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33. What is
radiation therapy? Is radiation therapy given for every type of brain tumor?
To kill a cancer cell,
it is necessary to interfere with its ability to grow and divide and form
more cancer cells. A form of energy called ionizing radiation creates
a high enough energy to knock the electrons in the molecules of living
cells out of their normal orbits. This creates enough energy to disrupt
other nearby electrons, which, in turn, affects the DNA of the cell.
Radiation can cause breaks in the strands of DNA, causing cell injury and
eventually, cell death. Both x-rays and gamma rays are forms of ionizing
radiation.
Radiation therapy
uses x-rays, a man-made form of ionizing radiation, to penetrate through
tissue into a tumor. A linear accelerator is one machine that
produces such radiation. The linear accelerator delivers external beam
radiation (also known as conventional radiation).
Both normal cells and
cancer cells can repair radiation cellular damage to a variable degree. By
dividing the dose of radiation into small daily doses called fractions, normal cells are relatively spared because they are better able to
repair DNA damage. Most cancer cells, however, lack the ability to
completely repair DNA damage, and over the course of several days of
treatment, the cancer cells will die. The amount of radiation energy
absorbed by the body is measured in Gray. The amount of radiation
used in cancer therapy is typically divided in hundredths of a Gray, called centiGray, abbreviated cGy. An older term sometimes used in
radiation measurement is the rad, which is equal to one cGy.
Not all brain tumors
are treated with radiation therapy, and different types of brain tumors
require different radiation fields (the volume of brain tissue to be
treated). For example, multiple small tumors throughout the brain, which
commonly occur in metastatic lung cancer, are usually treated with whole
brain radiation therapy. This therapy is also used for primary brain
tumors that have multiple tumors present at the same time, including primary
CNS lymphoma. Most primary brain tumors, which occur as a single
abnormality on MRI, are treated with radiation therapy directed at the tumor
and a margin of 2 or 3 centimeters around it. This treatment approach is
called local, or partial brain, radiation therapy. Sometimes the
central portion of the tumor is treated with a high dose of fractionated
radiation called a boost.
Tumors vary in their radiosensitivity, which means that some are easy to control with the
standard doses of radiation therapy and some shrink little or none at all.
Following surgical resection, some types of tumors will begin to grow back
if any microscopic tumor is left behind. Other tumors cannot be removed
completely because of their location, and radiation becomes the primary
mode of treatment.
Additional types of
radiation therapy include stereotactic radiation and stereotactic
radiosurgery. These approaches focus radiation energy to a small area of
tumor (usually less than 3 to 4 centimeters in diameter). These therapies do
not involve surgery, but they do have "surgical precision."
One type of
sterotactic radiosurgery is called Gamma Knife. Gamma Knife
radiation therapy uses a special radiation unit that is designed to deliver
radiation from multiple cobalt sources. A computer focuses the
radiation to a small area or multiple small areas. Gamma Knife is most
commonly used to treat small metastatic tumors. It may also be used to treat
other small benign tumors such as acoustic neuromas, meningiomas, and
pituitary tumors. Stereotactic radiosurgery is delivered with one single
large dose, 15-30 Gy (ten times the usual daily dose for fractionated
radiation therapy). Both Gamma Knife and stereotactic radiosurgery use some
type of frame or fixation to keep the patient exactly in position during
treatment.
Stereotactic
radiotherapy also uses highly localized radiation, but the doses are divided
into fractions over a few days. In this case, the frame or fixation used
still keeps the patient in an exact location, but can be removed between
treatments.
Brachytherapy
delivers radiation therapy from the inside of the tumor to the surrounding
area. The radiation can be delivered in several different ways. Sometimes
radioactive pellets or seeds are implanted. Sometimes removable sources of
radiation are used. Sometimes radioactive liquid is inserted into the tumor
cavity or into a balloon catheter that is surgically inserted into the
tumor. Gliasite, a balloon device, has recently been approved for insertion
into a tumor cavity for the administration of radioactive iodine.
Radioactive isotopes have also been linked to monoclonal antibodies to the
tumor cells in an effort to more specifically direct radiation therapy to
spare normal cells. (See Question 39.)
M.L.'s comment:
After my craniotomy my
neurosurgeon and radiologist recommended further treatment with radiation
therapy. Additional treatments with chemotherapy were also recommended, but
I didn't start them until after my radiation treatments. Even though my
neurosurgeon had indicated that he had been able to remove the entire tumor,
it was likely that some cancer cells remained. Those cells needed to be
treated with radiation therapy.
