Effect of high-intensity ultrasound soymilk pretreatment on the physicochemical properties of microbial transglutaminase-catalyzed tofu gel.

Tofu prepared by conventional methods often has a bitter taste and poor water-holding capacity (WHC). To improve the quality of the product, alternative processes must be developed. Herein, the effect of ultrasound pretreatment on the properties of soymilk and tofu gel derived thereof were investigated. Treatment of soymilk with ultrasound gave rise to a reduction in the particle size and an enhancement in the surface hydrophobicity, whereby optimum values were obtained after 15 min treatment. Subsequently, microbial transglutaminase (MTG) was added to ultrasound-treated soymilk to promote the soy protein crosslinking. The gel strength, WHC, and nonfreezable water content of MTG-catalyzed tofu gel obtained from treated soymilk increased with the extension of the ultrasound pretreatment time, whereas the free sulfhydryl content decreased because of the formation of disulfide bonds. Fourier transform infrared spectroscopy demonstrated variations in the secondary structure of MTG-catalyzed tofu gel. Furthermore, soymilk's exposure to high-intensity ultrasound pretreatment led to a tofu gel with a dense, homogenous, and stable network structure, as evidenced by scanning electron microscopy. Therefore, this study answers for the theoretical support of the industrial production of MTG-catalyzed tofu gel from ultrasound-treated soymilk. PRACTICAL APPLICATION: High-intensity ultrasound pretreatment improved the texture properties of MTG-catalyzed tofu gel. The resulting MTG-catalyzed tofu gel has potential application in industrial production.

Enhancement of gel properties of Scomberomorus niphonius myofibrillar protein using phlorotannin extracts under UVA irradiation.

The effect of phlorotannin extracts (PTE) (from sporophyll of Undaria pinnatifida) added at different levels (0, 25, 125, 625 µmol/g protein) on the gel properties of mackerel (Scomberomorus niphonius) myofibrillar protein (MP) was studied with and without ultraviolet A (UVA) irradiation. The results showed that the gel strength and cooking yield increased in a PTE dose-dependent manner, and at the level of 625 µmol/g protein PTE, the highest gel strength of 308.43 ± 8.12 (mN·cm) and cooking yield of 76.16 ± 1.40% were obtained in the samples treated with UVA irradiation. The same samples also showed increased carbonyl content, decreased total sulfhydryl, unwinding of α-helix, and quenching of fluorescence intensity of endogenous tryptophan, all of which indicated that elevated protein oxidation in these samples led to enhanced protein cross-linking. Results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) indicated aggregation of myosin heavy chains (MHCs) in the UVA-treated gels with PTE, also evidenced by the dense three-dimensional network structure in these samples visualized by scanning electron microscopy (SEM). Electron spin resonance (ESR) and spin trapping results indicated that free radicals were produced during the gelation process, possibly originated from UVA-treated PTE, which played a critical role of oxidizing fish MPs, and eventually led to the improvement of the textural properties of the mackerel MP gel. PRACTICAL APPLICATION: Brown algae are a family of high-yield marine algae. Phlorotannin extracts are highly active natural substances extracted from brown algae that can have many applications. Ultraviolet A (UVA) as a green and environmentally friendly physical processing method has been widely used in food processing in recent years. The method proposed in this study could be utilized to improve properties of fish protein gel made from poorly performing low-priced fishes, and provide workable guidance for industry to expand the application of brown algae in food processing to better meet consumer's demand for high-quality marine foods.

UV irradiation of Type I collagen gels changed the morphology of the interconnected brain capillary endothelial cells on them.

