3018 - Tracking the Invisible: Primary Analysis of Real-Time Image Guidance in Liver SBRT from the XXXX : XXXX Trial

Y. Y. Lee^1,2, C. Sengupta³, D. Nguyen¹, H. Ball³, J. Chu⁴, J. Booth⁵, K. Van Gysen⁶, N. Hardcastle⁷, T. Moodie⁸, S. F. Liu², E. Brown², D. Mason⁹, B. Tacon¹⁰, B. Zwan¹⁰, S. C. Tang¹⁰, R. OBrien³, V. Gebski¹¹, T. W. Wang^1,8, and P. Keall³; ¹University of Sydney, Sydney, NSW, Australia, ²Princess Alexandra Hospital, Brisbane, QLD, Australia, ³ACRF Image X Institute, University of Sydney, Camperdown, NSW, Australia, ⁴Peter MacCallum Cancer Centre, Melbourne, VIC, Australia, ⁵Institute of Medical Physics, School of Physics, University of Sydney, Sydney, NSW, Australia, ⁶Nepean Cancer & Wellness Centre, Kingswood, NSW, Australia, ⁷Department of Physical Sciences, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia, ⁸Department of Radiation Oncology, The Crown Princess Mary Cancer Centre, Westmead, NSW, Australia, ⁹Napean Cancer & Wellness Centre, Kingswood, NSW, Australia, ¹⁰Central Coast Cancer Centre, Gosford, NSW, Australia, ¹¹NHMRC Clinical Trials Centre, University of Sydney, Sydney, Australia

Purpose/Objective(s): Stereotactic Ablative Body Radiotherapy (SABR) is an effective option in treating primary and metastatic liver cancers. Motion management and image guidance address liver deformation and target motion related to respiration and gastrointestinal motion. The primary aim of this study was to assess the dosimetric influence of using KIM, a real-time image guidance technology, over Cone Beam Cone Beam Tomography (CBCT).

Materials/

Methods: In this multi-institutional prospective trial, 32 patients with either hepatocellular carcinoma or oligometastatic liver disease suitable for SBRT using KIM guidance were enrolled, with each institution credentialled and treatment plans reviewed. Target motions were corrected during each fraction using KIM + external surrogate (a precision radiation medicine company or a technology company) gating, implanted fiducials serving as surrogates. A 3 – 5 mm gating threshold over 5 seconds was applied for beam-off and couch shifts, except in two cases where Breath-hold (BH) were inconsistent (15mm). Using a dose reconstruction method, the accuracy of KIM guided treatment was evaluated against standard of care relying on external surrogate.

Results: From January 2020 to November 2023, thirty-two patients were treated across six institutions in Australia, receiving 122 treatment fractions, with a median age of 66.5 years. The cases included 21 liver metastases and 11 hepatocellular carcinomas.

Th majority of patients (25/32) had a single lesion and primarily treated in breath-hold (25/32) and free-breathing (5/32) technique, with a median dose of 50 Gy over 5 fractions (range: 27.5 – 51 Gy in 3 – 5 fractions) using a 2 arc VMAT technique. The mean lesion diameter was 41.1mm (range: 17 – 103mm). Two patients were treated using standard treatment using CBCT without KIM guidance. The median PTV margin used was 5mm.

During 122 fractions, 107 motion correction events occurred in 25 of 32 patients (87%), with single events in 24 fractions and multiple events (up to four or more) in 30 fractions. To date, the evaluation of the first 20 patients demonstrated that all patients treated with KIM received doses within 5% of the planned dosimetry. Without KIM, two patients would have had >5% dose errors to GTVD100 and one patient would have exceeded the stomach dose constraint. For two of 24 BH patients, KIM detected irregular motion, requiring PTV margin increases to 15 mm, motion undetectable with external surrogates alone. There was no > grade 2 toxicity related to radiation treatment observed in the patient cohort.

Conclusion: This study demonstrates that integrating continuous KIM guidance enhances precision and confidence of liver SBRT delivery. Without continuous intrafraction image guidance, at least a 5mm PTV expansion would be advised to counter intrafraction motion. Future applications may include safe reduction of PTV margins and customisation for individual patients.