Evaluation of Anatomical and Dose Variations in Stereotactic Body Radiotherapy of Early-Stage Lung Cancer Using a GPU-Based Deformable Image Registration Framework
C Han1*, A Santhanam2, B Stiehl2, L Naumann2, S Seshan3, A Liu1, (1) City of Hope National Medical Center, Duarte, CA, (2) University of California, Los Angeles, Los Angeles, CA, (3) SegAna Inc, Orlando, FL
Presentations
PO-GePV-M-173 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To evaluate daily anatomical and dose variations in stereotactic body radiotherapy (SBRT) for patients with early-stage lung cancer using RTapp®, a novel GPU-based deformable image registration (DIR) framework.
Methods: Ten clinical SBRT plans and associated daily imaging data for early-stage lung cancer were retrospectively retrieved. Each plan delivered a total dose from 40 to 60 Gy in three to five fractions using 6-MV photon beams. A compression belt was used in the abdominal region to limit respiratory motion. Daily cone-beam CT (CBCT) images were registered to the planning CT both by soft tissue matching and by bony landmark matching. Planning and treatment data were sent to a prototype GPU-based DIR framework for automated evaluation of daily anatomical changes and dose variations. DIR results for every fraction were validated according to AAPM TG-132 guidelines.
Results: Relative to thoracic bony landmarks, the planning target volume (PTV) had an average inter-fractional shift of 0.36±1.25 mm, 0.10±2.08 mm, and -0.10±2.24 mm in the lateral, anterior-posterior, and superior-inferior direction, respectively. Compared to planning CT simulations, the ipsilateral lung volume had an average daily variation of -2.5±42.8 cc (range: -108.3 – 114.4 cc), and the PTV had an average daily variation of -1.2±1.0 cc (range: -4.4 – 0.8 cc). Critical organ dose still met planning constraints despite daily dose variations. On average, daily mean dose to the PTV was reduced by 1.2±1.6%, while the prescription dose coverage V(Rx)(%) was reduced by 5.1±5.4% (range: -2.6 – 29.1%) compared to the treatment plans. DIR results gave a mean target registration error of 0.3 mm demonstrating high accuracy.
Conclusion: Significant anatomical and dose variations could happen despite the use of an abdominal compression belt system in SBRT of early-stage lung cancer. The DIR framework allowed rapid assessment of daily dose variations and could facilitate adaptive treatment planning.
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