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RADIOTHERAPY
Procedure: Bodypart: Patient Group: Female Male Child
Summary
Other terms: Radiation Therapy, X-ray therapy Radiation Treatment, Cobalt
Therapy, Electron Beam Therapy, Irradiation, Radiology Oncology
Radiation therapy (or radiotherapy) is the medical use of ionizing radiation as
part of cancer treatment to control malignant cells (not to be confused with
radiology, the use of radiation in medical imaging and diagnosis). Radiotherapy
may be used for curative or adjuvant cancer treatment. It is used as palliative
treatment (where cure is not possible and the aim is for local disease control
or symptomatic relief) or as therapeutic treatment (where the therapy has
survival benefit but is not curative). Total body irradiation (TBI) is a radiotherapy
technique used to prepare the body to receive a bone marrow transplant.
Radiotherapy has a few applications in non-malignant conditions, such as
the treatment of trigeminal neuralgia, severe thyroid eye disease, pterygium,
prevention of keloid scar growth, and prevention of heterotopic bone formation.
The use of radiotherapy in non-malignant conditions is limited partly by worries
about the risk of radiation-induced cancers.
Radiotherapy is commonly used for the treatment of malignant tumors (cancer),
and may be used as the primary therapy. It is also common to combine
radiotherapy with surgery and/or chemotherapy and/or hormone therapy.
Most common cancer types can be treated with radiotherapy in some way.
The precise treatment intent (curative, adjuvant, neoadjuvant, therapeutic, or
palliative) will depend on the tumour type, location, and stage, as well as the
general health of the patient.
Patient undergoing radiation therapy on a linear
accelerator to treat Hodgkin's disease. The illuminated
discs over the patient's chest indicate the areas that
are to receive radiation. The pattern is defined by an
arrangement of lead blocks suspended below the head
of the accelerator, which shields the lungs from excess
irradiation
© eNotes Martin Dohrn, Photo (Photograph by
Researchers, Inc. Reproduced by permission.)
Radiation therapy is commonly applied to the gross tumour. The radiation fields
may also include the draining lymph nodes if they are clinically or radiologically
involved with tumour, or if there is thought to be a risk of subclinical malignant
spread. It is necessary to include a margin of normal tissue around the tumour
to allow for uncertainties in daily set-up and internal tumor motion. These
uncertainties can be caused by internal movement (for example, respiration
and bladder filling) and movement of external skin marks relative to the tumour
position.
To spare normal tissues (such as skin or organs which radiation must pass
through in order to treat the tumour), shaped radiation beams are aimed from
several angles of exposure to intersect at the tumour, providing a much larger
absorbed dose there than in the surrounding, healthy tissue.
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Technique
What it is
Radiation therapy uses high energy, penetrating waves or particles such as x rays, gamma rays, proton rays, or neutron rays
to destroy cancer cells or keep them from reproducing.
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How it works
The protein that carries the code controlling most activities in the cell is called deoxyribonucleic acid or DNA. When a cell
divides, its DNA must also double and divide. High-energy radiation kills cells by damaging their DNA, thus blocking their ability
to grow and increase in number.
One of the characteristics of cancer cells is that they grow and divide faster than normal cells. This makes them particularly
vulnerable to radiation. Radiation also damages normal cells, but because normal cells are growing more slowly, they are better
able to repair radiation damage than are cancer cells. In order to give normal cells time to heal and reduce side effects, radiation
treatments are often given in small doses over a six or seven week period.
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Equipment
The type of machines used to administer external radiation therapy and the material that provides the radiation vary depending
on the type and location of the cancer. Generally, the patient puts on a hospital gown and lies down or sits in a special chair.
Parts of the body not receiving radiation are covered with special shields that block the rays. A technician then directs a beam of
radiation to a pre-determined spot on the body where the cancer is located. The patient must stay still during the administration
of the radiation so that no other parts of the body are affected. As an extra precaution in some treatments, special molds are
made to make sure the body is in the same position for each treatment. However, the treatment itself is painless, like having
a bone x-rayed.
