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External beam radiation therapy
External beam radiation therapy is also called external radiation therapy or teletherapy. A machine directs a beam of radiation through the skin to the tumour and a small amount of normal surrounding tissue. This approach can treat larger areas of the body or more than one area, such as the tumour and nearby lymph nodes. Most people who have radiation therapy for cancer receive external beam radiation.
External beam radiation therapy:
- doesn’t hurt
- doesn’t make the person radioactive
- can’t be seen, felt or smelled
Each treatment session can last 15–30 minutes because it takes times to properly position the person and set up the equipment. It usually only takes a few minutes to give the dose of radiation. Total body irradiation (TBI) sessions can last up to 30 minutes.
External beam radiation therapy is given with machines that direct beams of high-energy rays or particles, including:
- x-rays and gamma rays
- electron, proton and neutron particles
When radiation is one of the main cancer treatments, it is usually given once a day, 5 days a week, for about 3–8 weeks, with a rest on the weekend. Giving treatments over several days, rather than a single treatment, allows normal cells to recover and repair themselves.
Occasionally, treatments are given more than once a day or every other day. This depends on:
- the type of cancer
- the person’s overall health
- the total dose
- the fractionation schedule
- whether other types of treatment are given at the same time
When radiation therapy is given to relieve symptoms caused by advanced cancer (palliative radiation therapy), the course of treatment is shorter, such as a few days or weeks.
The radiation oncologist (a doctor who specializes in treating cancers using radiation therapy) decides on the total dose of radiation that will be given to kill cancer cells and spare normal cells as much as possible. This dose is divided into a number of smaller doses called fractions. Fractionation schedules can vary.
- standard (conventional) fractionation
- The most common schedule for external beam radiation divides the total dose of radiation into several smaller doses or fractions. Treatments are usually given once a day, 5 days a week, and may last for several (about 3–8) weeks.
- With hyperfractionated radiation, the daily dose of radiation is given over 2 or more sessions each day. The total period of time to complete the treatment schedule is not changed. By using multiple smaller doses of radiation, a higher overall dose can be given.
- accelerated fractionation
- With accelerated radiation therapy, the total dose of radiation is given over a shorter period of time by giving the same dose of radiation more than once a day. Accelerated fractionation does not change the total radiation dose.
- With hypofractionated radiation therapy, fewer radiation treatments are given. This is done by giving either a short course of daily treatments or by giving fewer large doses (sometimes just a single treatment).
- For some tumours, radiation may be given to a small area after the regular radiation treatment is finished. This radiation boost may be given externally or internally. It is used to reduce the risk of recurrence in a certain area. Radiation boosts can also be used to treat the tumour or area around the tumour with a higher dose than nearby normal tissues would tolerate.
Linear accelerators (LINACs) or cobalt-60 machines are used to deliver external beam radiation. Different models of linear accelerators produce varying amounts or voltages of energy. The kind of machine used depends on the location, depth, type and extent of the tumour being treated.
- Orthovoltage machines produce lower energy beams that do not go very deeply into the skin. They are used to treat surface tumours like skin cancers.
- Megavoltage machines produce higher energy beams that go more deeply into the body. They are used to treat deeper, internal tumours.
Other types of external beam radiation therapy include:
A simulation is a planning session that takes place at a cancer treatment centre before the first radiation treatment. It is done to decide the dose of radiation and plan the treatment sessions precisely. The healthcare team makes sure the radiation is aimed at exactly the same area each time treatment is given.
Simulation is usually done in one session and takes anywhere from 15 minutes to an hour or more.
Receiving radiation therapy can be a frightening experience if children don’t know what is happening to them. Because they are frightened, children may not want to or can’t cooperate during the treatment process. Helping children understand what is happening and preparing them for treatment will reduce their fears and will allow them to work with the radiation therapy team.
Before treatment begins
Children and parents are usually given a tour of the radiation department and treatment room so they can see what the machines look like. Children are often less fearful of a big machine if they see it with their parents first and understand how it works before being treated.
All radiation therapy centres in Canada now have access to a special educational interactive DVD. Children and their families can explore this DVD on their home computer to learn more about what is involved in receiving radiation therapy. (This DVD was developed by Princess Margaret Hospital and Sick Kids Hospital in Toronto, ON.)
During treatment sessions
Children who are awake and don’t need a sedative might become bored during the treatment.
