Fricke-Xylenol orange-Gelatin gel characterization with dual wavelength cone-beam optical CT scanner for applications in stereotactic and dynamic radiotherapy

Feasibility of new polymeric matrices in the production of ferrous sulphate dosimeters

External beam radiotherapy is a treatment modality that employs high doses for curative or palliative purposes. Safety in such treatments, particularly with high-precision equipment, necessitates strict adherence to quality control protocols to ensure the efficacy of oncological treatments. In this context, chemical dosimeters, particularly the Fricke gel, have emerged as valuable tools for quantitatively analysing absorbed radiation doses. These dosimeters can be applied both as tissue-equivalent phantoms and as radiation detectors in radiotherapy centers. The objective of this study was to evaluate the feasibility of new gelling matrices, comprising common materials such as CMC, GGU, and PVA, for producing ferrous sulphate dosimeters aimed at the relative quantification of radiation dose. A rheological study was conducted for different Fricke gel dosimetric formulations. Initially, the performance of these dosimeters, produced at various gel concentrations, was evaluated in terms of their consistency at room temperature. This was achieved through the straightforward process of humidification the gels with glycerine. These matrices consist of both natural and synthetic polymers that are readily accessible, easy to handle, and can be easily incorporated into the acidic ferrous sulphate solution. Parameters such as the influence of gelling matrix concentration, linearity, and stability were assessed and correlated with those previously investigated for Fricke gel produced with bloom 300 pig skin gelatine (GEL). Ferrous sulphate dosimeters fabricated with sodium carboxymethylcellulose (CMC), guar gum (GGU), and polyvinyl alcohol (PVA) exhibited a coefficient of variation of less than 1% relative to the dose response evaluated in this study. By using readily available and easily manageable materials, it is possible to replicate dosimeters with a favourable dosimetric response for high-dose measurements.

End-to-end quality assurance for stereotactic radiotherapy with Fricke-Xylenol orange-Gelatin gel dosimeter and dual-wavelength cone-beam optical CT readout

PURPOSE

The end-to-end (E2E) quality assurance (QA) test is a unique tool for validating the treatment chain undergone by patients in external radiotherapy. It should be conducted in three dimensions (3D) to get accurate results. This study aims to implement these tests with Fricke-Xylenol orange-Gelatin (FXG) gel dosimeter and a newly developed dual-wavelength reading method on the Vista16™ optical Computed Tomography (CT) scanner (ModusQA) for three treatment techniques in stereotactic radiotherapy, on Novalis (Varian) and CyberKnife (Accuray) linear accelerators.

METHODS

The tests were performed in head phantoms. Gel measurements were compared with planned dose distributions and measured by film and ion chamber measurements by plotting isodose curves and dose profiles, and by conducting a 3D local gamma-index analysis (2%/2mm criteria).

RESULTS

Gamma passing rates were higher than 95 %. Point dose differences between treatment planning and gel and ion chamber measurements at the isocenter were < 2.3 % for both treatments delivered on the Novalis accelerator, while this difference was higher than 4 % for the treatment delivered on the CyberKnife, highlighting a small overdosing of the tumor volume. A good agreement was observed between gel and film dose profiles.

CONCLUSIONS

This study presents the successful implementation of 3D E2E QA tests for stereotactic radiotherapy with FXG gel dosimetry and a dual-wavelength reading method on an optical CT scanner. This dosimetric method provides 3D absolute dose distributions in the 0.25 - 10 Gy dose range with a high spatial resolution and a dose uncertainty of around 2 % (k=1).

An investigation into the dose rate and photon energy dependence of the GENA gel dosimeter in the MeV range

PURPOSE

In the current study, the energy and dose rate dependence of a new genipin-based gel dosimeter, named GENA gel dosimeter, were investigated.

METHODS

Prepared gel dosimeters exposed using a Varian clinical linac. Beam qualities of 6 and 18 MV were applied to investigate the GENA gel dosimeter's energy dependence. Furthermore, the gel dosimeters were exposed to 50, 100, 200, and 350 cGy/min dose rates, ranging from 0 to 8 Gy. The irradiated gel dosimeters were read out using a double beam UV-Visible spectrophotometer. The absorbance peak (AP) and area under spectrum (AUS) were evaluated.

RESULTS

Absorbance-dose sensitivities of (8.0 ± 0.18) × 10^-3 cm^-1Gy^-1 and (7.8 ± 0.15) × 10^-3 cm^-1Gy^-1 were obtained for GENA gel dosimeter for 6 and 18 MV beam qualities, respectively. Results specified no significant difference (p > 0.05) between the GENA gel dosimeter's sensitivities irradiated using the two energies mentioned above. For the mentioned dose rates, AP-dose sensitivities of (8.2 ± 0.22) × 10^-3, (8.1 ± 0.21) × 10^-3, (8.1 ± 0.2) × 10^-3 and (8.0 ± 0.18) × 10^-3 cm^-1Gy^-1 were obtained, respectively. Results showed no significant difference (p > 0.05) between the GENA gel dosimeter's sensitivities for the investigated dose rates and energies. In addition, results revealed that when the incident photon energy and dose rate changed, there were no significant differences (p > 0.05) between the GENA gel dosimeter's dose resolution values.

CONCLUSIONS

It is concluded that the response of the GENA gel dosimeter is not dependent on the energy and dose rate (p > 0.05) within the studied energy and dose rate ranges.

Radio-fluorogenic nanoclay gel dosimeters with reduced linear energy transfer dependence for carbon-ion beam radiotherapy

PURPOSE

The precise assessment of the dose distribution of high linear energy transfer (LET) radiation remains a challenge, because the signal of most dosimeters will be saturated due to the high ionization density. Such measurements are particularly important for heavy-ion beam cancer therapy. On this basis, the present work examined the high LET effect associated with three-dimensional gel dosimetry based on radiation-induced chemical reactions. The purpose of this study was to create an ion beam radio-fluorogenic gel dosimeter with a reduced effect of LET.

METHODS

Nanoclay radio-fluorogenic gel (NC-RFG) dosimeters were prepared, typically containing 100 μM dihydrorhodamine 123 (DHR123) and 2.0 wt% nanoclay together with catalytic additives promoting Fenton or Fenton-like reactions. The radiological properties of NC-RFG dosimeters having different compositions in response to a carbon-ion beam were investigated using a fluorescence gel scanner.

RESULTS

An NC-RFG dosimeter capable of generating a fluorescence intensity distribution reflecting the carbon-ion beam dose profile was obtained. It was clarified that the reduction of the unfavorable LET dependence results from an acceleration of the reactions between DHR123 and H₂ O₂ , which is a molecular radiolysis product. The effects of varying the preparation conditions on the radiological properties of these gels were also examined. The optimum H₂ O₂ catalyst was determined to include 1 mM Fe³⁺ ions, and the addition of 100 mM pyridine was also found to increase the sensitivity.

CONCLUSIONS

This technique allows the first-ever evaluation of the depth-dose profile of a carbon-ion beam at typical therapeutic levels of several Gy without LET effect.