RADIOTHERAPY METHODS, THERAPEUTIC TECHNIQUES, AND THE BIOLOGICAL BASIS OF RADIATION THERAPY

Radiotherapy is a cornerstone of modern cancer care and a key component of multimodal management for both curative and palliative intent. Contemporary practice combines physical dose shaping with biological principles to maximize tumor control while limiting normal tissue injury. This article reviews major radiotherapy methods, including external beam photon techniques, particle therapy, and brachytherapy, together with the technical workflow that supports accurate delivery, such as simulation, target volume definition, treatment planning, image guidance, motion management, and quality assurance. The biological basis is discussed through DNA damage mechanisms, linear–quadratic modeling, fractionation and the 4Rs, relative biological effectiveness, oxygen effects, and clinical endpoints such as tumor control probability and normal tissue complication probability. The synthesis emphasizes that technique selection is inseparable from radiobiology: dose per fraction, total dose, overall time, and spatial dose distribution jointly determine outcomes. A practical framework is offered to help learners link technology to patient-centered goals and to understand why modern radiotherapy is both a physics-driven and biology-driven discipline.