Preliminary clinical experience with Calypso anchored beacons for tumor tracking in lung SBRT

Abstract

Purpose: To present our preliminary experience with the recently released Calypso lung beacons to track lung tumor location during stereotactic body radiation therapy (SBRT). Materials/Methods: Five recent lung SBRT patients had Calypso lung beacons implanted for tumor tracking during treatment. Beacons were placed by a pulmonologist using fluoroscopic navigation within 1 week prior to planning four-dimensional computed tomography (4DCT) acquisition. Patients were immobilized in a full-body double-vacuum bag. For the first three patients, a verification 4DCT was obtained prior to the first fraction with the patient in the treatment position to assess both beacon migration and motion of tumor and beacons relative to planning day. For each treatment fraction, Calypso was used to position the patient. A verification cone-beam CT (CBCT) confirmed the Calypso-defined target position was appropriate. Real-time Calypso tracking information was also acquired and compared to an action level that was used to determine if the tumor migrated outside of the planning target volume. Results: For four patients, the implant procedure was well tolerated, with average CBCT-based shifts being within 0.2 mm of the shifts reported by Calypso at the time of imaging. The other patient had a small pneumothorax due to very peripheral tumor location and experienced beacon migration. However, the patient quickly recovered from the pneumothorax, and after deactivating that beacon, motion tracking was possible throughout his treatment. Conclusions: All patients were successfully treated with SBRT using the newly released Calypso lung beacons, with initial positioning confirmed by this clinic's current clinical standard of CBCT. The system allowed us to validate, with real-time confirmation, that the planned internal target volumes were appropriate to each day's extent of actual tumor motion. An efficient and effective workflow for utilizing the new lung beacons for SBRT treatments was developed.

Can bronchoscopically implanted anchored electromagnetic transponders be used to monitor tumor position and lung inflation during deep inspiration breath‐hold lung radiotherapy?

“…39 One study used a verification CBCT acquired before treatment and compared the shifts determined from the CBCT and planning CT registration to the shifts reported by Calypso during the CBCT acquisition and found the differences to be ≤1.5 mm. 37 The same study also used the GR reported by the Calypso system at the time of setup as an indication of EMT stability throughout treatment. 38 McDonald et al evaluated the long-term stability of EMTs by registering follow-up CTs with the planning CT and found that the long-term stability was comparable to other commercially available lung fiducial markers.…”

“…37 The same study also used the GR reported by the Calypso system at the time of setup as an indication of EMT stability throughout treatment. 38 McDonald et al evaluated the long-term stability of EMTs by registering follow-up CTs with the planning CT and found that the long-term stability was comparable to other commercially available lung fiducial markers. 36 Schmitt et al found that intra-and interfractional variations in EMT distances varied up to 3.2 mm for patients treated with free breathing.…”

A simulated comparison of lung tumor target verification using stereoscopic tomosynthesis or radiography

“…27 One clinic has reported using implanted electromagnetic transponders similarly, as an added layer of safety during lung SBRT treatments. 7 When only one viewing angle is necessary and only one angle provide sufficient image quality for visualization, then verification images could be acquired from that angle alone. This would halve the required radiation dose.…”

Quality management in radiotherapy treatment delivery

“…Fiducial markers are of considerable help in this 60 ‘Image guidance’ may not require an image. For example, implanted radio transponders that can be localised from outside can determine the location of a target, but do not provide an image 61,62 Training of staff is an essential part of image guidance, in particular for modalities such as ultrasound which may require experienced users 63 …”