Improving fiducial and prostate capsule visualization for radiotherapy planning using MRI

Area of Science:

• Radiotherapy
• Medical Imaging
• Prostate Cancer Treatment

Background:

• Fiducial markers (FM) are crucial for accurate radiotherapy (RT) delivery in prostate cancer.
• Assessing geometric integrity and contouring consistency is vital for RT planning.

Purpose of the Study:

• To evaluate the geometric accuracy and contouring consistency of T2*-weighted (T2*W) MRI sequences for prostate radiotherapy.
• To determine if T2*W sequences alone can visualize fiducial markers and delineate the prostate.

Main Methods:

• Ten patients from the PACE trial underwent CT, T2-weighted (T2W), and T2*W MRI.
• Three clinicians contoured the prostate on each imaging set.
• Interobserver variability was assessed using Monaco ADMIRE.
• Geometric accuracy and marker positioning were tested using specialized objects.

Main Results:

• T2*W MRI demonstrated significantly lower interobserver variability in prostate contouring compared to CT.
• All fiducial markers were visible in T2*W images (29/30 correctly identified), versus only 3/30 in T2W images.
• MRI showed minimal geometric distortion (<0.375 mm in-plane displacements), with symmetric signal loss around markers.

Conclusions:

• Prostate T2*W MRI sequences are geometrically accurate and provide consistent prostate contours.
• T2*W imaging effectively identifies fiducial markers and enables prostate delineation.
• This single sequence is suitable for use in mixed MR-CT workflows for radiotherapy planning.