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Is Pretreatment Imaging at Each Treatment Fraction Needed in Spine SBRT to Enable Margin Reduction?


D Mynampati

D Mynampati1*, R Yaparpalvi1 , M Garg1 , L Hong1 , H Kuo1 , W Tome'1,2 , (1)Montefiore Medical Center, Bronx, New York, (2)Albert Einstein College of Medicine, Bronx, New York

Presentations

SU-E-J-202 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To study translational setup errors of Spine SBRT treatments using BodyFIX immobilization system and the potential for margin reduction using pretreatment imaging.

Methods: 148 online match results of 39 Spine SBRT patients treated at our institution were reviewed. All treatments performed using Varian, TrueBeam and MI™, BodyFIX immobilization device. Prescriptions (dose-fractionation schedules) for the patients in the study are 8 Gy X 3 (n=24), 6 Gy X 4 (n=10) and 16Gy X 1 (n=5). For all patients, OBI was performed on verification day and before each treatment. Recorded shifts are from adopted couch positions after physician online review of KV image-pair and CBCT. Data analyzed by computing Mean error (M), Systematic error (Σ) and Random error (σ) for three translation directional shifts and 3D Vector length. To estimate correlation between imaging sessions, Anova-test and T-Test with alpha of 0.05 performed over the data.

Results: Mean error (M), Systematic error (Σ) and Random error (σ) of Vertical direction are -1.81mm, 4.05mm and 2.01mm respectively. Similarly, Errors in Longitudinal direction are 0.76mm (M), 4.21mm (Σ) and 1.34mm (σ ). Errors in Lateral direction are -0.16mm (M), 3.22mm (Σ) and 1.83 mm (σ). Mean, SD and CI95% of 3D Vector lengths are 7.93mm, 4.41mm and 0.7mm respectively. Anova-test results show, P-Values for longitudinal and lateral shifts are > 0.3 and P-value of vertical shift is 0.054. This signifies mean of the each imaging session are not significantly different. T-Test on treatment sessions data of vertical shifts with respect to verification day shows, mean of Vertical shifts on verification day are different from Vertical shifts on treatment sessions.

Conclusion: Results shows immobilization with BodyFIX is reproducible in the mm range. To eliminate systematic error component and to enable margin reduction, pretreatment imaging prior to each treatment fraction is indispensable.



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