SS 30 - Radiation and Cancer Physics 4: Novel Treatment Techniques and Early Clinical Experience
Presenter(s)
C. Glide-Hurst1, J. Slagowski2, Y. Yan2, J. Miller3, J. Hayes4, C. Hoffman4, A. N. Schreuder4, B. Burger5, C. Harari6, M. Kang7, S. E. O'Reilly6, B. Durkee8, and P. M. Harari9; 1Department of Human Oncology and Medical Physics, University of Wisconsin Hospitals and Clinics, Madison, WI, 2Department of Human Oncology, University of Wisconsin-Madison, Madison, WI, 3Department of Human Oncology, University of Wisconsin Hospitals and Clinics, Madison, WI, 4Leo Cancer Care, Middleton, WI, 5Leo Cancer Care, middleton, WI, 6University of Wisconsin-Madison, Madison, WI, 7University of Wisconsin, Madison, WI, 8Department of Human Oncology, University of Wisconsin, Madison, WI, 9Department of Human Oncology, University of Wisconsin School of Medicine and Public Health, Madison, WI
Purpose/Objective(s):
The advent of a novel upright patient positioning system (PPS) coupled with diagnostic-quality vertical CT introduces significant opportunities to support high precision upright simulation, image guidance, and online adaptive proton therapy.
Upright positioning offers advantages to supine treatment including more favorable organ and tumor positioning, enhanced patient comfort, and a compact footprint that increases accessibility to proton therapy.
Here, we present a comprehensive technical characterization of this state-of-the-art upright CT scanner, highlighting its groundbreaking image-guided radiation therapy (IGRT) capabilities for the first time.
Materials/Methods:
A preclinical upright CT system (85 cm diameter bore, 6 degree-of-freedom PPS) underwent technical characterization. PPS isocentricity was evaluated using a precision dial gauge. The weighted Computed Tomography Dose Index (CTDIw) was measured for body and head configurations and compared to manufacturer stated values. To evaluate inter- and intra-session CT number repeatability over several months of operation, a Multi-Energy CT phantom with tissue-mimicking inserts was scanned (120 kVp, 250 mAs) over 6 separate sessions (5 repeat scans/session). Longitudinal image quality was assessed using an ACR 464 phantom. End-to-end (E2E) testing consisting of simulation, data transfer, treatment planning with a 3D isocenter shift, image registration, and couch shift was conducted. Stopping-power ratios (SPRs) were computed using the Bethe equation and fitted with piecewise linear regression to yield the Hounsfield look-up table. Proton dose calculation was verified in an anthropomorphic head and neck phantom and compared to supine CT (technology company, 120 kVp).
Results:
PPS isocentricity was within 0.5 mm. CTDIw results were within 5% of manufacturer stated values. Excellent intra- and inter-session CT number repeatability was observed (standard deviation <1.3 HU and <1.1 HU, respectively). Image quality metrics were consistent over time for high contrast resolution (8 lp/cm) and uniformity (17-19 HU). For E2E testing, image-based automatic online image registration to a reference position yielded phantom shifts within 1 mm from expected. Couch correction and subsequent re-imaging demonstrated residual shifts <0.3 mm in all directions. Point dose agreement between upright and supine thoracic treatment plans was within 1%.
Conclusion:
This pioneering study has provided the technical groundwork for the integration of upright CT in particle therapy. Upcoming research will focus on human imaging trials and the combination with our proton beam line to achieve high-precision, online adaptive particle therapy.
