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Radiation therapy
Answers to your patients' questions
and concerns
an interview with Tien Phan, MD and
Elizabeth Kurien, MD
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How is radiation
therapy used to treat cancer?
Radiation therapy, or radiotherapy, uses ionizing radiation to treat
cancer. It destroys cells in the targeted area by damaging their
DNA, eliminating their ability to grow and divide. Because malignant
cells often have faulty DNA repair mechanisms as compared to normal
cells, radiotherapy is an effective method for treating and controlling
many different types of cancer.
Normal cells in the targeted area are also
affected by the radiation, but -- unlike tumour cells -- most of
them recover from the effects of radiation. The dose delivered to
normal tissue is limited by shielding as much of it as possible
while aiming the radiation beam(s) at the site of the cancer. Spreading
the treatment out over time (fractionation) also improves the ability
of irradiated normal tissues to repair damage. With this approach,
the higher doses that are required to treat a tumour can be administered
without exceeding the tolerances of the normal tissue.
What are
the different types of radiation treatment?
External beam radiotherapy delivers targeted beams from a distant
mechanical source outside of the body to the patient's cancer site.
Radiation oncologists have a variety of different beams and techniques
to choose from, allowing them to shape the delivered radiation to
hit the target while minimizing the dose that nearby normal tissues
receive.
Internal radiotherapy, or brachytherapy, places
radioactive sources directly in a tumour or body cavity. In this
treatment, the radiation dose is concentrated in a small area. A
high dose is delivered from the implant to the targeted tissue,
while the surrounding tissues are spared thanks to the short range
of the radiation source that's used.
When is radiation
therapy indicated?
About half of all cancer patients will receive some form of radiation
therapy during the course of their illness. Treatment of cancer
involves a multi-disciplinary approach, and radiation therapy can
be used in conjunction with surgery, chemotherapy or a combination
of both -- depending on the disease and goals of treatment.
When the aim is to eradicate the tumour, the
approach is referred to as radical radiation therapy. Cancers that
are commonly treated in this manner include early stage prostate
cancer, locally advanced lung cancer (in combination with chemotherapy)
and locally advanced head and neck cancers.
Adjuvant therapy uses radiation as an additional
tool to improve tumour control following primary treatment of a
cancer. It's usually given after surgery when all detectable malignant
cells have been removed but there remains a statistical risk of
relapse from occult disease. The most common scenario is adjuvant
radiation in the treatment of breast cancer after segmental resection
(lumpectomy).
Sometimes, radiotherapy is used to treat a
cancer prior to resection -- with or without chemotherapy. This
is known as neoadjuvant radiation therapy. Possible rationales include
shrinking the tumour to boost the likelihood of a complete resection,
decreasing the amount of normal tissues that need to be removed
at the time of surgery, and increasing local tumour control over
that achievable with surgery alone.
Finally, palliative radiation therapy is an
integral part of the radiation oncologist's practice and accounts
for approximately 50% of cases. It's an effective method for controlling
a variety of symptoms and improving quality of life. Depending on
the situation, 60-90% of patients who receive radiation therapy
will experience improvements as the tumour shrinks in the treated
area. Palliative radiation therapy is particularly effective for
pain control from bony metastases, for reducing tumour volume that's
causing obstruction of vital structures such as airways and vessels,
and for controlling hemorrhage from a growth.
What's involved
in the process?
At the first appointment, the patient will meet with a radiation
oncologist to review the diagnosis and available treatment options,
so that she can make an informed decision. If radiation therapy
is indicated and accepted, the next step is a process called "simulation,"
which is done to delineate the area to be treated. Simulation often
involves fluoroscopy or computed tomography scans, and the individual
can expect to be in the building for approximately 1-1.5 hours.
This usually doesn't take place on the day of the initial consultation
unless the condition in question -- e.g. spinal cord compression
-- requires emergency radiation treatment.
 Tien
Phan, MD, is a 4th year resident in Radiation Oncology at the University
of Calgary.
Elizabeth Kurien, MD, CM, FRCPC is a radiation oncologist working
at the Tom Baker Cancer Centre in Calgary.
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