Assessment of dosimetric sensitivity enhancement of xylenol orange Fricke gel by AuNPs: optical and MR imaging investigation.

Metallic nanoparticles, such as gold (Au, Z = 79) and silver (Ag, Z = 47) nanoparticles (AuNPs and AgNPs, respectively), possess strong surface plasmonic resonance (SPR) and high atomic number, which makes them ideal candidates for enhancing dosimeter sensitivity. In this study, we have inserted different mass percentages (from 0 to 0.015 wt%) of AuNPs into a gelatinous Fricke-xylenol-orange (FXO-f) gel matrix and irradiated it with doses ranging from 2 to 32 Gy, using a source of x-ray of low energy with an effective energy of 42 keV. Optical absorption increased significantly; sensitivity gains of up to 50% were achieved for the FXO-f gel matrix containing 0.011 wt% AuNPs. To elucidate the mechanism underlying this increased sensitivity, we also evaluated FXO-f gel matrixes containing AgNPs. AgNPs insertion into the FXO-f gel matrix did not enhance sensitivity, which suggested that the AgNPs plasmonic absorption band and the FXO-f gel matrix absorption band at 441 nm overlapped, to increase absorption even after the gel matrix was irradiated. To visualize the dose distribution, we recorded optical tomography and acquired 3D reconstruction maps. In addition, we analyzed the dose enhancement factor (DEF) by using magnetic resonance images. AuNPs insertion into the FXO-f gel matrix resulted in a DEF gain of 1.37, associated with the photoelectric effect originating from the increased number of free radicals.

Arbovirus investigation in patients from Mato Grosso during Zika and Chikungunya virus introdution in Brazil, 2015-2016.

Arboviruses have become a major public health concern in Brazil, especially after Zika virus (ZIKV) and Chikungunya virus (CHIKV) introduction, leading to massive epidemics. We conducted an investigation of arboviruses in patients with acute febrile illness for less than five days in Mato Grosso state (MT) during the period of ZIKV and CHIKV dissemination in Brazil. To achieve that, 453 human serum samples of patients suspected of Dengue (DENV), Yellow Fever (YFV), ZIKV or CHIKV collected in health units of 31 cities of MT were subjected to RT-PCR protocols for 10 flaviviruses, 5 alphaviruses and orthobunyaviruses from Simbu serogroup, nucleotide sequencing and viral isolation. Regarding flaviviruses, five (1.1%) patients were infected with DENV-1 genotype V, 22 (4.4%) with DENV-4 genotype II, 3 (0.7%) with YFV South American genotype II and five (1.1%) with ZIKV Asian genotype. The first human case of ZIKV in MT was detected in this study during August, 2015 in Tapurah. Alphaviruses were detected in 2 (0.4%) patients infected with CHIKV genotype ECSA, 1 (0.2%) with Madariaga (EEEV) lineage III and 34 (7.5%) with Mayaro (MAYV) genotype L. Four (11.4%) patients presented dual infections with DENV-1/ZIKV, DENV-1/DENV4, DENV-4/MAYV and ZIKV/MAYV. The majority - 13/34 positive for MAYV, one for Madariaga virus - are residents in Várzea Grande (VG), metropolitan region of Cuiabá, capital of MT. The first CHIKV infection in MT was detected in this study in Mirassol D'Oeste, during July, 2015. In addition, 20 (4.4%) patients were positive for OROV Segment S genotype IA. These results reinforce the variation in arboviruses frequency and distribution during outbreaks, highlinghing the importance of differential diagnosis to identify agents silently co-circulating with major health problem arboviruses.

Biological X-ray irradiator characterization for use with small animals and cells.

This study presents the characterization of an X-ray irradiator through dosimetric tests, which confirms the actual dose rate that small animals and cells will be exposed to during radiobiological experiments. We evaluated the linearity, consistency, repeatability, and dose distribution in the positions in which the animals or cells are placed during irradiation. In addition, we evaluated the performance of the X-ray tube (voltage and tube operating current), the radiometric survey (leakage radiation) and safety devices. The irradiator default setting was established as 160 kV and 25 mA. Tests showed that the dose rate was linear overtime (R2=1) and remained stable for long (constant) and short (repeatability) intervals between readings. The mean dose rate inside the animal cages was 1.27±0.06 Gy/min with a uniform beam of 95.40% (above the minimum threshold guaranteed by the manufacturer). The mean dose rate inside the cell plates was 0.92±0.19 Gy/min. The dose rate dependence with tube voltage and current presented a quadratic and linear relationship, respectively. There was no observed mechanical failure during evaluation of the irradiator safety devices and the radiometric survey obtained a maximum ambient equivalent dose rate of 0.26 mSv/h, which exempts it from the radiological protection requirements of the International Atomic Energy Agency. The irradiator characterization enables us to perform radiobiological experiments, and assists or even replaces traditional therapy equipment (e.g., linear accelerators) for cells and small animal irradiation, especially in early research stages.

Three-dimensional quality assurance of IMRT prostate plans using gel dosimetry.

Intensity modulated radiotherapy (IMRT) is one of the most modern radiation therapy treatment techniques. Although IMRT can deliver high and complex conformational doses to the tumor volume, its implementation requires rigorous quality assurance (QA) procedures that include a dosimetric pre-treatment verification of individual patient planning. This verification usually involves measuring a small volume of absolute dose with an ionization chamber and checking bi-dimensional fluency with an array of detectors. The planning technique has tri-dimensional characteristics, but no tridimensional dosimetry has been established in the clinical routine. One strategy to perform three-dimensional dosimetry is to use polymeric gels associated with magnetic resonance imaging to evaluate dose distribution. Here, we have compared the results of conventional QA procedures involving one- and two-dimensional dosimetry to the results of three-dimensional dosimetry conducted with MAGIC-f gel in 10 cases of prostate cancer IMRT planning. More specifically, we used the gamma index (3%/3mm) to compare the results of three-dimensional dosimetry to the expected dose distributions obtained with the treatment planning system. Except for one IMRT treatment plan, the gel dosimetry results agreed with the conventional quality control and provided an overview of dose distribution in the target volume.

Tomotherapy dose distribution verification using MAGIC-f polymer gel dosimetry.

PURPOSE: This paper presents the application of MAGIC-f gel in a three-dimensional dose distribution measurement and its ability to accurately measure the dose distribution from a tomotherapy unit. METHODS: A prostate intensity-modulated radiation therapy (IMRT) irradiation was simulated in the gel phantom and the treatment was delivered by a TomoTherapy equipment. Dose distribution was evaluated by the R2 distribution measured in magnetic resonance imaging. RESULTS: A high similarity was found by overlapping of isodoses of the dose distribution measured with the gel and expected by the treatment planning system (TPS). Another analysis was done by comparing the relative absorbed dose profiles in the measured and in the expected dose distributions extracted along indicated lines of the volume and the results were also in agreement. The gamma index analysis was also applied to the data and a high pass rate was achieved (88.4% for analysis using 3%∕3 mm and of 96.5% using 4%∕4 mm). The real three-dimensional analysis compared the dose-volume histograms measured for the planning volumes and expected by the treatment planning, being the results also in good agreement by the overlapping of the curves. CONCLUSIONS: These results show that MAGIC-f gel is a promise for tridimensional dose distribution measurements.