A method for obtaining three-dimensional measurements of HDR brachytherapy dose distributions using Fricke gel dosimeters and optical computed tomography

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.

Three-Dimensional Dosimetry by Optical-CT and Radiochromic Gel Dosimeter of a Multiple Isocenter Craniospinal Radiation Therapy Procedure

Craniospinal irradiation (CSI) is a complex radiation technique employed to treat patients with primitive neuroectodermal tumors such as medulloblastoma or germinative brain tumors with the risk of leptomeningeal spread. In adults, this technique poses a technically challenging planning process because of the complex shape and length of the target volume. Thus, it requires multiple fields and different isocenters to guarantee the primary-tumor dose delivery. Recently, some authors have proposed the use IMRT technique for this planning with the possibility of overlapping adjacent fields. The high-dose delivery complexity demands three-dimensional dosimetry (3DD) to verify this irradiation procedure and motivated this study. We used an optical CT and a radiochromic Fricke-xylenol-orange gel with the addition of formaldehyde (FXO-f) to evaluate the doses delivered at the field junction region of this treatment. We found 96.91% as the mean passing rate using the gamma analysis with 3%/2 mm criteria at the junction region. However, the concentration of fail points in a determined region called attention to this evaluation, indicating the advantages of employing a 3DD technique in complex dose-distribution verifications.

The new Scopus CiteScore formula and the Journal Impact Factor: a look at top ranking journals and middle ranking journals in the Scopus categories of General Physics and Astronomy, Materials Science, General Medicine and Social Sciences

In June 2020 Elsevier announced that the CiteScore metric of journals underwent a change. This work examines the effect of these changes for 40 journals, chosen from the top five and middle five (ranked by CiteScore) journals in the subject areas of General Physics and Astronomy, Materials Science, Medicine, Social Sciences) and compares to the Journal Impact Factor. It is shown that in the data studied here, the new methodology is less susceptible to influence of the proportion of editorial material in a journal, but tends to favour journals in research fields that publish articles which get cited more quickly.

Verification of dose distribution in high-dose-rate brachytherapy using a nanoclay-based radio-fluorogenic gel dosimeter

Dose distributions have become more complex with the introduction of image-guided brachytherapy in high-dose-rate (HDR) brachytherapy treatments. Therefore, to correctly execute HDR, conducting a quality assurance programme for the remote after-loading system and verifying the dose distribution in the patient treatment plan are necessary. The characteristics of the dose distribution of HDR brachytherapy are that the dose is high near the source and rapidly drops when the distance from the source increases. Therefore, a measurement tool corresponding to the characteristic is required. In this study, using an Iridium-192 (Ir-192) source, we evaluated the basic characteristics of a nanoclay-based radio-fluorogenic gel (NC-RFG) dosimeter that is a fluorescent gel dosimeter using dihydrorhodamine 123 hydrochloride as a fluorescent probe. The two-dimensional dose distribution measurements were performed at multiple source positions to simulate a clinical plan. Fluorescence images of the irradiated NC-RFG were obtained at a high resolution (0.04 mm pixel^-1) using a gel scanner with excitation at 465 nm. Good linearity was confirmed up to a dose range of 100 Gy without dose rate dependence. The dose distribution measurement at the five-point source position showed good agreement with the treatment planning system calculation. The pass ratio by gamma analysis was 92.1% with a 2%/1 mm criterion. The NC-RFG dosimeter demonstrates to have the potential of being a useful tool for quality assurance of the dose distribution delivered by HDR brachytherapy. Moreover, compared with conventional gel dosimeters such as polymer gel and Fricke gel dosimeters it solves the problems of diffusion, dose rate dependence and inhibition of oxygen-induced reactions. Furthermore, it facilitates dose data to be read in a short time after irradiation, which is useful for clinical use.