The treatments didn't
hurt at all. I think the most uncomfortable part of my regular radiation
treatments was having the "mask" made for my head and face. I had to lie
still — and I mean still — for what seemed like forever while a plastic
mesh-like form was molded to my head and face. This was done so that the
radiologist could mark in ink the locations where the radiation beams would
be targeted every single time that I had a treatment. Before having the
technology to make these masks, it's my understanding that the radiologist
would make these marks on your skin, and these marks don't just come off
with soap and water. Needless to say, the mask is certainly the preferred
method, but having to lay still for so long hurt the back of my head a lot
more than the regular radiation treatments ever did.
When I refer to
"regular" radiation treatments, I'm talking about the daily "conventional"
treatments that I received every day for six weeks. I did, however, have
additional radiation therapy called stereotactic radiosurgery, but it wasn't
the gamma knife procedure. The stereotactic radiosurgery that I received had
recently been developed and was called the M3. It was developed by BrainLAB.
What the M3 does is allow precisely focused, high-dose x-ray beams to be
delivered to a very small area of the brain. With M3, special planning with
the computer allows a large dose of radiation to be delivered to the tumor
site with minimal radiation going to the normal or "good" brain tissue that
surrounds the tumor site. In my situation, the radiosurgery was delivered as
a local "boost" after my 6 weeks of regular or conventional radiation.
This procedure isn't
painful; however, you should be prepared for the fact that you have to wear
what the doctors call a "halo." It's a metal frame that is placed on your
head and attached with screws in four places: two in the back of your head
and two in the front. The halo ensures that your head doesn't move during
the treatment. The doctors put a topical anesthetic on so that the screws
don't hurt too much as the halo is being attached. I also received pain
medication, which helped. After the frame was attached, I had a CT scan. The
results of that were paired up with the results of the MRI that I had
received two days before. By doing this, the medical team that was
performing this procedure was able to pinpoint the exact size, shape, and
location of the affected area as well as plot the dose of radiation that I
would receive that day. The amount of radiation that I received the day of
my radiosurgery was almost as much radiation as I would have received during
an entire week of conventional treatment. The actual treatment only took
about an hour, but the whole process took the entire day because the
"planning" procedure took about 6 hours.
I will say that the
most painful part was when the halo was removed. I think the pain medication
had worn off and when the screws were removed I experienced a terrible wave
of pain in my head. It was like having a terrible headache all of a sudden.
It didn't last for too long, but that was the only time that the "halo"
actually felt more like a "crown of thorns!" If you undergo this procedure,
you should make sure that you have been given enough pain medication so that
when the halo is removed you don't have to experience the same kind of pain
I experienced.
My radiation
oncologist said that the headache I experienced after the frame was removed
is common. It's caused by a sudden drop in intracranial pressure. You see,
the frame produces an intense pressure on the skull, equivalent to 80 pounds
per square inch. This pressure on the skull deforms the skull during the
hours that the frame is in place. The amount of spinal fluid actually
decreases in volume in response to the pressure on the skull. When the frame
is taken off, the skull springs back, causing a drop in spinal fluid
pressure and a headache. Aside from that one painful moment, I do NOT regret
having this procedure because the end result that was most important.
34. What are
the side effects of radiation therapy?
Several factors
influence the risk of developing side effects from radiation therapy. They
include the total volume of the brain irradiated, the location of the
radiation fields, the total dose received, and the age of the patient. These
factors vary from patient to patient.
Radiation side effects
may also vary over the course of time. Cells that grow relatively quickly,
including those of the skin and hair follicles, are affected relatively
quickly, often during the course of radiation. Hair loss in the area of the
scalp overlying the tumor is typical. Patients who receive whole brain
radiation therapy may have almost total loss of hair. Hair may grow back for
some patients, but for others hair loss may be permanent. Other types of
cells, including the normal glial cells of the brain and the blood vessels,
are affected months to years after radiation. Occasionally, patients
complain of fatigue, weakness, or feeling mentally "foggy" during and for
several weeks after radiation therapy. These side effects are quite variable
in their severity and duration. Despite these side effects, many patients
are able to continue their normal activities.
