3396 - Surface-Guided End-Exhale Breath-Hold for Primary Kidney Cancer Stereotactic Ablative Radiotherapy

Purpose/Objective(s):

Reliable respiratory motion management is essential for safe and effective kidney stereotactic ablative radiotherapy (SAbR), where millimeter-level accuracy directly impacts target coverage and organ-at-risk sparing. We evaluated whether a surface-guided radiation therapy (SGRT) end-exhale breath-hold (ExBH) technique could provide more reproducible renal positioning than conventional spirometry-guided deep-inspiration breath-hold (DIBH), and whether this approach is clinically feasible for routine renal SAbR delivery.

Materials/Methods:

Feasibility was first evaluated retrospectively using simulation CT data from a pancreatic SAbR patient cohort treated with a comparable workflow. Patients underwent four single-breath-hold CT acquisitions (spirometry DIBH, n=8; SGRT DIBH, n=8; SGRT ExBH, n=9). Inter–breath-hold kidney position offsets were quantified using rigid registration focused on the evaluated kidney and analyzed in the superior–inferior (SI), anterior–posterior (AP), and left–right (LR) directions, reporting the percentage of offsets within 3 mm and 5 mm (typical target margin in this clinic). After feasibility was established, two renal cancer patients (5 fractions) were treated with SAbR using SGRT ExBH, with a validation CBCT acquired after every ~1000 MUs. Kidney offsets between breath-holds were assessed immediately after each fraction to ensure continued safety.

Results:

In the feasibility cohort, SGRT ExBH demonstrated improved SI reproducibility (largest motion direction), with 98.3% of SI offsets within 5 mm (vs 85.1% spirometry DIBH and 90.7% SGRT DIBH) and 90.0% within 3 mm (vs 44.7% and 72.1%, respectively). AP and LR offsets were also consistently within 5 mm across techniques, with ExBH maintaining high agreement (AP 98.3%, LR 100.0%). In delivered treatments, 100% of kidney offsets were within 5 mm, with a mean absolute SI offset of 1.3 ± 1.0 mm; only one CBCT exceeded 3 mm, for which SGRT monitoring showed a concordant offset.

Conclusion:

SGRT end-exhale breath-hold improved renal tumor targeting accuracy and precision compared with conventional spirometry-guided breath-hold for renal SAbR. These findings support further study of margin reduction strategies using SGRT ExBH.

BH Technique	Spirometry DIBH	SGRT DIBH	SGRT ExBH
	Superior-Inferior
Kidney Offset <= 5 mm	85.1%	90.7%	98.3%
Kidney Offset <= 3 mm	44.7%	72.1%	90.0%
	Anterior-Posterior
Kidney Offset <= 5 mm	93.6%	97.7%	98.3%
Kidney Offset <= 3 mm	89.4%	90.7%	96.7%
	Left-Right
Kidney Offset <= 5 mm	97.9%	100.0%	100.0%
Kidney Offset <= 3 mm	93.6%	100.0%	100.0%