Fiducial markers for stereotactic lung radiation therapy: review of the transthoracic, endovascular and endobronchial approaches

Abstract

Stereotactic body radiation therapy is an alternative to surgery for early-stage, inoperable peripheral non-small cell lung cancer. As opposed to linear accelerator (linac)-based (e.g. gating) and free-breathing techniques, CyberKnife® with Synchrony® technology allows accurate radiation delivery by means of a real-time respiratory motion tracking system using, in most cases, metal fiducial markers (FMs) placed in the vicinity of the target. The aims of this review are as follows. First, to describe the safety and efficacy of the transthoracic, endovascular and endobronchial FM insertion techniques for peripheral pulmonary lesions (PPLs). Second, to analyse performance in terms of the migration and tracking rates of different FM types. Recent developments in FM tracking for central lesions will also be reviewed. In conclusion, for PPLs, the endobronchial approach provides a low rate of pneumothorax, offers the possibility of concurrent diagnostic sampling for both the PPL and the lymph nodes, and, finally, reduces the intervention time compared to other techniques. In this context, coil-tailed and coil-spring FMs have shown the lowest migration rate with a consequently high tracking rate.

FIGURE 1

Flowchart of stereotactic lung radiation therapy using Cyberknife® guided by fiducial markers.

FIGURE 2

a) Linear gold (5.0 mm length and 0.5 mm diameter) fiducial marker (white star; Visicoil™ IBA Dosimetry, Bartlett, TN, USA). Reproduced from [47] with permission. b) Coil-spring (diamond-shaped 3:2 mm) fiducial marker (black star; Tornado®, Cook Medical, Bloomington, IN, USA). In the left part of the photograph, the distal part of the Progreat® (Terumo, Shibuya, Japan) guidewire (black arrow) inserted in the microcatheter (white arrow) can be seen.

FIGURE 3

Fiducial marker (FM) types.

FIGURE 4

a) Reformatted planification computed tomography (CT) scan (performed before irradiation) image of lung windowing with maximum intensity projection (MIP) and an inverted-colour effect. The solid peripheral pulmonary lesion (PPL, measuring on long axis 11 mm, 440 mm³) is located at the lateral segment of the left lower lobe and surrounded by two visible coil-spring fiducial markers (cs-FMs; diamond-shaped 3:2 mm; Tornado®, Cook Medical, Bloomington, IN, USA) in this oblique reformat. b) Reformatted planification CT scan (performed before irradiation) image of lung windowing with MIP of the same PPL. The minimal distance between the PPL and the border of the closest cs-FM is measured (17.5 mm). c) Reformatted planification CT scan (performed before irradiation) image of lung windowing with MIP of the same PPL. Three cs-FMs are identifiable in this oblique reformat.