The Differences Between Internal And External Radiotherapy

radiotherapy centre - Doctor shows information on blackboard

When someone opts for treatment at a radiotherapy centre, they might be surprised at the sheer diversity of the range of treatments on offer, many of which are bespoke and targeted at treating particular types of cancer located in specific parts of the body.

As well as this, despite being a cancer treatment type that is over a century old, it is also constantly evolving, with methodologies and technologies developing at an exceptional pace in order to help treat a wide variety of cases, improving efficacy without leading to overly intense treatments.

To that end, whilst you can categorise radiotherapy treatments in a lot of different ways, from the isotope used, the part of the body they target and the intent of the treatment, every radiotherapy treatment can be grouped into one of two separate categories.

Both are used to treat different types of tumours in varying parts of the body and are vital parts of a radiotherapist’s toolkit, particularly since they are often used in tandem with each other and alongside other treatments such as surgery and chemotherapy.

What Is External Radiotherapy?

When most people think of radiotherapy, particularly when it comes to treatments for brain cancer, they are most likely thinking of a form of external beam radiotherapy.

External radiotherapy is when a machine is used to aim targeted high-energy beams of radiation shaped and targeted to destroy cancerous tissue as well as other types of malignant growths and tissues.

This can take a wide variety of forms depending on the type of treatment required. For example, stereotactic radiosurgery treatments such as Gamma Knife use a wide number of different radiation beams that converge on a particular point, delivering a precise, strong dose of radiation.

This is achieved using a dedicated frame and is used because any treatments on the brain need to be as precise as possible and avoid unnecessary tissue damage.

By contrast, there are some external radiotherapy treatments that are not targeted at all, such as total body irradiation, used to treat cancers that affect entire systems such as myeloma (plasma cancer), leukaemia (cancer of the white blood cells), lymphoma and as part of bone marrow transplants.

It is typically used for curative purposes, where the radiotherapy is intense enough to kill the cancer cells and avoid potential regrowth of cells, which is the reason why radiotherapy is typically intensive.

It can also be used in combination with surgical treatments, often used after the excising of a tumour to kill any remaining cancer cells, or alongside chemotherapy to enhance the effects of both treatments.

In other cases it is used as a palliative treatment; if after close examination removing the cancer entirely is not an option, then radiotherapy is typically used at lower doses to help relieve pain and reduce symptoms, which varies considerably depending on the treatment itself.

What Is Internal Radiotherapy?

By contrast, whilst external radiotherapy treatments tend to be noninvasive outpatient procedures (although some are done during surgery or require overnight stays), internal radiotherapy involves placing radioactive material inside the body to treat certain types of cancer.

There are a few ways this can be achieved, but typically it takes the form of either radionuclide therapy or brachytherapy, depending on what type of radioactive material is used.

Radionuclide therapy, sometimes known as radioisotope therapy, is the consumption or injection of a radioactive liquid that flows through certain parts of the body, destroying cancer cells.

For example, the most common type of radionuclide therapy, Iodine-131, is taken as a capsule that is absorbed by the thyroid gland, treating certain types of thyroid cancer in the process.

Alternatively, radium-223 is used to treat prostate cancer that has spread to the bone, and lutetium, which is used to treat certain types of cancer that afflict the neuroendocrine system.

On the other hand, brachytherapy is typically a solid radioactive source that is precisely positioned either in or close to the tumour, emitting radiation only to tissue close to its source.

It is typically used to treat cervical and prostate cancers, as well as cancers of the gullet, the skin and the womb.

It is typically applied via surgery, but can also be applied using applicator tubes, which launch pellets of radioactive material into the target area. 

Alternatively, in some specific types of liver cancer treatment, radioactive beads can be injected into the target area in a process known as selective internal radiotherapy treatment (SIRT).

Depending on the treatment the source of radiation is either absorbed by the body directly or is removed with a subsequent operation.