Three long-term side
effects that often concern patients bear special mention. Patients are often
concerned about short term memory loss or cognitive changes following
radiation therapy. Again, the volume of brain irradiated, the areas of the
brain irradiated, the total dose received, and the age of the patient are
factors that impact the cognitive changes that are observed at least one
year after treatment. The use of chemotherapy during radiation may also be
associated with cognitive changes. Although the best studies of the effects
of whole brain radiation therapy on cognition, as measured by IQ testing,
have been done in children, there is ample evidence to suggest that adults
can suffer cognitive loss, particularly in short-term memory, following
whole brain radiation therapy. Although partial brain irradiation has also
shown some effect on cognition, the effects tend to be less pronounced and
may take longer to become apparent.
A second long-term
side effect that may affect patients who have received relatively high-dose
radiation therapy is radiation necrosis. Radiation necrosis is an area of
injured normal glial cells and blood vessels. It can occur anywhere from
several months to 2 to 3 years after radiation therapy. The appearance of
radiation necrosis on CT or MRI may be indistinguishable from tumor
recurrence. There is typically an area of enhancement, surrounded by edema,
and the area may appear to enlarge over subsequent scans. Patients
experiencing radiation necrosis may develop neurological symptoms such as
weakness, loss of coordination, or visual disturbances that may mimic tumor
recurrence. Surgery may be required to remove the area of necrosis.
Radiation necrosis is more common after high doses of focused radiation
therapy, such as radiosurgery or brachytherapy.
A third complication
of radiation therapy, although rare, may occur several years after
treatment. A secondary malignancy is a cancer that develops as
a result of previous cancer therapy. Secondary malignancies may occur in
patients who have received curative radiation therapy for childhood or early
adult brain tumors, or may occur following whole brain radiation therapy for
acute leukemia. The original tumor has not recurred, but a new type of tumor
— often a malignant glioma — appears within the radiation field. The risk
of secondary malignant tumors 15 years after radiation therapy is estimated
at less than 5%. However, a secondary malignant tumor may be more difficult
to treat, since the patient has previously had radiation therapy to the same
area. In addition to secondary malignancies, benign tumors, including
meningiomas and nerve sheath tumors, may also develop following radiation
therapy.
M.L's comment:
The side effects that
I experienced during radiation were primarily fatigue and hair loss. Some
days the fatigue was greater than others, but I soon realized that I needed
to just give in to the fact that I was tired and needed to take a nap.
However, a nap or a good night's sleep may not always relieve your fatigue.
It's very common for cancer patients to experience fatigue, and it can
affect you in many ways other than just feeling tired or weary. In addition
to not having as much energy during the day, I experienced periods of
depression. I would begin to cry whenever I would talk to a loved one —
especially my mother or sister. Because they both live far away, I felt sort
of alone. I really wasn't alone, though. In fact, I had an overwhelming
amount of support and comfort throughout the worst part of my treatments.
Despite such support, I found that I couldn't help crying at times. In my
case, this aspect of fatigue didn't go on for too long.
If you find that
you're having a difficult time with fatigue, you should know that there are
things that you can do to minimize the feelings of fatigue and frustration.
Try to remember to rest when you feel like you need it; don't fight the
fatigue. Also, try to eat right. Eat foods that will give you energy. Your
doctors should be able to give you some helpful ideas of what you should and
shouldn't eat. Try to get some sort of exercise every day, even if it's just
a short walk around the block. I found that just getting outside and getting
a bit of fresh air every day helped to relieve some of the fatigue that I
was feeling. And finally, don't forget to have some sort of a social life.
Just because you have a brain tumor doesn't mean you have to stop having
fun. A reduction in your social life will help to conserve some of your
energy, but you shouldn't feel like you have to cut out all of the things
that you enjoy doing. It's all about being able to prioritize and balance
the activities you have to do in order to keep from being too tired for
activities that you love to do.
35. My tumor
was completely resected, but I understand that there could still be
microscopic tumor left behind. How does the radiation oncologist decide how
much of the brain to radiate if nothing is visible on the MRI?
The MRI scans
performed before surgery help determine how much area around the tumor
cavity should be included in the radiation field. For tumors that infiltrate
into the surrounding brain, a margin of at least 2 centimeters around the
tumor is often recommended. Well-circumscribed tumors may require a smaller
margin, and tumors with extensive surrounding edema may require a larger
margin. Clinical trials that include radiation therapy often specify how the
radiation field will be designed and the margin that will be used.
36. A
patient in my support group said that he had whole brain radiation therapy.
My radiation oncologist said that whole brain radiation isn't appropriate
for my tumor. Why do some patients have whole brain radiation and others do
not? Are there more side effects from whole brain radiation?