We cultured mouse brain capillary endothelial cell line bEnd.3 on the UV-irradiated Type I collagen gel. Morphology of bEnd.3 cells on the Type I collagen gel was drastically changed if the gel was crosslinked by UV irradiation. The interconnecting network of bEnd.3 cells which have cord-like morphology on the soft collagen gels was converted to the monolayer of the flat cells, tightly-bound each other covering the gel surface, in a confluent state. The collagen gels were mechanically stiffened by UV irradiation for 15 min with UV light at 254 nm showing approximately two times higher value of Young's modulus E (1.51 ± 0.58 kPa) than the control gel (3.17 ± 1.17 kPa). AFM images of the collagen fibrils were not severely changed after irradiation. Collagen subunit proteins were crosslinked and degraded simultaneously under UV irradiation proved by results of SDS-PAGE and separation by centrifugation. Expression of Integrin gene was measured by quantitative real-time PCR. Expression of the integrin α2 gene, tight junction protein 1 gene, and claudin 5 gene were down-regulated in cells on the UV irradiated collagen gel in comparison with the unirradiated one while expression of the integrin ß1 gene and Integrin α1 gene did not significantly change. Thick actin filaments were more clearly observed in the cells on the UV-irradiated collagen gel than the unirradiated one by fluorescent microscopy. We conclude that UV irradiation made the collagen gel stiffened and changed the physiological state of bEnd.3 cells including their adhesion, extension, and proliferation.

Molecular environment and reactivity in gels and colloidal solutions under identical conditions.

A PEG-Tyr block copolymer forms a kinetically stable colloidal solution in water at room temperature which undergoes an irreversible conversion to a gel phase upon heating. A micellar solution and a gel can therefore be studied under identical experimental conditions. This made it possible to compare physical properties and chemical reactivity of micelles and gels in identical chemical environments and under identical conditions. EPR spectra of the spin-labelled copolymer showed that tyrosine mobility in gels was slightly reduced compared to micelles. Chemical reactivity was studied using photochemical degradation of tyrosine and tyrosine dimerization, in the absence and in the presence of an Fe(iii) salt. The reactivity trends were explained by reduced tyrosine mobility in the gel environment. The largest reactivity difference in gels and micelles was observed for bimolecular dityrosine formation which was also attributed to the reduction in molecular mobility.

Management of otitis externa with an led-illuminated gel: a randomized controlled clinical trial in dogs.

BACKGROUND: Canine otitis externa is a painful condition which can be challenging to treat due to difficulties in the administration of otic medication. This can be due to lack of owner compliance in the application of ear drops or due to the resentment that some dogs demonstrate when attempts are made to administer topical medication into a sensitive ear canal. The aim of the study was to assess the efficacy of a topical LED-illuminated gel (LIG) in canine otitis externa in comparison to standard of care therapy. Dogs with spontaneous otitis externa were randomly allocated in three groups: groups QW received LIG once weekly; BW received LIG twice weekly; group C received enrofloxacin and silver sulfadiazine twice daily. LIG consists of a topical application of a gel containing chromophores that, when illuminated by a LED lamp, re-emit fluorescent light which can stimulate physiological responses, promoting healing and controlling bacteria. The evaluation protocol (T0 to T5) considered clinical assessment (OTIS-3-index-scoring-system; pruritus-severity-scale; pain-severity-score; aural temperature), cytological scoring system, quali-quantitative bacteriologic assessment. RESULTS: All groups (QW, n = 21; BW, n = 23; C, n = 20) showed improvement during the study (QW: P < 0.02 for cytological and pain scores, P < 0.003 for bacteriologic assessment, P < 10- 4 for pruritus, total OTIS-3 and temperature assessments; BW: P < 10- 4 for all clinical, cytological and bacteriologic assessments; C: P < 0.02 for all clinical and cytological assessments, P < 10- 4 for bacteriologic assessment). The highest clinical score reduction occurred in Group BW (P < 0.014 in T3; P < 0.001 in T4 and P < 10- 4 in T5). BW reached the clinically relevant effect level at T3 (- 3.26 ± 1.21 levels), QW reached it at T4 (- 3.24 ± 0.99), C did not reach it. No differences between groups were seen in the reduction of CFU/mL (T0-T5). CONCLUSIONS: All treatment groups showed a positive clinical effect. LIG administered twice-a-week was the most favourable protocol of the study. LIG may be considered beneficial in the management of canine otitis externa; it seems to be effective in controlling the clinical condition, including the signs of inflammation and local pain, the bacterial growth, and it may help increasing treatment compliance.

Improvement of myofibrillar protein gel strength of Scomberomorus niphonius by riboflavin under UVA irradiation.

