Purpose: To study how much Cherenkov photons are generated with and without a gold implant/marker in a water phantom for utilizing the Cherenkov photons in radiation therapy.
Methods: The Geant4-based Monte Carlo code, GAMOS, was employed for simulating the number of Cherenkov photons produced with and without a gold marker implanted in a homogeneous water phantom under photon beam irradiation. A 10 x 10 x 10 cm³ phantom was modeled. A thin gold plate with a 10 mm diameter and 1.0 mm thickness was placed at the center of the phantom. 6, 10, and 15 MV photon beams with a 5 x 5 cm² field size directed towards the phantom. The integrated dose and the number of Cherenkov photons produced within 5 mm above and below the gold plate, designated as ROI1 and ROI2, were calculated. Those quantities with the gold were compared with those without the gold.
Results: The integrated dose in the ROI1 increased by 28.0, 27.2, and 24.4% for 6, 10, and 15 MV beams, respectively. The dose difference in the ROI2 increased as the photon energy increased. The differences in the numbers of the Cherenkov photons in ROI1 between with and without the gold were 23.2, 11.8, and -19.2% for the 6, 10, and 15 MV beam, respectively, whereas the difference was -0.06, 7.71, and -6.04% in the ROI2.
Conclusion: Monte Carlo simulations showed the increase of the dose in the ROI1; thus, resulting in an enhancement of the Cherenkov photon yield by a gold marker. The difference in the Cherenkov photon yield between with and without the gold marker in the ROI1 was significant for 6 and 10 MV beams. A potential application of this phenomenon includes a non-invasive real-time identification of the maker location implanted in a tumor for motion tracking.