Radiation therapy, or radiotherapy, is the medical use of radioactive particles to kill and/or control the growth of malignant (cancerous) cells.
In this treatment, high-energy subatomic particles are used to remove electrons from their atomic and/or molecular structure: a process known as ionization. When atoms composing a cancer cell are separated from their electrons, it may result in the death of the cell.
Radiotherapy can be used as a curative, adjuvant, and/or palliative treatment. Its use as a curative or palliative treatment depends on the type and stage of the patient’s cancer, as well as their overall health. In most cases, radiation therapy is used alongside other treatments (i.e. immunotherapy, anti-cancer drugs, and/or chemotherapy) in order to treat the cancer in a more comprehensive manner. This is known as adjuvant treatment.
Typically, radiotherapy is focused on a specific region of the body, such as the abdomen in the case of stomach cancer. Focused radiation techniques utilize multiple beams of radiation that intersect the tumor from several angles. This produces a high concentration of radiation in the intended area, while affecting surrounding tissues and structures with a milder absorbed dose.
Before a patient can receive a bone marrow transplant, however, total body irradiation (TBI) is necessary. This technique affects the entire body with ionizing radiation. Although vital in many cases, TBI may damage tissues, such as the skin and certain internal organs.
How does it Work?
Radiotherapy damages the DNA structure of cancer cells, or any cell for that matter, by sending a photon, electron, proton, or neutron ion beam through the malignant cells. This, in turn, ionizes the cells, resulting in the restructuring of the cells’ DNA. A normal cell can usually withstand the effects of radiotherapy because there are mechanisms within the cell whose purpose is to repair DNA damage.
Cancer cells, on the other hand, are often undifferentiated, or underdeveloped. This means that they are less able to counteract the influence of ionization.
Solid tumors have a tendency to outgrow the body’s ability to supply them with oxygen, a state known as hypoxia. Unfortunately, hypoxia renders radiotherapy less effective than it would be in an oxygen-rich environment because oxygen makes cellular DNA damage permanent. Ongoing research is being conducted in order to reverse the onset of hypoxia.
Types of Radiation Therapy
CONVENTIONAL EXTERNAL BEAM RADIATION
Conventional external beam radiation, or 2DXT, uses linear accelerator machines to deliver a two-dimensional beam of radiation to the patient from several different angles. These beams are often sent one at a time, after which the machine is adjusted, the next beam is sent, and so on and so forth. With 2DXT, the true dosage of radiation being delivered to the cancer cells is difficult to gauge. As a result, 3-dimensional radiotherapy has become the standard treatment option for a variety of tumors.
Modern imaging techniques, such as MRI and CT, have allowed physicians to differentiate tumors from healthy tissue in the third dimension. Conventionally, a 2-D rendering of the cancer would be produced with an x-ray machine. This rendering is comparable to a painting on a canvas. Today, however, physicians are able to walk around the cancer, metaphorically speaking, like sculpture observers.
In 3-dimensional radiotherapy, or 3DCRT, a machine known as a multileaf collimator is used to conform a series of beams to the shape of their target. The shape of the beam differs depending on the angle from which it is shot. For instance, if you used a flashlight to cast a shadow of your hand against a wall, the shadow would change as you moved your hand. 3DCRT’s beams have the same effect. Because 3DCRT essentially engulfs a tumor in radiation, it may increase healthy tissue’s exposure to ionization.
RADIOISOTOPE THERAPY (RIT)
In radioisotope therapy, a radioactive substance is injected into the bloodstream. These substances, just like radiation beams, causes cellular DNA damage and cell death. Examine the following analogy in order to better understand this treatment. If you want to catch any fish in the sea, then you should use a big net. But if you are trying to catch a shark, then you should throw some chum in the water because only sharks like chum. If you want to radiate large portions of the body, you should use a beam.
But if you want to radiate, say, the thyroid gland, then you should use radioiodine because only the thyroid absorbs radioiodine. When it is injected into the bloodstream, it passes through most of the body unabsorbed until it reaches the thyroid. There are other substances that have a similar effect throughout the body.
Side Effects of Radiation Therapy
Radiotherapy is painless, but may result in a series of unpleasant side effects. Low-dose treatments often yield no side effects at all. Common side effects include:
- Infertility: Radiotherapy can easily damage the body’s sensitive gonads (ovaries and testes). This may result in infertility.
- Fatigue: Radiation may result in a general feeling of tiredness and/or the sensation of being mentally exhausted.
- Swelling: General inflammation throughout the body may occur as a result of radiation treatment.
- Epithelial Damage: Radiotherapy may damage the body’s epithelial surfaces, such as the skin and certain membranous substances that cover the body’s organs. It is very common for the skin to turn pink and sore following treatment. The mouth, throat, and esophagus are also common candidates for soreness and swelling. This reaction is rarely permanent and may be diminished with the use of several available medications.
The long-term effects of radiotherapy may include:
- Hair Loss: Unlike the temporal hair loss associated with chemotherapy, radiotherapy may result in a more gradual and permanent loss of hair.
- Other Cancers: Radiation can cause cellular mutations that may result in the development of other cancers.
- Fatigue: Recipients of radiotherapy commonly report feelings of tiredness for many years following initial treatment.
- Fibrosis: Radiotherapy may result in tissues that lose their elasticity.
- Dryness: Many glands, such as the salivary and tear glands, may produce less fluid following radiation therapy. In some cases, these glands stop working altogether.
History of Radiation in Cancer Treatment
Radiation was being used to treat cancer more than 100 years ago. The discovery of x-rays in 1895 marked the beginning of its medical use. The German physicist Wilhelm Conrad Röntgen was the first to discover that x-rays had therapeutic affects on cancer patients.
In the 1900s, the Nobel Prize-winning scientist Marie Curie-Sklodowska ushered radiotherapy into the contemporary era of medical treatment in which we practice to this day. Curie-Sklodowska’s discovery of the radioactive elements polonium and radium generated an enormous influx in the use of radiation to treat cancer. Polonium and radium have since been replaced with cobalt and caesium.
In 1971, Godfrey Hounsfield invented computed tomography (CT scan). This three-dimensional imaging technique allowed doctors to target ionizing beams more specifically in the body, resulting in less damage to surrounding tissues. Hounsfield’s invention has paved the way for contemporary technologies such as magnetic resonance imaging (MRI) and positron emission tomography (PET), making radiotherapy techniques more effective and less invasive.
Röntgen, Curie-Sklodowska, and Hounsfield are the founding fathers and mothers of radiotherapy. The hard work and diligence of physicians, researchers, various organizations, and patients around the world have all contributed to the blossoming of this wonderful anti-cancer tool. It is often the unknown soldiers that win the battle.
The Future of Radiotherapy
As long as people like Marie Curie-Sklodowska are still being born, we can certainly expect radiation therapies to become more precise and less harmful to normal tissues. Currently, researchers are developing a technique known as microbeam radiation.
In this treatment, a lethal dose of radiation is beamed into one cell, triggering what is known as the “bystander effect”. The bystander effect is when a damaged cell sends self-destruct signals to surrounding cells. One day, technologies such as microbeam radiation may result in a radiotherapy that is free of side effects.