Magnetic resonance imaging in postprostatectomy radiotherapy planning.

Area of Science:

• Radiotherapy
• Medical Imaging
• Oncology

Background:

• Accurate definition of the clinical target volume (CTV) is crucial for effective prostate bed radiotherapy.
• Conventional treatment planning relies on computed tomography (CT), which may have limitations in soft-tissue visualization.

Purpose of the Study:

• To evaluate the impact of magnetic resonance imaging (MRI) on defining the CTV and organs at risk in prostate bed radiotherapy planning.
• To compare CTV delineation using CT versus T1-weighted (T1w) and T2-weighted (T2w) MRI.

Main Methods:

• Retrospective analysis of 21 patients undergoing prostate bed radiotherapy.
• Delineation of CTV on CT, T1w MRI, and T2w MRI according to European Organization for Research and Treatment of Cancer guidelines.
• Evaluation of CTV magnitude, agreement, and spatial differences between imaging modalities.

Main Results:

• MRI significantly reduced CTV size compared to CT (13% for T1w, 9% for T2w).
• Spatial differences were noted, with CTV generally smaller in the superior and superolateral aspects on MRI.
• Organs at risk, such as the urinary bladder and rectum, showed differential delineation between CT and MRI, and between T1w and T2w MRI.

Conclusions:

• MRI-based planning reduces the CTV for prostate bed radiotherapy, particularly in the superior region.
• T2w MRI provides a more precise definition of the prostate bed CTV compared to conventional CT planning.
• These findings suggest MRI integration can optimize radiotherapy targeting and potentially reduce toxicity.