The following excerpt is taken from Chapter
9 of Colon & Rectal Cancer: A Comprehensive Guide for
Patients & Families by Lorraine Johnston, copyright 2000 by
O'Reilly & Associates, Inc. For book orders/information, call
(800) 998-9938. Permission is granted to print and distribute this
excerpt for noncommercial use as long as the above source is
included. The information in this article is meant to educate and
should not be used as an alternative for professional medical care.
The information this article provides is not a substitute for your doctor's
knowledge. Always ask your doctor when an aspect of your treatment is unclear,
and report immediately to your doctor any adverse reactions that arise during
or after treatment.
If you would like greater detail on radiation therapy, The Chemotherapy and
Radiation Therapy Survival Guide, by Judith McKay, Nancee Hirano, Myles
Lampenfeld, Making the Radiation Therapy Decision, by David Brenner and
Eric Hall, and Coping with Radiation Therapy: A Ray of Hope, by Daniel
Cukier and Virginia McCullough, are books that focus on radiation therapy from
the patient's perspective.
Although there are different kinds of radiation, including x-rays and electron,
proton, or neutron beams, for the sake of readability we will not distinguish
among them. We will use only the term "radiation."
There are several ways to administer radiation therapy:
All of these delivery techniques are used for rectal cancer. For some colon
cancers at certain stages, external radiotherapy is used, but use of abdominal
radiotherapy for colon cancer remains controversial owing to the significant
risk of permanent damage to the small bowel and adjacent organs.
External radiation therapy might be used before rectal surgery to shrink
tumors, or after surgery to kill any remaining microscopic tumor cells.
- External radiotherapy, also called external beam irradiation, involving
narrow x-ray beams aimed at your body while you lie on a table. This is the
most common form of radiotherapy used for rectal cancer.
- Radioimmunotherapy, an injection of radioisotopes into a vein. The
radioisotopes are attached to a carrier that homes preferentially to tumors
instead of healthy tissue. The most common homing substances in use today are
monoclonal antibodies, proteins produced by white blood cells and capable of
traveling preferentially to tumors. Use of this technique against colon and
rectal cancers is still in clinical trials.
- Intra-operative radiotherapy, which is aimed directly and only at the
tumor bed, the empty spot in your body where the tumor once was. This is done
while your body is still open during surgery, but after tumor removal. This
technique is not discussed in this article, as the patient needn't prepare for
or anticipate it in ways that differ from preparation for and anticipation of
- Brachytherapy, the positioning of a radioactive substance within the
body very near or within the tumor. This technique might be used for rectal
cancer, but not for colon cancer.
- Interstitial radiotherapy, involving implants of radioactive material,
often permanent, stored in capsules, wires, or similar sealed delivery
- Endocavitary radiation therapy, which utilizes a wand that emits
radiation of very short wavelength that is placed in the rectum or vagina. This
is expensive, specialized equipment that is not yet widely accessible, and is
not discussed in this article as it is not often used for colorectal cancer.
The following sections will walk you through preparation and treatment
simulation, scheduling, receiving therapy, departure, and the days that follow
Your first one or two treatment visits to the radiation oncology treatment
offices will be spent determining precise details of how best to treat you:
positioning you on the treatment bed, marking your skin with small dots of
temporary or permanent ink, taping body parts in place for stability, and
creating lead shields for sensitive organs. If you have rectal cancer, the bed
you'll be lying upon may have an opening for your abdomen so that the small
intestine will drop down out of the path of the radiation beam, or you may be
positioned head-down to shift the small intestine upward. All of these
preparations are called simulation, and may take several hours spread over one
or more visits.
Several medical specialists are involved in this stage of your treatment: your
radiation oncologist, the radiation therapy technician who will administer the
treatment, a dosimetrist who calculates the correct dose, and the radiation
physicist who calibrates the machine. Some of these staff members may work
behind the scenes.
For these initial visits, which may be lengthy, make yourself as comfortable as
possible by wearing clothing that doesn't bind, that goes on and off easily,
and has no metal zippers. Bring a cassette player if you like, and use the
restroom before the simulation starts.
