MARS MRI assessment of fatty degeneration of the gluteal muscles in patients with THA: reliability and accuracy of commonly used classification systems.

INTRODUCTION: Fatty degeneration of the gluteal muscles on metal artefact reduction sequence (MARS) MRI has been shown to correlate with poor functional outcomes, particularly in patients with total hip arthroplasty (THA). Standardized, reliable classification systems that permit assessment of fatty gluteal infiltration are needed for clinical decision making. This study aimed to compare the reproducibility and accuracy of commonly used MRI classification systems for fatty gluteal atrophy in THA patients. METHODS: MARS magnetic resonance images of 82 patients with unilateral THA were analysed by three independent trained observers. The readers evaluated fatty degeneration of the gluteus minimus, gluteus medius, and gluteus maximus according to 3 widely used classification systems: Goutallier, Quartile, and Bal and Lowe. Interobserver and intraobserver repeatability were determined using the weighted Kappa test. Quantitative evaluation of the proportion of intramuscular fat based on MR signal intensities was obtained and represented the gold standard. RESULTS: Mean interobserver agreement for the Quartile classification system (0.93) was higher compared with Goutallier classification system (0.87) and the Bal and Lowe classification system (0.83; range 0.79-0.88; p = 0.04). Intraobserver repeatability was significantly higher for the Quartile classification system (weighted kappa 0.91, 0.89, 0.85) compared with the Bal and Lowe classification system (weighted kappa 0.83, 0.77, 0.75; p < 0.01) and Goutallier classification system (weighted kappa 0.83, 0.77, 0.75; p = 0.04). Agreement with the gold standard measurements was significantly higher in the Quartile classification system (0.88, 0.84, 0.81) compared with the Goutallier classification system (0.80, 0.77, 0.78; p = 0.02) and Bal and Lowe classification system (0.76, 0.74, 0.73; p < 0.01). DISCUSSION: This study directly compared three clinically used MRI classification systems for fatty gluteal muscle atrophy in THA patients. Our findings demonstrate that although all three classification systems demonstrate good reproducibility and accuracy, the Quartile classification system is superior to the others in terms of intraobserver reliability and accuracy to quantify fatty gluteal degeneration in THA patients.

Evaluating Intensity Modulated Proton Therapy Relative to Passive Scattering Proton Therapy for Increased Vertebral Column Sparing in Craniospinal Irradiation in Growing Pediatric Patients.

PURPOSE: At present, proton craniospinal irradiation (CSI) for growing children is delivered to the whole vertebral body (WVB) to avoid asymmetric growth. We aimed to demonstrate the feasibility and potential clinical benefit of delivering vertebral body sparing (VBS) versus WVB CSI with passively scattered (PS) and intensity modulated proton therapy (IMPT) in growing children treated for medulloblastoma. METHODS AND MATERIALS: Five plans were generated for medulloblastoma patients, who had been previously treated with CSI PS proton radiation therapy: (1) single posteroanterior (PA) PS field covering the WVB (PS-PA-WVB); (2) single PA PS field that included only the thecal sac in the target volume (PS-PA-VBS); (3) single PA IMPT field covering the WVB (IMPT-PA-WVB); (4) single PA IMPT field, target volume including thecal sac only (IMPT-PA-VBS); and (5) 2 posterior-oblique (-35°, +35°) IMPT fields, with the target volume including the thecal sac only (IMPT2F-VBS). For all cases, 23.4 Gy (relative biologic effectiveness [RBE]) was prescribed to 95% of the spinal canal. The dose, linear energy transfer, and variable-RBE-weighted dose distributions were calculated for all plans using the tool for particle simulation, version 2, Monte Carlo system. RESULTS: IMPT VBS techniques efficiently spared the anterior vertebral bodies (AVBs), even when accounting for potential higher variable RBE predicted by linear energy transfer distributions. Assuming an RBE of 1.1, the V10 Gy(RBE) decreased from 100% for the WVB techniques to 59.5% to 76.8% for the cervical, 29.9% to 34.6% for the thoracic, and 20.6% to 25.1% for the lumbar AVBs, and the V20 Gy(RBE) decreased from 99.0% to 17.8% to 20.0% for the cervical, 7.2% to 7.6% for the thoracic, and 4.0% to 4.6% for the lumbar AVBs when IMPT VBS techniques were applied. The corresponding percentages for the PS VBS technique were higher. CONCLUSIONS: Advanced proton techniques can sufficiently reduce the dose to the vertebral body and allow for vertebral column growth for children with central nervous system tumors requiring CSI. This was true even when considering variable RBE values. A clinical trial is planned for VBS to the thoracic and lumbosacral spine in growing children.