Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_16_3273 - Dosimetric Impact of MRI Geometric Inaccuracy in MRI Only Based Radiation Therapy Workflow for Liver

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Dosimetric Impact of MRI Geometric Inaccuracy in MRI Only Based Radiation Therapy Workflow for Liver
T. Torfeh, R. W. Hammoud, S. P. Paloor, S. Aouadi, and N. Al Hammadi; Hamad Medical Corporation, Doha, Qatar

Purpose/Objective(s): Within the context of radiation oncology, the use of MR to improve tumor delineation remains challenging due mainly to artifacts present in the images. The purpose of this work is to evaluate the dosimetric impact of the MR geometric inaccuracy for liver cancer patients.

Materials/Methods: A digital phantom composed of different 3D targets simulating the liver, kidneys, the spine and a modular tumor was created. This phantom was used to generate an initial dataset composed of 10 axial slices of 512*512 pixels2 and 3 mm thickness. Geometrically distorted images were then generated by applying an inverse MR distortion map on the initial dataset. This map was calculated for a Cine sequence which is the standard sequence for target delineation in liver cancer RT using a control point based phantom. Targets on the original and distorted datasets were automatically delineated on an existing clinical software tool to eliminate inter-observer variations. A treatment plan for liver cancer treatment was computed on a commercially available planning system using the distorted dataset. This plan was then copied on the original dataset and the dose distribution was analyzed. A highly conformal volumetric modulated arc therapy (VMAT) technique using multiple noncoplanar arcs was used. Dose Volume Histograms (DVH) including D95, D50 Dmin and Dmean were benchmarked for accuracy measurements.

Results: The mean magnitude of the geometric distortion was 0.5, 0.7 and 0.9mm for radial distances of 50, 100 and 150 mm respectively.Our preliminary results showed differences of less than 5% in the DVH parameters for liver, kidneys and spine. Results also showed that the difference in the DVH is sensitive to the size and position of the tumor. Higher differences were recorded as the distance to the isocentre increases and/or the tumor size decreases.

Conclusion: The present work is a preliminary study aimed at putting in place an infrastructure allowing addressing the dosimetric impact of image deformation with any anatomy of interest. Further investigations using more realistic shapes will be carried out with the idea of producing 3D patient specific models for SBRT evaluation.

Author Disclosure: T. Torfeh: None. R.W. Hammoud: None. S.P. Paloor: None. N. Al Hammadi: None.

Rabih Hammoud, PhD

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