CT- and MRI-based seed localization in postimplant evaluation after prostate brachytherapy

Area of Science:

• Medical Physics
• Radiotherapy Oncology
• Image Analysis

Background:

• Accurate postimplant evaluation is critical for effective prostate seed brachytherapy.
• Uncertainties in seed reconstruction can impact treatment dosimetry.
• Comparing imaging modalities for seed localization is essential for improving accuracy.

Purpose of the Study:

• To compare uncertainties in CT- and MRI-based seed reconstruction after prostate seed brachytherapy.
• To evaluate interobserver variability in seed localization.
• To quantify the dosimetric impact of seed detection variability across different postplan techniques.

Main Methods:

• Seven physicists performed seed reconstruction on postimplant CT and MRI-T1 images from three patients.
• Interobserver variability was calculated against a reference seed set for each modality.
• Dosimetric impact on D90 was assessed for CT, CT+MRI-T2, and MRI-T1+MRI-T2 techniques.

Main Results:

• CT-based seed reconstruction showed lower interobserver variability (1.1 mm) compared to MRI-T1 (3.0 mm).
• Variability in D90 due to seed reconstruction was 1.5% for CT and 1.3% for CT+MRI-T2.
• MRI-T1-based reconstruction resulted in a 6.6% D90 variability.

Conclusions:

• Seed reconstruction accuracy is higher with CT compared to MRI-T1-weighted imaging.
• The difference in seed reconstruction uncertainties must be considered alongside contouring and fusion uncertainties.
• This comparison aids in evaluating the overall reliability of postplan techniques in prostate brachytherapy.