Purpose
The purpose of radiation therapy is to kill or damage cancer cells. Radiation therapy is a common form of cancer therapy. It is
used in more than half of all cancer cases. Radiation therapy can be used:
•# alone to kill cancer
• before surgery to shrink a tumor and make it easier to remove
#
• during surgery to kill cancer cells that may remain in surrounding tissue after the surgery (called intraoperative radiation)
#
• after surgery to kill cancer cells remaining in the body
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• to shrink an inoperable tumor in order to and reduce pain and improve quality of life
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• in combination with chemotherapy
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For some kinds of cancers such as early-stage Hodgkin's disease, non-Hodgkin's lymphoma, and certain types of prostate, or
brain cancer, radiation therapy alone may cure the disease. In other cases, radiation therapy used in conjunction with surgery,
chemotherapy, or both, increases survival rates over any of these therapies used alone.
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Target Patient Group
•# External radiation therapy
• Internal radiation therapy
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• Radioimmunotherapy
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Radiation used to treat cancer
•#PHOTON RADIATION. Early radiation therapy used x rays like those used to take pictures of bones, or gamma rays. X rays
and gamma rays are high energy rays composed of massless particles of energy (like light) called photons. The distinction
between the two is that gamma rays originate from the decay of radioacive substances (like radium and cobalt-60), while x
rays are generated by devices that excite electrons (such as cathode ray tubes and linear accelerators). These high energy
rays act on cells by disrupting the electrons of atoms within the molecules inside cells, disrupting cell functions, and most
importantly stop their ability to divide and make new cells.
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•# PARTICLE RADIATION. Particle radiation is radiation delivered by particles that have mass. Proton therapy has been
used since the early 1990s. Proton rays consist of protons, a type of positively charged atomic particle, rather than photons,
which have neither mass nor charge. Like x rays and gamma rays, proton rays disrupt cellular activity. The advantage of
using proton rays is that they can be shaped to conform to the irregular shape of the tumor more precisely than x rays and
gamma rays. They allow delivery of higher radiation doses to tumors without increasing damage to the surrounding tissue.
• Neutron therapy is another type of particle radiation. Neutron rays are very high-energy rays. They are composed of
#
neutrons, which are particles with mass but no charge. The type of damage they cause to cells is much less likely to be
repaired than that caused by x rays, gamma rays, or proton rays.
Neutron therapy can treat larger tumors than conventional radiation therapy. Conventional radiation therapy depends on
the presence of oxygen to work. The center of large tumors lack sufficient oxygen to be susceptible to damage from
conventional radiation. Neutron radiation works in the absence of oxygen, making it especially effective for the treatment
of inoperable salivary gland tumors, bone cancers, and some kinds of advanced cancers of the pancreas, bladder, lung,
prostate, and uterus.
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Procedure
Preparation
Before radiation therapy, the size and location of the patient's tumor are determined very precisely using magnetic resonance
imaging (MRI) and/or computed tomography scans (CT scans). The correct radiation dose, the number of sessions, the interval
between sessions, and the method of application are calculated by a radiation oncologist based on the tumor type, its size,
and the sensitivity of the nearby tissues.
The patient's skin is be marked with a semi-permanent ink to help the radiation technologist achieve correct positioning for each
treatment. Molds may be built to hold tissues in exactly the right place each time.
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Precautions
Radiation therapy does not make the person having the treatments radioactive. In almost all cases, the benefits of this therapy
outweigh the risks. However radiation therapy can have has serious consequences, so anyone contemplating it should be sure
understand why the treatment team believes it is the best possible treatment option for their cancer. Radiation therapy is often
not appropriate for pregnant women, because the radiation can damage the cells of the developing baby. Women who think
they might be pregnant should discuss this with their doctor.
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Process
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Radiation therapy is a local treatment. It is painless. The radiation acts only
on the part of the body that is exposed to the radiation. This is very different
from chemotherapy in which drugs circulate throughout the whole body. There
are two main types of radiation therapy. In external radiation therapy a beam
of radiation is directed from outside the body at the cancer. In internal radiation
therapy, called brachytherapy or implant therapy, where a source of radioactivity
is surgically placed inside the body near the cancer.
Linear-accelerator
© Wikipedia
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Experience
Radiotherapy is in itself painless.
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After procedure
Many patients experience skin burn, fatigue, nausea, and vomiting after radiation therapy regardless of the where radiation is
applied. After treatment, the skin around the site of the treatment may also become sore. Affected skin should be kept clean
and can be treated like sunburn, with skin lotion or vitamin A and D ointment. Patients should avoid perfume and scented skin
products and protect affected areas from the sun.
