LAUSR

PURPOSE The precise assessment of the dose distribution of high linear energy transfer (LET) radiation remains a challenge, since 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. This article is protected by copyright. All rights reserved.