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