ESTRO 2024 - Abstract Book

S3777

Physics - Image acquisition and processing

ESTRO 2024

Hospital, Department of Radiation Oncology, Heidelberg, Germany. 4 Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Charlestown, USA. 5 Harvard Medical School, Department of Radiology, Boston, USA. 6 Harvard Medical School, Department of Radiation Oncology, Boston, USA

Purpose/Objective:

The availability of and demand for proton therapy is growing exponentially. Yet the long-term projected availability of such therapy is still very limited due to the high cost and large size of the equipment [1]. A proton therapy system without a gantry could reduce capital costs by having the patient rotate in front of a horizontally fixed proton beamline [1, 2]. In such settings, it is crucial to monitor the tumor location before and during treatment to enhance precise dose delivery. Combining ultra-low field (ULF) MRI (≤ 0.01 T) with proton therapy may offer several advantages: ULF MRI costs significantly less than other techniques, it has negligible effect on proton beams, it is easy to maintain, and it is safe to operate. However, as of yet, no study has investigated employing ULF MRI for imaging in different patient orientations that facilitate a horizontal proton beamline treatment. Breast tumors could be one of the disease sites to be treated with the patient in a sitting position. The aim of this in vivo study was to demonstrate the feasibility of using ULF MRI for breast imaging in healthy female participants in the sitting and prone positions, and to conduct an analysis of the attainable image quality. To this end, we developed an experimental setup for breast imaging in prone and sitting positions utilizing an ULF MRI scanner. The acquired images were analyzed to determine which anatomical structures were recognizable and whether the signal strength achieved in the chest wall was sufficient to visualize organs-at-risk, specifically the heart. Since treatment planning in proton therapy relies heavily on sparing organs-at risk, it is crucial to evaluate the visibility of the heart and chest wall in ULF MR breast images. Furthermore, the variations between the prone and sitting positions were assessed.

Material/Methods:

Imaging was conducted on 10 healthy female volunteers (ages: 21–65 years old) using a custom built 6.5 mT MRI system with a Larmor frequency of 276.18 kHz [3]. The ULF MRI scanner’s open design enables both prone and sitting position imaging. In-house developed wooden patient table and chair were used for imaging in prone and sitting positions (Figure 1). A single channel, conical shaped, single breast volume coil, developed in-house, was used. The imaging was conducted using a 3D balanced steady state free precession (bSSFP) sequence with an undersampling rate of 70%, 50 averages, a matrix of 64 × 72 × 21, and a spatial resolution of (3 × 3 × 8) mm 3 in the axial orientation. The total scan time was about 21 minutes.