Also referred to as x-ray therapy and radiotherapy, radiation therapy is one of the most commonly used medical procedures for cancer treatment (in addition to chemotherapy and surgery). Radiation is administered by doctors in carefully controlled amounts to affected areas of the body with the intention of destroying cancerous cells. However, it is a challenge to administer radiation therapy for mesothelioma since the pleura is large and spread out. Since the lungs and the rest of the thorax also get exposed when radiation is administered at the pleura, brachytherapy is usually preferred for mesothelioma.
Radiation therapy – how it works
Radiation therapy works by inducing damage to the genetic structure of malignant cells. Radiation beams alter the atoms that make up the DNA helix of cancer cells. Since cells have the ability to heal damaged genetic material, effective radiation techniques attempt to split both strands of the helix molecule. Moreover, since malignant cells do not have the ability to heal their damaged DNA as fast as normal cells, they carry over their damaged DNA as they reproduce. Damage inflicted by radiation therapy inhibits the ability of cancer cells to sustain the malignancy, causing the tumor to reduce in size and eventually die. Radiation is used commonly in diagnostic CT scans, x-rays and dental x-rays. However, the x-ray energy administered for the treatment of cancer is several times stronger during radiation therapy. Such high doses can eliminate malignant cells by inducing damage to the genetic material that controls the growth and development of these cells. Some normal cells will also get damaged, but the primary objective of this treatment is to destroy as many malignant cells as possible while reducing the impact on healthy cells. Cancer cells are more prone to damage induced by radiation therapy since they divide at a faster rate and are susceptible to damage while dividing. Radiation therapy can help in the fight against cancer since normal cells can recover from the treatment more quickly and effectively in comparison to cancer cells.
How is radiation therapy administered?
There are two modes of administering radiation therapy – externally and internally.
Externally – This is the most commonly used form of radiation therapy.
Typically administered in an outpatient setting, external methods are
used primarily to reduce the size of tumors and mitigate the pain associated
with them. In this technique, a large machine – a linear accelerator –
is used to deliver strong doses of radiation to the affected region. Radiation
is delivered by the machine in a constant stream of fast-moving subatomic
particles. Depending on the case profile, this treatment is administered
for around 4-6 weeks on a daily basis.
Internally – Also referred to as brachytherapy (short distance therapy),
this method includes both interstitial and intracavitary radiation. Special
radioactive substances called seeds or pellets, usually the size of a
rice grain, are used in this treatment. Other necessary equipment may
include wires, tubes or containers. A hospital stay is usually required
for internal procedures since insertion of implants, catheters or radioactive
substances together with the surgical procedures initiated for installing
the device, increase the recovery time. Internal treatments can also be
administered by infusion through the bloodstream.
In intracavitary radiation, a container of radioactive substance is planted
inside a specific body cavity. Doctors use CT scans, x-rays or ultrasound
to place the radioactive sources in the right place. Based on the prescribed
treatment plan, these implants can either be temporary or permanent.
• Permanent – involves low dose radiation through the placement of seeds
or pellets directly inside tumors with the aid of extremely fine hollow
needles. Once planted, these seeds continue to give off radiation for
many weeks or even months. Since they are minute in size, they can be
left in place even after they have used up their radioactivity.
• Temporary – high dose radiation is administered and involves a procedure
where hollow needles, tubes and balloons filled with fluid are planted
inside the affected area. After being left inside the targeted region
for a short period of time, they are later removed. This procedure is
repeated for several days or weeks. To prevent the implant from shifting,
it is necessary to lie calm and still throughout the treatment.
• Radiopharmaceuticals – These are drugs that hold radioactive substances.
They can be administered orally, through an IV line or placed inside a
body cavity. Based on the type of drug used and how it was administered
to the patient, these radioactive substances travel to different parts
of the body. This procedure is most commonly used for certain conditions
such as bone pain and thyroid cancer.
Some examples of radiopharmaceuticals are given below:
• Phosphorus 32 – is injected using a catheter and placed in the space
in the abdomen or in the middle of the linings surrounding the lungs.
• Strontium 890 and Samarium 153 – both are used for the treatment of
tumors that have spread to the bone. Can be administered through an IV
and these travel to cancerous areas of the bone.
• Iodine 131 – eliminates cancer cells present in the thyroid gland while
limiting damage to the rest of the body. The dose administered during
radiation therapy is measured in Grays (Gy), with 1 Gray equaling 100
rads. Depending on the treatment prescribed for the tumor, total radiation
may vary from 60-80 Grays during the treatment schedule. To avoid damage
to healthy tissues, the treatment is usually administered over multiple
sessions, spread out over several weeks. The average dose per session
is usually 1.5 to 2 Grays.
Researchers have discovered numerous radiation sources and a variety of delivery methods that are effective for the treatment of cancer. All types of radiations including x-rays, gamma rays and proton beams are utilized at different stages of cancer radiation therapy. Doctors use techniques such as the three-dimensional conformal radiotherapy and stereotactic radiotherapy to target tumor cells without damaging the surrounding healthy tissues.
Radiation therapy is not a part of the typical mesothelioma treatment, but it can be administered if an oncologist considers it appropriate for the patient. It can also be useful for palliative care.
A major concern is that mesothelioma can be triggered by radiation therapy.
If a patient with known exposure to asbestos is being treated for another
type of cancer, there is a risk that mesothelioma may develop.