New developments in MRI for target volume delineation in radiotherapy.

Area of Science:

• Oncology
• Radiotherapy
• Medical Imaging

Background:

• Increasing use of Magnetic Resonance Imaging (MRI) in oncology for staging, response assessment, and radiotherapy treatment planning (RTP).
• Need for improved target volume definition in conformal and intensity-modulated radiotherapy.
• Comparison of MRI with CT, highlighting MRI's soft tissue characterization advantages despite lacking electron density information.

Purpose of the Study:

• To review the current and potential applications of advanced MRI techniques in radiotherapy treatment planning.
• To assess how MRI developments can improve target volume delineation and overcome limitations for RTP.
• To explore the role of MRI in enabling treatment individualization, dose escalation, and image-guided radiotherapy.

Main Methods:

• Review of MRI developments including new contrast agents (e.g., ultrasmall superparamagnetic iron oxide particles).
• Evaluation of advanced MRI techniques like dynamic contrast-enhanced MRI and diffusion MRI for tissue characterization.
• Assessment of ultrafast volumetric or cine MR sequences for dynamic target and organ at risk assessment.
• Discussion of MR distortion correction algorithms and image co-registration/fusion programs.

Main Results:

• MRI offers superior soft tissue characterization compared to CT for radiotherapy treatment planning.
• Advanced MRI techniques enhance the ability to define tumor regions, identify abnormal lymph nodes, and assess tissue characteristics.
• Ultrafast MRI sequences provide insights into temporal variations of target and organ at risk positioning.
• Correction algorithms and fusion programs effectively address MRI's limitations in electron density information and image distortion.

Conclusions:

• MRI, with its advanced techniques and correction strategies, significantly enhances radiotherapy treatment planning (RTP).
• These developments facilitate precise target volume delineation, leading to potential treatment individualization and dose escalation.
• MRI is poised to play a crucial role in the advancement of precision high-dose radiotherapy and image-guided treatments.