Radiotherapy: radiobiology, delivery and acute and late toxicity
How ionising radiation kills cells, the linear-quadratic model and BED calculations behind fractionation and hypofractionation, the 4 Rs, oxygen and the cell cycle, and how acute and late radiation toxicity differ in timing and mechanism.
Tier 2Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- Radiotherapy kills cells mainly through DNA double-strand breaks. Most cells die a mitotic death at their next division, so effects take days to weeks to appear.
- Fractionation exploits the difference between tumour and late-responding normal tissue in repair capacity. The linear-quadratic (LQ) model and alpha/beta ratio describe it.
- The 4 Rs (repair, redistribution, repopulation, reoxygenation; a 5th is radiosensitivity) explain why splitting dose works.
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Sources
- Radiobiology for the Radiologist (8th ed.)Wolters Kluwer (Hall and Giaccia, 2019), 2019
- eviQ radiation oncology treatment protocolsAU/NZCancer Institute NSW, 2026
- Targeting Cancer: radiation therapy informationAU/NZFaculty of Radiation Oncology, RANZCR, 2026
- Common Terminology Criteria for Adverse Events (CTCAE) version 5.0US National Cancer Institute, 2017
- Use of normal tissue complication probability models in the clinic (QUANTEC)International Journal of Radiation Oncology Biology Physics (Marks et al., 2010;76:S10-9), 2010
- Last updated
- 14 November 2026
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