Dosimetric Comparison of Gated Versus Reconstructed Non-Gated Treatment Delivery of Pancreas Lesions in MRgRT
B Lee1,2, S Hoffman3, A Podgorsak1,2*, A Abusubha1,2, G Sawa1,2, A Sethi1,2, W Small1,2, T Refaat1,2, (1) Department of Radiation Oncology, Stritch School of Medicine, Cardinal Bernardin Cancer Center, Loyola University Chicago, Maywood, IL, 60153, USA (2) Department of Radiation Oncology, Loyola University Medical Center, Maywood, IL, 60153 USA (3) Department of Medical Physics, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA,
Presentations
TU-D930-IePD-F5-5 (Tuesday, 7/12/2022) 9:30 AM - 10:00 AM [Eastern Time (GMT-4)]
Exhibit Hall | Forum 5
Purpose: To quantify the dosimetric variation for organs-at-risk (OARs) between gated and non-gated treatment delivery by retrospective analysis of MRgRT sagittal cine video logs acquired during patient treatment.
Methods: An IRB-approved retrospective study was performed for pancreas patients treated with respiratory-gated MRgRT. 2D-sagittal cine delivery records for five pancreas patients were analyzed for GTV motion and to reconstruct respiratory phases using baseline treatment plans. A 10-phase respiratory cycle was simulated by binning the GTV centroid positions, with the zero-position assumed at end-of-exhale. Dose was recalculated with an isocenter shift corresponding to the respiratory phases, and a plan summation approximated the equivalent non-gated treatment delivery of the same plan. Dosimetric variation to OARs were evaluated based on published and institutional dose criteria for D0.5cc <36Gy for stomach, duodenum, and small and large bowel.
Results: The average magnitude of respiratory motion for pancreas patients was 8.6 ± 3.8mm (max 14.8mm, min 5.4mm), with superior-inferior motion of -8.3 ± 3.4mm (max 5.4mm, min -13.7mm) and anterior-posterior motion of 0.76 ± 2.9mm (max 5.4mm, min -2.4mm). All baseline plans met institutional dose criteria. Changes in duodenal D0.5cc was 1.92 ± 5.73Gy (max 9.78Gy, min –3.09Gy), stomach D0.5cc was 0.72 ± 1.08Gy (max 2.19Gy, min –0.21Gy), small bowel D0.5cc was –0.593 ± 1.85Gy (max 1.60Gy, min –2.59Gy), and large bowel D0.5cc was –1.10 ± 0.56Gy (max –0.42Gy, min –1.79Gy). Two non-gated patient calculations exceeded institutional criteria (D0.5cc=41.98Gy to stomach, D0.5cc=39.90Gy to duodenum).
Conclusion: This work demonstrates a method for quantifying the dosimetric variations of OARs for gated and non-gated treatments using the 2D-sagittal cine logs from MRgRT. OAR dose can vary significantly in gated versus non-gated treatment for pancreas patients, although some patterns appear random. This method will be applied to assess OAR dose equivalence of gated versus non-gated plans of equivalent PTV coverage.
Keywords
Not Applicable / None Entered.
Taxonomy
TH- External Beam- Photons: Motion management - intrafraction
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