gel dosimetry using modified nPAG polymer gels for quality assurance purposes in stereotactic radiosurgery treatments using Leksell Gamma Knife© Icon™ facility is discussed in this paper. It is shown that due to their polymerization ability upon irradiation nPAG gels might be potentially used as a quality assurance tool in Gamma knife radiosurgery: they indicate well pronounced linear dose response in hypo-fractionated (up to 10 Gy) dose range and are sensitive enough to irradiation dose changes with a high (at least 0.2 mm) spatial resolution. Dose assessment sensitivity of gels depends on parameters of a dose evaluation method (optical or magnetic resonance imaging), however, is similar to this estimated using film dosimetry, which is set as a standard dosimetry method for dose verification in radiotherapy.

Fluorescent organic particle doped polymer-based gel dosimeter for neutron detection

The purpose of this work is to develop a material capable of detecting neutrons produced by photodisintegration in a linear accelerator for its medical use. In this study, we have developed a gel-like material doped with fluorescent organic particles. PPO at 1 wt% is used as primary dopant and POPOP as secondary one at 0.03 wt%. A set of four samples is produced, with boric acid concentrations of 0, 400, 800 and 1200 ppm. The viscoelastic properties of the material are characterized with rheological measurements, finding a gel-like behavior, i.e., a material that can keep its original shape if no stresses are applied, but can also be deformed by applying a moderate shear rate. Furthermore, the material was irradiated with gamma, electron, and neutron emission sources from ¹³⁷Cs, ²²Na, ⁶⁰Co, ²¹⁰Po, ⁹⁰Sr and ²⁴¹AmBe, and its response was measured in two different experimental settings, in two different institutions, for comparative purposes. From these measurements, one can clearly establish that the new material detects neutrons, electrons, and gammas within the MeV regions and below. Thus, our findings show that the developed material and its properties make it a promising technology for its use in a neutron detector.

Superiorization versus regularization: A comparison of algorithms for solving image reconstruction problems with applications in computed tomography

PURPOSE

A system matrix can be built in order to account for the refractions in an optical computed tomography (CT) system. In order to utilize this system matrix, iterative methods are employed to solve the image reconstruction problem. The purpose of this study is to compare potential iterative algorithms to solve this image reconstruction problem. Comparisons examine both solution time and the quality of the reconstructed image. While our work is motivated by optical CT, the results can be extended more generally to CT.

METHODS

A collection of 21 algorithms for solving the image reconstruction problem were evaluated. Specifically, algorithms using (i) superiorization techniques and (ii) regularization to avoid overfitting were compared. Multiple test problems are investigated using 18 different image phantoms, parallel-beam and fan-beam system matrices, and varying noise levels. Comparison of the algorithms is done using performance profiles on three different performance measures.

RESULTS

The results for both the synthetic and clinical test problems show that there is not one single algorithm outperforming all others, but instead a set of top algorithms that give the best values on the performance profiles. When qualitative analyses such as reliance on stopping conditions, number of input parameters, and run time are also considered, FISTA-TV shows slight advantages over the other top algorithms.

CONCLUSIONS

There is a set of top algorithms that all show good results in the performance profiles with a mix of superiorized and regularized model algorithms. As to which of these top algorithms outperforms the rest is undetermined and further research needs to be investigated.

Rare-earth doped radioluminescent hydrogel as a potential phantom material for 3D gel dosimeter

Cancer prevention and treatment are currently the focus of most research. Dose verification is an important step for reducing the improper dose deposition during radiotherapy. To mend the traditional gel dosimeters for 3D dose verification, a novel rare-earth nanoparticle-based composite gel was prepared, which has good radioluminescence property and reusability. It is a promising phantom material for the new 3D gel dosimeter. TEM, DLS, FT-IR, TGA, and spectrofluorometer were used to determine the chemical structure, micromorphology, and optical performance. Compared to the traditional gel dosimeters, the composite gel has a good linear relationship between the light intensity excited by X-ray and the tube current. Furthermore, it may measure the dose distribution immediately in situ, which reduces errors and saves time. This work provides a new idea for the research of 3D gel dosimeters and promotes the safe and effective use of radiotherapy.

Multiresponsive hydrogels and organogels based on photocaged cysteine

Here we present the readily accessible amino acid 4,5-dimethoxy-2-nitrobenzyl-l-cysteine (DNC), as an ultra-low molecular weight gelator (MW = 316 g mol-1). Sonication of DNC in water or organic solvents as well as pH adjustment in water trigger gelation. A diverse set of stimuli (UV irradiation, oxidation, heat or pH change) induce a gel-sol transition. Moreover, the photo-triggered gel-sol transition was used to obtain a controlled cysteine release from the hydrogel.

