Y. Liu1, S. N. Lim1, A. Jawahar2, B. B. Mittal1, and T. O. Thomas1; 1Department of Radiation Oncology, Northwestern University Feinberg School of Medicine, Chicago, IL, 2Department of Diagnostic Radiology, Northwestern University Feinberg school of Medicine, Chicago, IL
Purpose/Objective(s): Pain management for pancreatic cancer is crucial for patients, often involving high doses of opioids with associated side effects. Trials have been performed irradiating the celiac plexus (CP) for pain management, however, accurately delineating the CP using CT images is challenging. Due to limited soft tissue resolution, a large CP surrogate structure is required to ensure that the plexus is actually irradiated. To address this, use of MR-Linac based treatments is evaluated to determine whether MR can provide superior soft tissue contrast and allow for smaller treatment volumes by targeting individual ganglion. Materials/
Methods: MRIs and CTs from ten pancreatic cancer patients treated on 0.35T MR-Linac were retrospectively acquired. CP surrogate and celiac ganglia were contoured on MRI, while CTs were used only for electron density information. Planning was performed on a technology company treatment planning system, generating two sets of plans: CT plans treating surrogate structure and MR plans treating celiac ganglia. A proof-of-principle, unilateral plan was generated to demonstrate potential of targeting unilateral pain. Results: MR treatment plans delivered high dose to the celiac ganglia while treating significantly smaller tissue volumes, thereby protecting surrounding organs-at-risk (OARs) compared to CT plans. Average size of irradiated volumes for MRI plans was 1.16±1.24cc versus for 32.04±5.8cc CT plans (p<0.001). In comparison, mean dose to ganglia for MRI plans was 25.4±1.2Gy versus 20.8±2.4Gy for CT plans (p<0.001). Unilateral MRI plans can be created and delivered with comparable plan quality. Conclusion: This study suggests MR-Linac based celiac plexus irradiation could deliver higher dose to specific ganglia and lower dose to surrounding OARs, potentially reducing complications and enhancing pain control. Although prospective data is needed to evaluate achievable pain control and other clinical outcomes, this emphasizes the importance of MR-based treatment for more precise and effective radiation therapy in palliative care.
