of radiation therapy
therapy uses controlled high-energy rays to treat tumors and other diseases
of the body. Radiation works by damaging the DNA inside cells making
them unable to divide and reproduce. Abnormal cancer cells are more
sensitive to radiation because they divide more quickly than normal
cells. Over time, the abnormal cells die and the tumor shrinks. Normal
cells can also be damaged by radiation, but they can repair themselves
more effectively, as when your skin heals itself after sunburn (a mild
form of radiation exposure).
of radiation therapy is to maximize the dose to abnormal cells while
minimizing exposure to normal cells. The effects of radiation are not
immediate; the treatment benefit occurs over time. Typically, more aggressive
tumors, whose cells divide rapidly, respond more quickly to radiation.
Radiation therapy is painless and will not make you radioactive.
is often given with the intent of destroying the tumor and curing the
disease (curative treatment). However, not all disease or cancer can
be cured with radiation. Sometimes radiation is used to relieve symptoms,
such as pain or seizures (palliative treatment). Sometimes it is used
to prevent tumors from developing or spreading (prophylactic treatment).
Radiation may be used alone or in combination with other treatments
such as surgery, chemotherapy or immunotherapy. If used before surgery,
radiation will shrink the tumor to make it easier to remove. If used
after surgery, radiation will destroy tumor cells that may have been
two ways to deliver radiation:
beam radiation is delivered from outside the body by using a machine
to aim high-energy rays (x-rays, gamma rays or photons) at the tumor.
radiation (brachytherapy) is delivered from inside the body by
surgically placing radioactive material, sealed in catheters or seeds,
directly into the tumor.
of radiation therapy follow these general principles:
locate the target
the target still
aim the radiation beam
the radiation beam to the target
a radiation dose that damages abnormal cells yet spares normal cells
locate the target
Any tumor, lesion or malformation to be treated with radiation is called
a target. When locating a target, the doctor needs to know several things:
its location in the body, its size and shape, and how close it is to
important organs and structures. Small targets are harder to locate
than large ones. Diagnostic scans such as computerized tomography (CT)
and magnetic resonance imaging (MRI) have greatly improved over the
years, allowing doctors to locate tumors and diseases earlier, when
they are smaller. Also, positron emission tomography (PET) and functional
MRI (fMRI) scans provide information about the function of critical
areas next to the target.
the exact location and border of a target within normal tissue is not
always clear on diagnostic scans. Doctors can use a technique called
stereotaxis to precisely locate targets, especially small deep ones.
Stereotactic means to locate a structure by use of three dimensional
coordinates (x, y, and z axis). First, a stereotactic head or body frame
is attached over the target area. Next, a CT or MRI scan is taken and
interpreted by computer software. The stereotactic frame shows up on
the scan and helps the doctor pinpoint the exact location of the target
(Fig. 1). In some cases, stereotactic localization is performed using
internal landmarks, such as bones, and a frame is not necessary.
1. The stereotactic frame serves as a reference on the MRI
scan allowing the computer to plot the exact coordinates (x,
y and z axis) and create a 3D reconstruction of the tumor or
the target still
Once the target is located, the doctor must hold the body as still as
possible to accurately aim the radiation only at the target and to avoid
healthy tissue. This is especially difficult in areas that are normally
moving, such as the lungs and abdominal organs. Immobilization also
is important for smaller targets, because a slight shift in position
can move the target out of the radiation beams path. Immobilization
devices are used to prevent movement and secure the body area to the
treatment table. These devices include molds, masks and stereotactic
head or body frames (Fig. 2). Molds and masks are custom-made from plastic
to fit your body exactly and are used during each treatment.
2. Immobilization devices such as masks (left) or stereotactic
head frames (right) attach to the treatment table to hold the head
aim the radiation
Multiple radiation beams are aimed so that they all meet at a central
point within the target, where they add up to a very high dose of radiation.
In order to accurately aim radiation, both you and the machine must
be correctly aligned with each other.
alignment. Depending on the body area to be treated, different techniques
may be used to position your body, including: skin markers, laser lights,
field lights, infrared cameras and x-ray positioners. Laser lights are
used to make sure you are level and straight on the table. Field lights
correspond to the skin marks. Infrared cameras use body markers to detect
your position and match the markers to the position in the treatment
plan. X-ray positioners take stereoscopic x-rays of your anatomy and
match them to the position in the treatment plan images (Fig. 3).
