Organic-Gelatin-Free Nanocomposite Fricke Gel Dosimeter

Abstract

We report a nanocomposite Fricke gel (NC-FG) dosimeter prepared using only Fe and nanoclay in water, without any organic gelling agents. This dosimeter gels due to its thixotropic properties and exhibits linear energy transfer (LET)-independent radiological properties under carbon ion beam irradiation. The radiation sensitivity of this dosimeter was 1.8 [s kGy], which is three times higher than that reported previously (0.6 [s kGy]) for a similar dosimeter containing gelatin. The Fe yield was determined to be 0.19 μmol/J by evaluating the difference in spin-lattice relaxivity between Fe and Fe. A further increase in the radiation sensitivity was observed upon addition of the hydrated electron scavenger NO, suggesting the reduction of Fe by a hydrated electron. LET-dependent variations of the contributions of OH radicals and hydrated electrons compensate each other in the oxidation yield of NC-FG. This is the main mechanism of the suppression of LET effects in the Bragg peak compared to conventional Fricke dosimeters. The radiation-induced oxidation yield G(Fe) can be described by the stoichiometric equation {G(Fe) = G(OH) - G(e) + 2G(HO) + G(H)} with the reported LET dependence of the primary yield of water decomposition radicals. The calculated results are in approximate agreement with the absolute value of the experimental oxidation yield of NC-FG. The effects of the addition of small amounts of radical scavengers (nitrate, selenate, or cadmium) are also evaluated. The sensitivity was divided into two types, and influences of intermediate radicals after scavenging reaction are indicated.

Whole Three-Dimensional Dosimetry of Carbon Ion Beams with an MRI-Based Nanocomposite Fricke Gel Dosimeter Using Rapid T1 Mapping Method

“…Maeyama et al [ 32 ], developed a novel nanocomposite Fricke gel (NC-FG) with nano-sized clay particles and degassing operation to improve LET dependence. The carbon beam depth dose distribution was found to be in good agreement with the ionization chamber measurements [ 32 , 33 , 34 ].…”

“…However, before and after the Bragg peak, the R 1 values were higher and lower, respectively, than the IC measurement values. This phenomenon was not shown in our previous MRI measurement conditions [ 34 ], and thus, it was considered to represent a truncation artifact due to its sharp edges [ 63 ]. Truncation artifacts occur when the MR signal obtained by finite sampling is Fourier transformed to reconstruct an image [ 64 , 65 ].…”

“…The radiation chemical yield G (Fe 3+ ) NC-FG can be calculated, as shown in the following Equation (4), by using the sensitivity characteristic at the entrance surface. where is a density of 1.007 ± 4 [ 34 ]. The result is 0.188 ± 0.005 μmol/J, which is almost the same as the value of previous our reported (0.19 μmol/J) [ 34 ].…”

Radiochromic Films for the Two-Dimensional Dose Distribution Assessment

“…It should be noted that HD-V2 Gafchromic™ films have a different structure from the other Gafchromic™ films as they feature a 12 µm thin active layer on a 97 µm polyester substrate. The LET dependence is common to other types of dosimeters; however, recently developed nanocomposite Fricke gel dosimeters have shown to have no dependence on the LET in a wide LET range [116,117].…”

Sensitivity enhancement of DHR123 radio-fluorogenic nanoclay gel dosimeter by incorporating surfactants and halogenides

“…As a typical gel dosimeter, 7 there are Fricke gel [8][9][10][11] and polymer gel [12][13][14][15] dosimeters, and many radiosensitizers 2, [16][17][18][19][20] have been investigated because improving sensitivity is an issue, up to now. On the other hand, there are not many reports in the gel dosimeters utilizing uorometry using radiosensitizers, although there are several type of radio-uorogenic gels.…”