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.
Not Applicable / None Entered.