ABSTRACT
Radiotherapy is the use of ionizing radiation to treat disease. The various types of radiation are alpha, beta, gamma, proton, neutron, and heavy ion particles. This chapter highlights the biological actions of ionizing radiation which causes direct and indirect damage to the cellular DNA. External beam radiotherapy is the most common form of treatment in clinical use. A range of x-ray beams is available, varying according to their energy. Electron beams are also produced by linear accelerators and are used when a tumour is overlying a radiosensitive structure such as the spinal cord. The great advantage of brachytherapy is the rapid fall-off of dose at a short distance from the source. Specific examples of internal isotope therapy are the use of radioiodine for thyroid cancer and also neuroblastoma when conjugated in meta-iodobenzyl guanidine. The three components to biological radiation dose are total dose, number of treatments (fractions) of a given dose, and overall time of treatment.