Studies of patients
with malignant gliomas who received whole brain radiation therapy showed
that tumor recurrence frequently occurred within 2 to 5 centimeters of the
original site. Those studies also found that new tumors separate and distant
from the original tumor occurred in only about 5% of patients. Therefore,
most radiation for malignant glioma (and many other solitary brain tumors)
is limited to the area of the tumor and a margin around the tumor.
Whole brain radiation
is still recommended for some tumors that are more likely to spread
throughout the brain. Tumors that have metastasized from a systemic cancer
such as breast or lung cancer are usually treated with whole brain
radiation. Some primary tumors with multiple sites of disease at diagnosis
(such as lymphoma, germinoma, and gliomatosis cerebri) may also be treated
with whole brain radiation therapy.
Whole brain radiation
therapy may be associated with an increased risk of narrowing of the blood
vessels of the brain, radiation necrosis, and memory impairment. For this
reason, whole brain radiation therapy is often less that radiation limited
to a solitary focus of tumor (4000 cGy vs. 6000 cGy).
37. What is
the difference between stereotactic radiosurgery (SRS) and Gamma Knife?
Which patients should receive SRS and which should receive Gamma Knife?
Stereotactic
radiosurgery (SRS) and Gamma Knife are both forms of highly focused
radiation therapy. Despite the names, neither involves surgery. Both
procedures are performed by a team of neurosurgeons, radiation oncologists,
and radiation physicists. Some communities have both a Gamma Knife unit and
a linear accelerator that is modified for SRS.
Stereotactic
radiosurgery can be performed by a linear accelerator modified to produce a
focused beam of photons to a small (3 to 4 cm) tumor. The fixation of the
patient's head in a stereotactic frame enables the radiation source to move
around the target over a period of minutes, delivering a single high dose.
Computer imaging can direct the beam to conform to the shape of the tumor.
With some types of fixation systems, the dose can also be fractionated over
several treatments.
Gamma Knife uses
cobalt as a radiation source. The radiation sources are symmetrically
arranged in a helmet-like pattern over the patient's head. The radiation
beams converge on the target with a high degree of accuracy, but the
radiation sources do not move. Gamma Knife is not fractionated, but multiple
lesions can be treated in the same setting, if necessary.
Both SRS and Gamma
Knife are best suited for small, spherical tumors, particularly metastases
and acoustic neuromas. Gamma Knife is also used to treat vascular
malformations and other non-tumor conditions in the brain. While it is
difficult to compare Gamma Knife outcomes and SRS outcomes, the Gamma Knife
procedure appears to provide more tumor control and have fewer
complications. However, the modifications to the linear accelerator used for
SRS may also be used for the treatment of other types of tumors, meaning
facilities that use this procedure can treat a variety of conditions,
whereas Gamma Knife facilities only treat intracranial lesions.
Most patients will
have access to a center with Gamma Knife or SRS. Your doctor may prefer one
type of treatment over the other for your specific type of tumor. More
information regarding Gamma Knife or SRS treatment will be available at your
initial evaluation with your radiation oncologist.
38. I have
seen two radiation oncologists. One says that he uses three-dimensional
imaging to plan treatment. He says this targets the tumor more precisely,
which makes the treatment safer. The other radiation oncologist says that
the precision of three-dimensional imaging does not make the treatment
safer; only the total dose of radiation determines the extent of side
effects. Who's right?
Both doctors are
right. When a patient undergoes radiation therapy, the total dose of
radiation delivered must not exceed safe parameters, and radiation delivery
must avoid those sensitive brain structures that are not affected by the
tumor. Conformal radiation therapy, a three-dimensional radiation
treatment, uses images from CT or MRI to plan precise fields of radiation
that can be contoured around sensitive structures such as the eyes or the
brainstem. By using conformal radiation therapy, the total radiation dose
delivered to the tumor may be the same as conventional external beam
radiation therapy, but the dose delivered to the surrounding normal brain
may be less (Color Plate 8).
The dose delivered to
the tumor and the dose delivered to the surrounding brain may cause side
effects. Doses of radiation therapy high enough to cause tumor necrosis can
create a focus of dead tissue that may eventually cause symptoms. If this
occurs, the dead tissue may need to be surgically removed. It may seem
optimal to simply limit the dose of radiation to the normal brain
surrounding the tumor, but some tumors spread into the normal brain far away
from the tumor mass that appears on an MRI. Treating this area of normal
brain with a lower dose of radiation may place the patient at risk for tumor
recurrence, and a subsequent course of radiation therapy may not be possible
if there is an overlap with the previous radiation field.
39. What is
interstitial brachytherapy?
