Optimizing the feasibility of polyvinyl alcohol-potassium iodine gel for medical dosimeter.

This work aims to improve the post stabilty of reusable potassium iodide hydrogel dosimter. A reusable and low-cost radiochromic dosimeter containing a gel matrix of polyvinyl alcohol, potassium iodide dye, froctose as reducing agent and glutaraldehyde as cross-linking agent was developed for dose calibration in radiotherapy. The gel samples were exposed to different absorbed doses using a medical linear acceleration. UV-vis Spectrophotometry was utilized to investigate the changes in optical-properties of irradiated gels with regard to peak wavelength of 353 nm. The stability of the gel (one of the most limitation of using this dosimeter) was improved significantly by the addition of certain concentrations of dimethyl sulfoxide. The two-dimensional optical imaging system of charge-coupled-device (CCD) camera with a uniform RGB light-emitting-diode (LED) array source was used for diffusion coefficient purpose using two dimensional gel template. The value of diffusion coefficient reported is significant and highly reduced compared with other dosimeters reported in the literatures. Moreover, heating the improved gels to certain temperatures results in resetting their optical properties, which makes it possible to reuse for multiple times.

Improved Dose Response of N-(hydroxymethyl)acrylamide Gel Dosimeter with Calcium Chloride for Radiotherapy.

The impact of calcium chloride (CaCl2) on the performance of N-(hydroxymethyl)acrylamide (NHMA) polymer gel dosimeter is studied in this article. The dosimeter was exposed to doses of up to 10 Gy with radiation beam-energy of 10 MV and dose-rates of 300 cGy/min. The relaxation rate (R2) parameter was utilized to explore the performance of irradiated NHMAGAT gels. The dose response in terms of R2 increased from 0.29 to 0.63 Gy-1·s-1 with increasing calcium chloride concentration from 0 to 1000 mM. The results show no substantial impact of dose-rates as well as radiation energies on NHMAGAT samples. For the steadiness of irradiated NHMAGAT dosimeters, it was found that there is no apparent variation in R2 (less than ±3%; standard deviation) up to 3 days. The overall uncertainty of the gel dosimeter with calcium chloride is 4.96% (double standard deviation, 95% confidence level).

Nuclear magnetic resonance analysis of a chemically cross-linked ferrous-methylthymol blue-polyvinyl alcohol radiochromic gel dosimeter.

A new formulation of hydrogel dosimeter consisting of ferrous-methylthymol blue (MTB)-polyvinyl alcohol (PVA) cross-linked chemically with glutaraldehyde (GTA) was studied and evaluated by nuclear magnetic resonance analysis by means of the R2 spin-spin relaxation rate. Previous optical studies of this transparent solid chemically cross-linked gel showed important dosimetric features in terms of sensitivity, auto-oxidation rate, and diffusion. This study shows that the MTB-PVA-GTA dosimeter has a reproducible linear dose response up to 40 Gy. For the optimum formulation of 0.1 mM MTB, 2.5% PVA, and 26.6 mM GTA, the measured R2 sensitivity was higher than that of traditional natural matrix-containing gels (MTB-gelatin) and all other reported PVA gel-based radiochromic dosimeters with MTB, xylenol orange (XO), or GTA (MTB-PVA, XO-PVA, XO-PVA-GTA). Additionally, the auto-oxidation rate was approximately ten times lower than that of the Fricke-MTB-gelatin system, which is consistent with the spectrophotometry results. The results of the independent experimental spectrophotometry and nuclear magnetic resonance analyses indicate that the transparent cross-linked dosimeter has good and consistent dosimetric features.

New normoxic N-(Hydroxymethyl)acrylamide based polymer gel for 3D dosimetry in radiation therapy.

A novel composition of normoxic polymer gel dosimeters based on radiation-induced polymerization of N-(Hydroxymethyl)acrylamide (NHMA) is introduced in this study for 3D dosimetry for Quality Assurance (QA) in radiation therapy. Dosimeters were irradiated by 6, 10 and 18MV photon beams of a medical linear accelerator at various dose rates to doses of up to 20Gy. The dose response of polymer gel dosimeters was studied using nuclear magnetic resonance (NMR) spin-spin relaxation rate (R2) of hydrogen protons within the water molecule. Also, we measured gel response using absorption spectroscopy and found that this novel gel can be successfully utilized for both MRI- and OCT- (Optical Computed Tomography) based 3D dosimetry. We investigated dosimetric properties of six different compositions of the new NHMA-based gel in terms of dose rate, radiation beam quality and stability of dose-dependent polymerization after irradiation. We found no significant effects of these parameters on the novel gel dosimeter performance in both relaxation rate and absorbance measurements.

Novel radio-chromic solution dosimeter for radiotherapy treatment planning.

Nitro blue tetrazolium (NBT) solution dosimeters were prepared and investigated based on radiation-induced reduction of NBT(2+). NBT solution dosimeters containing different concentrations of NBT dye from 1 to 5 mM were prepared in a solution of ethanol. The dosimeters were irradiated with 6 MV X-ray beam at doses up to 30 Gy. The dose sensitivity of NBT solution increases strongly with increase of concentrations of NBT dye. The dose response of NBT dosimeters increases remarkably by addition of various concentrations of sodium formate (0.5, 2.5 and 5 mM). It becomes more remarkable with increasing pH value of NBT-sodium formate dosimeters. The sensitivity of the solution increased fairly with increase of irradiation temperature, therefore, the response of the solutions has to be corrected under actual processing conditions. The stability of solution dosimeters after irradiation was very high up to 30 days.