Introduction
All radiotherapy treatments use radiation to kill cancer cells. There are a number of different forms of radiation and different delivery systems, each with a technical name which will be unfamiliar to people who have not come across these terms before. This section describes how radiotherapy works, the different forms of radiotherapy that you may come across and what they do. All the unfamiliar terms are explained in the glossary, and where possible also within the text.
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How Radiotherapy Works
Radiation damages all cells, including cancer cells. Radiotherapy uses radiation to kill cancer cells whilst protecting, as far as possible, normal cells from its effects.
Radiation damages the genetic material in the cell nucleus making it impossible for the cell to grow and divide, so shrinking the tumour as a whole. It can be used to treat almost all solid tumour including cancers of the breast, cervix, prostate, bowel and lung but is more effective for some cancer types than others.
Radiotherapy can be used on its own or in combination with surgery or drug treatments. These multimodality treatments are often much more successful in treating cancer than using just one form of treatment on its own. Sometimes radiotherapy is used to stop a cancer spreading to another area of the body. This form of preventative treatment is called prophylactic or adjuvant treatment.
There are two broad groups of radiotherapy treatment:
- external radiotherapy, where the radiation is generated from machines outside the body
- internal radiotherapy or brachytherapy where the radiation source is placed inside the body, either in or very close to the cancer.
External radiation machines are like X-ray machines, and send a beam of radiation into the cancer. By directing the beam from different angles the maximum effect of radiation can be targeted at the cancerous tumour with the surrounding tissues receiving much smaller doses.
In brachytherapy, radioactive pellets, wires or other radiation sources are carefully inserted into the treatment area and may be left there or more commonly withdrawn again after a set time period.
Exactly how often the treatment is given and how it is applied varies according to the treatment plan drawn up for each patient. External radiotherapy is usually given in small doses, often on a daily basis (referred to as treatment fractions), which gives normal cells a chance to recover between doses. Cancer cells do not recover in this way, so the beneficial effects build up over the course of treatment whilst the impact on normal cells is minimised. Internal radiotherapy may be given as a single treatment or as repeated treatment.
External Beam Radiotherapy
External radiotherapy uses radiation beams, generated from machines outside the body to kill cancer cells. Some normal cells will also be affected, but the treatment is planned so that the radiation is focussed on the affected areas from multiple different angles. Normal tissues receive a smaller dose, and in addition normal cells are better at repairing themselves than cancer cells.
External radiotherapy is normally given as a series of short regular treatments in a radiotherapy department (each treatment may be referred to as a fraction), which are carefully calculated by the treatment team.
All radiotherapy treatments follow the shape of the cancer, so a higher dose of radiation can be more precisely targeted at the cancer avoiding neighbouring healthy tissue and resulting in fewer side effects. Shaping of the beam is achieved using metal plates to block specific areas, so they are in effect in shadow and so not exposed to radiation (see Conformal Radiotherapy below).
External beam radiotherapy is usually given when:
- not all of the cancer can be removed during surgery or there may be tumour cells left behind after surgery
- lymph nodes removed during surgery contain some cancer cells and treatment to other lymph nodes in the same areas is required
- needed to treat other areas of the body, if the body of the tumour is likely to have spread to these areas
- given as an alternative to surgery
- needed to treat pain, pressure symptoms or an obstruction caused by the cancer
External beam radiotherapy is usually given over a four to five week period with up to 5 treatments a week, so as many as 25 treatments in total. Giving a large number of small doses reduces the damage to healthy tissues.
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Radiotherapy Machines and Techniques
Linear Accelerator
The linear accelerator (Linac) is a source of powerful x-rays, used in radiotherapy. Electrons produced in the machine are accelerated in a straight line, hitting a metal target within the machine. This produces high energy x-rays, which are then focussed into a beam that can be used for treatment.
Linear accelerators are the devices most commonly used to provide external beam radiotherapy. The beam itself comes out of a gantry, part of the machine, which rotates around the patient. The patient lies on a moveable bed and lasers are used to check that the patient is in the proper position. The linear accelerator can deliver radiotherapy from any angle by rotating the gantry and moving the treatment bed.
The linear accelerator is housed in a room with lead and concrete walls so that radiation cannot escape.
Conformal Radiotherapy
This is a way of matching the shape of the radiation beam used to treat a cancer to the shape of the cancer. Using an attachment called a multi-leaf collimator to a standard linear accelerator.
