The discovery of x-rays by Wilhelm Conrad Roentgen and natural radiation by Henry Becquerel and Marie and Pierre Curie at the end of the 19th century was the cornerstone for the development of a new discipline: Radiology. Soon after the discovery of radiation, its diagnostic and therapeutic applications became evident and for more than 100 years it has been utilized in the diagnosis and treatment of cancer. During the last three decades the invention of computerized tomography, magnetic resonance and the development of fractionated therapy have improved planning and provided more accurate dosing. The current radiation techniques are capable of delivering more individualized treatment with less harm to normal adjacent tissue; therefore, more patients are treated with some form of radiation. Current radiation treatment planning modalities include three-dimensional conformational radiation therapy (3D-CRT), which accounts for tumor volume to approximate the radiation beam to the shape of the tumor; intensity-modulated radiation therapy (IMRT), a more advanced form of 3D-CRT, which utilizes varying intensities of radiation beams to produce dosage distributions that are more precise than with 3D-CRT; and fourdimensional radiation therapy (4D-RT) which not only accounts for volume and tumor shape but also considers patient and organ motion. Radiation treatment modalities can be divided into external beam radiation treatment, brachytherapy, and targeted radiotherapy. This chapter will focus on the historical events that have led to the current progress in radiation therapy, the generation of therapeutic radiation, mode of action, current radiation planning and treatment modalities, and side effects.
Keywords: Cancer, radiation therapy, ionizing radiation, x-rays, threedimensional conformational radiation therapy (3D-CRT), intensity-modulated radiation therapy (IMRT), four-dimensional radiation therapy (4D-RT), brachytherapy, external beam radiation treatment, targeted radiotherapy, radium, nuclear reactors, particle accelerators, cycle accelerators, linear accelerator, conformal radiotherapy, stereotactic radiotherapy, gamma knife, neutron beam therapy, proton beam therapy, Bragg peak.