What is Radiation?
Radiation describes the way energy moves from one place
to another. Sometimes this is in the form of particles such as protons, while
other times it is in the form of waves like x-rays or visible light. The
various types of radiation are grouped according to how much energy they
contain. Low energy radiation, like radio waves and heat, is known as
non-ionizing radiation. High energy radiation, such as ultraviolet (UV) light from
the sun and x-rays, is known as ionizing radiation because it has enough energy
to break chemical bonds and knock electrons (negatively charged particles) out
of atoms. When these changes take place in cells, it can sometimes cause enough
damage to kill the cells. As a result, such high-energy x-rays or other
particles can be used to destroy cancer cells in a treatment called radiation
therapy.
What is Radiation
Therapy?
Radiation therapy is the use of high-energy x-rays or other
particles to destroy cancer cells. A doctor who specializes in giving radiation
therapy to treat cancer is called a radiation oncologist. The most common type
of radiation treatment is called external-beam radiation therapy, which is
radiation given from a machine outside the body. A radiation therapy regimen
(schedule) usually consists of a specific number of treatments given over a set
period of time.
When it is Prescribed?
Radiation therapy may be given for pancreatic cancer in
the following situations:
* After surgery for patients who have a high risk of
their cancer coming back in the area of surgery. This includes patients with a
tumor that is large or was removed with close or positive surgical margins,
meaning that cancer cells are seen up to or very close to the edge of the
tissue removed during surgery.
* Before surgery to try to shrink a borderline resectable
tumor.
* For patients with locally advanced, unresectable
disease.
* To relieve severe pain for people with metastatic
cancer.
What are the
different types of radiation therapy?
There are two main types of radiation therapy, external
beam radiation therapy and internal radiation therapy.
External beam radiation therapy
delivers radiation by using a machine outside the body which directs a beam or
multiple beams of radiation through the skin to the tumor or tumor bed. External beam radiation therapy is commonly
used in treating pancreatic cancer patients.
Internal radiation therapy (brachytherapy)
delivers radiation through radioactive material implanted in or near the
cancer. This type of radiation therapy
is rarely used in pancreatic cancer patients.
In addition to standard external beam radiation therapy,
the following two methods of planning and delivering external beam radiation
are currently used in pancreatic cancer treatment. These specialized methods are able to
minimize the amount of radiation delivered to normal tissues and are used when
a higher dose of radiation is recommended:
Intensity-modulated radiation therapy (IMRT)
is a type of external beam radiation therapy that delivers focused radiation to
the tumor by modulating (varying) the intensity of the radiation beam under
precise computer control. By using
three-dimensional computer imaging to determine the size, shape and location of
the tumor, and by varying the intensity of the radiation dose, IMRT allows a
higher dose of radiation to be administered to the tumor while minimizing the
amount of radiation delivered to healthy tissue near the pancreas, such as the
duodenum (the first portion of the small intestine). This may lead to fewer side effects and allow
higher doses of radiation to be delivered safely, compared to standard
radiation therapy.
Stereotactic body radiation therapy (SBRT)
is a type of external beam radiation therapy designed to deliver high doses of
radiation precisely to small tumors, usually in five or fewer treatments. SBRT uses multiple narrow radiation beams to
target small, well-defined areas. In
order for SBRT to be delivered safely in pancreatic cancer patients, the tumor
must remain motionless or the machine delivering the radiation must be able to
adjust for any movement of the tumor, such as during breathing. Patients may be fitted with a customized
device to keep the body perfectly still or the treatment machine may have the
ability to limit, monitor and adjust for any movement during the treatment. Also, small metallic seeds may be implanted
near the tumor before treatment begins to better track the location of the
tumor during treatment. CyberKnife is
one type of SBRT. Some studies have
suggested that the delivery of high doses of radiation in a few treatments is
difficult to accomplish without damaging the intestinal tract.
There is currently no evidence that this type of
radiation therapy is better than standard radiation therapy for pancreatic
cancer. In fact, one study has shown
that stereotactic radiation for pancreatic cancer caused ulcers to develop in
the duodenum. There are ongoing studies
to determine the appropriate radiation dose and frequency of radiation doses
given using SBRT to avoid damaging the duodenum. Therefore, SBRT is still being studied in
clinical trials for pancreatic cancer and its usage is only recommended as part
of a clinical trial.
Proton beam radiation therapy is a
type of external beam radiation therapy that uses proton beams rather than
x-rays. Protons are charged particles
that deposit most of their energy at a very narrow area within the body. Because of this characteristic, proton beam
therapy allows a higher, more conformed dose of radiation to be delivered to
the tumor, while sparing surrounding healthy tissue. Therefore, it generally
causes fewer side effects. Proton
therapy is only available at very few centers throughout the country and is
being studied in clinical trials for pancreatic cancer.
Chemotherapy Given
with Radiation Therapy
Often, chemotherapy will be given at the same time as
radiation therapy because it can enhance the effects of the radiation therapy,
which is called radio-sensitization. Combining chemotherapy and radiation
therapy may occasionally help shrink the tumor enough so it can be removed by surgery.
However, chemotherapy given at the same time as radiation therapy often has to
be given at lower doses than when given alone.
It is important to note that radiation may be helpful for
decreasing the likelihood of a pancreatic cancer returning or re-growing at the
original location, but that there remains much uncertainty as to how much, if
at all, it lengthens a person’s life.
The chemotherapy drugs most commonly used with radiation
therapy are fluorouracil (5-FU), capecitabine (Xeloda®) and gemcitabine
(Gemzar®). 5-FU is used most often since
there is more experience using this drug in combination with radiation and
there are generally fewer side effects.
Side Effects
Some of the common side effects of radiation therapy
include:
* Skin changes (like a sunburn) in areas getting
radiation
* Nausea and vomiting
* Diarrhea
* Fatigue
* Poor appetite
* Weight loss
Radiation can also lower blood counts and can increase
the risk of serious infection.
Usually these effects go away a few weeks after the
treatment is complete. When radiation is given with chemotherapy the side
effects are often worse. Ask your doctor what side effects to expect and how to
prevent or relieve them.
Sources and Additional Information:
