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.
Occupational radiation exposure monitoring is well-established in clinical or industrial environments with various different dosimeter systems. Despite the availability of many dosimetry methods and devices, a challenge with the occasional exposure registration, which may occur due to the spilling of radioactive materials or splitting of these materials in the environment, still exists, because not every individual will have an appropriate dosimeter at the time of the irradiation event. The aim of this work was to develop radiation-sensitive films—color-changing radiation indicators, which can be attached to or integrated in the textile. Polyvinyl alcohol (PVA)-based polymer hydrogels were used as a basis for fabrication of radiation indicator films. Several organic dyes (brilliant carmosine (BC), brilliant scarlet (BS), methylene red (MR), brilliant green (BG), brilliant blue (BB), methylene blue (MB) and xylenol orange (XiO)) were used as a coloring additives. Moreover, PVA films enriched with Ag nanoparticles (PVA-Ag) were investigated. In order to assess the radiation sensitivity of the produced films, experimental samples were irradiated in a linear accelerator with 6 MeV X-ray photons and the radiation sensitivity of irradiated films was evaluated using UV–Vis spectrophotometry method. The most sensitive were PVA-BB films indicating 0.4 Gy−1 sensitivity in low-dose (0–1 or 2 Gy) range. The sensitivity at higher doses was modest. These PVA-dye films were sensitive enough to detect doses up to 10 Gy and PVA-MR film indicated stable 33.3% decolorization after irradiation at this dose. It was found that the dose sensitivity of all PVA-Ag gel films varied from 0.068 to 0.11 Gy−1 and was dependent on the Ag additives concentration. Exchange of a small amount of water with ethanol or isopropanol caused the enhancement of radiation sensitivity in the films with the lowest AgNO3 concentration. Radiation-induced color change of AgPVA films varied between 30 and 40%. Performed research demonstrated the potential of colored hydrogel films in their applications as indicators for the assessment of the occasional radiation exposure.
Tikslas. Tyrimo tikslas įvertinti gama peilio talamotomijos efektyvumą, stabdant tremorą sergantiesiems Parkinsono liga (PL) ir esencialiniu tremoru, kai kiti invaziniai gydymo metodai nerekomenduotini. Tiriamieji ir tyrimo metodai. Nuo 2019 m. birželio iki 2021 m. sausio dėl esencialinio tremoro ir PL sąlygoto tremoro atitinkamai atlikta 27 ir 20 vienpusių gama peilio talamotomijų. Naudojant Leksell G stereotaksinį rėmą, pagal standartizuotą metodiką, naudojant 4 mm diametro kolimatoriaus šūvį, į n.ventralis intermedius (VIM) zoną paskirta 130-140 Gy dozė. Tyrime pooperacinis vertinimas planuotas atlikti praėjus 6 ir 12 mėnesių po taikyto gydymo. Tačiau dėl besikartojančio karantino dėl COVID-19 buvo apsunkintas ligonių kontaktinis vertinimas, todėl rezultatai vertinti telefoninės apklausos metu. Iš 20 ligonių, sergančių PL, pavyko susisiekti tik su 12, iš kurių aštuoniems gydymas buvo taikytas mažiau nei prieš 6 mėnesius. Nuspręsta PL grupės ligonių gydymo rezultatų analizę atlikti po 6 mėnesių. Rezultatai. Iš 27 sergančiųjų esencialiniu tremoru telefonu pakalbinti pavyko 23 ligonius. Viena ligonė per stebėjimo laikotarpį mirė nuo COVID-19 infekcijos. Iš apklaustų 22 ligonių 16 (72 %) teigė, kad jaučia žymų tremoro rankoje sumažėjimą ar visišką jo išnykimą priešingoje, nei atlikta VIM talamotomija, pusėje. Likę 6 ligoniai (28 %) taikyto gydymo efekto iki šiol ne-jaučia. Iš 22 ligonių 4 (18 %) teigė, kad kurį laiką buvo sutrikusi koordinacija ir vargino laikinas rankos nevikrumas, kuris praėjo per kelis mėnesius. Išvados. Gama peilio talamotomija yra saugi ir efektyvi esencialinio rankų tremoro mažinimo priemonė. Pagrindiniai šio gydymo trūkumai yra kelis ar keliolika mėnesių trunkantis latencinis periodas iki pastebimo klinikinio efekto ir laikina ataksija.
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