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Breathing Pattern of Patients with and Without SBRT Immobilization Device

D Michalski

D Michalski1*, M Huq1, G Bednarz1, R Lalonde2, Y Yang1, D Heron1,(1) University of Pittsburgh Medical Center, Pittsburgh, PA, (2) D3 Radiation Planning, Pittsburgh, PA,

SU-E-T-231 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To investigate the effect of SBRT immobilization device on patients breathing pattern.
SBRT requirements for setup errors are more stringent than for standard radiation therapy. The patients are placed in an immobilization device and tumor motion management is applied if respiration induced tumor motion exceeds 0.5 cm. Patients' respiration pattern is a crucial component of the performance of gating technology. For our ongoing IRB approved project we acquire pretreatment 4DCT scan of patients immobilized in a device and with immobilization foil removed.
These scans provided 20 pairs of breathing tracks of the Varian RPM external block placed on patients abdomen. The motion amplitude and time was read from the files. Cubic spline based resampling of the track was applied to space the point evenly. Recursive moving average filter covering 1 second was applied to demarcate peaks and troughs and identify the individual respiratory cycles. The Fourier low pass filter of 1Hz was applied to remove the high frequency noise that is not related to respiration. The base line drift was extracted applying ideal Fourier low pass filter of 0.1Hz. The descriptive statistics was used for respiratory peaks, troughs and their variability. The normality of the data was ascertained with Box-Cox transformation. Period, exhalation and inhalation time were analysed. Welch t-test for means and F- test for variances was used. To examine the characteristics of the distribution Shapiro-Wilk and Kolgomorov-Smirnov test were used.
The base drift affects motion but does not have an effect on respiration cycles. Peaks has smaller than troughs variability. Shannon entropy and Lempel-Ziv multilevel complexity are statistically dissimilar for both scans. The same is for other extracted parameters. Immobilization reduces base line shift.
Conclusion: Immobilization devices tends to reduce the drift in patient breathing which can be viewed as a time dependent systematic error.

Funding Support, Disclosures, and Conflict of Interest: We wish to acknowledge the support of Varian Medical Systems for this project through a research grant.

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