None of these preparations are painful, but they may be embarrassing or
unpleasant, for instance, if the staff decides that the best access to a rectal
tumor is achieved by taping the buttocks into an open position, or if you are
asked to drink a barium contrast solution to clarify the position of the small
Special shields or blocks may be made to shape the radiation beam to match
exactly your tumor's shape, or the shape of nearby surgical scars. Beams of
invisible radiation generated by the machinery are usually emitted shaped like
rectangles, from two to fifteen inches in any dimension. If these beams were
trained against your tumor, nearby healthy tissue within the two- to
fifteen-inch rectangle would be irradiated, too, suffering damage. To avoid
this effect, shields or blocks with cutaways in the silhouette of your tumor
are created using your x-ray films as guides.
The shields made for you are used only by you. You may see the same kinds of
devices belonging to other patients hanging nearby or in other treatment areas.
The machinery used during simulation looks and moves just as the genuine
radiation equipment does, but instead it generates only a plain light beam to
verify positioning, ink markings, and the fit of shields.
After all shields and blocks are made and your skin is marked, the entire
simulation will be repeated with all pieces in place--exactly like a dress
As your treatment progresses and your tumor shrinks, new blocks may be made to
match the new shape of your tumor, and these simulations may be repeated.
Radiation therapy often makes many patients increasingly tired as it
progresses. For this reason, once treatment starts, it would be wise to have a
friend or loved one along, not only for emotional support, but to handle issues
such as saving written instructions for diet and aftercare; understanding and
remembering verbal instructions; communicating insurance information; handling
the co-pay, if any; and assisting with the drive home.
Ask the medical staff about avoiding products such as skin lotion before
treatment. They may interfere with treatment, or they may cause your skin to
become hypersensitive if they are exposed to radiation. Ask as well about
pacemakers, surgical staples, and clothing with metal zippers.
Years of research have shown that a large amount of radiation can be delivered
to a tumor safely if the dosage is spread out over several weeks. This is
called fractionating the dose, or simply fractionation. It spares healthy
tissue from unnecessary damage and gives it time to recover.
Dosage fractionation means that you will have to visit the treatment center
several times a week, or perhaps every day, for several weeks, depending on
your treatment plan. It also means that each dose of radiation lasts only two
to four minutes. If your tumor is irradiated from several different angles (and
most are), each angle may take two to four minutes after the machine is
repositioned. After the lengthy time spent in simulation, you may feel that ten
to thirty minutes of treatment time is an anticlimax.
Don't be surprised if the schedule on which your radiotherapy is administered
differs from the schedules you hear others discussing, because your radiation
schedule always is tailored to your particular circumstances, based on
the size, number, and location of tumors; your overall health; your body size;
and the type of cancer you have.
Depending on what treatments are being used, the timing of your radiation
therapy may be influenced by the quantity of white blood cells remaining in
your blood after your last chemotherapy or radiotherapy treatment. Your blood
may be tested when you arrive, using a standard measurement known as a complete
blood count, or CBC. If your white blood counts are too low, treatment may be
delayed a few days or a week.
For each treatment, you might want to call the treatment center before leaving
home or work. Radiation therapy machines sustain heavy use, and must be taken
offline periodically for recalibration or repair. You can save time by calling
first to see whether appointments are running on time.
After a few treatments, you may begin to feel that most of your time is spent
traveling or chatting in the waiting room, because treatment itself is so
Make a point of discussing nausea and diarrhea medications with your doctor
before treatment starts. With the excellent anti-emetics (antinausea
drugs) available, you shouldn't have to endure nausea. If you become nauseous
after treatment, though, request a change in medication. Although the new
anti-emetics are excellent, ask for suppositories in case oral medications
won't stay in your stomach. If nausea becomes a problem, subsequent treatments
may be preceded by an injection of one of the new antinausea drugs, such as
Ask your doctor if you should avoid possibly dangerous circumstances such as
excessive sunlight or crowds.