A number of metal sheets are used to block the beams from areas where there is no cancer, but allowing the radiation beams to target the area of the cancer. So high doses of radiation is given where it is needed whilst at the same time protecting healthy surrounding tissues, so side effects are reduced.
Making sure that the patient is in exactly the right position is very important so that the treatment reaches the target area. Scanning machines are used to ensure that the radiation is correctly targeted before each treatment.
Intra-operative Radiotherpay (IORT)
Intra-operative radiation therapy (IORT) provides high radiation doses to a cancer site during surgery whilst having only minimal effects on healthy tissues. During the operation, a single high dose of radiotherapy is targeted on the area at risk of residual disease. A single dose of radiotherapy during surgery is now recommended in some centres as an alternative to longer, 6-7 week courses of radiotherapy after surgery. It is used in the treatment of early stage breast cancer as well as sarcomas, neuroblastomas and head and neck cancer that has returned after initial treatment.
Intensity Modulated Radiotherapy (IMRT)
This form of radiotherapy uses a linear accelerator and a multi-leaf collimator, which can be moved as the treatment is being given. This allows the treatment to be focused very precisely and different doses of radiotherapy to be given to different parts of the treatment area. The result is less damage to the surrounding normal tissues.
Image Guided Radiotherpay (IGRT)
Image guided radiotherapy (IGRT) uses a linear accelerator and sophisticated scanning equipment to deliver higher doses of radiation to precise areas of the body. IGRT combines high-tech scanning technology with IMRT so that radiation treatment beams can be constantly adjusted during treatment to allow for movements caused by breathing, and other body movements. Consequently the treatment is always focused on the treatment area, and has minimal effect on the normal surrounding tissues, and there is a shorter treatment process for the patient.
Stereotactic Radiotherapy
Stereotactic radiotherapy is a form of external radiotherapy for treating brain tumours. Radiotherapy is given from hundreds of different angles so that high dose treatment can be delivered to the tumour whilst causing minimal harm to surrounding healthy tissue. Computerised scans locate the precise area for treatment. Generally several treatment sessions are required.
Stereotactic Radiosurgery (Gamma Knife)
The gamma knife is a type of radiotherapy for brain tumours, using beams of gamma radiotherapy from hundreds of different angles to deliver an intense dose of radiotherapy to small parts of the brain usually no more than 1-2cms across. Treatment is given in one long session. Scans are used to locate the precise treatment area.
Cyberknife
The cyberknife consists of a linear accelerator, which generates the radiotherapy beam, and a robot, capable of positioning the linear accelerator so that it can provide treatment from different angles and imaging equipment that means any change in the tumour position is detected. The robot then compensates by re-targeting the linear accelerator before administering the radiation beam. Continuously checking and correcting ensures accurate radiation targeting throughout treatment.
Chemoradiation
Chemoradiation or concurrent chemotherapy is radiotherapy (most often external beam radiotherapy) and chemotherapy given at the same time. The combined effect of the two treatments given together is frequently greater that the effect of giving the same doses of drugs and radiotherapy one after the other. The chemotherapy drugs vary according to the patient’s needs. This form of treatment is frequently used in a wide variety of cancers including head and neck, liver, lung and rectal cancer.
Internal Radiotherapy - Brachytherapy
Internal radiotherapy is provided using a source of radiation inside the body. Brachytherapy uses radioactive seeds, ribbons, or capsules placed in the body, near or in the cancer itself. High doses of radiation are therefore given where they are required without having to pass through healthy tissues first. Brachytherapy can be used to treat cancers of the head, neck, breast, uterus, cervix, prostate, gall bladder, oesophagus, and lung.
Internal radiation can also be given in liquid form, for example in the treatment of thyroid cancer and non-Hodgkin's lymphoma. This is used where cancer cells will absorb the radioactive material more than healthy cells in the body.
There are three types of brachytherapy:
- Low-dose rate (LDR) implants, where the radiation source remains in place radiation usually for a few days, and perhaps up to one week. At the end of the treatment period the radiation source in removed.
- High-dose rate (HDR) implants use a radiation source that remains in place for just 10 to 20 minutes. Treatments are repeated on a daily or twice daily basis, often for several weeks. To allow the radioactive source to be applied and removed easily an applicator may stay in place throughout this period.
- Permanent implants are radiation sources that stay in the body.
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Summary
Radiotherapy is very effective in treating many different types of cancer. Radiotherapy is now very sophisticated with different forms of radiation, delivered in different ways and combined with other forms of treatment to obtain the best results.
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