Miniature Transponder Guides Radiation Therapy Procedures

A new implanted transponder can help enhance the precision of radiotherapy (RT) and radiosurgery treatments for cancer by providing real-time, continuous information on tumor position.

The Calypso 17G soft tissue Beacon transponder emits a non-ionizing electromagnetic signal that is tracked in real-time by the Calypso system, guiding treatment beams to target tumors during treatment with medical linear accelerators. The size of a grain of rice, the 17G Beacon has a smaller cross-section area than the current, 14G version, and can be implanted within the soft tissue throughout the body, with the exception of the lung. The Calypso System can then deliver real-time, continuous three dimensional (3D) tumor position information, improving clinician confidence that the prescribed dose has been delivered to the tumor.


Based on the transponder signals, the Calypso System can track even the slightest movement of the tumor without using ionizing radiation, and can precisely target even tumors that exhibit respiratory motion, as the system allows the beam to be gated on only when the tumor is in the planned position. The increased precision can enable treatment margin reduction, protecting healthy tissue and reducing side effects. The Calypso 17G soft tissue Beacon transponder and the Calypso System are products of Varian Medical Systems (Varian, Palo Alto, CA, USA).

“The new 17G implantation device has half the cross-sectional area as the prior 14G technology, increasing patient comfort and improving access to tumors,” said Zachary Collins, MD, section head of interventional radiology at Kansas University Medical Center (Kansas City, USA). “The smaller technology may make the use of Calypso viable in a broader population of liver patients, and may make it possible for interventional radiologists to implant Beacon transponders in the pancreas without an open surgical procedure.”

Organ motion is variable and unpredictable, posing challenges during delivery of external beam RT treatments for cancer. The ability to track target motion in real time during treatment and gate the delivery beam can enable reduction in the margins between the clinical target volume (CTV) and the planning target volume (PTV).

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