Low-Diffusion Fricke Gel Dosimeters with Core-Shell Structure Based on Spatial Confinement

The diffusion of ferric ions is an important challenge to limit the application of Fricke gel dosimeters in accurate three-dimensional dose verification of modern radiotherapy. In this work, low-diffusion Fricke gel dosimeters, with a core-shell structure based on spatial confinement, were constructed by utilizing microdroplet ultrarapid freezing and coating technology. Polydimethylsiloxane (PDMS), with its excellent hydrophobicity, was coated on the surface of the pellets. The concentration gradient of the ferric ion was realized through shielding half of a Co-60 photon beam field size, and ion diffusion was measured by both ultraviolet-visible spectrophotometry and magnetic resonance imaging. No diffusion occurred between the core-shell pellets, even at 96 h after irradiation, and the diffusion length at the irradiation boundary was limited to the diameter (2-3 mm) of the pellets. Furthermore, Monte Carlo calculations were conducted to study dosimetric properties of the core-shell dosimeter, which indicated that a PDMS shell hardly affected the performance of the dosimeter.

Hydrogels for Three-Dimensional Ionizing-Radiation Dosimetry

Radiation-sensitive gels are among the most recent and promising developments for radiation therapy (RT) dosimetry. RT dosimetry has the twofold goal of ensuring the quality of the treatment and the radiation protection of the patient. Benchmark dosimetry for acceptance testing and commissioning of RT systems is still based on ionization chambers. However, even the smallest chambers cannot resolve the steep dose gradients of up to 30-50% per mm generated with the most advanced techniques. While a multitude of systems based, e.g., on luminescence, silicon diodes and radiochromic materials have been developed, they do not allow the truly continuous 3D dose measurements offered by radiation-sensitive gels. The gels are tissue equivalent, so they also serve as phantoms, and their response is largely independent of radiation quality and dose rate. Some of them are infused with ferrous sulfate and rely on the radiation-induced oxidation of ferrous ions to ferric ions (Fricke-gels). Other formulations consist of monomers dispersed in a gelatinous medium (Polyacrylamide gels) and rely on radiation-induced polymerization, which creates a stable polymer structure. In both gel types, irradiation causes changes in proton relaxation rates that are proportional to locally absorbed dose and can be imaged using magnetic resonance imaging (MRI). Changes in color and/or opacification of the gels also occur upon irradiation, allowing the use of optical tomography techniques. In this work, we review both Fricke and polyacrylamide gels with emphasis on their chemical and physical properties and on their applications for radiation dosimetry.

The radioprotective effects of alpha-lipoic acid on radiotherapy-induced toxicities: A systematic review

PURPOSE

Radiation therapy is one of the main cancer treatment modalities applied in 50-70% of cancer patients. Despite the many advantages of this treatment, such as non-invasiveness, organ-preservation, and spatiotemporal flexibility in tumor targeting, it can lead to complications in irradiated healthy cells/tissues. In this regard, the use of radio-protective agents can alleviate radiation-induced complications. This study aimed to review the potential role of alpha-lipoic acid in the prevention/reduction of radiation-induced toxicities on healthy cells/tissues.

METHODS

A systematic search was performed following PRISMA guidelines to identify relevant literature on the "role of alpha-lipoic acid in the treatment of radiotherapy-induced toxicity" in the electronic databases of Web of Science, Embase, PubMed, and Scopus up to January 2021. Based on the inclusion and exclusion criteria of the present study, 278 articles were screened. Finally, 29 articles were included in this systematic review.

RESULTS

The obtained results showed that in experimental in vivo models, the radiation-treated groups had decreased survival rate and body weight compared to the control groups. It was also found that radiation can induce mild to severe toxicities on gastrointestinal, circulatory, reproductive, central nervous, respiratory, endocrine, exocrine systems, etc. However, the use of alpha-lipoic acid could alleviate the radiation-induced toxicities in most cases. This radio-protective agent exerts its effects through mechanisms of anti-oxidant, anti-apoptosis, anti-inflammatory, and so on.

CONCLUSION

According to the obtained results, it can be mentioned that co-treatment of alpha-lipoic acid with radiotherapy ameliorates the radiation-induced toxicities in healthy cells/tissues.