Ask about skin care, too. External beam radiation must pass through your skin
to reach tumor sites, and irritation may result. Newer, higher voltage
equipment used today causes less damage to skin because the damaging rays
concentrate in deeper layers, but some skin reaction still is possible,
particularly in sensitive areas such as the skin between anus and genitals.
The source of radiation will be a machine that either safely contains a
radioactive substance such as Cobalt 60, or generates its own radiation as
needed. Like a CT scanner or a gamma camera, the radiation machine is designed
to move around you and your bed as you hold still. Many models are almost
silent, but some make a sound like a vacuum cleaner, and of course they may
click and whir as they reposition.
The room in which treatment is given has thick walls and is lead-clad to
prevent the very small amount of radiation that bounces off your shields, known
as scatter, from affecting the medical staff, those in the waiting room, and
random passers-by. For the safety of the staff, the treatment room will contain
only you when the machine is engaged. (The small dose of radiation they would
sustain if they stayed with you would probably not harm them, but if they
stayed with all patients, all day, every day, the dose from scatter would
indeed accumulate to dangerous levels.)
The staff can see and hear you at all times, because there are microphones and
cameras connecting you and them. If you feel at all bad, just let them know.
Music and wall art sometimes are available in the treatment room to lower your
boredom and stress levels.
Delivery of external radiation therapy
External radiotherapy is administered using the blocks and shields made
expressly for you, and perhaps on a special table that will shield the healthy
parts of your intestines if needed, perhaps with sandbags to hold your arms and
legs still, and blankets to keep you warm. If you have a rectal tumor, your
buttocks may be taped into an open position so that the radiation beam
targeting the rectum or lower pelvis will avoid healthy skin.
You may have your bladder filled with saline water prior to treatment in order
to lift the small intestine away from the treatment area, thus protecting the
You should feel no pain, no heat, no sensation at all during treatment,
although some survivors say that they feel a sensation of energizing--not quite
a tingling--in the area of the tumor during treatment. It may indeed be that
some of us can sense a highly active biological entity such as a tumor reacting
to the disruption of its DNA.
Some find the absence of sensation eerie, but most people are grateful that the
treatment is comfortable and brief.
Dosage of external radiation therapy always is tailored to the patient's
specific circumstances, depending on where the rectal or colon tumors are
located, and how much radiation a given organ can withstand. The liver, for
instance, is very sensitive to radiation, and cannot survive doses high enough
to kill most tumors. Moreover, doses for control of symptoms differ from those
used for cure.
A typical curative dosage for rectal cancer is 180 to 200 centiGreys (cGy) per
day, repeated a few times a week for several weeks until a total dosage of
4,500 to 5,000 cGy is achieved. Additional radiation boosts of 540 to 900 cGy
to smaller areas occupied or once occupied by tumor, called the tumor bed, are
sometimes added. A variation sometimes introduced is delivering 120 to 160 cGy
twice a day, 4 to 6 hours apart, for several weeks. In patients at high risk of
recurrence of disease, a total of 6,000 to 7,000 cGy might be used in areas
local to the tumor if the small bowel and other sensitive organs can be
shielded. It's important to remember, though, that your radiation oncologist
will adjust dosage to suit your individual needs.
If a higher dosage is required for certain sites, more sessions are added, but
the dose per exposure is not raised. Because external beam radiation often must
pass through healthy tissue to reach the site of the tumor, a moderate dose per
exposure has been determined to be the best means for killing colorectal cancer
cells while allowing healthy cells to recover.
Some patients question why lower doses over a longer period of time aren't used
in order to reduce the side effects of treatment. Doses lower than those
outlined above might allow a surge of cancer growth to go unchecked, as some
researchers have noted accelerated growth in head and neck cancers apparently
stimulated by radiotherapy. While this finding is not directly applicable to
colon and rectal cancers, the risk of cancer regrowth after reducing the single
fractionated dose is considered too great in the absence of more solid
After each of your first few treatment sessions, make sure before leaving the
doctor's office that you have received written instructions regarding any
necessary dietary or behavioral changes, information about possible side
effects such as possible inflammation of hemorrhoidal tissue, prescriptions,
and phone numbers for emergencies. Often, side effects of radiation therapy do
not emerge until you've had two or more weeks of treatment. If you have
prepared for these possibilities by asking questions during the treatment
visits when you feel well, side effects may be easier to deal with.