Interstitial
brachytherapy (interstitial = within
space, brachy = short) refers to radiation therapy that is administered from
the inside of the tumor cavity. Sources of radiation include iodine or
iridium. In this treatment approach, radioactive seeds or pellets are
implanted directly into the tumor cavity. The seeds or pellets deliver a low
dose of radiation continuously to nearby surrounding tissue. Patients who
are suitable candidates for brachytherapy have a well-circumscribed,
resectable tumor less than 5 centimeters in diameter.
Recently, a balloon
catheter system called GliaSite was developed for placement into a tumor
resection cavity. The balloon is inflated to a diameter of 2 to 4
centimeters and filled with a radioactive iodine solution, Iotrex. The
solution remains in place for 3 to 6 days. Then, the Iotrex and balloon
catheter are removed.
Although in some
studies brachytherapy has been associated with an improvement in overall
survival, some patients have needed another operation to remove radiation
necrosis. In the initial GliaSite study, no patients required another
operation for radiation necrosis, and the median survival time for patients
who underwent the procedure exceeded one year.
40. I had a
biopsy of a tumor in my left hemisphere that measures 2 X 2 centimeters. The
biopsy determined the tumor was a low-grade astrocytoma. I have seen a
radiation oncologist who suggested immediate radiation therapy. When I got a
second opinion from another radiation oncologist, he suggested that
radiation therapy could be delayed for a few years. Why are the
recommendations so different?
Treatment
recommendations for brain tumors, particularly for low-grade gliomas, are
guided by many factors. To help guide treatment decisions, many doctors
refer to practice guidelines. The National Comprehensive
Cancer Network (NCCN), a committee composed of neuro-oncologists, radiation
oncologists, and neurosurgeons around the country, publishes such practice
guidelines. The NCCN practice guidelines provide treatment recommendations
that are based on current cancer research as well as the clinical experience
of the committee members.
Many physicians use
the NCCN guidelines as a reference, but many do not. Some academic centers
and research institutions have developed their own guidelines for the
treatment of specific brain tumors. However, all practice guidelines assume
that doctors exercise good medical judgment in the patient's care, taking
into consideration the patient's age and general health. Even the NCCN
recommendations are not a "cookbook" approach for the treatment of any type
of brain tumor. This is why different doctors may have different
recommendations for treatment. Practice guidelines provide doctors with
information that help guide treatment, but the factors involved in your
specific case also impact treatment decisions.
Low-grade gliomas can
be quite variable in their behavior, making general recommendations
difficult. Some gliomas are surgically resectable, but others spread into
the surrounding brain and cannot be removed safely. If the tumor can be
completely resected, some studies have shown that survival improves. Other
studies have demonstrated that aggressive surgical resection does not
improve survival.
Radiation therapy is
often recommended for patients with low-grade gliomas that cannot be
resected. However, because some patients have few if any symptoms, their
doctors may recommend delaying radiation therapy until symptoms develop or
until there is a change in the appearance of the tumor on MRI scan. Again,
clinical trials have shown conflicting results on which approach (immediate
or delayed radiation) makes a difference in overall survival.
At least 50% of
low-grade tumors do become more malignant over a period of several years,
progressing to anaplastic astrocytoma (Grade 3) or glioblastoma multiforme
(Grade 4). This change can occur whether or not the patient has received
radiation therapy. However, patients who have previously received a full
course of radiation therapy may not be able to receive more radiation if the
tumor recurs as a higher grade tumor. Also, radiation can increase the risk
of developing a second tumor, but this risk is considered very small
(probably less than 5% fifteen years after radiation).
Although neither group
of physicians you have seen recommended chemotherapy, some clinical trials
have studied regimens such as PCV (Procarbazine, CCNU, and Vincristine) or
Temodar in low grade glioma patients with or without radiation therapy. It
is not yet clear how chemotherapy impacts on overall survival. Particularly
for patients who have a low grade oligodendroglioma, or mixed oligo-astrocytoma,
chemotherapy may allow patients to defer radiation therapy for months or
years.
In summary, despite
the development of practice guidelines, it is still up to you and your
doctor when you should undergo radiation therapy. You may also want to
consider participation in a clinical trial studying new treatment approaches
to the management of low-grade glioma.
41. Losing
part of my hair during radiation therapy has been very hard for me. What can
I do to make the experience more tolerable?
Hair loss in the area
that received radiation is very common during radiation therapy. Hair loss
from chemotherapy, on the other hand, affects hair all over the body. Being
prepared for the loss of your hair will make the experience somewhat easier.
