Objectives: To evaluate intrafractional fiducial marker position variations during stereotactic body radiotherapy (SBRT) in patients treated for liver metastases in visually guided, voluntary deep inspiration breath-hold (DIBH).
Comment on methods: 10 patients with implanted fiducial markers were studied. Three DIBH CTs were acquired for treatment planning. Pre- and post-treatment CBCTs were acquired for each of the three treatment fractions. Per-fraction marker position was evaluated on planar 2D kV images acquired during treatment fractions for 4 patients that each had three Gold Anchor markers implanted.
Results: The median difference in marker position was 0.3 cm (range, 0.0-0.9 cm) between the three DIBH CTs and 0.3 cm (range, 0.1 to 1.4 cm) between pre- and post-treatment CBCTs. The maximum intrafractional variation in marker position in craniocaudal (CC) direction on planar kV images was 0.7 to 1.3 cm and up to 1.0 cm during a single DIBH.
Conclusion: In order to increase treatment accuracy, it is necessary to apply real-time monitoring of the tumour or a reliable internal surrogate when delivering liver SBRT in visually guided, voluntary DIBH.