Radiation therapy is a common treatment for many types of cancer and uses high frequency radiation to damage the DNA of cancer cells, which usually replicate at a faster rate than normal cells in the body.

It can be used as the sole treatment of cancer or in combination with other treatments such as chemotherapy and surgery. It also plays a role to control symptoms of cancer when there is no known cure available.

Mechanism of Action

Cancer cells can be distinguished from normal cells in the body, as they tend to replicate more quickly and take over tissue with healthy cells. Radiation therapy manipulates this characteristic of cancer cells by attacking the DNA of cells that are in the process of replicating, rendering the cells unable to multiply sufficiently and eventually leading to their death.

Types of Radiation Therapy

The radiation needed in therapy can be administered in three different ways.

• External radiation therapy – A linear accelerator is a machine that is used to focus radiation beams from outside the body directly towards the area of the tumor.
• Internal radiation therapy (brachytherapy) – A small radioactive object is placed inside the body inside or next to the tumor and releases radiation to the area over a set period of time.
• Radiopharmaceuticals – Drugs with radioactive properties are administered to the patient orally or via another route such as intravenously or inside a cavity like the vagina or rectum.

Radiation Dosage

The dosage of radiation used in therapy is important, as it should be high enough to effectively eliminate the cancerous tumor, whilst minimizing damage to surrounding healthy cells.

The total dose is usually broken up into fractions administered once a day for five days each week, over a period of five to eight weeks. This helps to deliver the total dose over an extended period, continually attacking the cell DNA. There are also different dosage fractioning techniques available that may involve treatments more or less often than once a day.

Side Effects

The immediate effects of radiation therapy are usually painless. As the exposure to radiation continues, however, the body begins to notice the effect of the constant damage to its cells and a few weeks into treatment side effects may include:

• Fatigue
• Local inflamed skin
• Alopecia

These effects tend to worsen as therapy continues, reaching a peak about a week after therapy and then improving from thereafter. The skin usually heals well, although may lose some elasticity in comparison to prior to therapy.

Long-term fertility may also be affected, although this can usually be evaded by avoiding exposure of radiation to at least one of the gonads needs for reproduction. Additionally, radiation therapy is linked to a second cancer.

Secondary Cancer

This risk of a second cancer is duly considered in the therapeutic decision of cancer treatment and the role of radiation therapy. There is a well-established risk of a second cancer, in the form of leukemia or a solid tumor, several years after exposure to radiation, usually from five to twenty years.

However, the benefit the treatment offers with its ability to greatly reduce or eliminate the primary tumor greatly outweighs this risk in most cases. Radiotherapy generally leads to increased survival rates that warrant the use of the treatment, despite the fact that it carries a slightly higher risk of second cancer.

References

• http://www.nhs.uk/Conditions/Radiotherapy/Pages/Introduction.aspx
• http://www.cancer.org/acs/groups/cid/documents/webcontent/003019-pdf.pdf
• http://large.stanford.edu/courses/2012/ph241/ali1/docs/002043-pdf.pdf