Radiotherapy and cytokines: A systems view of immunotherapy and toxicity (Review).

Radiotherapy (RT) is increasingly recognized as a system‑level immunomodulator capable of reshaping cytokine networks across spatial, temporal and dosimetric dimensions. This review synthesizes existing evidence on RT parameters, key signaling axes, major effector cells, organ‑specific contexts and clinical translation. It describes how the cyclic GMP‑AMP synthase/stimulator of interferon genes (STING)/IFN‑I, NF‑κB and TGF‑β pathways coordinate immune activation and immune suppression after irradiation. It then summarizes macrophage‑centered regulatory circuits and chemokine axes, including C‑C motif chemokine ligand (CCL)2/CCR2 and CCL22/CCR4 that govern T‑cell trafficking and functional states. A map of organ‑specific cytokine programs that link therapeutic benefit and toxicity in the brain, lung, gastrointestinal tract, oral mucosa and liver is then provided, and actionable targets within inflammasome‑associated pyroptosis and fibrogenic cascades are highlighted. RT technical parameters, including fractionation, treatment volume, stereotactic body RT, Fast Linear Accelerator‑based Scanning Hybrid ultra‑high dose-rate delivery and proton therapy can differentially shape cytokine dynamics and modify the therapeutic window. The DNA damage response network with poly (ADP‑ribose) polymerase (PARP)1 as a central node represents a second hub that interfaces with antigen presentation and IFN signaling, supporting rational combinations with PARP inhibitors and immune checkpoint blockade. Finally, a translational algorithm with three pillars is proposed. The first pillar uses IFN‑related gene signatures and circulating cytokine profiles to stratify tumors by baseline IFN activity. The second pillar aligns RT timing with endogenous STING or IFN pulses and incorporates CCR2, CCR4 or colony stimulating factor 1 receptor blockade to counter myeloid cell‑mediated immunosuppression. The third pillar co‑manages treatment‑related toxicities by targeting the NLR family pyrin domain containing 3/gasdermin D axis or by using fibrosis‑modulating interventions. Furthermore, ongoing clinical trials of cytokine-directed agents combined with RT are summarized. This framework positions cytokines as measurable and modifiable variables for individualizing combined RT and immunotherapy.