Radiobiological characterization of 60 keV quasi-monoenergetic convergent photons.
basic_science · Level V
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- Also identified by DOI 10.1016/j.ijrobp.2026.06.3056.
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Abstract
To characterize the biological effects of low-energy photons generated by a ∼60-keV quasi-monoenergetic focused convergent-beam system (patented X-ray converging lens) compared with orthovoltage and 6-MV clinical photon beams. Human (NCI-H460, NCI-H2172) and murine (KLN-205 and LKR-13) lung cancer cell lines and a normal human bronchial epithelial cell line (Beas-2B) were irradiated with photons from a 6 MV linear accelerator (linac), an 180 kVp orthovoltage unit (average energy ∼60 keV), or a system that generates 60-keV quasi-monoenergetic convergent photons. Clonogenic cell survival was analyzed to assess dose-response metrics and relative biological effectiveness (RBE) in all cell lines. DNA damage and cell cycle analysis were assessed in the human-origin lung cancer cell lines. A human lung cancer (NCI-H460) xenograft model was used to test tumor growth delay in vivo. Relative to 6 MV photons, the 60 keV quasi-monoenergetic convergent and orthovoltage photons induced comparable cell kill effect and RBE for the LKR-13, KLN-205, and Beas-2B cell lines and higher cell kill effect and RBE for the NCI-H460 (significant) and NCI-H2172 (non-significant) cell lines. The enhanced biological response to orthovoltage and 60 keV quasi-monoenergetic convergent photons in NCI-H460 cells was also evidenced by increased DNA damage signaling and cell cycle checkpoint activation. Radiosensitivity differed considerably among cell lines, even for the same radiation type. The 60-keV quasi-monoenergetic convergent photons significantly delayed tumor growth, achieving effects comparable to 6-MV photons, in the NCI-H460 xenograft model. In vitro and in vivo evaluations confirmed that the biological effectiveness of 60 keV quasi-monoenergetic convergent photons is similar to that of photons from an orthovoltage unit (average energy ∼60 keV) and either comparable (three cell lines) or higher (two cell lines, but one was not significant) than photons from a 6-MV linac.