Leuco-crystal-violet micelle gel dosimeters: II. Recipe optimization and testing.

In this study, recipe optimization of Leuco Crystal Violet (LCV) micelle gels made with the surfactant Cetyl Trimethyl Ammonium Bromide (CTAB) and the chemical sensitizer 2,2,2-trichloroethanol (TCE) was aided by a two-level three-factor designed experiment. The optimized recipe contains 0.75 mM LCV, 17.0 mM CTAB, 120 mM TCE, 25.0 mM tri-chloro acetic acid (TCAA), 4 wt% gelatin and ~96 wt% water. Dose sensitivity of the optimized gel is 1.5 times higher than that of Jordan's standard LCV micelle gel. Spatial integrity of the 3D dose distribution information in 1L phantoms filled with this recipe is maintained for >120 d. Unfortunately, phantoms made using the optimized recipe showed dose-rate dependence (14% difference in optical attenuation at the peak dose using electron beam irradiations at 100 and 400 MU min(-1)). Further testing suggests that the surfactant CTAB is the cause of this dose rate behaviour.

Leuco-crystal-violet micelle gel dosimeters: I. Influence of recipe components and potential sensitizers.

Radiochromic leuco crystal violet (LCV) micelle gel dosimeters are promising three-dimensional radiation dosimeters because of their spatial stability and suitability for optical readout. The effects of surfactant type and surfactant concentration on dose sensitivity of LCV micelle gels are tested, demonstrating that dose sensitivity and initial colour of the gel increases with increasing Triton x-100 (Tx100) concentration. Using Cetyl Trimethyl Ammonium Bromide (CTAB) in place of Tx100 produces gels that are nearly colourless prior to irradiation, but reduces the dose sensitivity. The separate effects of Tri-chloro acetic acid concentration and pH are investigated, revealing that controlling the pH near 3.6 is crucial for achieving high dose sensitivity. The sensitizing effect of chlorinated species on dose sensitivity is tested using 2,2,2-trichloroethanol (TCE), chloroform, and 1,1,1-trichloro-2-methyl-2-propanol hemihydrate. TCE gives the largest improvement in dose sensitivity and is recommended for use in micelle gel dosimeters because it is less volatile and safer to use than chloroform. Preliminary experiments on a new gel containing CTAB as the surfactant and TCE show that this new gel gives a dose sensitivity that is 24% higher than that of previous LCV micelle gels and is nearly colourless prior to irradiation.

Evaluation of the potential for diacetylenes as reporter molecules in 3D micelle gel dosimetry.

Radiochromic micelle gel dosimeters are promising for three-dimensional (3D) radiation dosimetry because they can be read out by optical CT techniques and they have superior spatial stability compared to polymer and Fricke gel dosimeters. This study evaluates the use of diacetylenes as reporter molecules in micelle gel dosimeters. Several gels containing pentacosa-10,12-diynoic acid (PCDA) emulsified using sodium dodecyl sulfate (SDS) changed from colourless to blue upon irradiation. Unfortunately, all phantoms that experienced a colour change were turbid and would be unsuitable for 3D dosimetry. Two techniques (use of organic solvent and aqueous-phase additives) were successful in increasing colloidal stability to prevent the turbidity problem, but none of the resulting transparent gels changed colour in response to radiation. Transparent PCDA emulsions were prepared using NaOH solutions with no SDS or other emulsifier, but these transparent emulsions also did not change colour. Only turbid gels and emulsions with precipitated particles responded to radiation. These results indicate that the colour change was due to the oligomerization within precipitated PCDA crystals, and that liquid-phase emulsified PCDA did not undergo oligomerization. As a result, PCDA is not suitable for use in micelle gel dosimeters, and other radiochromic reporter molecules will need to be identified.