Mechanisms of interaction

• Additive: total effect = RT + chemo (independent).

• Synergistic (radiosensitization): chemo enhances radiation effect (e.g., cisplatin).

• Spatial cooperation: RT and chemo target different sites (local + systemic).

Classic radiosensitizers

• Cisplatin: forms DNA adducts, interferes with repair.

• 5-FU: inhibits thymidylate synthase, enhances radiosensitivity in GI tumors.

• Taxanes: arrest cells in G2/M (radiosensitive phase).

Clinical examples

• Concurrent cisplatin + RT in head & neck cancer → standard of care.

• RT + temozolomide in glioblastoma (Stupp protocol).