In this study, effects of different concentrations of riboflavin (0, 0.02, and 0.1 µmol/g protein) on myofibrillar protein (MP, Scomberomorus niphonius) gel were characterized. The gel structure and properties were studied with or without Ultraviolet A (UVA) irradiation. Electron spin resonance results showed that riboflavin produced ·OH under UVA irradiation, which subsequently oxidized the MP. Compared with the control group, the addition of riboflavin with UVA irradiation increased the strength of the MP gel. The rheological results showed that under UVA irradiation, addition of riboflavin facilitated the sol-gel transition between 45 and 52°C, indicating that oxidation led to significant structural changes which in turn resulted in a more compact and uniform gel network. The presence of riboflavin led to increased carbonyl content and decreased sulfhydryl and free amino groups, which decreased the protein solubility and promoted alpha-helical conformational loss in the secondary structure of the MP. These results all indicated that the MP has been oxidized. Electrophoresis revealed that myosin heavy chains were aggregated in the UVA-treated riboflavin-added MP gel, indicating that protein cross-linking has been induced. All the results indicated that the ·OH produced by riboflavin under UVA irradiation oxidized the MP, and improved protein crosslinking and gel properties.

A very low diffusion Fricke gel dosimeter with functionalised xylenol orange-PVA (XOPVA).

A gel dosimeter has been developed utilising a recently reported system for reducing Fe3+ diffusion in a Fricke gel dosimeter which chelates xylenol orange to the gelling agent poly(vinyl alcohol) (PVA). Formulations were investigated using both gelatin and PVA as the gelling agent, along with the inclusion of glyoxal. The resulting gel had an optical density dose response of 0.0031 Gy-1, an auto-oxidation rate of 0.000 23 h-1, and a diffusion rate of 0.132 mm2 h-1 which is a significant improvement over previously reported gelatin based Fricke gel dosimeters. The gel was also shown to be energy and dose-rate independent and could be reused after irradiation. Thus, this gel dosimeter has the potential to provide a safe and practical solution to three dimensional radiation dosimetry in the medical environment.

Low-density gel dosimeter for measurement of the electron return effect in an MR-linac.

Radiation therapy in the presence of a strong magnetic field is known to cause regions of enhanced and reduced dose at interfaces of materials with varying densities, in a phenomenon known as the electron return effect (ERE). In this study, a novel low-density gel dosimeter was developed to simulate lung tissue and was used to measure the ERE at the lung-soft tissue interface. Low-density gel dosimeters were developed with Fricke xylenol orange gelatin (FXG) and ferrous oxide xylenol orange (FOX) gels mixed with polystyrene foam beads of various sizes. The gels were characterized based on CT number, MR signal intensity, and uniformity. All low-density gels had CT numbers roughly equivalent to lung tissue. The optimal lung-equivalent gel formulation was determined to be FXG with <1 mm polystyrene beads due to the higher signal intensity of FXG compared to FOX and the higher uniformity with the small beads. Dose response curves were generated for the optimal low-density gel and conventional FXG. The change in spin-lattice relaxation rate (R1) before and after irradiation was linear with dose for both gels. Next, phantoms consisting of concentric cylinders with low-density and conventional FXG were created to simulate the lung-soft tissue interface. The phantoms were irradiated in a conventional linear accelerator (linac) and in a linac combined with a 1.5 T magnetic resonance imaging (MRI) unit (MR-linac) to measure the effects of the magnetic field on the dose distribution. Hot and cold spots were observed in the dose distribution at the boundaries between the gels for the phantom irradiated in the MR-linac but not the conventional linac, consistent with the ERE.

Effects of UV-C irradiation and traditional thermal processing on acemannan contained in Aloe vera gel blends.

The effects of pH (3.5, 4.5, and 5.5) and UV-C irradiation dose (12.8, 24.2, 35.8, and 54.6 mJ/cm2) on the physicochemical properties changes in 10% Aloe vera gel blends; in addition, the acemannan concentration and structural changes in the precipitated polysaccharides were evaluated. A thermal treatment (TT; 45 s at 90 °C) was used for comparison. In contrast to TT, a dose of 24.2 mJ/cm2 did not induce significant changes of free sugar content. Moreover, TT and UV-C irradiation did not significantly affect the content of mannose but increased those of galactose, fructose, and glucose. 1H NMR analysis revealed minimal changes in the isolated fractions of acemannan, indicating that compared to the unprocessed control sample, the acemannan deacetylation was more pronounced by TT (27%) than by UV-C irradiation (11% at 54.6 mJ/cm2), without any significant difference between the two. UV-C irradiation of Aloe vera gel blends at pH 3.5 and 24.2 mJ/cm2 was an alternative to TT and efficiently preserve the characteristics of acemannan.

