Radiotherapy, also called radiation therapy, is a cancer treatment that uses high doses of radiation to kill cancer cells and shrink tumors. It works by damaging the DNA inside cancer cells, making it difficult for them to grow and multiply. Radiotherapy can be used to treat many types of cancer including lung cancer, breast cancer, prostate cancer, colorectal cancer, lymphoma, and more. It is most often used in combination with other treatments like surgery, chemotherapy, targeted therapy or immunotherapy.

External Beam Radiotherapy
External beam radiotherapy involves delivering controlled doses of high-energy X-rays or other types of radiation to the tumor from a machine outside the body. The machine aims the radiation directly at the cancer site, reducing damage to healthy surrounding tissues. During treatment, the patient usually lies still on a table while a linear accelerator rotates around their body to deliver the radiation from many different angles. This helps damage the tumor and protects normal organs and tissues as much as possible.

Internal or Brachytherapy
Brachytherapy involves placing radioactive material directly inside the body, either temporarily or permanently, to irradiate the tumor. For this type of treatment, tiny pellets or seeds containing radioactive material are surgically implanted in or near the cancer site. This allows a very high dose of radiation to be delivered to the tumor with little effect on surrounding healthy tissue. Brachytherapy is often used to treat cervical, prostate, breast and skin cancer as well as some other tumor types. Implants may be temporary or permanent depending on the type of cancer and treatment plan.

Intensity-Modulated Radiotherapy
Intensity-modulated radiotherapy (IMRT) is an advanced form of external beam radiotherapy that uses computer-controlled X-ray accelerators to deliver precise radiation doses to the tumor area. In IMRT, the radiation beams are divided into smaller beamlets that can be individually modulated to different intensities. This allows the radiation dose to be shaped to the tumor size and location, limiting damage to nearby normal tissues. IMRT may also be used to boost radiation to certain tumor areas while reducing radiation exposure of other structures. This improves treatment accuracy and safety.

Stereotactic Radiotherapy
Stereotactic radiotherapy delivers very precise radiation doses to tumors using a specialized device to precisely locate and target the tumor. It may involve either a single high dose of radiation or multiple smaller doses delivered over several days. The CyberKnife and Gamma Knife are types of stereotactic radiosurgery that deliver higly focused radiation from many angles, precisely converging on the tumor site with sub-millimeter accuracy. This allows for higher radiation doses to be used while minimizing damage to nearby normal tissues and structures. Stereotactic techniques are used to treat brain tumors, spinal tumors and certain tumors elsewhere in the body.

Proton Beam Therapy
Proton beam therapy is a type of external beam radiation that uses protons rather than X-rays to treat cancer. Protons deposit most of their energy at a certain depth in tissue, rather than releasing their energy continuously throughout their path like X-rays. This allows higher radiation doses to be delivered precisely to the tumor with little exit dose beyond it. As a result, proton therapy may further reduce unwanted exposure of healthy tissues to radiation compared to X-ray or IMRT methods. It is used to treat tumors near critical organs and structures, especially in children, for tumors of the brain, spinal cord, eye, head and neck region.

Effectiveness and Side Effects of Radiation Therapy
When combined with other treatments, radiotherapy can cure early stage cancers in some cases and control tumor growth or reduce cancer symptoms in others. It may take several weeks of daily treatments before its full effects are seen. Common short-term side effects during a course of external beam radiation may include fatigue, skin irritation at the treatment site and nausea. Longer term side effects are uncommon but depend on the dose and location of radiation. Brachytherapy seed implantation has very localized side effects. Overall, advancements in radiotherapy techniques have significantly reduced damage to healthy cells and improved quality of life for cancer patients undergoing treatment.

So in summary, radiotherapy provides an important non-surgical treatment option either alone or alongside chemotherapy, surgery or other therapies to cure cancer or control symptoms. Newer techniques enable very precise targeting of radiation doses to tumors while minimizing damage to adjacent normal tissues and structures. This improves treatment outcomes as well as quality of life for cancer patients. Radiotherapy remains a vital method for treating many cancer types.