Basics of Radiation Therapy

Published on 04/03/2015 by admin

Filed under Hematology, Oncology and Palliative Medicine

Last modified 04/03/2015

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Chapter 27

Basics of Radiation Therapy

Summary of Key Points

The Radiobiology of Radiotherapy

• Ionization of biomolecules from the deposition of energy by photons or particles can occur directly and indirectly. The most important cellular target for radiation is DNA, with irreparable or “misrepaired” double-stranded breaks believed to be the lesions most responsible for cell killing.

• Irradiation elicits diverse cellular responses that include the sensing of DNA damage, mobilization of DNA repair proteins, repair (or attempted repair) of DNA damage, triggering of cell cycle checkpoints, and, for irreparable or mis-rejoined damage, cell death by one of several mechanisms (e.g., mitotic catastrophe, apoptosis, and senescence).

• The most commonly applied model of cell survival probability is the linear quadratic (α/β) model, with the surviving fraction of irradiated cells described by the equation image. The α/β ratio is a convenient metric for describing cellular radiosensitivity and has been adapted to describe the response of irradiated tissues as a function of time, dose, and fractionation.

• DNA damage and repair were initially inferred by monitoring increases in cell survival or tissue tolerance with fractionation. These phenomena were termed sublethal and potentially lethal damage repair or recovery.

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