Nausea and vomiting are most likely to occur when the radiation dose is high or if the abdomen or another part of the digestive
tract is irradiated. Sometimes nausea and vomiting occur after radiation to other regions, but in these cases the symptoms
usually disappear within a few hours after treatment. Nausea and vomiting can be treated with antacids, Compazine, Tigan,
or Zofran.
Fatigue frequently starts after the second week of therapy and may continue until about two weeks after the therapy is finished.
Patients may need to limit their activities, take naps, and get extra sleep at night.
Patients should see their oncologist (cancer doctor) at least once within the first few weeks after their final radiation treatment.
They should also see an oncologist every six to twelve months for the rest of their lives so they can be checked to see if the
tumor has reappeared or spread.
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Dosage
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Once a doctor called a radiation oncologist determines the proper dose of radiation for a particular cancer, the dose is divided into
smaller doses called fractions. One fraction is usually given each day, five days a week for six to seven weeks. However, each
radiation plan is individualized depending on the type and location of the cancer and what other treatments are also being used.
The amount of radiation used in radiation therapy is measured in grays (Gy), and varies depending on the type and stage of
cancer being treated. For curative (radical) cases, the typical dose for a solid epithelial tumor ranges from 50 to 70 Gy, while
lymphoma tumors are treated with 20 to 40 Gy. Preventative (adjuvant) doses are typically around 50 - 60Gy in 2 Gy fractions
(for Breast, Head and Neck cancers respectively.) Many other factors are considered by radiation oncologists when selecting a
dose, including whether the patient is receiving chemotherapy, whether radiation therapy is being administered before or after
surgery, and the degree of success of surgery.
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Results
Normal results
The outcome of radiation treatment varies depending on the type, location, and stage of the cancer. For some cancers such
as Hodgkin's disease, about 75% of the patients are cured. Prostate cancer also responds well to radiation therapy. Radiation
to painful bony metastases is usually a dramatically effective form of pain control. Other cancers may be less sensitive to the
benefits of radiation.
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Consideration
Risks
Radiation therapy can cause anemia, nausea, vomiting, diarrhea, hair loss, skin burn, sterility, and rarely death. However, the
benefits of radiation therapy almost always exceed the risks. Patients should discuss the risks with their doctor and get a second
opinion about their treatment plan.
Radiotherapy is in itself painless. Many low-dose palliative treatments (for example, radiotherapy to bony metastases) cause
minimal or no side effects. Treatment to higher doses causes varying side effects during treatment (acute side effects), in the
months or years following treatment (long-term side effects), or after re-treatment (cumulative side effects). The nature, severity,
and longevity of side effects depends on the organs that receive the radiation, the treatment itself (type of radiation, dose,
fractionation, concurrent chemotherapy), and the patient.
Most side effects are predictable and expected. One of the aims of modern radiotherapy is to reduce side effects to a minimum,
and to help the patient to understand and to deal with those side effects which are unavoidable.
Acute side effects
•# Damage, possibly severe, to epithelial surfaces (skin, oral, pharyngeal and bowel mucosa, urothelium)
The rates of onset and of recovery depend on the rate of turnover of the epithelial cells. Typically the skin starts to become
pink and sore one week to ten days into treatment. The reaction may become more severe during the treatment and for
up to about one week following the end of radiotherapy, and the skin may break down. Although this moist desquamation
is uncomfortable, recovery is usually quick. Skin reactions tend to be worse in areas where there are natural folds in the
skin, such as underneath the female breast, behind the ear, and in the groin.
Similarly, the lining of the mouth, throat, esophagus, and bowel may be damaged by radiation. If the head and neck area is
treated, temporary soreness and ulceration commonly occur in the mouth and throat. If severe, this can affect swallowing,
and the patient may need painkillers and nutritional support. The esophagus can also get sore if it is treated directly, or if,
as commonly occurs, it receives a dose of collateral radiation during treatment of lung cancer.
The lower bowel may be treated directly with radiation (treatment of rectal or anal cancer) or be exposed by radiotherapy
to other pelvic structures (prostate, bladder, female genital tract). Typical symptoms are soreness, diarrhea, and nausea.