3. Using skin markers, infrared cameras and x-ray images,
the patients anatomy is matched to the position in the treatment
planning software to verify correct positioning.
alignment. Several types of machines used to create a radiation beam and aim it
at the target. Each machine offers a different level of accuracy and
ability to deliver various radiation techniques to treat the target.
4. A linear accelerator aims a single radiation beam by traveling
in an arc around the tumor. Multiple arcs are delivered by rotating
the patient table and the gantry. Common LINAC systems include LEXAR
or X-knife (Radionics), Novalis (BrainLAB), Peacock (NOMOS), Clinac
(Varian), Precise (Elekta), and CyberKnife (Accuray).
Accelerator (LINAC), the most common type of radiation machine, uses
electricity to form a stream of fast-moving subatomic particles (Fig.
4). The radiation beam produced by a LINAC can be shaped and aimed at
the target from a variety of directions by rotating the machine and
moving the treatment table. The advantage of LINAC-based systems is
their versatility. They:
used for both radiotherapy and radiosurgery treatments
any area of the body
large and small tumors
highly focused radiation sources
high intensity radiation
use techniques such as Intensity Modulated Radiotherapy (IMRT)
Knife system uses 201 converging beams of gamma radiation (cobalt-60).
All 201 beams meet at a central point within the target, where they
add up to a very high dose of radiation. In contrast to LINAC, the Gamma
Knife does not move around you. Rather, you are placed in a helmet unit
that allows the target to be placed exactly in the center of the converging
beams. The features of Gamma Knife systems include:
for radiosurgery only
to treating head and neck lesions
the radiation beam
It is crucial that the radiation dose is delivered only to the target.
Shaping the beam to match the target minimizes exposure to normal tissue.
The problem is that most tumors are irregularly shaped and most radiation
beams are round. Beams can be shaped using treatment planning software
planning software. High-end computers and software are used to plan
the treatment so that all beams meet at a central point within the target,
where they add up to a very high dose of radiation. The software uses
your CT or MRI images to form a 3D view of your anatomy and the target
(Fig. 5). The radiation oncologist uses different settings in the software
to create a final radiation prescription specifically for you. The prescription
radiation dose of each beam (measured in rads or Gy)
size and shape of the beams
and angle of treatment arcs
of treatment sessions
Radiation beams can be shaped by attaching blocks or collimators to
the radiation machine to block a portion of the beam (similar to placing
your finger in the path of a flashlight to cast a shadow). The goal
is to shape the beam to the exact contour of the tumor and minimize
exposure to normal tissue. Block devices shape the beam in a linear
fashion and are only able to squarely shape the beam (Fig. 6). Collimator
devices are able to shape the beam into circular or elliptical shapes
(Fig. 7). Multileaf collimators can focus and shape the beam in infinite
ways and are the most precise method at this time (Fig. 8).
6. Conventional radiotherapy delivers a radiation beam along
a single treatment arc. It uses blocks to shape the radiation
beam in a square-edged fashion.
7. 3D conformal radiotherapy delivers radiation beams in multiple
arcs at various angles. It uses collimators to shape each radiation
beam in an elliptical-shaped fashion to conform the dose to the
8. Intensity modulated radiotherapy (IMRT) delivers radiation
beams in multiple arcs, similar to 3D conformal. It uses sophisticated
inverse planning software and multileaf collimators to both shape
the radiation beam and change the intensity within each beam to
deliver the optimum dose.
an optimal dose
Radiation works best when given in high rather than low doses; however,
normal cells that border the target cannot repair themselves very well
after a high-dose exposure. Determining the best radiation dose is a
balance between the maximum dose tolerated by normal cells versus the
minimum dose necessary to cause tumor cell death. Doctors can take advantage
of the bodys own healing process by delivering a fraction of the
complete dose over multiple sessions. In this method, called fractionated
radiotherapy, normal cells are allowed time to repair between each radiation
session and are protected from permanent injury or death. The fewer
the treatment fractions, the more the radiation affects tumor and normal
tissue equally. The greater the number of treatment fractions, the less
the risk of injury to normal cells and the fewer the side effects. During
fractionated radiotherapy, patients receive treatment daily for 3 to
of Radiation Therapy
many forms of radiation therapy, all of which use the general principles
discussed previously. Each patients treatment is individualized.
