Factors related to fixedness after transbronchial fiducial marker placement for image-guided proton therapy: A retrospective study.

Background: The usefulness of transbronchially inserted gold fiducial markers has been reported in radiation therapy and proton therapy for mobile lesions, such as lung tumors. However, there is occasional dropout of inserted markers. This retrospective study investigated the factors related to dropout of markers inserted for image-guided proton therapy (IGPT).

Methods: Between June 2013 and October 2021, 535 markers were inserted in 171 patients with lung tumors. We investigated whether marker dropout was affected by the location of marker insertion, distance between the marker and the chest wall (DMC), and difference in forced expiratory volume in 1 s (FEV)/forced vital capacity (FVC). Marker dropout from the time of planning computed tomography (CT) to follow-up CT was also evaluated.

Results: Of the 535 inserted markers, 417 were confirmed on planning CT and 356 on follow-up CT after IGPT. Multivariate analysis revealed that marker insertion into the upper lobe and FEV/FVC ≥70% were factors associated with total marker dropout. Marker dropout between planning CT and follow-up CT was associated with DMC, FEV/FVC ≥70%, and planning CT performed within 4 days of marker insertion.

Conclusions: Marker dropout can be minimized by inserting markers more peripherally, by considering the planned insertion location, and FEV/FVC. Additionally, planning CT should be scheduled at least 5 days after marker insertion.