Analysis of induced error by susceptibility effect in low-density gel dosimeters.

PURPOSE: In low-density (LD) gel dosimeter, diffusive spin-spin relaxation rate (R2)-dispersion caused by susceptibility-induced internal gradient leads to a significant deviation in the measured R2 from the real value. In this study, the effect of induced internal gradient on R2 was visualized and quantified algebraically as an important cause of inaccuracy in LD gel dosimeters. MATERIALS AND METHODS: In this method, two sets of LD and unit-density (UD) gel dosimeters were prepared. The LD gel was made by mixing the UD gel with expanded polystyrene spheres. The R2 was used to determine the spatially resolved decay rates due to diffusion in internal magnetic field. The internal gradient was calculated for a multiple spin-echo sequence. RESULTS: It is shown that in a LD gel, the internal gradient leads to overestimation of mean R2 value (R2mean). Pixel-by-pixel R2 measurements inside a LD gel showed significant deviation from R2 mapping in UD gel. CONCLUSION: It appears that significant differences between R2mean in a selected region of interest and pixel-by-pixel R2 values are the main source of inaccuracy in dose mapping of a LD gel.

The effect of gel homogeneity on dose response in a low-density polymer gel dosimeter for radiation therapy.

BACKGROUND: The human body consists of a variety of tissues and cavities with different physical and radiological properties. The most important among these are tissues and cavities including lungs, oral cavities, teeth, nasal passages, sinuses, and bones. Thus, the dose distribution in these tissues cannot be verified with soft tissue equivalent polymer gel dosimeters. This study is conducted to evaluate the effect of homogeneity on dose response of an anoxic low-density polymer gel dosimeter for radiation therapy. MATERIALS AND METHODS: The low-density polymer gel dosimeter is composed of 12% gelatin, 5% methacrylic acid, 0.15% sodium dodecyl sulfate, 10 mm tetrakis (hydroxymethyl) phosphonium chloride, and 83% ultrapure deionized water. The time between irradiation and scanning for all gels experiments was 18 h. The gel dosimeters were imaged using a 1.5 T clinical magnetic resonance imaging scanner in a transmitter/receiver head coil. RESULTS: The low-density gels had a mass density between 0.35 g/cm 3 and 0.45 g/cm 3 and the computed tomography (CT) values varied from approximately -650 to -750 Hounsfield units. It is clear that the CT numbers of the fabricated gel are close to those of the normal human lung tissue, which ranges from -770 to -875 Hounsfield units. CONCLUSION: Findings of the present study showed that if the density and homogeneity of the low-density polymer gel dosimeters are equal to those of the normal lung tissue, it may be used to measure the three dimensional dose distributions in lung tissue during radiation therapy.

Introduction of a deformable x-ray CT polymer gel dosimetry system.

This study introduces the first 3D deformable dosimetry system based on x-ray computed tomography (CT) polymer gel dosimetry and establishes the setup reproducibility, deformation characteristics and dose response of the system. A N-isopropylacrylamide (NIPAM)-based gel formulation optimized for x-ray CT gel dosimetry was used, with a latex balloon serving as the deformable container and low-density polyethylene and polyvinyl alcohol providing additional oxygen barrier. Deformable gels were irradiated with a 6 MV calibration pattern to determine dosimetric response and a dosimetrically uniform plan to determine the spatial uniformity of the response. Wax beads were added to each gel as fiducial markers to track the deformation and setup of the gel dosimeters. From positions of the beads on CT images the setup reproducibility and the limits and reproducibility of gel deformation were determined. Comparison of gel measurements with Monte Carlo dose calculations found excellent dosimetric accuracy, comparable to that of an established non-deformable dosimetry system, with a mean dose discrepancy of 1.5% in the low-dose gradient region and a gamma pass rate of 97.9% using a 3%/3 mm criterion. The deformable dosimeter also showed good overall spatial dose uniformity throughout the dosimeter with some discrepancies within 20 mm of the edge of the container. Tracking of the beads within the dosimeter found that sub-millimetre setup accuracy is achievable with this system. The dosimeter was able to deform and relax when externally compressed by up to 30 mm without sustaining any permanent damage. Internal deformations in 3D produced average marker movements of up to 12 mm along the direction of compression. These deformations were also shown to be reproducible over 100 consecutive deformations. This work has established several important characteristics of a new deformable dosimetry system which shows promise for future clinical applications, including the validation of deformable dose accumulation algorithms.

