Radiation therapy

Radiation therapy is a nuclear medical treatment that employs ionizing radiation to kill abnormal cells or control their growth. It is one of the three main approaches to the treatment of malignant tumors alongside chemotherapy and surgery, but can also be used to treat noncancerous diseases such as benign hyperthyroidism, Cushing disease, Dupuytren contracture, and plantar fibromatosis. Radiation therapy is typically employed as a supplement to other treatments and rarely represents the sole approach. There are three forms of radiation therapy: external beam radiation therapy (teletherapy), which involves irradiation from an external source; unsealed source radiotherapy (systemic radioisotope therapy), which involves the administration of radiopharmaceuticals that accumulate in target tissues and irradiate these internally; and sealed source radiotherapy (brachytherapy), which involves the implantation of radioactive material beside or within the tissue to be irradiated. The type of radiation therapy employed depends on the disease and the specific type of cancer being treated. Radiation therapy can be employed curatively (i.e., to kill the diseased tissue completely) or palliatively (e.g., to shrink a tumor, control its growth, or relieve symptoms caused by a tumor). Palliative indications include bone pain, spinal cord and nerve compression, and hemostasis. As with all medical use of ionizing radiation, the radiation dose should be maintained as low as reasonably achievable (ALARA principle) and appropriate safety measures should be observed to minimize carcinogenic effects.

The division of the total dose of radiation into smaller doses administered over the course of several days or weeks; total dose and duration of treatment depends on tumor type.

• Conventional fractionation (conventional radiation therapy): standard radiation dose per fraction (1.5–2 Gy) of a standard total radiation dose (45–70 Gy) over the standard duration of treatment (5–7 weeks).
• Hypofractionation
  • Reduced fractionation; i.e., higher radiation dose per fraction (> 2 Gy/1 × per day) of a reduced total radiation dose (< 45 Gy) over a shorter duration of treatment (3–5 weeks)
  • Indications include patient wish in palliative setting to reduce hospitalization time
• Hyperfractionation
  • Increased fractionation; i.e., lower radiation dose per fraction (1.15 Gy/2 × per day) of increased total radiation dose (> 70 Gy) over a prolonged duration of treatment (7 weeks); allows for application of higher total doses of radiation
  • Indications include tumors with a high cell division rate
• Acceleration
  • Increase of fractionation rate at the same total radiation dose; allows for reduction of duration of treatment and increased effect at a higher risk of side effects.
  • Indication: tumors that quickly develop resistance to radiation

By objective

• Curative: applying radiotherapy with the intent of curing a patient (e.g., completely removing a malignancy)
• Palliative: applying radiotherapy with the intent of prolonging life and/or alleviating symptoms. Examples include:
  • Preventive local radiation of osteolytic bone metastases
  • Radiation therapy in painful bone metastases to alleviate symptoms
  • Treatment of venous congestion associated with mediastinal tumors

By timing

By technology

• External beam radiotherapy (EBRT; teletherapy): radiation therapy using a source of radiation outside the body
  • Procedure: irradiation of target tissue from different angles in order to spare surrounding tissue
  • Options
    • Conventional high-energy EBRT: irradiation of internal organs and CNS
    • Soft x-ray therapy: radiation of dermatological diseases (such as basal cell carcinoma, keloids, psoriasis)
• Brachytherapy (sealed source radiation therapy): radiation therapy involving the implantation of radioactive seeds (approx. the size of a grain of rice) within or next to the target tissue
  • Low-dose radiation possible
• Unsealed source radiotherapy (systemic radioisotope therapy): radiation therapy involving the administration of radiopharmaceuticals that accumulate in target tissues and irradiate these internally

Radiation injury

High doses of ionizing radiation (e.g., radiotherapy, nuclear accidents) cause DNA and cellular damage via reactive oxygen species and photons or particles, which cause inflammation and progressive tissue damage. Certain rapidly regenerating tissues (e.g., skin, gastrointestinal tissue, bone marrow) are more susceptible due to the depletion of immature parenchymal stem cells. Cancerous cells are more susceptible to radiation than healthy cells due to their high replication rates and dysfunctional DNA repair mechanisms.

See also “Complications of anticancer therapy.”

Radiation proctitis

We list the most important complications. The selection is not exhaustive.