Radiation may be used alone or in combination with other therapies such
as surgery, chemotherapy and immunotherapy. Two patients - even if they
have the same kind of cancer - may not receive the same kind of radiation
Radiosurgery (SRS) delivers a high dose of radiation during a
single session. Because a single radiosurgery dose is more damaging
than multiple fractionated doses, the target area must be precisely
located and completely immobilized with a stereotactic head or body
frame. Although it is called surgery, no incision is made. Patients
spend most of the day at the center while the tumor is precisely located,
a treatment plan is developed, and a radiation dose is delivered.
For details, see:
Stereotactic Radiotherapy (FSR) delivers radiation over many visits
and uses stereotaxis to precisely locate the target and accurately
reposition the patient for each treatment session. Until recently,
fractionation was not possible using stereotaxis because there was
no way to keep the rigid frame in place after the first treatment
session. Repositionable masks and molds along with x-ray and infrared
positioners ensure treatment accuracy, making multiple radiosurgery
sessions possible. FSR offers the precision of stereotaxy for those
with lesions near critical structures that cannot tolerate high doses.
Patients return daily over several weeks to receive the complete radiation
Radiotherapy delivers fractionated radiation doses over many visits.
The target area usually includes a margin of normal tissue. Patients
have an initial consultation and simulation in which a treatment plan
is developed, and will return daily over several weeks to receive
the complete radiation dose. In whole brain radiotherapy (WBRT), the
radiation dose is delivered to the entire brain and is often used
to treat multiple brain tumors.
Stereotactic Radiotherapy (FSR)
standard diagnostic scans
a rigid stereotactic head or body frame
a repositionable stereotactic mask or body mold
use a mask or body mold
aim radiation beam
Uses laser, infrared and x-ray body tracking
precise, Uses laser, infrared and x-ray body tracking
target area that includes normal brain margin
or 3D conformal
or 3D conformal
or 3D conformal
high dose delivered during one treatment session
fractions of the complete high dose delivered over
multiple treatment sessions
fractions of the complete dose delivered over multiple
Brachytherapy delivers a high dose of radiation from within the tumor
through the surgical implantation of radioactive material into the tumor.
The radioactive material is sealed in catheters, seeds or capsules.
For some procedures, the patient stays in the hospital for several days
while the radioactive seeds deliver their dose to the tumor. The seeds
are then removed and the patient can go home. In other instances, the
radioactive implant stays in permanently, and the patient may go home
soon after the procedure is completed.
Immunotherapy activates your own immune system (T-cells and antibodies) to destroy
cancer cells. Researchers are also exploring ways to prevent or treat
cancer through vaccines. This research is still in an experimental stage.
therapy uses viruses or other vectors to introduce new genetic material
into tumor cells. This can cause them to die, or make them more susceptible
to other cancer therapies. Gene therapy is currently experimental.
oxygen uses oxygen at higher than normal levels to promote wound
healing and help fight infection. It may also improve the tumors
responsiveness to radiation, which is being studied experimentally.
Currently it is being used to help the body naturally remove dead tumor
cells and treat radiation necrosis.
Radiosensitizers are drugs used before or during radiation therapy to make tumor cells
more sensitive to radiation therapy. Once taken into the body, the drug
concentrates in the abnormal tumor cells. 5-flourouracil, topotecan
and tirapazamine are some radiosensitizers.
Radioprotectors are drugs used to protect normal cells from the effects of radiation
therapy in select cases.
I a candidate?
that you have a tumor, cancer or other disease raises many concerns
and questions. Learning as much as possible about your condition and
available treatment options is critical in selecting the best course
of treatment, as well as providing peace of mind for you and your family.
How well a particular tumor will respond to radiation treatment depends
on its cell type, grade and stage.
type. Different types of cells respond differently to radiation. The
cell type also refers to whether the tumor is benign (non-cancerous)
or malignant (cancerous).
Grade refers to the aggressive-ness of the tumor cell type (how fast
it will grow on a scale of 1 to 4).