A fast dual wavelength laser beam fluid-less optical CT scanner for radiotherapy 3D gel dosimetry I: design and development.

Three dimensional dosimetry by optical CT readout of radiosensitive gels or solids has previously been indicated as a solution for measurement of radiotherapy 3D dose distributions. The clinical uptake of these dosimetry methods has been limited, partly due to impracticalities of the optical readout such as the expertise and labour required for refractive index fluid matching. In this work a fast laser beam optical CT scanner is described, featuring fluid-less and dual wavelength operation. A second laser with a different wavelength is used to provide an alternative reference scan to the commonly used pre-irradiation scan. Transmission data for both wavelengths is effectively acquired simultaneously, giving a single scan process. Together with the elimination of refractive index fluid matching issues, scanning practicality is substantially improved. Image quality and quantitative accuracy were assessed for both dual and single wavelength methods. The dual wavelength scan technique gave improvements in uniformity of reconstructed optical attenuation coefficients in the sample 3D volume. This was due to a reduction of artefacts caused by scan to scan changes. Optical attenuation measurement accuracy was similar for both dual and single wavelength modes of operation. These results established the basis for further work on dosimetric performance.

Evaluation of the Accuracy of Polymer Gels for Determining Electron Dose Distributions in the Presence of Small Heterogeneities.

The aim of this study is to evaluate the application and accuracy of polymer gels for determining electron dose distributions in the presence of small heterogeneities made of bone and air. Different cylindrical phantoms containing MAGIC (Methacrylic and Ascorbic acid in Gelatin Initiated by Copper) normoxic polymer gel were used under the slab phantoms during irradiation. MR images of the irradiated gel phantoms were obtained to determine their R2 (spin-spin) relaxation maps for conversion to absorbed dose. One- and 2-dimensional lateral dose profiles were acquired at depths of 1 and 4 cm for 8 and 15 MeV electron beams. The results were compared with the doses measured by a diode detector at the same positions. In addition, the dose distribution in the axial orientation was measured by the gel dosimeter. The slope and intercept for the R2 versus dose curve were 0.509 ± 0.002 Gy s and 4.581 ± 0.005 s, respectively. No significant variation in dose-R2 response was seen for the two electron energies within the applied dose ranges. The mean dose difference between the measured gel dose profiles was smaller than 3% compared to those measured by the diode detector. These results provide further demonstration that electron dose distributions are significantly altered in the presence of tissue inhomogeneities such as bone and air cavity and that MAGIC gel is a useful tool for 3-dimensional dose visualization and qualitative assessment of tissue inhomogeneity effects in electron beam dosimetry.

On the development of a VIPARnd radiotherapy 3D polymer gel dosimeter.

This work presents an improvement of the VIPARnd ('nd' stands for 'normoxic, double', or VIP) polymer gel dosimeter. The gel composition was altered by increasing the concentration of the monomeric components, N-vinylpyrrolidone (NVP) and N,N'-methylenebisacrylamide (MBA), in co-solvent solutions. The optimal composition (VIPARCT, where 'CT' stands for computed tomography, or VIC) comprised: 17% NVP, 8% MBA, 12% t-BuOH, 7.5% gelatine, 0.007% ascorbic acid, 0.0008% CuSO4 × 5H2O and 0.02% hydroquinone. The following characteristics of VIC were achieved: (i) linear dose range of 0.9_30 Gy, (ii) saturation for radiation doses of over 50 Gy, (iii) threshold dose of about 0.5 Gy, (iv) dose sensitivity of 0.171 Gy-1 s-1, which is roughly 2.2 times higher than that of VIP (for nuclear magnetic resonance measurements). It was also found that VIC is dose- rate-independent, and its dose response does not alter if the radiation source is changed from electrons to photons for external beam radiotherapy. The gel responded similarly to irradiation with small changes in radiation energy but was sensitive to larger energy changes. The VIC gel retained temporal stability from 20 h until at least 10 d after irradiation, whereas spatial stability was retained from 20 h until at least 6 d after irradiation. The scheme adopted for VIC manufacturing yields repeatable gels in terms of radiation dose response. The VIC was also shown to perform better than VIP using x-ray computed tomography as a readout method; the dose sensitivity of VIC (0.397 HU Gy-1) was 1.5 times higher than that of VIP. Also, the dose resolution of VIC was better than that of VIP in the whole dose range examined.

