Radiation oncology

Absorption of radiation by target tissue causes death at mitosis. Cancer cells are particularly sensitive due to their high rate of proliferation. The caveat of radiotherapy is that normal tissue is also at risk of being destroyed by the beams. To overcome this, radiotherapy is administered to tumors infractions over a period of weeks to allow for the normal tissue to recover between treatments. Radiotherapy is generally more effective for smaller lesions, this is because larger tumors require a greater dosage of irradiation, which thereby increases the risk of damage to surrounding normal tissue.

Radiotherapy has three key applications in oncology, as a primary cure, as an adjuvant treatment of as palliation. The value of ionizing radiation in treating cancer was recognized soon after the discovery of X-rays in 1895, since then radiotherapy has become a widely used approach for the treatment of malignant tissue. Orthovoltage X-rays were the most widely used in conventional radiotherapy, until the invention of megavoltage irradiation in the late 1950s. Following this, cobalt-60 machines were used as they provided more penetrating radiation, however, these were superseded by linear accelerators that can exude photon beams with an energy range of 5-20 MeV.

The dose of radiation is measured in Gray (Gy) and can be directed to the tumor in three ways. The first method, called external beam irradiation, is the most commonly used for both skin and deeply located tumors. The second technique is the local application of radioisotopes, which involves placing the radiation source on or within the malignant tissue. Thirdly we have systemic radioisotope therapy, whereby radioactive iodine is administered via the mouth.