Proton Flash Therapy-Induced Radioisotopes As a Source of Entangled 511 Kev Photons
Abstract
Purpose
Ultra-high dose rate (FLASH) proton therapy generates positron-emitting radioisotopes, including C-11, O-15, and F-18, which decay via β⁺ emission. Each annihilation produces a pair of 511 keV photons naturally entangled in momentum and polarization. We evaluated the entangled photon yield and temporal profile from realistic FLASH pulses and explored their potential as spatially localized reporters of tumor microenvironment (TME) changes and adaptive radiotherapy biomarkers, leveraging the Bragg peak dose localization.
Methods
A 1 ms proton FLASH pulse containing protons traversing 1 cm of tissue (atomic density atoms/cm³) was modeled. Isotope production cross-sections were taken from literature (C-11: 1×10⁻²⁶ cm², O-15: 5×10⁻²⁶ cm², F-18: 1×10⁻²⁷ cm²) with 100% β⁺ branching. Decay and entangled photon emission were calculated using . Data was generated as a function of dose. The Bragg peak localization of proton dose was considered to estimate spatial concentration of isotope production and photon emission.
Results
Isotope yields per FLASH pulse were: C-11: 6×10⁵; O-15: 3×10⁶; F-18: 6×10⁴. Photon emission during the 1 ms pulse was negligible due to short pulse duration relative to isotope half-lives. Total entangled photons emitted over several half-lives were: C-11: 1.2×10⁶; O-15: 6×10⁶; F-18: 1.2×10⁵. Short-lived isotopes such as O-15 dominate early post-pulse photon flux. The Bragg peak concentrates isotope production, yielding spatially localized entangled photons in the high-dose tumor region, while minimizing photon flux from surrounding healthy tissue.
Conclusion
Proton FLASH therapy predominantly generate entangled photon pairs after the pulse, with both temporal and spatial profiles determined by isotope half-lives and Bragg peak localization. These photons provide a quantitative, spatially precise measure of dose deposition and may serve as functional reporters of TME changes, including hypoxia and perfusion, offering potential biomarkers for adaptive radiotherapy. This framework establishes a basis for exploiting quantum-correlated photons as both a theranostic tool and a novel biomarker platform.