Definition: New, histologically distinct cancers arising years after radiation exposure.

Epidemiology

  • Risk is dose- and volume-dependent.

  • Latency: typically 10–30 years.

  • Children have higher lifetime risk.

Examples

  • Breast cancer after mantle RT for Hodgkin’s lymphoma.

  • Sarcomas (osteosarcoma, fibrosarcoma) in irradiated fields.

  • Leukemias after total body irradiation.

Risk models

  • Stochastic effect: probability increases with dose; no threshold.

  • Linear-no-threshold (LNT) model often applied.

Modern RT and risk

  • IMRT/VMAT increases low-dose bath → may slightly raise second cancer risk.

  • Proton/particle therapy may reduce risk by lowering integral dose.

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