- Some centres will allow them to play a favourite music CD during the treatment session.
- Some centres encourage children to imagine a favourite place or think about planning a special event to help them pass the time during the treatment session.
The machines used for external beam radiation therapy are quite large. They may make strange buzzing noises as they work. The machines may also move around to deliver the radiation from different angles.
- The machine might frighten a child who is awake during the treatment, so it is important to explain what is happening to make sure the child understands the noises.
- Sometimes a play therapist or child-life educator is available to help children use imagination techniques to lessen their anxiety.
Sedatives for children
A light sedative (anesthetic) is usually given to children under 4 years of age to help them lie perfectly still during the radiation treatment session. Children between 4 and 6 years of age may need a sedative, depending on their ability to understand why they have to lie still, their level of activity and their level of anxiety. In some cases, children in this age group may need sedation at the beginning, but over the course of the treatment they may gradually learn ways to hold still without sedation. Children over 7 years old usually do not need sedation.
- Sedation is usually given through a mask or an intravenous line, if the child has one. An anesthetist (a doctor who is specially trained to give the sedation) will give the sedation.
- During the treatment, the anesthetist will be just outside the treatment room, using monitors to check the child’s heartbeat and breathing.
- Depending on the treatment centre’s policy, parents may be allowed to be with their child while the sedation is given, but they will have to leave the treatment room when the radiation therapy is given.
- After the radiation therapy is given, the anesthetist or another member of the radiation therapy team will be close by until the child is fully awake and has recovered from the sedation. The entire procedure usually takes no more than 90 minutes.
- If sedation is needed, children cannot eat or drink anything for a period of time before the session. Children can eat and drink again as soon as they wake up from the sedative and can swallow.
- When children receive radiation twice a day, a nutritionist will monitor their nutrition. These children have their treatments early in the morning and afternoon so they can eat and drink later in the day.
- Sedation does not usually cause any side effects except for occasional nausea and vomiting. The anesthetist will prescribe an antinausea drug if these become a problem.
- Sometimes during the course of radiation therapy, a child will develop resistance to the sedative. This means that the sedation no longer puts the child to sleep. If this happens, the anesthetist will increase the dose of the drug or use a different drug. Every effort is made to let the parents know about changes to the sedative.
- Once the treatment is over, the radiation therapist turns the machine off and removes any immobilization devices. The healthcare team monitors children as they recover from the sedation and decide when they can go home. Children who did not need sedation during the treatment session can go home right after treatment.
External beam radiation therapy is given in the radiation therapy department of a cancer treatment centre, usually on an outpatient basis. Having external beam radiation therapy is similar to having an x-ray. Before external beam radiation treatment, the person may need to change into a hospital gown. They also need to remove anything metal, such as jewellery, zippers or diaper pins, in the treatment area (treatment field). Anything with tight elastic, such as socks or diapers, should be loosened or removed.
During the treatment session:
- The radiation therapist positions the person on the treatment table based on the simulation.
- Marks or tattoos made on the skin or alignment lasers help locate the treatment area.
- Immobilization devices, forms, foam wedges or rolls may be used to ensure the person is in the proper position and lies still during the treatment.
- Special shielding blocks may be placed between the radiation machine and certain parts of the body to help protect healthy tissue and organs.
- Once the person is positioned and the equipment is set up properly, the radiation therapist leaves the treatment room.
- Parents are not allowed in the treatment room when children have treatment because they would be exposed to radiation. Depending on the treatment centre’s policy, parents may be allowed to watch their child through a window into the treatment room. Parents may be asked to wait in the waiting room until the treatment is complete.
- The radiation therapist controls and turns on the machine from the next room. The therapist can watch the person through a window or a monitor. They can communicate through an intercom.
The radiation oncologist monitors the person’s progress throughout the course of treatment and adjusts the dose or length of treatment as necessary. The radiation therapy team often take special x-rays (port films) during treatment. They review these x-rays to ensure the treatment beam stays on target. Sometimes blood tests, x-rays or other tests are done during the course of treatment to see how the tumour is responding to treatment.
Occasionally, radiation therapy treatments may need to be stopped temporarily if side effects are severe. Missed treatments can be made up later.
External beam radiation doesn’t make a person radioactive. It is safe to be around other people, including children, right after treatment.
Some people can work and continue to do their regular leisure activities while receiving radiation therapy. Others find they tire easily and need to rest more.
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