Technical Note: Three-dimensional QA of simultaneous integrated boost radiotherapy treatments by a dose-volume histogram methodology and its comparison with 3D gamma results

PURPOSE

Intensity-modulated radiotherapy with simultaneous integrated boost (SIB) presents several attractive advantages to be employed in clinical practice. Its secure application demands a rigorous quality assurance (QA) procedure, ideal for three-dimensional (3D) dose distribution measurements. Thus, a gel dosimetry methodology to evaluate the dose delivery of SIB treatments is presented and compared to conventional gamma evaluation.

METHODS

MAGIC-f gel dosimeter with magnetic resonance images for dose reading were used following its standard procedures. Four SIB QA plans created in gel dosimeter phantoms were used. The gel measured and treatment planning system (TPS) calculated doses were compared using 3D gamma analyses (3%/3mm/15% threshold). Two structures were artificially on the TPS dose distribution expected on the phantom by converting the 1.7 and 2.0 Gy isodose levels into structures to represent the treatment. The gel and TPS dose-volume histogram (DVH) were compared based on five dose points: D95%, D90%, D50%, D10%, and D5%.

RESULTS

Approvals of 93%, 96%, 98%, and 92% were achieved in the 3D gamma analyses for the plans QA 1, 2, 3, and 4. In the DVH analyses, QA plan 1 measured and expected curves showed a good agreement. QA plan 2 showed deviations in the highest doses for both structures with a maximum deviation (Δ_máx ) of 8.0%. QA plans 3 and 4 showed the highest dose variation between the gel and TPS in the smaller doses of the DVH (Δ_máx of 7.2% and -8.9%, respectively). For QA plan 4, the curves of the 1.7 Gy structure presented a good agreement, but deviations in the smaller dose region of the DVH occurred for the 2 Gy structure (Δ_máx of 7.7%).

CONCLUSIONS

A methodology for 3D dose evaluation of complex SIB treatments was proposed. It provided an important overview of the dose distributions. Their results significantly complemented the usual gamma analysis results.

A review of brachytherapy physical phantoms developed over the last 20 years: clinical purpose and future requirements

Within the brachytherapy community, many phantoms are constructed in-house, and less commercial development is observed as compared to the field of external beam. Computational or virtual phantom design has seen considerable growth; however, physical phantoms are beneficial for brachytherapy, in which quality is dependent on physical processes, such as accuracy of source placement. Focusing on the design of physical phantoms, this review paper presents a summary of brachytherapy specific phantoms in published journal articles over the last twenty years (January 1, 2000 - December 31, 2019). The papers were analyzed and tabulated by their primary clinical purpose, which was deduced from their associated publications. A substantial body of work has been published on phantom designs from the brachytherapy community, but a standardized method of reporting technical aspects of the phantoms is lacking. In-house phantom development demonstrates an increasing interest in magnetic resonance (MR) tissue mimicking materials, which is not yet reflected in commercial phantoms available for brachytherapy. The evaluation of phantom design provides insight into the way, in which brachytherapy practice has changed over time, and demonstrates the customised and broad nature of treatments offered.

Linac-integrated kV-cone beam CT polymer gel dosimetry

X-ray CT polymer gel dosimetry (PGD) remains a promising tool for three dimensional verification of high-dose treatment deliveries such as non-coplanar stereotactic irradiations. Recent demonstrations have shown a proof-of-principle application of linac-integrated cone beam CT-imaged (LI-CBCT) PGDs for 3D dose verification. LI-CBCT offers advantages over previous CT based PGD, including close to real-time imaging of the irradiated dosimeter, as well as the ability to maintain the dosimeter in the same physical location for irradiation and imaging, thereby eliminating spatial errors due to dosimeter re-positioning for read-out that may occur for other systems. However the dosimetric characteristics of a LI-CBCT PGD system remain to be established. The work herein determines the dosimetric properties and critical parameters needed to perform cone beam PGD. In particular, we show that imaging the dosimeter 20-30 min post irradiation offers excellent recovery of maximum polymerization yield ([Formula: see text]90%), averaging with as few as 10 image averages can provide ∼90% gamma pass rates (3%, 3 mm) as compared to treatment planning, and that eliminating outlier averaging points can improve the precision and signal to noise ratio of resultant images. In summary, with appropriate methodology LI-CBCT PGD can provide dosimetric data capable of verification of complex high dose radiation deliveries in three dimensions and may find use in commissioning and validation of novel complex treatments.

