Image Guided Radiation Therapy – (IGRT)

IGRT – refers to the use of sophisticated imaging technologies to guide the delivery of precise forms of radiation therapy. Varian’s On-Board Imager® (OBI) imaging system offers three different imaging modalities to locate the targeted tumor every day prior to treatment. The imaging modes include:

  • Radiographic (two-dimensional)
  • Fluoroscopic (moving, in real time)
  • Cone-beam CT (three dimensional)


The OBI imaging system is mounted on a pair of robotic arms. It then rotates around the body while the patient lays on the treatment table and takes low dose high resolution X-ray images prior to treatment. These new images are overlaid on top of the existing images in order to determine if the tumor has moved since the last treatment. Because tissue and organs can settle around bones differently each time the patient lies down on the treatment table, tumors can end up in a different position from one treatment session to another. In addition, tumors can move several centimeters due to a patient’s normal respiratory cycle. Once the tumor location has been determined, the table remotely moves and makes the adjustment to the targeted position.

The Benefits of IMRT

  • Higher doses of radiation can be delivered directly to tumors and cancer cells, while surrounding organs and tissues are protected.
  • Lower doses to healthy normal tissue may mean fewer complications or side effects.
  • In prostate cancer studies, local tumor control rates were significantly improved.  In addition, the use of IMRT significantly reduced treatment side effects.
  • Physicians can treat cancers that were previously untreatable with radiotherapy.
  • IMRT can be a non-invasive alternative to surgery.
  • IMRT targets the tumor and not the entire body.


Knowing exactly where the tumor is allows the clinicians to reduce the volume of tissue irradiated, targeting only the tumor and sparing the surrounding normal tissue.

Contact Us

LARGO, FL 33777
PH: 727 320 0200
FX: 727 394-8934
Dr. Kevin S. Tralins, Medical Director