Medical uses and effectiveness of radiation therapy
- Radiation therapy is commonly used as part of cancer therapy to kill or control the growth of malignant cells.
- It can be curative for localised cancers and used as adjuvant therapy to prevent tumor recurrence after surgery.
- Radiation therapy is synergistic with chemotherapy and can be used before, during, and after chemotherapy.
- The subspecialty of oncology concerned with radiotherapy is called radiation oncology.
- Radiation therapy can also be used in non-malignant conditions such as trigeminal neuralgia and severe thyroid eye disease.
- Different cancers respond to radiation therapy in different ways.
- Highly radiosensitive cancers are rapidly killed by modest doses of radiation, while some cancers are notably radioresistant.
- The radiosensitivity of a tumor is different from its radiation curability in clinical practice.
- Leukemias are generally not curable with radiation therapy, while lymphoma can be curable if localised.
- Metastatic cancers are generally incurable with radiation therapy.
- The impact of radiation therapy varies between different types of cancer and patient groups.
- For example, radiation therapy after breast-conserving surgery can halve the rate of disease recurrence in breast cancer.
- In pancreatic cancer, radiotherapy has increased survival times for inoperable tumors.
Treatment planning and techniques of radiation therapy
- Modern radiation therapy relies on CT scans to identify the tumor and surrounding structures.
- Patient positioning is crucial, and various devices like masks and cushions are used to ensure consistency.
- Image-guided radiation therapy corrects positional errors during treatment sessions.
- Tumor size affects the response to radiation therapy, and strategies like surgical resection and neoadjuvant chemotherapy are used to overcome this.
- Certain drugs can enhance the radiosensitivity of cancer during radiation therapy.
- Radiation therapy damages the DNA of cancer cells.
- Two types of energy used: photon or charged particle.
- Indirect ionization of atoms in DNA chain caused by ionization of water.
- Double-stranded DNA breaks are difficult to repair, leading to chromosomal abnormalities.
- Cancer cells have diminished ability to repair sub-lethal damage.
- Photon therapy primarily affects cancer cells through free radicals.
- Single-strand DNA damage is passed on through cell division.
- Solid tumors can become deficient in oxygen, making them more resistant to radiation damage.
- Charged particles cause direct damage to cancer cell DNA through high-LET and have an antitumor effect independent of tumor oxygen supply.
- Amount of radiation measured in grays (Gy).
- Dose varies depending on type and stage of cancer.
- Curative cases typically receive 60-80Gy, while lymphomas are treated with 20-40Gy.
- Preventive doses are around 45-60Gy in 1.8-2Gy fractions.
- Factors considered when selecting dose include chemotherapy, patient comorbidities, and surgery success.
- Treatment planning determines delivery parameters using specialised software.
- Multiple angles or sources may be used to sum to the total necessary dose.
- Planner aims to deliver uniform prescription dose to tumor and minimize dose to surrounding healthy tissues.
- Three-dimensional dose distributions can be evaluated using gel dosimetry.
- Different effects observed between intensity-modulated radiation therapy (IMRT) and charged particle therapy.
- Fractionation spreads total dose over time.
- Allows normal cells time to recover while tumor cells are less efficient in repair.
- Helps tumor cells cycle into a sensitive phase and reoxygenate, improving cell kill.
- Typical fractionation schedule for adults is 1.8-2Gy per day, five days a week.
- Hypofractionation and concomitant boost regimens are used in certain cases for faster tumor regeneration or completion within a specific timeframe.
Side effects of radiation therapy
- Radiation therapy itself is painless, but there can be side effects.
- Common side effects include fatigue, skin changes, and hair loss.
- Side effects are generally temporary and can be managed with supportive care.
- Advanced techniques like intensity-modulated radiation therapy (IMRT) help minimize side effects.
- The risk of radiation-induced cancers in non-malignant conditions limits the use of radiation therapy.
- Nausea and vomiting associated with treatment of the stomach or abdomen.
- Damage to epithelial surfaces, including the skin, oral mucosa, pharyngeal, bowel mucosa, and ureter.
- Mouth, throat, and stomach sores commonly occur in the head and neck area.
- Intestinal discomfort, such as soreness, diarrhea, and nausea.
- Swelling of soft tissues, especially in the treatment of brain tumors.
- Fibrosis, causing tissues to become less elastic over time.
- Epilation (hair loss) on any hair-bearing skin within the radiation field.
- Dryness of salivary glands, tear glands, and vaginal mucosa.
