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

Abstract

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 H2O2, 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 H2O2 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.

Validation of complex radiotherapy techniques using polymer gel dosimetry

“…While the new sequence allowed measuring the R1-map in 20 min, the sensitivity was 35% lower and truncation artifacts were observed in the images. Just recently, Maeyama et al (2023) proposed nanoclay radiofluorogenic gels employing the OH-radical triggered dihydrorhodamine 123/rhodamine 123 reaction. Adding additionally catalytic Fe 3+ -ions and the dispersant pyridine resulted in a stable gel with a significantly reduced LET-dependence (Maeyama et al 2023) and with a higher sensitivity than nanoclay Fricke gels.…”

A phantom to simulate organ motion and its effect on dose distribution in carbon ion therapy for pancreatic cancer

“…To extend this to 3D, a possibility would be to use dosimetry gel, a technique that was used in an anthropomorphic phantom with a breathing feature (Mann et al 2017). However, the irradiation modality used in this study was photons and dosimetry gel presents challenges for carbon ion irradiation due to its LETdependent response (Maeyama et al 2023).…”