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A Patient’s Guide to IGRT
Image-Guided Radiation Therapy
Introduction
Your doctor believes that you’re a good candidate for image-guided radiation therapy (IGRT),
which is one of the most cutting edge innovations in fighting cancer. IGRT combines imaging
and treatment capabilities on single machine. Because tumors move, this new technology allows
your doctors to see and track the tumor at the time of treatment, and to make very fine
adjustments to your position so as to greatly increase the precision and accuracy of your
radiation treatment therapy.
The topics covered here include the basics of IGRT and a description of what you can
expect throughout the treatment process. The information is intended to be a starting point for
your discussion. Your medical team can fully answer any questions you may have.
Radiation Therapy and IGRT
In medicine radiation has been used to treat cancer and other abnormalities with good results for
many years. Today it is prescribed in one form or another for half of all cancer patients.
Medical radiation is nothing more than pure energy, delivered in beams. It works by
damaging the DNA of cancer cells so that they can no longer reproduce. The physician
prescribes the amount, or dose, of radiation and the method of administering it in much the same
way as drugs are prescribed.
IGRT treatment- IGRT is the most advanced form of radiation therapy currently available, in
large part because it is so precise. Tumors can shift and move slightly between treatments, and
even during treatment because of normal physiological processes, such as breathing. IGRT use
advanced imaging techniques to verify your position and your tumors exact location at the
moment of treatment.
Knowing exactly where the tumor is allows clinicians to irradiate only the tumor, sparing
the surround normal tissue. This accuracy results in higher radiation doses to the tumor and
thereby the increased likelihood of controlling or eliminating the cancer.
With IGRT, the full radiation dose can be delivered in one session or over a course of
several treatment sessions. Most patients can be treated as outpatients, and can return home
immediately after the procedure.
IGRT is well suited in treating tumors virtually anywhere in the body including those
areas that are affected by respiratory motion. It is now being used to treat tumors in the brain,
breast, head and neck, lung, liver, prostate, and other areas.
The technology involved
Your doctor decides which form of treatment is best for you. In making this decision physicians
look at many factors including the size, location, and type of tumor, as well as your overall state
of health.
Treatment requires certain tools and technologies, such as specialized treatment planning
software, a source of high-energy radiation, devices to shape the radiation beams, high-resolution
imaging systems that can quickly track tumor motion, and quality assurance tools that check and
fine-tune a patient’s position relative to the radiation beam before treatment begins.
Treatment planning software- Sophisticated computer software and three dimensional images of
your lesion and surrounding anatomy indicate the optimal way of treating your condition. The
resulting treatment plan-unique-to you- specifies the number of radiation beams as well as the
angles required to precisely deliver the radiation dose prescribed by your doctor without harming
surrounding healthy tissue.
Medical linear accelerator- A specifically equipped linear accelerator is used in your treatment. It
is optimized to generate and deliver high radiation doses to very small targets with great
accuracy.
Beam-shaped devices- Located in the head of the accelerator, a beam-shaping device helps shape
the radiation beam as it passes through. This limits the radiation dose to the region of
abnormality, leaving healthy tissue untouched.
The linear accelerator employs a beam-shaping device called a multileaf collimator, or MLC.
The MLC has 120 computer controlled tungsten metal plates, or leaves, that can be individually
adjusted. During treatment, these leaves move automatically, blocking the beam in different
places for different amounts of time, according to the treatment plan. This ability to change the
beam over time gives the doctors very fine control over how and where, the radiation dose is
administered.
Imaging systems- Using state-of-the-art imaging, your exact position (and the tumor’s) is
carefully established and tracked- before, during, and after treatment. Adjustments can be made
to the position of the treatment couch, as required, so that you are positioned for treatment with
submillimeter accuracy.
Two imaging systems are involved. One coordinates your treatment with your breathing,
compensating for tumor motion due to respiration. The second system is used to verify that
treatments are, in fact, being delivered precisely to the tumor.
The treatment process
Image-guided radiation therapy is a carefully controlled process that consists of a series of steps:
consultation, initial imaging, treatment planning, treatment delivery, and follow-up care.
Consultation- Your initial visit will be with the physician leading your radiation team. This is
likely to be a radiation oncologist or, if your tumor is in the brain or other part of the central
nervous system, a neurosurgeon. The physician will review your medical history and reports,
make a recommendation about your further tests that may be required, discuss the options
available to you, and work with you to chose the optimal course of treatment.
Imaging- Prior to the actual day of treatment, you’ll need to be scanned to create reference
images of the area to be treated. A high-resolution CT scanner will be used. Your radiotherapy
team will use this information- along with any other CT, PET, MRI, or X-ray images that may
already exist- to create your treatment plan, and also to ensure that you are positioned correctly
at the time of treatment.
Treatment planning- With the information gathered during the positioning and imaging steps, a
dedicated medical team will design the best treatment plan for your situation. They will use a
sophisticated software program to generate a customized plan for your treatment. The planning
team may include experts from different disciplines, such as radiation oncology, neurosurgery,
and medical physics.
Treatment delivery- IGRT treatments usually take less than 30 minutes. Most of that time is used
ensure that you are accurately positioned. For the most part you will be alone in the radiotherapy
room, but your therapists will be able to see and hear you at all times through intercom and
closed-circuit television systems. They will control the accelerator, the imagers, and the
treatment couch from outside the room.
First, you’ll be carefully positioned on the treatment couch. You may see laser lights.
These will be helping your medical team make sure that you’re level and straight on the couch.
You may both see and hear the robotic imager arms as they extend from the linear
accelerator and move into position. Usually, two or more images are taken from different angles.
A complete rotation of the accelerator may also be used to generate a three-dimensional image.
The therapist will use these images to guide adjustment of the treatment couch.
This same, low dose X-ray system on the robotic arms can also be used to observe how
the tumor moves due to your breathing cycle. This information can then be used to design a
“respiratory gating” strategy that coordinates treatment with your respiration, compensating for
tumor motion due to breathing.
You may hear a buzzing sound as the linear accelerator produces the radiation beams.
Although the radiations effect on the tumor is quite dramatic, you will not see or feel it, just as
you do not see or feel chest X-rays and CT scans. You may, however, hear the quiet whirring of
the beam shaping device, and see the MLC’s leaves adjusting.
The medical linear accelerator will move around you to deliver beams from different
angles, according to your treatment plan. Sometimes the couch will move as well. This is all
normal and part of the treatment process. An electronic portal imaging device will verify that
treatments are being delivered correctly.
Follow-up care
After you complete your treatment, your doctor will monitor your progress with a series of
follow-up visits. Blood tests, diagnostic X-rays, and even additional CT and MRI scans may be
requested at these appointments.
These appointments are your opportunities to discuss and problems and review how to
stay healthy after treatment. Ask about nutrition, exercise, and other basics for maintaining a
healthy lifestyle. You can find out about support groups for those treated for cancer.