Radiobiological effects of flattening filter and flattening filter free radiotherapy x-ray on inflammatory and apoptotic pathways in cardiac and pulmonary tissues in an MCF-7 xenograft breast cancer model.

This study investigated early inflammatory and apoptotic molecular responses in heart and lung tissues following flattening filter (FF) and flattening filter-free (FFF) radiotherapy in a murine MCF-7 xenograft breast cancer model. Mice received a single 20 Gy fraction in FF (400 MU/min) or FFF (1820 MU/min) mode, and cardiopulmonary tissues were analyzed 48 h post-irradiation. Gene expression of Tnf, Il1b, Nfkb and p53 was assessed by RT-qPCR, while NF-κB p65 activation and caspase-3-mediated apoptosis were evaluated by western blot. Both irradiation modalities significantly increased inflammatory cytokine expression and NF-κB signaling compared with controls (P < 0.05), with consistently stronger responses following FFF irradiation. Lung p53 expression increased progressively across tumor-bearing and irradiated groups, indicating enhanced DNA damage signaling, while elevated cleaved caspase-3 levels reflected apoptotic activation, particularly in irradiated groups. Overall, high-dose-rate FFF radiotherapy elicits more pronounced early inflammatory and apoptotic responses in non-target heart and lung tissues than conventional FF delivery, highlighting the importance of incorporating normal tissue radiobiological effects into high-dose-rate radiotherapy strategies.