Abstract
PurposeProton therapy precisely delivers radiation to cancers to cause damaging strand breaks to cellular DNA, kill malignant cells, and stop tumor growth. Therapeutic protons also generate short-lived activated nuclei of carbon, oxygen, and nitrogen atoms in patients as a result of atomic transmutations that are imaged by positron emission tomography (PET). We hypothesized that the transition of 18O to 18F in an 18O-substituted nucleoside irradiated with therapeutic protons may result in the potential for combined diagnosis and treatment for cancer with proton therapy.Materials and MethodsReported here is a feasibility study with a therapeutic proton beam used to irradiate H218O to a dose of 10 Gy produced by an 85 MeV pristine Bragg peak. PET imaging initiated >45 minutes later showed an 18F decay signal with T1/2 of ∼111 minutes.ResultsThe 18O to 18F transmutation effect on cell survival was tested by exposing SQ20B squamous carcinoma cells to physiologic 18O-thymidine concentrations of 5 μM for 48 hours followed by 1- to 9-Gy graded doses of proton radiation given 24 hours later. Survival analyses show radiation sensitization with a dose modification factor (DMF) of 1.2.ConclusionsThese data support the idea of therapeutic transmutation in vitro as a biochemical consequence of proton activation of 18O to 18F in substituted thymidine enabling proton radiation enhancement in a cancer cell. 18O-substituted molecules that incorporate into cancer targets may hold promise for improving the therapeutic window of protons and can be evaluated further for postproton therapy PET imaging.
Highlights
Fluorine atoms substituted into biologically active molecules are widely used in drug synthesis because of their powerful clinical effects [1,2,3,4]
A means of producing targeted fluorine in a cancer cell is reported here by using an 18O-substituted nucleoside [8,9,10,11,12] that is used to treat cells first and combined with therapeutic protons. This approach is similar to using therapeutic protons to generate positron emitters from 12C, 14N, and 16O atoms, which are short lived, and form the basis of in-room postproton positron emission tomography (PET) for range analysis that may be used to assess proton beam treatment accuracy [13, 14]
PET signal was observed from all 9 vials at different time points (Figure 2B)
Summary
Fluorine atoms substituted into biologically active molecules are widely used in drug synthesis because of their powerful clinical effects [1,2,3,4]. A means of producing targeted fluorine in a cancer cell is reported here by using an 18O-substituted nucleoside [8,9,10,11,12] that is used to treat cells first and combined with therapeutic protons. This approach is similar to using therapeutic protons to generate positron emitters from 12C, 14N, and 16O atoms, which are short lived, and form the basis of in-room postproton positron emission tomography (PET) for range analysis that may be used to assess proton beam treatment accuracy [13, 14].
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