Even before radiation or chemotherapy begins, many people look for a wig or
hairpiece in the same color or style as their natural hair to ease the
transition to hair loss. Your doctor may write a prescription for a wig or
hairpiece because the loss of your hair is associated with your cancer
treatment.
Cutting your hair
short before you begin to lose it makes it somewhat more manageable when it
does begin to fall out. You can also use a mild shampoo and conditioner and
avoid blow-drying it to help avoid irritating your scalp.
Scarves, turbans,
hats, and other head coverings can be used on the days when you prefer not
to wear a hairpiece. The American Cancer Society publishes a catalogue of
wigs and various head coverings. Also, many communities have a boutique
designed for men and women who have hair loss related to cancer treatment.
M.L.'s comment:
Although the amount of
hair loss that people have after radiation is variable, more than likely
you'll lose at least some of it. I did, and it was very upsetting to see
those first clumps of hair come out in the bathroom sink. I knew it would
happen; I just didn't know when it would happen. I tried to prepare for it,
but I still cried when it happened. You have to keep telling yourself it's
all part of the healing process. I continued to remind myself that the
radiation that was making my hair fall out was also continuing to eat away
at those "bad cells" in my brain, and that was a good thing. I just tried to
stay strong through all of it. I kept telling myself that my hair would grow
back. I found that wearing a "doo rag" on my head with a baseball cap over
it made me feel kind of cool. My husband has a motorcycle and he took me to
a shop where they sold motorcycles, clothing, and accessories. One of the
accessories that motocyclists wear when they are riding is a "doo rag". It
keeps the rider's hair from flying all over the place and it makes the
helmet a bit more comfortable. I found that they looked a lot better than a
scarf or bandanna, so I started wearing them every day. It was funny when
people started asking me where I had bought them.
What to
Expect During Radiation Therapy
Patients who will
receive radiation therapy as part of their treatment for a primary or
metastatic brain tumor meet with a radiation oncologist, a
doctor who specializes in treating tumors with radiation therapy. Although a
radiation oncologist may visit with you following surgery while you are
still in the hospital, most radiation therapy is conducted on an outpatient
basis.
After discussing the
potential benefits and risks of radiation therapy, the radiation oncologist
discusses the detailed treatment plan and the patient signs an informed
consent. This explains potential risks and complications of the
treatment.
The patient's MRI or
CT scans are reviewed by the radiation oncologist to determine the target
volume (the area that will be irradiated). Sometimes, additional
microscopic tumor cells grow at the edge of the tumor visualized on brain
scans. The radiation oncologist takes this into account by including a
margin of 1 to 3 centimeters around the tumor in the target volume. The
radiation oncologist also notes sensitive areas that should not receive full
doses of radiation, such as the eyes or the brain stem.
The radiation
oncologist and the radiation physicist determine the doses of
radiation that the patient will receive. They calculate the total amount of
radiation to the tumor as well as the amount that will be distributed over
the remaining portions of the brain. With conventional radiation therapy,
areas adjacent to the tumor may receive a percentage of the total dose (Color Plate 8).
To make sure that the
patient receives the dose in exactly the same configuration day after day,
the radiation technicians create a custom "mask” that holds the patient in
place. This is often a netlike device that allows the patient to breathe
normally but still holds the head firmly in place during treatment.
With the patient in
position, x-rays may be taken to provide a simulation of the exact
treatment field. When the radiation oncologist is satisfied with the
treatment planning, the actual treatment begins. The treatment session, once
planning is completed, is typically brief, often lasting about 15 minutes.
During treatment, the
linear accelerator, a source of radiation therapy, rotates around the
patient very precisely. Different angles may be used, from the sides of the
head or front to back, to focus intersecting beams of radiation at the
tumor. The treatment may be modified during radiation therapy if a smaller
section of the tumor will receive a "boost". This may require more CT or MRI
planning and a second planning session.
Typically the
radiation oncologist sees the patient at least weekly during treatment. The
radiation oncologist may recommend treatment with steroids if the patient
develops symptoms of swelling around the tumor during radiation therapy. Any
other side effects of treatment are also discussed with the radiation
oncologist.
After completing
radiation therapy, the radiation oncologist reviews the post-treatment MRI
with the patient. Because of changes in the tumor and surrounding tissue
that may occur during radiation therapy, the MRI is usually evaluated
several weeks after radiation therapy ends. However, the tumor may continue
to shrink for several months after the completion of radiation therapy, so
additional scans are often recommended to assess the success of treatment. |
