Program Information
Using Target Excursion and Deformation to Validate Planning Margins for SBRT Liver Patients Implanted with Electromagnetic Transponders
H Saleh1*, M Thompson2 , J Xu3 , M TenNapel4 , D Pokhrel5 , R Badkul6 , Y Altundal7 , (1) Univ of Kansas Hospital, Kansas City, KS, (2) University of Kansas Hospital, Kansas City, KS, (3) University of Kansas Hospital, Kansas City, KS, (4) University of Kansas, Kansas City, KS, (5) University of Kentucky, Lexington, KY, (6) University of Kansas Hospital, Kansas City, KS, (7) University of Kansas Hospital, Kansas City, KS
Presentations
TU-RPM-GePD-J(B)-2 (Tuesday, August 1, 2017) 3:45 PM - 4:15 PM Room: Joint Imaging-Therapy ePoster Lounge - B
Purpose: The primary objective of this study is to validate planning margins for liver SBRT patients implanted with electromagnetic transponders using daily target motion and target deformation.
Methods: Four liver SBRT patients were implanted with 3 electromagnetic transponders for patient setup, breathing motion tracking, and treatment gating. For each patient, a simulation CT scans and a 10-phase 4DCT scan were acquired. The Calypso system was used to track patient lesions at the rate of 30 Hz. Patients' ITVs ranged from 10 – 36 cm3. Patient were planned with uniform 7 mm CTV to PTV margins. The patients target motion and intertransponders distances were measured daily. Target daily motion and deformation were used to calculate new margins. Retrospectively, patients were re-planned using calculated margins. The mean CTV, PTV, normal liver tissue were evaluated. Repeated measures ANOVA was used to determine if average intrafraction target motion differed significantly between patients or over time.
Results: Average intrafraction target motions were 2.0±1.0 mm, 6.0 ±2.0, and 4.2±1.5 mm in the left/right, superior/inferior, and anterior/posterior directions respectively. Average target deformation is 0.8±0.5 mm. Calculated margins based on target motion and deformation are 2.8 ±1.1 mm, 6.0±2.0 mm, and 4.8 ±1.58 mm in the left/right, superior/inferior, and anterior/posterior directions respectively. Target motion did not significantly differ between patients or over time. With asymmetric margins plans, PTV volume was reduced by 25%, liver 21Gy volume was reduced by 12%, 100% of the ITV, and 95% of PTV are encompassed by the prescription dose.
Conclusion: This study shows that using implanted beacons during liver SBRT, an asymmetric margin can be used to reduce normal tissue toxicity without scarifying PTV coverage. Margin as small as 3, 6 and 7 mm in the Left/right, Superior/inferior, and Anterior/posterior directions respectively can be used to achieve desired dose coverage.
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