Radiotherapy uses the power of radiation to destroy cancer cells. Radiation can easily penetrate tissues and with current radiotherapy machines, we can focus it accurately on the target, the tumour.
As a key cancer treatment modality, radiotherapy cures patients from different types of cancer. Radiation can be applied as sole treatment agent or in combination with pharmacological agents (drugs). Radiation is also applied along with surgery. In this case, radiotherapy may be used before surgery to reduce the size of the tumour to allow surgical removal.
After surgery, radiation is delivered to eliminate and control outgrowth of isolated cancer cells that may have stayed in the body after the removal of tumours. Sometimes radiotherapy can help reduce the pain or other complications from cancer growth. Because today’s state-of-the-art radiotherapy can eliminate tumours while preserving organ function, it is also often applied instead of surgery.
Radiotherapy is, together with surgery and chemotherapy, the mainstay of successful cancer treatment.
Radiotherapy is a key cancer treatment modality. About half of all cancer patients should receive some type of radiotherapy during the course of their treatment. Radiotherapy helps 1.5 million cancer patients every year. Treatments involving radiotherapy are very carefully planned. This process involves a large team of radiation oncology professionals with different skills.
Radiotherapy is often applied alone or with chemotherapy (chemoradiation or chemoradiotherapy). When used prior to surgery (such as in preoperative or neoadjuvant radiotherapy) the aim is to reduce the size of the tumour to allow surgical removal. After surgery (postoperative or adjuvant radiotherapy), radiation is delivered to eliminate isolated cancer cells that remained undetected and were not removed.
Radiotherapy treatments can be divided into two broad groups: external radiotherapy, where the radiation is generated from machines outside the body, and internal radiotherapy or brachytherapy, where the radiation source is placed inside the body, either into or very close to the cancer.
External radiation machines use high-energy X-rays, electrons or protons to eradicate tumours. With these machines, beams of radiation are directed into the cancer. The concentration of the radiation within the tumour is achieved by pointing the beam from different angles directly into the tumour target while the surrounding healthy tissues receive much smaller doses.
The amount of radiation given and how it is applied varies according to the cancer type and the treatment plan drawn up for each individual patient.
External radiotherapy is usually delivered in small doses, often on a daily basis (referred to as treatment fractions). In some settings, this provides the normal healthy cells close to the targeted tumour tissue a chance to recover between doses. Cancer cells do not recover that way, so the beneficial effect for healthy tissues builds up over the course of treatment. There are different types of external radiotherapy machines and techniques. The linear accelerator (Linac) is a source of high-energy X-rays, that is used in radiotherapy. Electrons produced in the machine are accelerated linearly to energies of millions of electron-volts. These electrons hit a metal target which then emits high-energy X-rays. Linear accelerators are the most commonly used devices that provide external beam radiotherapy. The beam itself comes out of a gantry. This is the part of the machine that is able to rotate around the patient, who is positioned on a treatment couch. The combination of the movement of the treatment couch with the rotation of the radiation source allows the targeting of the tumour from any beam entry angle.
There are additional ways of targeting and matching the shape of the radiation beams used to treat a cancer to the shape of the tumour, termed as conformal radiotherapy and intensity-modulated radiation therapy (IMRT). This can be done with a collimator whose aperture can be formed into almost any shape (with a multi-leaf collimator). IMRT is an advanced conformal radiotherapy technique developed in the 1990s, which allows an exceptional radiation dose sparing of healthy tissues.
This is particularly important if the targeted tumour tissue is closely surrounded by normal, healthy tissues. In image-guided radiotherapy (IGRT) we use a linear accelerator and treatment integrated imaging modalities to precisely target the tumour with high doses of radiation. Here, the anatomical images of the patient generated in treatment position at the day of the treatment are used to optimise the treatment that day.
Internal radiotherapy (brachytherapy, for example) is provided using a source of radiation inside the body. In brachytherapy, radioactive pellets, wires or other radiation sources are carefully inserted into the treatment area and may be left there or withdrawn after a set time period.
Internal radiation can also be achieved by giving radiation sources in liquid, injectable forms (for example, in the treatment of thyroid cancer). In this case, the radioactive material accumulates in the tumour, depositing its energy and radiation in affected areas only.