- Chronic sinus drainage and fistulae from radiation therapy to head and neck regions.
- Lymphedema, localised fluid retention and tissue swelling, resulting from damage to the lymphatic system.
- Fatigue often sets in during the middle of treatment and can last for weeks after treatment ends.
- Skin irritation, similar to a mild to moderate sunburn, may occur and heal but may not regain full elasticity.
- Nausea and vomiting are not general side effects of radiation therapy.
- Associated with treatment of the stomach or abdomen, or certain nausea-producing structures in the head.
- Psychological response may cause immediate vomiting during or in anticipation of radiotherapy.
- Nausea can be treated with antiemetics.
- Gonads (ovaries and testicles) are sensitive to radiation and may be unable to produce gametes.
- Radiation therapy is a potential cause of secondary malignancies, but only a small minority of patients develop them.
- New techniques aim to reduce dose to healthy tissues and lower the risk of secondary cancers.
Cardiovascular and neurological effects of radiation therapy
- Radiation increases the risk of heart disease and death.
- The risk of a subsequent cardiovascular event is 1.5 to 4 times higher
Radiation therapy or radiotherapy (RT, RTx, or XRT) is a treatment using ionizing radiation, generally provided as part of cancer therapy to either kill or control the growth of malignant cells. It is normally delivered by a linear particle accelerator. Radiation therapy may be curative in a number of types of cancer if they are localised to one area of the body, and have not spread to other parts. It may also be used as part of adjuvant therapy, to prevent tumor recurrence after surgery to remove a primary malignant tumor (for example, early stages of breast cancer). Radiation therapy is synergistic with chemotherapy, and has been used before, during, and after chemotherapy in susceptible cancers. The subspecialty of oncology concerned with radiotherapy is called radiation oncology. A physician who practices in this subspecialty is a radiation oncologist.
| Radiation therapy | |
|---|---|
 Radiation therapy of the pelvis, using a Varian Clinac iX linear accelerator. Lasers and a mould under the legs are used to determine exact position. | |
| ICD-10-PCS | D |
| ICD-9-CM | 92.2-92.3 |
| MeSH | D011878 |
| OPS-301 code | 8–52 |
| MedlinePlus | 001918 |
Radiation therapy is commonly applied to the cancerous tumor because of its ability to control cell growth. Ionizing radiation works by damaging the DNA of cancerous tissue leading to cellular death. To spare normal tissues (such as skin or organs which radiation must pass through to treat the tumor), shaped radiation beams are aimed from several angles of exposure to intersect at the tumor, providing a much larger absorbed dose there than in the surrounding healthy tissue. Besides the tumor itself, the radiation fields may also include the draining lymph nodes if they are clinically or radiologically involved with the tumor, or if there is thought to be a risk of subclinical malignant spread. It is necessary to include a margin of normal tissue around the tumor to allow for uncertainties in daily set-up and internal tumor motion. These uncertainties can be caused by internal movement (for example, respiration and bladder filling) and movement of external skin marks relative to the tumor position.
Radiation oncology is the medical specialty concerned with prescribing radiation, and is distinct from radiology, the use of radiation in medical imaging and diagnosis. Radiation may be prescribed by a radiation oncologist with intent to cure or for adjuvant therapy. It may also be used as palliative treatment (where cure is not possible and the aim is for local disease control or symptomatic relief) or as therapeutic treatment (where the therapy has survival benefit and can be curative). It is also common to combine radiation therapy with surgery, chemotherapy, hormone therapy, immunotherapy or some mixture of the four. Most common cancer types can be treated with radiation therapy in some way.
The precise treatment intent (curative, adjuvant, neoadjuvant therapeutic, or palliative) will depend on the tumor type, location, and stage, as well as the general health of the patient. Total body irradiation (TBI) is a radiation therapy technique used to prepare the body to receive a bone marrow transplant. Brachytherapy, in which a radioactive source is placed inside or next to the area requiring treatment, is another form of radiation therapy that minimizes exposure to healthy tissue during procedures to treat cancers of the breast, prostate, and other organs. Radiation therapy has several applications in non-malignant conditions, such as the treatment of trigeminal neuralgia, acoustic neuromas, severe thyroid eye disease, pterygium, pigmented villonodular synovitis, and prevention of keloid scar growth, vascular restenosis, and heterotopic ossification. The use of radiation therapy in non-malignant conditions is limited partly by worries about the risk of radiation-induced cancers.
radiation therapy (uncountable)
