Medical physics plays an essential part in radiation oncology, providing the technical foundation for patient treatment process, research activity and education of the staff. Medical physicists are health care professionals with specialised training in the medical applications of physics. They work with scientific, technical, medical and administrative staff. The roles of a medical physicist in radiotherapy include treatment planning and radiotherapy machine testing and calibration as well as commissioning of new radiotherapy techniques. Medical physicists collaborate with radiation oncologists to design treatment plans for radiotherapy patients using external radiation beams and internal radioactive sources. They calculate, measure and verify radiation dose to ensure that an accurate amount is delivered to a well-defined treatment volume. They also monitor equipment and procedures through quality assurance programs. Quality assurance consists of activities designed to assure adequate quality, precision and accuracy of complete radiotherapy chain starting from treatment planning to the end of radiotherapy treatment. Medical Physicists have expertise in radiation safety and are responsible for controlling the beneficial use of ionising radiation.