Monomer zinc phthalocyanine/upconversion nanoparticle coated with hyaluronic acid crosslinked gel as NIR light-activated drug for in vitro photodynamic therapy.

Carboxyl group modified zinc phthalocyanines (ZnPc) are classic and widely used photosensitizers (PSs) in upconversion nanoparticles (UCNPs) mediated photodynamic therapy (PDT) for tumor treatment. To improve the PDT activity of the complex system of ZnPc and UCNPs, many UCNPs with high red emission intensity were design and prepared. ZnPc-(COOH)4 tends to aggregate both in water and under physiological conditions, which can sharply decrease its PDT activity. Therefore, choosing monomeric COOH groups modified ZnPc as PSs is an alternative way to improve their activity. In this manuscript, three zinc(ii) phthalocyanines, substituted with 4 (ZnPc-(COOH)4), 8 (ZnPc-(COOH)8) and 16 (ZnPc-(COOH)16) COOH groups, were synthesized. A comparison of the results indicated that ZnPc-(COOH)16 existed in its monomeric form under physiological conditions because of its large substituents. Moreover, ZnPc-(COOH)16 showed superior singlet oxygen (1O2) generation ability when compared to ZnPc-(COOH)4 and ZnPc-(COOH)8. Therefore, we chose ZnPc-(COOH)16 as PSs for absorption on the surface of the UCNPs. Then, they were encapsulated by crosslinked methacrylated hyaluronic acid (m-HA), which provides active tumor accumulation ability by binding its overexpressed receptors on the surface of cancer cells. The resulting nanoparticles can be effectively taken up by cancer cells and shows strong near-infrared (NIR) light triggered PDT in vitro.

Initial characterization of a gel patch dosimeter for in vivo dosimetry.

In vivo dosimetry is a greatly underutilized tool for patient safety in clinical external beam radiotherapy treatments, despite being recommended by several national and international organizations (AAPM, ICRU, IAEA, NACP). The reasons for this underutilization mostly relate to the feasibility and cost of in vivo dosimetry methods. Due to the increase in the number of beam angles and dose per fraction in modern treatments, there is a compelling need for a novel dosimeter that is robust and affordable while able to operate properly in these complex conditions. This work presents a gel patch dosimeter as a novel method of in vivo dosimetry. DEFGEL, a 6% T normoxic polyacrylamide gel, was injected into 1 cm thick acrylic molds to create 1 cm thick small cylindrical patch dosimeters. To evaluate the change in optical density due to radiation induced polymerization, dosimeters were scanned before and after irradiation using an in-house developed laser densitometer. The dose-responses of three separate batches of gel were evaluated and compared to check for linearity and repeatability. The response development time was evaluated to ensure that the patch dosimeter could be high throughput. Additionally, the potential of this system to be used as an in vivo dosimeter was tested with a clinically relevant end-to-end in vivo phantom test. All irradiations were performed with a Varian Clinac 21EX at the University of Wisconsin Medical Radiation Research Center (UWMRRC). The dose-response of all three batches of gel was found to be linear within the range of 2-20 Gy. At doses below 0.5 Gy the statistical uncertainties were prohibitively large to make quantitative assessments of the results. The three batches demonstrated good repeatability in the range of 2 Gy to up to 10 Gy, with only slight variations in response at higher doses. For low doses the dosimeter fully developed within an hour while at higher doses they fully developed within four hours. During the in vivo phantom test the predicted patch absorbed dose was 4.23 Gy while the readout dose was evaluated to be 4.37 Gy, which corresponds to a 3.2% discrepancy. The dosimeter and densitometer pairing shows promise as an in vivo dosimetry system, especially for hypofractionated or MRI-guided radiotherapy treatments where higher doses are prescribed.

