MIRD Pamphlet No. 14: a dynamic urinary bladder model for radiation dose calculations

Area of Science:

• Medical Physics
• Nuclear Medicine
• Radiological Dosimetry

Background:

• Standard MIRD phantom bladder models have limitations in physiological realism.
• Previous models have incorporated features like expanding bladder volume and variable urine input, but a comprehensive model was lacking.

Purpose of the Study:

• To develop and validate a new urinary bladder model that incorporates physiologically realistic factors.
• To calculate radiation dose to the bladder wall for various radiopharmaceuticals using the new model.
• To determine optimal voiding parameters for minimizing bladder radiation dose.

Main Methods:

• Developed a new urinary bladder model with a variable-volume spherical source and constant-volume spherical shell wall.
• Incorporated variable urine entry rate (three hydration states), initial volume, residual volume, and first void time.
• Calculated radiation dose estimates for multiple radiopharmaceuticals at various bladder wall depths.

Main Results:

• The new model simulates expanding bladder contents and variable wall thickness.
• Voiding schedule includes reduced nighttime urine entry rate.
• Determined specific initial bladder volumes and first void times that minimize radiation dose for each tested radiopharmaceutical.

Conclusions:

• The developed model offers improved physiological realism for urinary bladder dosimetry.
• Personalized voiding protocols based on initial bladder volume and first void time can reduce radiation dose.
• Findings provide guidance for establishing effective dose reduction protocols in nuclear medicine.