Variation in prostate position relative to adjacent bony anatomy

Area of Science:

• Radiation Oncology
• Medical Physics
• Prostate Cancer Imaging

Background:

• Accurate patient positioning is critical for high-precision conformal radiotherapy in prostate cancer treatment.
• The prostate gland is not directly visible on portal imaging, necessitating the use of bony anatomy for setup.
• Understanding the variability in prostate position relative to pelvic landmarks is essential for treatment accuracy.

Purpose of the Study:

• To quantify the variation in distance between the prostate and adjacent bony anatomy during external beam radiotherapy simulations.
• To establish the degree of prostate gland mobility in different directions relative to pelvic bone structures.

Main Methods:

• Nine patients with previously treated prostate cancer underwent multiple external radiotherapy treatment simulations.
• Simulator radiographs were acquired in anterior-posterior and lateral views after each patient setup.
• Implanted 125I seeds served as fiducial markers for prostate localization, visible on simulator films.

Main Results:

• The prostate exhibited a standard deviation of 0.8 mm in lateral movement.
• Ventrodorsal and craniocaudal movements showed greater variation, with standard deviations of 1.5 mm and 1.7 mm, respectively.
• Pelvic bone structures provided a reliable reference for prostate position, with least mobility laterally.

Conclusions:

• Pelvic bone anatomy serves as a reasonably accurate surrogate for prostate positioning in radiotherapy.
• The prostate demonstrates the least mobility in the lateral direction.
• Greater prostate displacement occurs in the craniocaudal and ventrodorsal directions, requiring consideration in treatment planning.