Quantification of the geometric uncertainty when using implanted markers as a surrogate for lung tumor motion

Background Fiducial markers are used as surrogates for tumor location during radiation therapy treatment. Developments in lung fiducial marker and implantation technology have provided a means to insert endobronchially tracking of tumors. This study quantifies the surrogacy uncertainty (SU) when using implanted surrogate position. Methods We evaluated SU 17 patients treated prospective electromagnetic-guided MLC trial. Tumor were segmented on all phases treatment planning 4DCTs frames pretreatment kilovoltage fluoroscopy acquired from lateral frontal views. The difference position relative end-exhale was calculated both imaging methods distributions uncertainties analyzed. Results mean (range) motion amplitude 4DCT scan 5.9 mm (1.7–11.7 mm) superior–inferior (SI) direction, 2.2 (0.9–5.5 left–right (LR) 3.9 (1.2–12.9 anterior–posterior (AP) direction. Population-based analysis indicated symmetric centered close 0 mm, with maximum 5th/95th percentile values over axes ?2.0 mm/2.1 4DCT, ?2.3/1.3 fluoroscopy. There poor correlation between measured that per-patient basis. observed increasing motion. Based analysis, (95% CI) 5% (2%–8%) magnitude SI 16% (6%–26%) LR 33% (23%–42%) AP no dependence distance tumor. Conclusion quantified due use Population 95th range up 2.3 indicating approximate contribution total geometric uncertainty. relatively small compared motion, but substantial Due estimations patient-specific SU, it is recommended population-based margins account this component