Reproducibility of the bladder shape and bladder shape changes during filling.

Area of Science:

• Medical Physics
• Radiotherapy
• Medical Imaging

Background:

• High-precision radiotherapy for bladder cancer is challenged by bladder motion and volume fluctuations.
• Accurate bladder localization and shape prediction are essential for effective treatment delivery.

Purpose of the Study:

• To investigate urinary inflow rates and bladder shape reproducibility over time.
• To develop a predictive model for short-term bladder shape changes in radiotherapy planning.

Main Methods:

• Acquired serial MRI scans over 1 hour for 18 healthy volunteers to measure urinary inflow.
• Recorded additional MRI series for 10 volunteers to assess long-term bladder shape reproducibility.
• Utilized a previously developed bladder shape model for localization and prediction.

Main Results:

• Bladder volume increased linearly over time, with significant inter-individual variation in urinary inflow (mean 9 ± 3 cc/min).
• Intra-volunteer variation in inflow was low (mean SD 0.4 cc/min), showing a negative correlation with age.
• Bladder shape reproducibility varied, with the caudal part being most stable; cranial and posterior parts showed greater variation due to bowel and rectal changes.

Conclusions:

• Urinary inflow reproducibility and a bladder shape model can accurately predict short-term bladder shape changes.
• This predictive capability is vital for enhancing image-guided radiotherapy for bladder cancer patients.
• Understanding bladder dynamics improves treatment accuracy and patient outcomes.