Late effects

• Appear months to years after radiotherapy.

• Typically seen in late-responding tissues with low α/β ratios (e.g., spinal cord, lung, rectum).

Fibrosis

• Chronic activation of fibroblasts → excess extracellular matrix.

• Leads to stiffening of tissues, impaired function (lung fibrosis, rectal strictures).

• Cytokines: TGF-β plays a central role.

Vascular damage

• Endothelial cells injured → vessel narrowing, thrombosis, ischemia.

• Example: radiation-induced heart disease, carotid stenosis after neck RT.

Necrosis

• Severe late endpoint (e.g., brain necrosis after high-dose CNS RT).

• Results from vascular injury and failure of tissue repair.