Sensitivity enhancement of DHR123 radio-fluorogenic nanoclay gel dosimeter by incorporating surfactants and halogenides

Dosimetry of spatial dose distribution of ionizing radiation in tissue equivalent materials is particularly important for cancer radiotherapy. Here, we describe a radio-fluorogenic gel-based dosimeter that has achieved 16 times higher sensitivity by incorporating surfactants and halogenides. The gel dosimeters were prepared from dihydrorhodamine 123 (DHR123) and small amounts of nano-sized clay and a radiosensitizer. By comprehensively changing the type of additives for the sensitizer (three surfactants: Triton X-100, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide, and three halogenides: trichloroacetic acid, tribromoacetic acid and 2,2,2-trichloroethanol), the increase in sensitivity can be explained by an increase in relative fluorescence quantum yield and an increase in radiation chemical yield. These highly sensitive gel dosimeters also show dose rate independent sensitivity under irradiation at 0.64 and 0.77 Gy min⁻¹ using a 6 MV X-ray therapeutic beam from the medical linac.

Dosimetry of spatial dose distribution of ionizing radiation in tissue equivalent materials using high sensitive radio-fluorogenic gel dosimeter using DHR123 with sensitizer. (Radiation therapy planning image courtesy of Varian Medical Systems, Inc. All rights reserved.)

A new formulation of polymer gel dosimeter with reduced toxicity: Dosimetric characteristics and radiological properties

The present study aimed to produce a new, less toxic, and cost-effective polymer gel dosimeter using potassium salt of 2-acrylamido-2 methyl-propane sulfonic acid (AMPS) monomer. The new formulation was called PAKAG. The irradiation of PAKAG polymer gel dosimeter was performed using a 6 MV clinical linear accelerator, and its response was evaluated using magnetic resonance imaging. The obtained images were post-processed to produce related R2 maps. Afterward, the Dose-R2 calibration curves were obtained. Response dependence on the imaging temperature was examined. Furthermore, response stability over time was investigated. To investigate the radiological characteristics, the elemental composition, effective atomic number, electron density, and photon attenuation coefficient of PAKAG polymer gel dosimeter were calculated. A maximum sensitivity of 0.152±0.007 with the goodness of fit of R2=0.999 in a dynamic range of 0-6Gy at 12h post-irradiation time was found. Such as other polymer gel dosimeter, the response of PAKAG polymer gel dosimeter was dependent on post-irradiation time and imaging temperature. Finally, it was concluded that the PAKAG polymer gel dosimeter could be used as a less toxic and cost-effective polymer gel dosimeter.

Application of high field magnetic resonance microimaging in polymer gel dosimetry

Purpose

The purpose of this work was to examine the suitability of VIPAR^nd polymer gel–9.4 T magnetic resonance microimaging system for high spatial resolution dose distribution measurements.

Methods

The VIPAR^nd samples (3 cm in outside diameter and 12 cm in height) were exposed to ionizing radiation by using a linear accelerator (Varian TrueBeam, USA; 6 MV x‐ray beam). In the calibration stage, nine gel dosimeter vials were irradiated in a water phantom homogenously to the doses from 1.5 to 30 Gy in order to obtain R2‒dose relation. In the verification stage, two gel dosimeter vials were irradiated in the half beam penumbra area of 10 × 10 cm radiation field using the amount of monitor units appropriate to deliver 20 Gy at the field center. The gels were imaged on a vertical 9.4 T magnetic resonance (MR) microimaging scanner using single slice and multislice (9 slices) multiecho (90 × 7 ms) sequences at the spatial resolutions of 0.2–0.4 × 0.2–0.4 × 3 mm³ and 0.2–0.4 × 0.2–0.4 × 1 mm³ respectively. The gels were subjected to microimaging during the period of two weeks after irradiation. The reference data consisted of the dose profiles measured using the diode dosimetry, radiochromic film, ionization chamber, and the water phantom system.

Results

The VIPAR^nd‒9.4 T MR microimaging system was characterized by the dose sensitivity of 0.067 ± 0.002 Gy⁻¹ s⁻¹ at day 3 after irradiation. The dose resolution at 10 Gy (at P = 95%) was equal to 0.42 Gy at day 3 after irradiation using a single slice sequence (0.2 × 0.2 × 3 mm³) and 2.0 Gy at day 4 after irradiation using a multislice sequence (0.2 × 0.2 × 1 mm³) for one signal acquisition (measurement time: 15 min). These values were improved by ~1.4‐fold when using four signal acquisitions in the single slice sequence, and by ~2.78‐fold for 12 signal acquisitions in the multislice sequence. Furthermore, decreasing the in‐plane resolution from 0.2 × 0.2 mm² to 0.4 × 0.4 mm² resulted in a dose resolution of 0.3 Gy and 1 Gy at 10 Gy (at P = 95%) for one signal acquisition in the single slice and multislice sequences respectively (measurement time: 7.5 min).

