(or external beam) radiation therapy is the most widely
used method of delivering radiation. The radiation is focused from
a source outside the body onto the area affected by the cancer.
It’s a lot like getting an x-ray, but for a longer time. Radiation
passes through but is not stored in the body. Patients do not become
External radiation is given by variety of machines,
most commonly a linear accelerator (or linac). Careful treatment
planning allows the x-rays to destroy cancer cells while limiting
any effect on surrounding normal tissue. The process of external
beam therapy can be divided into four parts: Simulation, Treatment
Planning, Plan Verification, and Treatment Delivery.
What's involved in planning my treatment?
After a physical exam and a review of your medical
history and test results, you will be scheduled for a Simulation
session. The radiation therapist will ask you to lie still on a
CT scan table while cross-sectional images of your anatomy are obtained.
These are used to define the exact place in your body where the
radiation will be aimed. The doctor checks the size of the tumor,
identifies the normal tissues in the area and also the areas where
the tumor is more likely to spread.
“Immobilization devices” may be custom-made for you
during Simulation to help you remain still during treatment and
to insure that the radiation beam is aimed correctly. The therapist
also marks the field with freckle-sized dots of semi-permanent ink
or with tiny permanent dots like a tattoo.
The dosimetrist, radiation physicist and radiation
oncologist then use a Treatment Planning computer system to calculate
the radiation dose, delivery time and treatment technique. Your
doctor analyzes all the relevant information and decides how much
radiation is needed, how it will be given, and how many treatments
The Plan Verification part of the process is really
a second “mini-simulation” that may happen on or before
your first Treatment Delivery day. It’s like a dress rehearsal
for a play where the therapy team finalizes all of the preparations
How long does the treatment take and what happens
during each visit?
External radiation therapy usually is given once a
day, 4-5 days a week for 3 to 8 weeks. The total dose of radiation
and the number of treatments you need will depend on the size, type
and location of your cancer, your general health, and any other
treatments you are receiving.
Radiation therapy treatments are totally painless
and take only a few minutes. However each session can last 15 to
30 minutes because of the time it takes to set up the equipment
and place you in the correct position. You will lie on a treatment
table positioned under the radiation machine. You should remain
still but do not have to hold your breath - just relax and breathe
Once you are in position, the radiation therapist
will leave the room to turn on the machine. Visual and voice contact
is always maintained by closed circuit television and by intercom.
The therapist controls the machine as it moves around you to aim
at the treatment area from different angles. You will hear the machine
making humming noises, but will feel nothing unusual. If you are
concerned about anything that happens in the treatment room, alert
your therapist. The machine can be stopped at any time.
What are: 3D Conformal Radiation Therapy? IMRT?
All of these terms refer to specific advanced treatment
planning and delivery technologies that enable Advanced ROS doctors
to protect normal tissues so that the highest possible dose of radiation
can be safely delivered to the tumor. These tools give us the most
accurate and specific information to plan your treatment and precise
control over the radiation delivered.
A 3D Conformal treatment planning computer uses CT
images to map the 3-dimensional location of the cancer in the body.
The physician can then visualize the tumor, bony anatomy and organs
from the radiation “beam’s eye view” and try different
arrangements on the patient, a process known as virtual simulation.
Radiation beams can then be directed to conform to the exact shape
of the cancer.
Intensity Modulated Radiation Therapy (IMRT) is a
3D CRT-based delivery technique which allows doctors to further
lessen injury to normal body tissues by varying the shape and intensity
of the radiation beam.
TomoTherapy® is the newest concept in radiation
therapy that combines the capabilities of a CT scanner and a linear
accelerator into a single unit. It delivers a very sophisticated
form of IMRT and integrates treatment planning, delivery and verification
into one system. Advanced ROS is the first facility in the Northeastern
U.S. and one of only thirty locations worldwide to offer TomoTherapy.