Magnetic Resonance Guided Radiation Therapy (MRgRT) Prostate Motion and Margins

Area of Science:

• Radiation Oncology
• Medical Imaging
• Prostate Cancer Treatment

Background:

• Planning target volume (PTV) margins are crucial for accurate radiation dose delivery.
• Magnetic resonance-guided radiation therapy (MRgRT) offers improved imaging for potential margin reduction.
• Optimal PTV margins in MRgRT for prostate cancer (PCa) require further investigation.

Purpose of the Study:

• To evaluate intra-fractional prostate movement during MRgRT.
• To determine appropriate PTV margins for PCa patients undergoing MRgRT.
• To assess the impact of adaptive radiotherapy on PTV margins.

Main Methods:

• Retrospective analysis of 18 PCa patients treated with a 1.5T MR-Linac.
• Offline registration of initial and verification MR scans to measure prostate displacement (AP, LR, SI).
• Calculation of random and systematic errors and PTV margins using the Van Herk formula.

Main Results:

• Mean translational displacement: 1.2±0.9 mm (AP), 0.6±0.5 mm (LR), 1.1±0.8 mm (SI).
• Calculated PTV margins: 3.2 mm (AP), 1.7 mm (LR), 3.2 mm (SI).
• A trend of increased prostate motion with longer treatment duration was observed.

Conclusions:

• MRgRT shows potential for PTV margin reduction in PCa treatment.
• Increased on-couch time may correlate with increased prostate motion.
• Further research with larger cohorts and real-time monitoring is recommended for optimizing margin strategies.