As reveals from the gamma index analysis the dose distributions measured at days 3–4 postirradiation using both VIPAR^nd verification phantoms agree with the data obtained using a silicon diode, assuming 1 mm/5% criterion. A good interphantom reproducibility of the polymer gel dosimetry was proved by monitoring of two phantoms up to 10 days after irradiation. However, the agreement between the dose distributions measured using the diode and polymer gel started to get worse from day 5 after irradiation.

Conclusion

The VIPAR^nd–9.4T MR microimaging system allows to obtain dose resolution of 0.42 Gy at 10 Gy (at P = 95%) for a spatial resolution of 0.2 × 0.2 × 3 mm³ (acquisition time: 15 min). Further studies are required to improve a temporal stability of the gel‐derived dose distribution.

Dosimetric evaluation of PASSAG-U polymer gel dosimeter: Dependence of dose rate and photon energy

OBJECTIVE

Several physical factors such as dose rate and photon energy may change response and sensitivity of polymer gel dosimeters. This study aims to evaluate the R2-dose response and sensitivity dependence of PASSAG-U gel dosimeters with 3% and 5% urea on dose rate and photon energy.

MATERIALS AND METHODS

The PASSAG-U gel dosimeters were prepared under normal atmospheric conditions. The obtained gel dosimeters were irradiated to different dose rates (100, 200, and 300 cGy/min) and photon energies (6 and 15 MV). Finally, responses (R2) of the PASSAG-U gel dosimeters with 3% and 5% urea were analyzed by MRI technique at 1, 10, 14 days after the irradiation process.

RESULTS

The findings showed that the R2-dose responses of PASSAG-U gel dosimeters with 3% and 5% urea do not vary under the differently evaluated dose rates and photon energies. The R2-dose sensitivity of PASSAG-U polymer gel dosimeter with 3% urea does not change under the differently evaluated dose rates and photon energies, but it changes for PASSAG-U polymer gel dosimeter with 5% urea. The dose resolution values ranged from 0.20 to 0.86 Gy and from 0.27 to 2.20 Gy for the PASSAG-U gel dosimeter with 3% and 5% urea for the different dose rates and photon energies, respectively. Furthermore, it was revealed that the R2-dose response and sensitivity dependence of PASSAG-U gel dosimeters with 3% and 5% urea on dose rate and photon energy can vary over post irradiation time.

CONCLUSIONS

The study results demonstrated that dosimetric characteristics (dependence of dose rate and photon energy, and dose resolution) of PASSAG-U gel dosimeter with 3% were better than those of PASSAG-U gel dosimeter with 5% urea.

[Exogenous hydrogen sulfide improves erectile dysfunction by inhibiting apoptosis of corpus cavernosum smooth muscle cells in rats with cavernous nerve injury]

OBJECTIVE

To explore the effects of exogenous hydrogen sulfide (H2S) on apoptosis of corpus cavernosum smooth muscle cells (CCSMCs) and erectile dysfunction (ED) in rats with bilateral cavernous nerve injury (BCNI).

METHODS

Twentyfour male SD rats were randomly divided into 3 groups (n=8):sham operation group, bilateral cavernous nerve injury group (BCNI group) and H2S intervention group (BCNI+NaHS group). In BCNI and BCNI+NaHS groups, BCNI was induced by clamp injury of the bilateral cavernous nerves, and the rats were subjected to daily intraperitoneal injection of normal saline and 100 μmol/kg NaHS solution for 4 weeks, respectively. After the treatment, the intracavernous pressure (ICP) and mean arterial pressure (MAP), ) of the rats were measured. Western blotting was used to detect the expressions of cystathionine β synthetase (CBS), cystathionine γ lyase (CSE), α-SMA, collagen-I, caspase-3, Bax and Bcl-2 in the penile cavernous tissue, and the expressions of CBS and CSE were also detected immunohistochemically. The ratio of cavernous smooth muscle to collagen was detected using Masson's Trichrome staining. The apoptosis level of CCSMC was detected by TUNEL + α-SMA immunofluorescence double staining.