• Swelling (edema or Oedema)
#
As part of the general inflammation that occurs, swelling of soft tissues may cause problems during radiotherapy. This is a
concern during treatment of brain tumours and brain metastases, especially where there is pre-existing raised intracranial
pressure or where the tumour is causing near-total obstruction of a lumen (e.g., trachea or main bronchus). Surgical
intervention may be considered prior to treatment with radiation. If surgery is deemed unnecessary or inappropriate, the
patient may receive steroids during radiotherapy to reduce swelling.
•Infertility
#
The gonads (ovaries and testicles) are very sensitive to radiation. They will be unable to produce gametes following direct
exposure to most normal treatment doses of radiation.
Generalized fatigue
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Medium and long-term side effects
These depend on the tissue that received the treatment; they may be minimal.
•#Fibrosis
Tissues which have been irradiated tend to become less elastic over time due to a diffuse scarring process.
• Hair loss
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This may be most pronounced in patients who have received radiotherapy to the brain. Unlike the hair loss seen with
chemotherapy, radiation-induced hair loss is more likely to be permanent, but is also more likely to be limited to the area
treated by the radiation.
• Dryness
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The salivary glands and tear glands have a radiation tolerance of about 30 Gy in 2 Gy fractions, a dose which is exceeded
by most radical head and neck cancer treatments. Dry mouth (xerostomia) and dry eyes (xerophthalmia) can become
irritating long-term problems and severely reduce the patient's quality of life. Similarly, sweat glands in treated skin (such
as the armpit) tend to stop working, and the naturally moist vaginal mucosa is often dry following pelvic irradiation.
•Cancer
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Radiation is a potential cause of cancer, and secondary malignancies are seen in a very small minority of patients, generally
many years after they have received a course of radiation treatment. In the vast majority of cases, this risk is greatly
outweighed by the reduction in risk conferred by treating the primary cancer.
Cumulative side effects
Cumulative effects from reirradiation should not be confused with long-term effects — when short-term effects have disappeared
and long-term effects are subclinical, reirradation can still be problematic.
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Authors
Recently, trials have begun to determine if there are ways to deliver radiation fractions so that they kill more cancer cells or
have fewer side effects. Some trials use smaller doses given more often.
A newer mode of treating brain cancers with radiation therapy is known as stereotactic radiosurgery. As of the early 2000s, this
approach is limited to treating cancers of the head and neck because only these parts of the body can be held completely still
throughout the procedure. Stereotactic radiosurgery allows the doctor to deliver a single high-level dose of precisely directed
radiation to the tumor without damaging nearby healthy brain tissue. The treatment is planned with the help of three-dimensional
computer-aided analysis of CT and MRI scans. The patient's head and neck are held steady in a skeletal fixation device during
the actual treatment. Stereotactic radiosurgery can be used in addition to standard surgery to treat a recurrent brain tumor, or
in place of surgery if the tumor cannot be reached by standard surgical techniques.
Two major forms of stereotactic radiosurgery are in use as of 2003. The gamma knife is a stationary machine that is most useful
for small tumors, blood vessels, or similar targets. Because it does not move, it can deliver a small, highly localized and precise
beam of radiation. Gamma knife treatment is done all at once in a single hospital stay. The second type of radiosurgery uses a
movable linear accelerator-based machine that is preferred for larger tumors. This treatment is delivered in several small doses
given over several weeks. Radiosurgery that is performed with divided doses is known as fractionated radiosurgery. The total
dose of radiation is higher with a linear accelerator-based machine than with gamma knife treatment.
Another advance in intraoperative radiotherapy (IORT) is the introduction of mobile devices that allow the surgeon to use
radiotherapy in early-stage disease and to operate in locations where it would be difficult to transport the patient during surgery
for radiation treatment. Mobile IORT units have been used successfully as of 2003 in treating early-stage breast cancer and
rectal cancer.
Radiation sensitizers are another recent innovation in radiation therapy. Sensitizers are medications that are given to make
cancer cells easier to kill by radiation than normal calls. Gemcitabine (Gemzar) is one of the drugs most commonly used for
this purpose.
Citations
30 - "Radiation Therapy." Encyclopedia of Medicine. Ed. Jacqueline L. Longe. Thomson Gale, 2002. eNotes.com. 2006. 16
Feb, 2007 <http://health.enotes.com/medicine-encyclopedia/radiation-therapy>
31 - http://en.wikipedia.org/wiki/Radiation_therapy
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