Migration of implanted markers for image‐guided lung tumor stereotactic ablative radiotherapy

Abstract

The purpose of this study was to quantify postimplantation migration of percutaneously implanted cylindrical gold seeds (“seeds”) and platinum endovascular embolization coils (“coils”) for tumor tracking in pulmonary stereotactic ablative radiotherapy (SABR). We retrospectively analyzed the migration of markers in 32 consecutive patients with computed tomography scans postimplantation and at simulation. We implanted 147 markers (59 seeds, 88 coils) in or around 34 pulmonary tumors over 32 procedures, with one lesion implanted twice. Marker coordinates were rigidly aligned by minimizing fiducial registration error (FRE), the root mean square of the differences in marker locations for each tumor between scans. To also evaluate whether single markers were responsible for most migration, we aligned with and without the outlier causing the largest FRE increase per tumor. We applied the resultant transformation to all markers. We evaluated migration of individual markers and FRE of each group. Median scan interval was 8 days. Median individual marker migration was 1.28 mm (interquartile range [IQR] 0.78−2.63 mm). Median lesion FRE was 1.56 mm (IQR 0.92−2.95 mm). Outlier identification yielded 1.03 mm median migration (IQR 0.52−2.21 mm) and 1.97 mm median FRE (IQR 1.44−4.32 mm). Outliers caused a mean and median shift in the centroid of 1.22 and 0.80 mm (95th percentile 2.52 mm). Seeds and coils had no statistically significant difference. Univariate analysis suggested no correlation of migration with the number of markers, contact with the chest wall, or time elapsed. Marker migration between implantation and simulation is limited and unlikely to cause geometric miss during tracking.PACS number: 87.57.N‐; 87.57.nm; 87.53.Ly

The Utility of Bronchoscopy for the Placement of Fiducial Markers for Stereotactic Body Radiotherapy

“…19 It also concluded that despite the difference in retention rates between FM, once retained, the migration distance was limited and similar among the various FMs. 19 At our institution, we utilized SBRT with Cyberknife in 235 patients for the management of nonoperable lung cancer. We made use of various methods of deployment of FM including bronchoscopy with fluoroscopy guidance alone and with electromagnetic navigation bronchoscopy (ENB) direction.…”

“…19 This is crucial in the setting of SBRT as it confirms the reliability of fiducials as markers for tumor tracking and treatment planning. 19 It also concluded that despite the difference in retention rates between FM, once retained, the migration distance was limited and similar among the various FMs. 19 At our institution, we utilized SBRT with Cyberknife in 235 patients for the management of nonoperable lung cancer.…”

“…The median time between implantation and simulation was 9.6 days (excluding 4 patients who had a delayed simulation time due to a failed biopsy, inpatient admission, and intervening radiation treatments). 19 The study used fiducial registration error as a metric measure to assess marker migration on computed tomographic (CT) scans and revealed that once the markers have been placed successfully in the peripheral lesions, they exhibit minimal migration, limited to <2 for both seeds and coils. 19 This is crucial in the setting of SBRT as it confirms the reliability of fiducials as markers for tumor tracking and treatment planning.…”

“…19 The study used fiducial registration error as a metric measure to assess marker migration on computed tomographic (CT) scans and revealed that once the markers have been placed successfully in the peripheral lesions, they exhibit minimal migration, limited to <2 for both seeds and coils. 19 This is crucial in the setting of SBRT as it confirms the reliability of fiducials as markers for tumor tracking and treatment planning. 19 It also concluded that despite the difference in retention rates between FM, once retained, the migration distance was limited and similar among the various FMs.…”

“…18 Another study compared migration rates between gold cylindrical seeds (seeds) and platinum vascular embolization coils (coils) as FMs. 19 In this study, a median of 4 of each were implanted per tumor. The study revealed that coils were retained at 100% rate compared with the seeds that retained at 93.2%.…”