Radiation therapy, or radiotherapy, is sometimes used to
treat cancers. This treatment involves giving the patient gamma rays or x-rays
to specific body parts to change the body tissues.
Treatment Goal
The goal of radiation therapy in the case of cancers
is to destroy the cancer tissue under treatment. In order to do this a specific
dose is given to the target tissue while a small dose is given to normal
tissue.
Administration of the Treatment
The radiation therapy is given to the patient in the
form of gamma rays or x-rays. The radiation oncologist establishes the
treatment dose. Equipment used to generate this form of therapy falls under two
main types. The most common is a linear accelerator, a machine that delivers
high volt x-rays, the other is a Cobalt 60 machine. Linear accelerators make it
possible to decrease or avoid skin reactions from radiotherapy. They also make
the treatments more focused so that there is less "scatter" of
radiation to nearby normal tissues. Electron beam therapy can also be used.
This radiation penetrates only into the skin and is very useful in the
treatment of cutaneous (skin) lymphomas.
The dose used depends on the disease and the reason
for the treatment. The total dose is delivered to the patient during a series
of visits, usually spread over several weeks. This approach is called
"fractionation of the dose" and is used because it minimizes side
effects. The planned fractional dose is delivered each day to the area
specified by the radiation oncologist.
A radiation oncologist is a physician who is trained
to administer radiation treatments and evaluate patients who may need radiation
treatment. The radiation oncologist also determines if a specific tumor will
respond to radiation treatments and the number of treatments that will be
required.
Preparation for Treatment
Prior to the start of treatment, patients are
prepared for the treatment by "simulation". The purpose of the
simulation procedure is to set up the best location for the treatment and
establish a position that will be used in each treatment. The simulation takes
place in equipment that is very similar to the actual treatment equipment. The
patient is positioned in a manner that will be repeated during each treatment
session. In this way the time consuming process of positioning the patient is
done once and only needs to be repeated for each treatment. The position used
is important since the patient must be comfortable and feel supported during
treatment. Sometimes, a device may be used to make it possible to repeat the
position.
During simulation the radiation oncologist and the
radiation treatment staff measure the body parts and may mark the skin with
indelible marks so that the treatment is aimed at the same body part each day.
These marks are referred to as a tattoo and do not wash off in the shower for
the treatment period, but can be removed later.
Radiation Treatment Session
Radiation has the ability to effect tissues and cells
by injuring the DNA in the cell nucleus. The effect of radiation, which does
not make the body radioactive, is to either destroy the cell or alter its
metabolism and hinder its ability to function normally. The cancer cells, which
usually copy themselves in rapid succession, either stop growing or die more
rapidly, after exposure to radiation. This process results in a decrease in the
size of the tumor or elimination of the cancer cells.
The treatment is not painful and most patients feel
nothing, although they may hear sounds of the equipment turning on and off. The
portions of the equipment that are visible to the patient are usually not the
parts that generate the x-rays. The radiation oncologist determines the
position for the treatment. Patients who receive whole body exposure may expect
either to stand in a special apparatus or to be positioned lying down (either
on the back or the abdomen). Protective shields are often used to cover the
parts of the body that may not need treatment.
Patients may be in the treatment area for 20 to 30
minutes although the actual treatment may only take a minute or two. Sometimes
the treatments are done on an outpatient basis and sometimes as an inpatient.
During the treatment, the staff leaves the room and stands behind a shield so
that they are not repeatedly exposed to radiation. They are within hearing
distance and can maintain visual contact through a window or by using a
closed-circuit television camera. Patients can talk to the staff during the
treatment and report any discomfort or special needs.
Treatment Schedules
Treatments are usually scheduled Monday through
Friday with a two day break on the weekend. This schedule continues for the
entire treatment period and could last from two to six weeks. Schedules for
treatment are based on prior clinical trials that tested dosage and treatment
intervals. Patients are usually asked to remain on schedule and report any
discomfort to the radiation oncologist so that decisions about schedule or
treatment change are planned rather than spontaneous.
Immediate or Very Early Side Effects
Many patients anticipate side effects during the
treatments and are surprised when there are very few. For others there can be
side effects, but this depends on the dose, location, and duration of the
radiation. Most of the side effects experienced by patients gradually go away
after treatments are finished. Side effects that may be noted are increased
fatigue, hair loss on the body part being treated, diarrhea
if the abdomen is treated. Nausea, loss of appetite, skin irritation, and a
sore mouth (mucositis) are also sometimes
experienced. These side effects are usually a result of the radiation on tissue
that contains rapidly dividing cells. This would include the hair follicles and
the gastrointestinal tract lining. The cells also recover and so, some of the
effects go away. If the radiation treatments are used prior to stem cell
transplant (total body radiation) then more profound side effects may be
expected. The therapist should inform patients about the course and effects of
their particular treatments.
Long-Term Effects of Radiation Therapy
Some effects of radiation may not occur for months or
years after treatment. These effects depend on the age of the patient and the
dose and location of treatment. One long-term effect is the possible development
of a secondary malignancy following the use of radiation. The physician usually
addresses the chances of such a long-term effect during discussions before
treatment.
Radiation in Combination
Some diseases, such as Hodgkin's lymphoma, may be
treated with combination therapy. This means a combination of chemotherapy and
radiation therapy is used. For patients who receive this approach to treatment,
chemotherapy may be administered in a cycle before the radiation therapy
starts. The treatment approach is discussed with the patient prior to the start
of treatment.
Revision Date 2/01
References:
Leibel SA, Phillips TL. Textbook of
Radiation Oncology.
Radiation Therapy and You: A Guide to Self-Help During Cancer Treatment. National Cancer Institute.