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Accuracy and Stability of Deep Inspiration Breath Hold in Gated Breast Radiotherapy; a Comparison of Two Tracking and Guidance Systems

A Kalet, N Cao*, WP Smith, L Wootton, L Young, J Meyer, University of Washington, Seattle, WA


(Wednesday, 8/1/2018) 10:00 AM - 10:30 AM

Room: Exhibit Hall | Forum 5

Purpose: To characterize displacement of patient breath-hold positioning and compare tracking system performance for Deep Inspiration Breath Hold (DIBH) gated left breast radiotherapy.

Methods: 29 consecutive left breast DIBH patients (655 fractions) were treated under the guidance of Calypso (Varian, Palo Alto) and 27 consecutive patients (490 fractions) were treated using Catalyst HD (C-RAD, Uppsala, Sweden). The Calypso system tracks a centroid determined by two radiofrequency transponders, with a manually enforced institutional tolerance of +/- 3mm, while the surface image based C-RAD system utilizes a form of real-time biometric feedback to track a pre-selected point with an institutional tolerance of +/- 2mm enforced by the Elekta Response gating interface. DIBH motion data from Calypso was extracted to obtain the displacement of breath hold marker in ant/post direction from a set-zero reference point. Ant/post point displacement data from C-RAD was interpreted by computing the difference between raw tracking points and the center of individual gating windows. Mean overall displacements were compared using Welsh's unequal variance t-test. Wilcoxon rank sum test were used for statistical analysis with P < 0.05 considered significant.

Results: Mean overall displacements for Calypso and C-RAD were 0.33 +/- 1.17 mm and 0.20 +/- 0.40 mm, respectively, with t-test comparison P-value < 0.012. Absolute errors for Calypso and C-RAD displacement were 0.95 +/- 0.75 mm and 0.35+/- 0.29 mm, respectively, with Wilcoxon rank sum test P-value < 2x10^-16. Average C-RAD standard deviation per fraction was found to be 0.27 +/- 0.05 mm vs. 0.75 +/- 0.19 mm for Calypso.

Conclusion: The 0.60 mm reduction in planned breath-hold error and 0.48 mm reduction in deviation per fraction suggest that the use of functionalities available in Catalyst HD, such as a biofeedback-based system and patient surface matching, improves accuracy and stability for DIBH gated left breast radiotherapy.


Not Applicable / None Entered.


TH- RT Interfraction motion management : Development (new technology and techniques)

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