A Novel 2D Probability Density Function Integrating the Rectal Motion and Wall Thickness in Prostate IMRT.

Area of Science:

• Radiation Oncology
• Medical Physics
• Image Analysis

Background:

• Prostate intensity-modulated radiotherapy (IMRT) requires accurate modeling of rectal variations.
• Rectal motion and wall thickness significantly impact radiation dose distribution.

Purpose of the Study:

• To develop a novel 2D probability density function (pdf) for rectal motion and wall thickness.
• To evaluate the impact of rectal variations on prostate IMRT dose distribution.

Main Methods:

• Developed a pdf model for rectal wall thickness variability based on 587 prostate cancer patients.
• Utilized a 2D Gaussian pdf combining rectal motion and thickness variability (2D pdfM&TW).
• Incorporated pdfs of rectal deformation, dose distribution, and wall thickness into planning optimization.

Main Results:

• The pdf for rectal wall thickness variability (pdfTW) was characterized as a three-mode Gaussian mixture representing different rectal states (full, partially full, empty).
• A 2D Gaussian pdf (2D pdfM&TW) was mathematically formulated as a product-mixture model.
• Numerical demonstrations showed the sensitivity of treatment plans to the 2D pdfM&TW.

Conclusions:

• The developed 2D pdfM&TW provides a mathematical framework for modeling rectal motion and thickness.
• This model aids in understanding and mitigating the impact of rectal variations on prostate IMRT.
• The study highlights the importance of incorporating rectal variability into radiotherapy planning.