Radiation therapy uses high-energy particles or waves, such as x-rays, gamma rays, electron beams or protons, to destroy or damage cancer cells.
Cells normally grow and divide to form new cells. But cancer cells grow and divide faster than most normal cells. Radiation works by making small breaks in the DNA inside cells. These breaks keep cancer cells from growing and dividing and cause them to die. Nearby normal cells can also ve affected by radiation, but most recover and go back to working the way they should.
Unlike chemotherapy, which usually exposes the whole body to cancer-fighting drugs, radiation therapy is usually a local treatment. In most cases, it is aimed at and affects only the part of the body being treated. Radiation treatment is planned to damage cancer cells, with as little as possible to nearby healthy cells.
Some radiation treatments (systemic radiation therapy) use radioactive substances that are given in a vein or by mouth. Even though this type of radiation does travel throughout the body, the radioactive substance mostly collects in the area of the tumour, so there’s little effect of the rest of the body.
Types of Radiotherapy
The types of radiation you might get depends on the kind of cancer you have and where it is. In some cases, more than one type is used. Radiation therapy can be given in 3 ways:
External Radiation (external beam radiation): This uses a machine that directs high-energy rays from outside the body into the tumour. Most people get external therapy over many weeks. It is done during outpatient visits to a hospital or treatment centre. Types of external radiation therapy include:
- Three-dimensional conformal radiation therapy (3D-CRT): This delivers radiation beams from different directions designed to match the shape of the tumour. This helps to reduce radiation damage to normal tissues and better kill the cancer by focusing the radiation dose on the tumour.
- Image guided radiation therapy (IGRT): is a form of 3D-CRT where imaging scans (like a CT scan) are done before each treatment. This allows the radiation oncologist to adjust the position of the patient pr re-focus as needed to hit the tumour and limit other damage.
- Intensity modulated radiation therapy (IMRT): This is like 3D-CRT, but it also changes the strength of some of the beams in certain areas. This gets stronger doses to certain parts of the tumour and helps lessen damage to nearby mortal body tissues.
- Helical – tomotherapy: This is a form of IMRT that delivers radiation inside a large “donut”. For this treatment, you lie on a table that slowly slides through the donut as the machine spirals around you. It delivers many small beams of radiation at the tumour from different angles around the body. This may allow for even more precisely focused radiation.
- Photon beam radiation therapy: This is another name for what is traditionally known as external beam radiation therapy. It uses photon beams to get to the timor but also can damage healthy tissue around the tumour. Photons are used in treatments that are given by a machine called a linear accelerator.
- Proton beam radiation therapy: This uses proton beam instead of photons or electrons. Protons are parts of atoms that cause little damage to tissues as they pass thorough but are very good at killing cells at the end of their path. This means that proton beam radiation may be able to deliver more radiation to the tumour while reducing side effects on normal tissues. Protons can only be put out by a special machine called a cyclotron or synchrotron.
- Stereotactic radiosurgery: This isn’t really surgery, but a type of radiation treatment that gives a large dose of radiation to a small tumour area, usually in one session It is used for brain tumours and other tumours inside the head. In some cases, a head frame or shell may be used to help keep the patients head still. Once the exact location of the tumour is known from brain scans, radiation is sent to the area from many different angles. The radiation is very precisely aimed to affect nearby tissues as little as possible.
- Stereotactic Body Radiation Therapy (SBRT): This is the treatment outside the brain. SBRT may be used for certain lung, spine, and liver tumours. In many radiation therapy clinics this technology is called by the name of the vendor that makes the machine. There are 3 main ways in which SBRT can be given:
- The most common type uses, a movable linac thats controlled by a computer. The machine moved around to target the tumour from many different angles. E.g. X-Knife, CyberKnife and Clinac.
- The Gamma knife uses about 200 small beams aimed at the timor from different angles for a short period to deliver a large dose of radiation. It’s usually given in one treatment session. Again, this is a type of radiation therapy – it does not use a knife and there’s no cutting.
- Another type aims heavy charged particle beams (like proton or helium ion beams) at the tumour from different angles. These particles release most of the radiation’s energy at the end of their paths, at more precise depths. This limits damage to nearby healthy tissues or organs.
Although most patients will be given the full radiation dose in one session with stereotactic radiosurgery, it may be repeated if needed. Sometimes doctors give the radiation in several smaller treatments to liver the same or slightly higher dose. This may be called fractioned radiosurgery pr fractioned stereotactic radiotherapy.
- Intraoperative radiation therapy (IORT): This is external radiation given directly to the tumour or tumours during surgery. It may be used if the tumours can’t be removed completely or if there’s a high risk the cancer will come back in the same area. While you are asleep, the surgeon moves normal tissues away from the tumour and protects them with special shields. This lets the doctor give one large dose of radiation to the cancer and limit the effects on nearby tissues. IORT is given in a special operating room that has radiation-shielding walls.
Internal Radiation: This is also called brachytherapy. A radioactive source is put inside the body into or near the tumour. Getting the implant placed is usually a painless procedure. Depending on your type of cancer and treatment plan, you might get a temporary or a permanent implant.
It allows a higher dose of radiation in a smaller area than might be possible with external radiation treatment. It uses a radiation source thats usually sealed in a small holder called an implant. Different types of implants may be called pellets, sends, ribbons, wires, needles, capsules, balloons or tubes. No matter which type of implant is used, it is placed in your body, very close to or inside the tumour. This way the radiation harms as few normal cells as possible. There are two types:
- Intracavitary radiation: Here the radioactive source id placed in a body cavity (space), such as the rectum or uterus.
- Interstitial radiation: Here the implants are placed in or near the tumour, but not in a body cavity.
Systemic radiation: Radioactive drugs given by mouth or put into a vein are used to treat certain types of cancer. These drugs then travel throughout the body. Certain cancers, such as thyroid, bone, and prostate are treated with radio-pharmaceuticals (radioactive drugs). It is sometimes bound to s special antibody (called a monoclonal antibody) that attaches to the cancer cells. Examples of radio-pharmaceuticals used for systemic radiation include radioactive iodine, strontium, samarium and radium.
These drugs may be given in a vein (IV) or taken by mouth. They travel in the blood throughout the body. The antibody makes them attach to the cancer cells. They then give off their radiation and kill the cancer cells.