Radiation therapy is a common treatment for many types of cancers and tumors of the body. A machine called a linear accelerator delivers the radiation therapy treatments.
The linear accelerator directs the beams of radiation from many different angles to target and kill cancer cells while sparing the normal tissue. These radiation beams conform and shape using multi-leaf collimators around the target areas. These beams can change their shape as the linear accelerator moves around the body.
By precisely targeting the high-dose radiation to the tumor and preventing radiation to adjacent organs, we are able to limit the side effects that someone could have,” said Dr. John Simmons, radiation oncologist with Marshfield Clinic Health System.
Typical treatment time takes less than 2-3 minutes to administer the radiation prescription dose. Most of the time taken is to setup and verify the area being treated is in the right position.
Radiation therapy process
After consultation and review of the imaging studies, the radiation oncologist sets up a CT simulation of the area being treated. Your care team uses molding and positioning devices during the simulation process to place you in the proper position.
The simulation process is an integral and important part of radiation therapy treatments. It ensures you are comfortable and in the right position for radiation treatments. Your care team then completes a CT scan of the body area being treated. This is done to get the latest information on the size and location of your tumor and to plan the radiation treatments.
Your radiation oncologist outlines parts of the body to treat and critical structures to avoid on CT scans. Your radiation oncologist then provides a prescription for the treatment plan that includes:
- The total dose for the treatment areas
- The dose the normal tissue and critical structures surrounding the treatment area can tolerate
A dosimetrist is a member of your care team who creates the treatment plan according to the radiation oncologist’s prescription. Once a treatment plan is acceptable, a physicist checks to make sure:
- The treatment plan is deliverable.
- Dose calculations are correct.
- Dose calculations can be properly delivered following the standards and guidelines.
The dosimetrist then places the treatment plan on the computer that controls radiation treatment.
Testing is important
Complex treatment plans are tested to make sure the treatment plan is delivered as prescribed. Your radiation oncologist and care team reviews many checklists and completes other reviews prior to delivering the treatment plan.
“There are a lot of double and triple checks before to ensure the patient receives the right amount of dose to the right area,” said Walter Tang, physicist with Marshfield Clinic Health System.
Your care team completes quality assurance tests for the linear accelerator daily, monthly and annually. This then ensures the accelerator is working and operating properly. This also includes an annual inspection by an independent and external group.
Types of treatments
Many linear accelerators can do different types of radiation therapy including:
- Intensity modulated radiation therapy (IMRT): Uses a computer to control the linear accelerator to deliver a precision radiation dose to the target volume.
- Volumetric modulated radiation therapy (VMAT): Similar to an IMRT except the linear accelerator rotates around the area being treated delivering a precise radiation dose to the target volume while sparing normal tissue.
- Image-guided radiation therapy (IGRT): Uses CT imaging to assist the setup process to position the body prior to radiation therapy treatments. This helps to define and position the body to match the position from simulation.
- Stereotactic body radiation therapy (SBRT): Uses many separate beams of radiation that meet at one point in the tumor to make a supercharged dose of radiation. Your radiation oncologist may use this to treat small tumors surrounded by important organs.
Side effects from these treatments depend on the treatment site. Talk to your radiation oncologist for more information.