RESULTS

After 4 weeks of treatment, the rats in BCNI+NaHS group showed a significantly higher ICP/MAP ratio than those in BCNI group (P < 0.05). The results of Masson's Trichrome staining showed that the ratio of cavernous smooth muscle/collagen was significantly higher in BCNI + NaHS group than in BCNI group (P < 0.05). Western blotting showed a significantly higher expression of α-SMA protein but a lower expression of collagen-I protein in BCNI + NaHS group than in BCNI group (P < 0.05). TUNEL+α-SMA immunofluorescence double staining revealed a significantly lower number of apoptotic CCSMCs in BCNI+NaHS group than in BCNI group (P < 0.05). Compared with those in BCNI group, the rats in BCNI+NaHS group had significantly decreased expressions of caspase-3 and Bax proteins (P < 0.05) with significantly enhanced Bcl-2 protein expression and an increased Bcl-2/Bax ratio (P < 0.05). The expressions of CBS and CSE were significantly lower in BCNI group than in the other two groups (P < 0.05).

CONCLUSIONS

Exogenous H2S enhance the expression of the classic apoptotic protein Bcl-2 and reduces apoptosis of CCSMC to improve the erectile function in rats with BCNI.

A systematic review of radiation-induced testicular toxicities following radiotherapy for prostate cancer

BACKGROUND

Prostate cancer is the second most common malignancy in men in the world, and radiotherapy is used as a standard treatment modality for this cancer. Although this treatment modality effectively kills prostate cancerous cells, it unavoidably irradiates the organs/tissues that are away from the treatment site. In this regard, radiation-induced testicular toxicities following prostate radiotherapy can affect sexual function, reproduction, and quality of life in cancer survivors. This review summarizes the available data on testicular exposure to radiation during prostate radiotherapy and the consequences on testicular function.

METHODS

To illuminate the radiation-induced testicular toxicities following prostate radiotherapy, a systematic search was conducted based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guideline in PubMed, Web of Science, Scopus, Embase, and clinical trials electronic databases up to September 2018. According to a set of prespecified inclusion and exclusion criteria, 31 eligible articles providing data on testicular function following radiotherapy in patients with prostate cancer were included in the study.

RESULTS

According to the different radiotherapeutic techniques used for prostate cancer treatment, the total tumor dose and scattered testicular dose values were ranging from 36.25 to 78.00 Gy and 0.06 to 6.48 Gy, respectively. Luteinizing hormone and follicle-stimulating hormone levels after prostate radiotherapy were significantly higher in comparison with the pretreatment levels. Around 60% of the studies showed that testosterone levels after prostate radiotherapy were significantly lower than the pretreatment levels. Furthermore, erectile dysfunction (ED), as an adverse side effect resulting from prostate radiotherapy, was reported and this complication is significantly correlated with lower satisfaction with sexual life. Testicular atrophy following prostate radiotherapy has also been observed and its frequency in patients with prior prostate radiotherapy is 2.5 times more than that in the patients without prior radiotherapy.

CONCLUSION

The data revealed that the scattered dose to testicular tissues during prostate radiotherapy can lead to testicular atrophy, variation of the male sex hormones, and quality of sexual life.

Evaluations of N-(Isobutoxymethyl) acrylamide gel dosimeter by NMR technique for radiotherapy and uncertainty in dose measurements

N-(Isobutoxymethyl) acrylamide (NIBMA) monomer in gelatin, named NIBMAGAT gel dosimeter, was prepared and investigated by nuclear magnetic imaging (NMR) for radiotherapy in the dose range of 0-30 Gy. NIBMA monomer polymerizes upon irradiation, increasing spin-spin relaxation rate R₂. The addition of glycerol as a co-solvent in the gel matrix improved its radiation sensitivity better than the co-solvents of acetone and methanol. The increase of glycerol content by 1% wt/wt enhanced the sensitivity by ˜ 3.1%. This gel has better radiation sensitivity as compared to the polyacrylamide gel (PAG) dosimeter; the sensitivities of NIBMAGAT gel and normoxic polyacrylamide gel (nPAG) are ≈0.13 and ≈0.1 s^-1.Gy^-1, respectively. By comparing NIBMAGAT gel dosimeter with PAG, nMAG and nPAG gel dosimeters, NIBMAGAT gel dosimeter is less influenced by scanning temperature than the last three dosimeters. The gel is water equivalent and has an energy-independent response from 80 keV to 20 MeV. The overall uncertainty of dose measurement using NIBMAGAT gel is 5.46% at 2σ. Our findings suggest the applicability of using NIBMAGAT gel dosimeter by NMR technique for dose verification/planning in the practice of clinical radiotherapy.