Role of gel dosimeters in boron neutron capture therapy.

Gel dosimeters have acquired a unique status in radiotherapy, especially with the advent of the new techniques in which there is a need for three-dimensional dose measurement with high spatial resolution. One of the techniques in which the use of gel dosimeters has drawn the attention of the researchers is the boron neutron capture therapy. Exploring the history of gel dosimeters, this paper sets out to study their role in the boron neutron capture therapy dosimetric process.

Ion therapy of prostate cancer: daily rectal dose reduction by application of spacer gel.

BACKGROUND: Ion beam therapy represents a promising approach to treat prostate cancer, mainly due to its high conformity and radiobiological effectiveness. However, the presence of prostate motion, patient positioning and range uncertainties may deteriorate target dose and increase exposure of organs at risk. Spacer gel injected between prostate and rectum may increase the safety of prostate cancer (PC) radiation therapy by separating the rectum from the target dose field. The dosimetric impact of the application of spacer gel for scanned carbon ion therapy of PC has been analyzed at Heidelberg Ion-Beam Therapy Center (HIT). MATERIALS AND METHODS: The robustness of ion therapy treatment plans was investigated by comparison of two data sets of patients treated with and without spacer gel. A research treatment planning system for ion therapy was used for treatment plan optimization and calculation of daily dose distributions on 2 to 9 Computed Tomography (CT) studies available for each of the 19 patients. Planning and daily dose distributions were analyzed with respect to target coverage, maximal dose to the rectum (excluding 1 ml of the greatest dose; Dmax-1 ml) and the rectal volume receiving dose greater than 90% of prescribed target dose (V90Rectum), respectively. RESULTS: The application of spacer gel did substantially diminish rectum dose. Dmax-1 ml on the treatment planning CT was on average reduced from 100.0 ± 1.0% to 90.2 ± 4.8%, when spacer gel was applied. The robustness analysis performed with daily CT studies demonstrated for all analyzed patient cases that application of spacer gel results in a decrease of the daily V90Rectum index, which calculated over all patient cases and CT studies was 10.2 ± 10.4 [ml] and 1.1 ± 2.1 [ml] for patients without and with spacer gel, respectively. CONCLUSIONS: The dosimetric benefit of increasing the distance between prostate and rectum using spacer gel for PC treatment with carbon ion beams has been quantified. Application of spacer gel substantially reduced rectal exposure to high treatment dose and, therefore, can reduce the hazard of rectal toxicity in ion beam therapy of PC. The results of this study enable modifications of the PC ion therapy protocol such as dose escalation or hypofractionation.

Gel phantom study with high-intensity focused ultrasound: influence of metallic stent containing either air or fluid.

We aimed to investigate whether a cylindrical structure containing either air or fluid and with or without a metallic stent affects the volume and density of cavitation produced by high-intensity focused ultrasound via a gel phantom study. Sixteen tissue-mimicking phantoms based on a polyacrylamide gel mixed with bovine serum albumin with a cylindrical hole 1 cm in diameter and 7.5 cm in length were divided into four groups of four phantoms with air in the holes (group 1), four phantoms with fluid in the holes (group 2), four phantoms with air-containing metallic stents (group 3) and four phantoms with fluid-containing metallic stents (group 4). A pulsed high-intensity focused ultrasound beam (50% duty cycle, 40-Hz pulse repetition frequency) at 75 W of acoustic power was directed perpendicularly to the longitudinal axis of the hole, with its focus at the posterior wall of the hole. The size of the cavitation on the x-, y-, and z-axes was measured, and the volumes of cavitation and coagulation were calculated using the formula for the volume of an elliptical cone. The density of cavitation was measured in the tissue phantom anterior to the hole with a 1 × 1-cm square region of interest. For statistical analysis, the Kruskal-Wallis test and Mann-Whitney U-test were used. The phantoms with air-containing holes (groups 1 and 3) developed larger and denser cavitations anterior to the focus, without unnecessary coagulation posterior to the focus, compared with the phantoms with fluid-containing holes (groups 2 and 4), regardless of the presence of stents. All of the axes and volumes of the anterior cavitations were significantly larger than those of the posterior cavitations in groups 1 and 3 (all p-values <0.05). The results of this study might be applied to maximize cavitation to enhance drug delivery into tumors.