What is external-beam radiation therapy?
In external beam radiation therapy, the radiation oncology team uses a machine called a linear accelerator, or linac.
A linac uses electricity to form a stream of fast-moving subatomic (electron) particles. This creates high-energy radiation that is used to kill cancerous cells.
External beam radiation therapy is usually delivered in daily treatment sessions over the course of several weeks.
The number of treatment sessions depends on many factors, including the total radiation dose that needs to be given.
What are the common methods of external beam radiation therapy?
External beam radiation therapy methods include:
- Intensity-modulated radiation therapy (IMRT)
- Image-guided radiation therapy (IGRT)
- Stereotactic radiosurgery
- Stereotactic body radiation therapy
What is intensity modulated radiation therapy (IMRT)?
IMRT aims to increase the radiation dose to the tumour or high-risk areas, while limiting radiation to healthy tissue nearby.
IMRT’s sophisticated software uses hundreds of tiny radiation beam-shaping devices (collimators) to deliver a tailored, almost sculptured, radiation dose.
Collimators can be still or moving during treatment. This lets the radiation oncologists moderate the intensity of the radiation beams – allowing certain areas to receive specific radiation doses.
During the IMRT treatment planning, radiation oncologists will work out the radiation dose needed using X-ray scans.
A high-powered computer program then calculates and optimises the beams and angles of the radiation treatment.
What is image-guided radiation therapy (IGRT)?
In IGRT, repeated imaging scans are performed during treatment.
These scans are reviewed by your radiation oncologists, and subtle radiation beam adjustments are made to ensure the targeted treatment is precise.
These scans can also help to identify changes in a tumour’s size and location.
Regular IGRT increases the accuracy of radiation therapy. In some situations, it may be able to reduce the amount of tissue that needs to be treated – decreasing the total radiation dose overall.
What is tomotherapy?
Tomotherapy is a type of image-guided IMRT.
A tomotherapy machine is a cross between a CT imaging scanner and an external-beam radiation therapy machine (linac).
Tomotherapy machines can capture CT images of tumours just before treatment sessions. This allows for very precise tumour targeting and sparing of normal tissue.
The part of the tomotherapy machine that delivers radiation for both imaging and treatment can rotate completely around the person being treated – just like a normal CT scanner can.
Like IMRT, tomotherapy can help to spare normal tissue from high radiation doses.