First clinical application of Image-guided IOERT in recurrent rectal cancer - Technical procedure.
PO-2034
Abstract
First clinical application of Image-guided IOERT in recurrent rectal cancer - Technical procedure.
Authors: Falk Roeder1, Gerd Fastner1, Christoph Fussl1, Felix Sedlmayer1, Markus Stana1, Johannes Berchtold1, Tarkan Jäger2, Jaroslav Presl2, Philipp Schredl2, Klaus Emmanuel2, Daniela Colleselli3, Gabriel Kotolacsi4, Philipp Scherer1, Philipp Steininger5, Christoph Gaisberger1
1Paracelsus Medical University Hospital, Department of Radiation Therapy and Radiation Oncology, Salzburg, Austria; 2Paracelsus Medical University Hospital, Department of Visceral and Thoracic Surgery, Salzburg, Austria; 3Paracelsus Medical University Hospital, Department of Urology, Salzburg, Austria; 4Paracelsus Medical University Hospital, Department of Anesthesiology, Salzburg, Austria; 5Paracelsus Medical University, Institute of Research and Development of Advanced Radiation Technologies, Salzburg, Austria
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Purpose or Objective
IOERT is a method for dose escalation applying high single doses during surgery. In contrast to EBRT, no 3D dose calculation based on the individual intraoperative patient´s anatomy was available so far. We developed a workflow to overcome this limitation using intraoperative CBCT imaging.
Material and Methods
Commercially available non-metal-containing operation table-top inserts and IOERT applicators were used. Our IOERT suite was recently equipped with a mobile CBCT scanner (ImagingRing, medPhoton GmbH) with a large effective bore (102 cm) capable of covering a variable FOV of up to 49.1x49.1x25.4 cm. Two orthogonal images are taken initially to define the optimal ROI including tumor bed and IOERT applicator base, which is subsequently captured in the course of CBCT acquisition using the independently rotable arms and four independently moveable collimator jaws. The system features an automated scaling (heuristic object and head scatter correction as well as beam hardening correction) of Hounsfield Units, which was checked prior to clinical use by suitable standardized phantoms with inserts of differing densities. This allows the application of one density conversion table independent of imaging preset, geometry, and patient anatomy, for standard clinical cases. After transfer of the images to the TPS (Radiance, GMV), dose calculation was performed using a Monte Carlo algorithm.
Results
Our patient suffered from locoregional recurrence of rectal cancer. He had already received neoadjuvant full course chemoradiation during initial treatment and was treated with neoadjuvant moderately dose-reduced re-chemoradiation prior to surgery for his recurrence. After gross total resection, we placed an adequate applicator and performed CBCT imaging via remote control. The applicator position was corrected after the CBCT scan and confirmed by a second scan. A dose distribution and the adequate monitor units were calculated to cover the tumor bed with 12 Gy (90% isodose) based on the intraoperatively aquired CBCT images. The patient was moved beneath the IOERT-LINAC (Mobetron, Intraop). After automated soft-docking, IOERT was performed while the patient was video-monitored.
Conclusion
Image-guided IOERT with real-time intraoperative CBCT based 3D-dose calculation is feasible. For the first time, precise intraoperative image-based verification of the correct applicator position and IOERT planning procedures similar to the standards of EBRT are enabled.