Stereotactic Body Radiation Therapy

Stereotactic body radiation therapy (SBRT) is a general term used to describe highly conformal precise treatment with external beam radiation therapy generated by linear accelerator. While the treatment is similar to external beam radiation therapy (EBRT), SBRT is more focused, allowing the ability to deliver a high dose of radiation with millimeter precision.

There are generally three components to the delivery of SBRT - simulation, treatment planning, and treatment delivery.

1. Simulation is the process in which the patient is positioned using an individually tailored immobilization device. This helps to keep the patient in the exact same position for each treatment. A CT scan is then performed in this treatment position. A special device with a camera and reflective marker allows tracking of the tumor's location as the patient breathes.
    
2. During treatment planning, the 4D images obtained during simulation are uploaded to Varian Eclipse treatment planning system. Precise outlining of the tumor volume and normal structures are performed and complex calculations are performed to generate a treatment plan.
    
3. The treatment delivery portion of stereotactic radiotherapy is best accomplished by using a system to track tumor movement during treatment.

• Rapid Arc technology is a specialized form of Intensity Modulated Radiation Therapy (IMRT) that allows for more timely delivery of a highly conformal treatment. In traditional IMRT, the linear accelerator is shifted to several different positions around the patient in order to target disease. With Rapid Arc, the machine gantry makes a continuous rotation in an arc shape, rather than stopping at specific sites. This provides for a quicker treatment and more uniform dose distribution. It is important for SBRT delivery and can also be used to treat other sites such as prostate cancer and head and neck cancer.

• This can be done in several ways, including Real-Time Position Management (RPM), which is a noninvasive method of monitoring patient and tumor movement. An infrared tracking camera and a reflective marker are used to measure a patient’s respiratory pattern. Using information obtained from simulation, thresholds are defined to turn the linear accelerator beam on and off based on the location in the respiratory cycle. This technique of respiratory gating (RPM) allows for more effective delivery of radiotherapy to the target structures while minimizing dose to surrounding normal tissues. It can be used in SBRT as well as in the treatment of select patients with breast cancer to minimize cardiac dose.

*Information provided by Varian Medical Systems