Stage refers to the extent of tumor spread. Tumors can remain in one
area (localized) or can spread to nearby organs (metastasized).
are the most common indication, many other conditions respond to radiation
treatment. Ask your doctor if radiation therapy can help provide a better
quality of life and longer survival for you..
performs radiation therapy?
oncologists are doctors with special training in treating cancer and
other diseases with radiation. Their role is to evaluate the patient
and determine the treatment plan, also called the prescription. The
radiation oncologist works with a team that includes a surgeon, medical
physicist, dosimetrist, radiation therapist and oncology nurse. The
surgeon and radiation oncologist decide what techniques to use to deliver
the prescribed dose. The physicist and the dosimetrist then make detailed
treatment calculations and set up the equipment. The radiation therapists
are specially trained technologists who deliver the daily treatments.
teama pathologist, surgeon, internist, chemotherapist and radiation
oncologistconsults and determines the best treatment for you.
Sometimes you may want to speak to another doctor to get a second opinion.
This is common practice and is sometimes required by your insurance.
However, you should ask whether it is safe to delay treatment while
you get a second opinion.
are the side effects?
vary depending on the tumor type, total radiation dose, size of the
fractions, length of therapy, and amount of healthy tissue in the target
area. Some side effects are temporary and some are permanent. Ask your
doctor about specific side effects you may experience. General side
effects may include:
Fatigue. Fatigue, or tiredness, is the most common side effect-. Make sure
you get plenty of sleep, take a nap after treatment, and eat a balanced
diet during treatment. Fatigue can continue for weeks or months after
treatment stops. Some may notice a lack of appetite and a loss of taste.
Nausea and diarrhea may occur; medications can provide relief.
irritation. The skin in the area where the radiation beams pass
through may occasionally become reddened and dry. This will resolve
after treatment stops.
Loss. You may experience hair loss in the treated area about 2 weeks
after treatment begins. This is often temporary; your hair will grow
back after treatment stops.
Radiation causes cells to lose their ability to regulate fluids, and
swelling may occur. This does not always happen. If swelling occurs,
it can cause headaches, seizures and confusion. Steroid medication may
be given to reduce the fluid within the tumor cavity.
On rare occasions, the radiation dose can cause the tumor tissue to
become necrotic several weeks to months after treatment. Dead or necrotic
tissue can become toxic to surrounding normal tissue, and swelling may
occur. Treatment for radiation necrosis may include steroid medication,
hyperbaric oxygen treatments or surgical removal.
trials are research studies in which new treatments - drugs, diagnostics,
procedures, vaccines and other therapies - are tested in people to see
if they are safe and effective. Research is always being conducted to
improve the standard of medical care and explore new drug and surgical
treatments. You can find information about current clinical investigations,
including their eligibility requirements, protocol, and participating
locations on the web: the National Institutes of Health (NIH) at clinicaltrials.gov,
sponsors many trials; private industry and pharmaceutical companies
also sponsor trials, see www.centerwatch.com
have more questions, please contact Precision Radiotherapy at 513-475-7777.
National Cancer Institute www.cancer.gov
Radiosurgery Association www.irsa.org
Brain Tumor Association www.abta.org
malformation (AVM): a congenital disorder in which there is an abnormal
connection between arteries and veins without an intervening capillary
benign: not cancerous.
brachytherapy: a type of radiation therapy where capsules containing
radioactive substances are surgically implanted into the tumor to deliver
radiation; also called internal radiotherapy.
cancer: generic term for more than 100 different diseases caused
by uncontrolled, abnormal growth of cells. Cancer cells can invade and
destroy normal tissue, and can travel through the bloodstream and lymphatic
system to reach other parts of the body.
chemotherapy: treatment with toxic chemicals (e.g., anticancer
fractionated: delivering the radiation dose over multiple sessions.
immunotherapy: treatment designed to improve or restore the immune
systems ability to fight infection and disease.
lesion: a general term that refers to any change in tissue, such
as tumor, blood, malformation, infection or scar tissue.
linear accelerator (LINAC): a machine that creates a high-energy
radiation beam, using electricity to form a stream of fast-moving subatomic
metastatic: cancerous tumor that has spread from its original
source through the blood or lymph systems.
radiation: high-energy rays or particle streams used to treat
stereotactic: a precise method for locating deep brain structures
by the use of 3-dimensional coordinates.
target: area where the radiation beams are aimed; usually a tumor,
malformation, or other abnormality of the body.
tumor: an abnormal growth of tissue resulting from uncontrolled
multiplication of cells and serving no physiological function. A tumor
can be benign or malignant.