IGRT: Image-Guided Radiotherapy




IGRT--or image-guided radiotherapy--is the most advanced form of radiation therapy currently available.  Tumors can move during treatment (usually due to patient respiration) and between treatments (usually due to day-to-day variations in patient setup).  IGRT uses advanced imaging techniques to verify patient position and tumor position at the time of treatment.  Knowing exactly where the tumor is allows clinicians to reduce the volume of tissue irradiated, targeting only the tumor and sparing the surrounding normal tissue.  Irradiating less normal tissue reduces the toxicity of radiotherapy, improving the patients quality of life, and may make it possible to deliver higher radiation doses to the tumor and thereby increase the likelihood of local tumor control.




When patients are positioned on the treatment table, an X-ray system mounted on a robotic arm is rotated around the body, to gather images that pinpoint a tumors exact location.  These images are then compared with existing images (MRI, CT or other kinds of scans) in order to determine if the tumor has moved since the last treatment.  Because tissues and organs can settle around bones differently each time a patient is placed on a treatment table, tumors can end up in different positions from one treatment session to another.

In addition, tumors can move several centimeters due to a patients normal respiratory cycle.  Trilogys advanced imaging capabilities produce low-dose, high-resolution kilovoltage X-ray images that pinpoint tumor position.  The Trilogy system employs other technologiesan electronic portal imaging device and a respiratory gating systemto enable clinicians to verify patient positioning and to account for tumor motion caused by respiration.




Through more precise targeting of the beam, dosage levels can be increased and target volumes (the three-dimensional areas to receive treatment) can be reduced--so tumors get a higher dose of radiation and healthy surrounding tissues get very little.  This may increase treatment effectiveness. At the very least, it can reduce treatment times and the possible side effects of radiotherapy.
-Smaller lesions can be treated more easily and effectively.
-State-of-the-art motion management techniques allow patients to breathe naturally during treatment sessions, increasing treatment accuracy, reducing stress and increasing patient comfort.



- Trilogys advanced imaging capability produces a variety of imaging modalities in order to view the tumor and surrounding anatomy:
o       Radiographic (two-dimensional)
o       Fluoroscopic (moving, in real-time)
o       Cone-beam CT (three-dimensional)

- Trilogy can deliver very high dose ratesup to 1000 MU (monitor units) per minuteso treatment times can be reduced, which reduces the burden on cancer patients.
-Trilogy offers the most precise isocenter, or beam focal point, available--a sphere that is 1mm in diameter.
-Trilogy is equipped with a highly accurate, high-resolution multileaf collimator (beam-shaping device).
-Trilogy incorporates a top-of-the-line portal imaging device that produces high-resolution images for patient positioning, treatment verification and quality assurance.
-Trilogy is fully integrated with Varians information management and treatment planning software systems.
-Trilogy enables clinicians to deliver the most advanced treatments in the same amount of time as a standard treatment, with increased ability to account for patient and tumor movement.
-Veterinarians can use Trilogy to treat smaller lesions and metastases, as well as larger tumors.  This means that some cancers that would have been considered untreatable with radiation can now be treated this way, rather than with more invasive techniques such as surgery or chemotherapy.

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Updated: May 12, 2008