ESTRO 2024 - Abstract Book

S69

Invited Speaker

ESTRO 2024

AmsterdamUMC, Radiotherapy, Amsterdam, Netherlands

Abstract:

In contemporary radiotherapy departments, technological advancements continuously redefine the landscape of treatment planning, aiming to optimize precision, efficiency, and patient outcomes. At the Radiation Oncology Department in the Amsterdam UMC (AUMC), we have built a vast experience with MRI-guided online adaptive radiotherapy. SBRT treatments are delivered with two MRIdian Linacs with online treatment plan adaptation and breath-hold delivery. This abstract presents a newly implemented approach at the AUMC for an MR-only workflow at the MR-linac without the need for a CT scan. Initially tailored for prostate cancer treatments is now extended to a broader spectrum of anatomical sites, starting with the pancreas cancer treatments. MR-only workflows on an MR-linac present several benefits; more efficient utilization of the CT scanner within the Radiation Oncology Department and increased patient comfort. For an MRI-only workflow several methods can be applied: Artificial Intelligence (AI) based synthetic-CT generation and bulk-density overrides. We have implemented an alternative method based on the utilization of a comprehensive database of CT scans of previous patients to find the best match to the current patient. The CT scan associated to a previous patient showing the highest anatomical agreement is registered with Deformable Image Registration (DIR) to the MR-scan of current patient to generate an Electron Density (ED) map. Initially successfully developed and implemented years ago for patients undergoing prostate treatments, the wish is to further extend this technique beyond prostate treatments. The first treatment site to extend this workflow further to is to pancreatic cancer patients. Therefore, a database with over a 100 CT scans of previously treated pancreatic cancer patients was built. A semi-automated application has been developed to search for the 4 CT-scans in the database with showing the highest agreement with the anatomy of the current patient. Subsequently, the CT scan of the best candidate undergoes a multimodality DIR-based registration with the MRI of the patient to be treated to generate an ED map for dose calculation purposes. This MR only workflow for pancreatic tumor patients has been tested retrospectively on 13 patients by recalculation and comparison with the ground truth (treatment plan with the actual CT-scan). An accuracy of <2% was found in all organ at risk structures and GTV coverage. Only the coverage of the PTV V95% ≥ 95% of the prescribed dose, showed a deviation of > 2% in 2 cases. Clinical implementation of this workflow was followed by training of the rest of dosimetrists and prospectively benchmarking the MR-only workflow for additional 5 patient cases. Prior to that, a multidisciplinary evaluation of the MR-only workflow took place to address questions and possible impact of changes. Additional anatomical sites will also benefit from the implementation of the MR-only workflow on the MR-linac. For instance, patients with kidney, adrenal gland and liver tumors may also benefit from such workflow. Hereby, about 80% of all MRIdian patients may only need an MRI-simulation appointment, no more CT-scan needed.

3436

MR-only treatment preparation

Francesca Nella

University Hospital of Zurich, Department of Radiation Oncology, Zurich, Switzerland

Abstract: