Impact of Rotational Deviations on a Single Fiducial Based Respiratory Tracking

Abstract

Purpose/Objective(s): Few treatment options exist for recurrent GBM. HFSRT has been used as a salvage treatment strategy. Gross tumor volume (GTV) is usually based on pretreatment contrast enhanced T1-weighted (T1-contrast pre ) MR image. T2-FLAIR pre may detect additional subtle signal of tumor infiltration. This study aimed to investigate the patterns of recurrence following salvage HFSRT using T2-FLAIR image in addition to T1-contrast in target delineation for HFSRT. Materials/Methods: We retrospectively examined 13 patients with recurrent GBM treated with HFSRT from 2015 to 2017 who had local recurrence following HFSRT. A median dose of 30 (25-35) Gy in 5 to 10 fractions was delivered. The median time between HFSRT and recurrence after HFSRT was 178 (48-259) days. Diagnostic MRI was performed before and 4 weeks after HFSRT, and then every 4 -8 weeks. Separate GTVs using T1-contrast pre only, T2-FLAIR pre only, or T1 pre +-T2 pre , were contoured blindly by a single radiation oncology physician. Recurrence volume was delineated on the post-treatment T1-contrast (T1-contrast post ) MRI at the time of progression. The volume overlapping between pretreatment GTV and recurrence volume was calculated. The centroid distance between pre-and post-treatment volumes was measured as well. Wilcoxon test was used to assess the statistical significance of differences. Results: The median volumes overlapping between T1-contrast pre , T2-FLAIR pre , T1 pre +T2 pre and T1-contrast post were 18% (range: 0-100%, Q1: 12%, Q3: 40%), 52% (range: 0-90%, Q1: 24%, Q3: 59%) and 53% (range: 0-100%, Q1: 26%, Q3: 77%), respectively. The recurrent volume overlapping with T1 pre +T2 pre was significantly larger than the overlap with T1-contrast pre (pZ0.003). The median volume difference between T1-contrast pre and T2-FLAIR pre volumes resided in the recurrence volume was 3.9 cm 3 (range: 0-11.5 cm 3 , Q1: 0.2 cm 3 , Q3 5.6 cm 3 ). The centroid distance between volumes did not show significant difference. The median centroid distances between recurrence volume and T1-contrast pre volume, T2-FLAIR pre volume, and T1 pre +T2 pre volume were 1.3 cm (range: 0.3-4.9 cm, Q1: 0.8, Q3: 2.00), 1.3 cm (range: 0.3-4.7 cm, Q1: 0.8 cm, Q3: 2 cm) and 1.2 cm (range: 0.2-1.2 cm, Q1: 0.7 cm, Q3: 2.1 cm), respectively. Conclusion: A significant volume of recurrence occurred in the T1 pre +T2 pre region beyond the T1-contrast pre region. Further studies to investigate techniques incorporating T2-FLAIR pre region may improve GTV delineation for salvage HFSRT.Purpose/Objective(s): The impact of rotational deviations is investigated for single fiducial tumor tracking. The hypothesis is that the yaw rotation of a single fiducial will increase the uncertainty parameter in the tracking system. Materials/Methods: When treating a moving target, tumor tracking can be employed using a single fiducial. However, tracking using a single fiducial is limited to linear chasing and does not track rotation. A mini ball cube with 3, gold fiducials on its surface was placed insi...

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“…Although it is possible to perform tracking using a single marker, there remains some uncertainty. Such tracking is limited to linear chasing and does not track rotations [30]. When using a single marker, there is an implicit assumption that the location of this fiducial marker represents the median/average of the target volume [31].…”

“…The estimated random and systematic prediction errors were ≤ 2.8 mm in any direction for distances up to 100 mm. Christ et al [30] investigated the impact of rotational deviations on single-fiducial-based respiratory tracking, with the hypothesis being that the yaw (clockwise) rotation would increase the tracking uncertainty. They reported that an angle of ≥ 40° caused treatment inaccuracy of > 1 mm with single fiducial inside the target.…”