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