Published online Nov 28, 2023. doi: 10.4329/wjr.v15.i11.315
Peer-review started: October 3, 2023
First decision: October 17, 2023
Revised: October 26, 2023
Accepted: November 17, 2023
Article in press: November 17, 2023
Published online: November 28, 2023
Processing time: 51 Days and 15.9 Hours
Cherenkov radiation (CR) is the emission of photons when a charged particle moves faster than the speed of light in a medium. Various radionuclides produce Cherenkov optical emission, which can potentially activate photosensitizers (PSs) in phototherapy.
Several researchers are investigating CR-induced photodynamic therapy using radioisotopes and Cherenkov energy transfer to PSs using optical imaging. However, the effective management of the process, particularly the cost-effective confirmation that a PS is excited by CR and identifying appropriate PSs, remains a challenge.
The purpose of this study is to propose a cost-effective method to determine whether the PS is excited by radionuclide-derived CR and to distinguish the fluorescence emission from PS excitation.
Tetrakis (4-carboxyphenyl) porphyrin (TCPP) and Copper-64 (64CuCl2) were utilized as a model PS and a CR-producing radionuclide, respectively. The photo-physical properties (absorbance and fluorescence spectra) of TCPP were measured using a microplate reader and fluorescence spectrometer. Imaging and data acquisition were performed with a charge-coupled device optical imaging system and appropriate long-pass filters of different wavelengths. To visually evaluate the TCPP fluorescence, differential image analysis was conducted using ImageJ software (National Institutes of Health).
Optical imaging coupled with high-transmittance long-pass filters and subtraction image processing separated the emission spectra of the radionuclide-derived CR and TCPP. The emission spectra of TCPP were obtained by calculation and subtraction based on the serial signal intensity (total flux) difference between 64CuCl2 + TCPP and 64CuCl2. In addition, the differential fluorescence images of TCPP were acquired by subtracting the 64CuCl2 image from the 64CuCl2 + TCPP image.
This simple and cost-effective method could confirm the PS fluorescence emission generated by radionuclide-derived CR. Moreover, the method can contribute to accelerating the development of Cherenkov energy transfer imaging and the discovery of new effective PSs.
Several laboratories with conventional optical imaging devices would be able to acquire suitable long-pass filters at low cost and easily apply this method to compare different PSs to identify the optimal PS. A potential limitation of this study, namely the use of limited experiments with only one PS and one radionuclide, could be addressed by conducting much more detailed examinations as the next step.