Radio-fluorogenic (RFG) gels become permanently fluorescent when exposed to high-energy radiation with the intensity of the emission proportional to the local dose of radiation absorbed. An apparatus is described, FluoroTome 1, that is capable of taking a series of tomographic images (thin slices) of the fluorescence of such an irradiated RFG gel on-site and within minutes of radiation exposure. These images can then be compiled to construct a 3D movie of the dose distribution within the gel. The historical development via a laboratory-bench prototype to a readily transportable, user-friendly apparatus is described. Instrumental details and performance tests are presented.

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We review the development and application of an organic polymer-gel capable of producing fixed, three-dimensional fluorescent images of complex radiation fields. The gel consists for more than 99% of γ-ray-polymerized (~15% conversion) tertiary-butyl acrylate (TBA) containing ~100 ppm of a fluorogenic compound, e.g., maleimido-pyrene (MPy). The radio-fluorogenic effect depends on copolymerization of the MPy into growing chains of TBA on radiation-induced polymerization. This converts the maleimido residue, which quenches the pyrene fluorescence, into a succinimido moeity (SPy), which does not. The intensity of the fluorescence is proportional to the yield of free-radicals formed and hence to the local dose deposited. Because the SPy moieties are built into the polymer network, the image is fixed. The method of preparing the gel and imaging the radiation-induced fluorescence are presented and discussed. The effect is illustrated with fluorescent images of the energy deposited in the gel by beams of X-rays, electrons, and protons as well as a radioactive isotope@en

We have filled a 24 mm diameter glass sphere with a transparent polymer-gel that is radio-fluorogenic, i.e., it becomes (permanently) fluorescent when irradiated, with an intensity proportional to the local dose deposited. The gel consists of > 99.9% tertiary-butyl acrylate (TBA), pre-polymerized to ~15% conversion, and ~100 ppm maleimido-pyrene (MPy). Its dimensions and physical properties are close to those of the vitreous body of the human eye. We have irradiated the gel with a 3 mm diameter, 200 kVp X-ray beam with a dose rate of ~1 Gy/min. A three-dimensional (3D) (video) view of the beam within the gel has been constructed from tomographic images obtained by scanning the sample through a thin sheet of UV light. To minimize optical artefacts, the cell was immersed in a square tank containing a refractive-index-matching medium. The 20-80% penumbra of the beam was determined to be ~0.4 mm. This research was a preparatory investigation of the possibility of using this method to monitor the millimetre diameter proton pencil beams used in ocular radiotherapy.

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In this work a 40 mm cube of an optically clear, radio-fluorogenic gel composed of partially-polymerized tertiary-butyl acrylate and maleimido-pyrene (~0.01%) is irradiated with orthogonally-crossed, 10 mm square and round, 200 kVp x-ray beams. A thin sheet of UV light is produced between two parallel plates with 2 mm slits illuminated by collimated, linear-array, LED sources. The gel is transported 1 mm at a time through the UV sheet and the fluorescence from the emissive, polymeric radiolytic product formed in the x-ray tracks is recorded, as both JPEG and raw-DNG files, using a CCD camera placed orthogonal to the plane of the excitation light. The resulting stack of 40 tomographic slices are imported into freely-available software to produce 3D animated images of the radiation-induced fluorescence.@en

We have measured the dose, D, and dose rate, D', dependences of the radiation-induced change in optical absorption of four radiochromic films currently used for (2D) dosimetry: GafChromic® types EBT3, MD-V3, HD-V2 and HD-810. We have irradiated the films using two ⁶⁰Co γ-ray sources with dose rates of ~2 and ~30 Gy/min and a 200 kVp X-ray source with dose rates from ~0.2 to ~1.0 Gy/min. The 48-bit RGB image files of the films, obtained using an Epson V700 flatbed scanner, were color-channel separated and the red, green and blue pixel levels, P(D), were determined using ImageJ software. The relationship P(D)/P(0)=[1+hD/m]/[1+D/m] is found to provide a good description of the dose dependence for all four films at all dose rates. The parameter h is the “plateau level” of P(D)/P(0) approached at high doses, i.e. P(∞)/P(0). The parameter m is the “median-dose” for which P(D)/P(0)(1+h)/2 which is the half point in the dynamic range of the particular film. The best-fit values of m over the dose rate range from ~0.2 to ~25 Gy/min using the red pixels were 1.42±0.03, 11.1±0.4, 63.6±0.9 and 60.6±1.6 Gy for EBT3, MD-V3, HD-V2 and HD-810 respectively. Using the green pixels the median dose is 1.8 times larger for the first 3 films and 2.5 times larger for HD-810. The blue pixels are considered unsuitable for dosimetry because of the large value of h (>0.4) and the resulting small dynamic range.

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A radio-fluorogenic (RFG) gel is a polymer gel that can be applied as a 3D radiation dosimeter in radiotherapy. The gel becomes fluorescent in UV light after exposure to high-energy radiation and the intensity of the fluorescence is proportional to the local radiation dose. This radiation-induced fluorescence is permanent, which distinguishes it from transitory optical emission or scintillation effects. In the thesis we demonstrate that a quasi-rigid RFG gel, consisting of tertiary-butyl acrylate (TBA) with ca 100 ppm maleimido-pyrene (MPy), has the potential to produce spatially resolved images of dose deposition. The work focuses on the fundamental radiation chemistry and photophysics of the medium. In particular, we have investigated the dose and dose-rate dependences of polymer formation and fluorescence intensity using cobalt-60 gamma-ray sources. We have also used collimated beams of 200 kVp X-rays to produce complex radiation fields for test purposes and constructed a tomographic method for reconstructing full 3D images of the dose distribution with submillimetre spatial resolution. Our ultimate goal is to provide a method of quantitative, spatially-resolved dosimetry that can be applied to particle beams and other forms of high-energy radiation that produce the complex radiation fields applied in modern radiotherapy treatment of cancer.@en