KEY POINTS
- This preclinical study compared quasi-monoenergetic convergent 60 keV photons, orthovoltage photons with an average energy of approximately 60 keV, and clinical 6 MV photons across four lung cancer cell lines and one normal bronchial epithelial cell line.
- Relative biological effectiveness varied substantially by cell type. For convergent photons, RBE at D10% ranged from 0.85 ± 0.15 to 1.33 ± 0.18 relative to 6 MV photons.
- Convergent photons produced significantly greater cell killing than 6 MV photons in NCI-H460 cells, with a nonsignificant trend in NCI-H2172 cells. LKR-13, KLN-205, and Beas-2B cells showed broadly comparable responses across radiation types.
- In NCI-H460 and NCI-H2172 cells, convergent photons increased selected DNA-damage markers and G2-phase arrest relative to 6 MV photons, although the magnitude and persistence of these effects depended on the cell line and endpoint.
- In NCI-H460 xenografts, 9 Gy in 3 fractions of convergent photons significantly delayed tumor growth compared with control and produced effects comparable to 6 MV photons. No clinically meaningful body-weight loss was observed.
CLINICAL TAKEAWAY
Quasi-monoenergetic convergent 60 keV photons demonstrated biological effectiveness comparable to orthovoltage radiation and, in selected cell lines, greater than 6 MV photons. The response was strongly cell dependent, while in vivo tumor control was similar to 6 MV treatment; clinical translation will require normal-tissue studies, therapeutic-dose-rate validation, and human trials.
SOURCE
International Journal of Radiation Oncology, Biology, Physics