Author: Soon N. Huh, Perry B. Johnson, Jiyeon Park, Ryan Stevens 👨🔬
Affiliation: University of Florida Health Proton Therapy Institute, UF Health Proton Therapy Institute, UFHPTI 🌍
Purpose:
Low-Tesla MRI (0.23T Panorama MR Scanner, Philips) has been used for tumor progression during proton therapy treatments, and for initial contouring in addition to diagnostic MRI. The pulse sequences are optimized for specific tumors, as well as normal organs.
Methods:
There are four major pulse sequences: B-FFE3D (balanced Fast Field Echo), THRIVE (T1 High Resolution isotropic volume examination), T1 FFE3D, DTSE (dual turbo Spin echo). These pulse sequences are chosen due to high signal-to-noise ratio (or scan times) due to long scan times that is inherent for low-Tesla Scanners. The pulse sequences are further optimized for tumor definition type. Most targets are cystic components of craniopharyngioma, low grade glioma, anatomical changes from surgery, sarcoma, extremity sarcoma, and spine imaging with and without hardware. All the pediatric patients are scanned without any anesthesia, and without contrast. For pediatric patients (less than 6 years-old) a need for faster scans, and house-made immobilizations are required. With open bore MRI, parents can stay with patient during MRI scanning to aid in the process.
Results:
Low-Tesla MR images are compared with diagnostic MR images for contouring, and tumor progression. The target definitions are better than, or equivalent to diagnostic MR images. The 0.23T Panorama MR Scanner has been used to scan more than 1,200 scans in the last 12 years. The Cine MRI for prostate/liver motions has been used to provide useful information about rectal gas and bladder filling.
Conclusion: These optimized pulse sequences can acquire clinically useful MR images for contouring and tumor progression. They will be further optimized for MR/Linac systems. The pulse sequences and Cine MRI are optimized for specific tumors, as well as normal organs.