You are not likely to feel unwell after your treatments, but if you do, do not
leave without telling the medical staff of your problem.
Radioimmunotherapy is a new treatment, still in advanced clinical trials, but
promising. It combines the principle of radiation therapy with one of the
newest treatments available, tumor targeting with monoclonal antibodies.
Radioimmunotherapy involves linking one molecule of a radioactive substance, a
radioisotope such as iodine-131 or yttrium-90, to a monoclonal antibody. The
proposed benefit of radioimmunotherapy over existing radiation treatments is
that less healthy tissue is exposed to radiation because the antibody attaches
preferentially to, but not only to, cancerous tissue. Some healthy tissue is
affected because the radioactive substance decays as the antibody travels to
the tumor and because monoclonal antibodies also will attach to some antigens
on healthy cells, but it is thought that this effect is less than that
sustained during external beam therapy. Radioimmunotherapy is administered into
a vein, like chemotherapy.
The correct dose of radioimmunotherapy must first be determined. To calculate
this dose, a small "tracer" amount of the substance will be injected first, and
visualized using a CT scan or other imaging device. Based on what is seen, the
doctors in charge will determine the total dose you should receive.
You will be kept in a lead-shielded hospital room throughout this treatment,
and your body wastes will be disposed of in accordance with rules for handling
hazardous waste. Face-to-face family visits will be very limited or denied
entirely. The nurses who care for you may wear protective clothing and will
limit contact with you.
If the radioisotope iodine-131 is to be used, your thyroid gland will be
shielded first. The radioactive isotope, I-131, will destroy the thyroid gland
if it is absorbed.
To shield the thyroid, large doses of nonradioactive iodine, iodine-123,
are given to you first. This substance is taken up by the thyroid in excess
compared to other body tissues. After the maximum amount has been absorbed, the
thyroid cannot absorb more iodine for several days. This protects the thyroid
gland from absorbing subsequent doses of I-131.
This method of treatment is not likely to be used for those who have had
previous allergic reactions to iodine in shrimp, other foods, or in other
Although external beam radiation is the most common form of radiotherapy used
for rectal cancer, for some rectal tumors, a radioactive substance placed very
close to or within the tumor may offer the best chance for cure. Often this
treatment is combined with surgical removal of as much tumor as possible.
Permanent implantation of a low-dose radioactive material often is done during
the surgery intended to remove the tumor. If not done at that time, implants
can be inserted in a second surgery while you're under a general anesthetic or
a sedative. Radioactive agents chosen for this type of treatment are those with
an active range of just a few centimeters, which ensures the safety of nearby
healthy tissue and of others around you.
For brachytherapies that involve implanting vessels that will temporarily hold
a radioactive substance, surgical implantation of small canisters or tubes
usually is done first in the absence of any radioactive substance.
Once the vessels are in place, the patient is returned to his hospital room.
After sufficient healing, the patient is moved to a lead-shielded isolation
room if not already so housed. A team specially trained to handle radioactive
material arrives dressed in protective clothing to insert the radioactive
substance into the vessel. It might be left in place for only a few minutes, or
for a few hours, or a few days, depending on the dose required and the isotope
Typically, a high dose of radiotherapy for a short period is delivered by
brachytherapy. This means that, while your body contains the radioactive
substance, the radiation will pass through your tissues and will continue to
travel beyond your body. Your bodily wastes might contain radioactive
byproducts. Consequently, during this time you will represent a radiation
hazard to others. Visits from family and friends will be discouraged or denied,
and nursing staff will wear protective gear and limit their contact with you.
They will provide you with all the care you need, but they may, for example,
speak to you from the doorway instead of the bedside.
After the designated amount of time has passed, the team will return to remove
and dispose of the radioactive substance. Once the agent is out of your body,
you are no longer a risk to others. You may be discharged from the hospital the
same day, or very soon after.