Program Information
Theoretical Investigation of Relationship Between Rectal Motion and Wall Thickness
G Grigorov1 , J Chow2*, G Bauman3 , (1) Grand River Regional Cancer Centre, Kitchener, ON, (2) Princess Margaret Cancer Centre, Toronto, ON, (3) London Health Sciences Centre, London, ON
Presentations
SU-I-GPD-T-393 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: This study analysed theoretically the possible correlation between the rectal motion and wall thickness in prostate IMRT.
Methods: The analytic model is based on two probability density functions (pdf), one for the wall thickness (pdfWT) and the other the rectal motion (pdfM). Histogram of the rectal wall thickness variability was obtained from more than 500 randomly selected prostate patients. The average wall thickness regarding the rectal contours was determined according to the planning CT dataset of the patient. The pdfTW is represented as a three-mode Gaussian mixture of specific (μF, σF); (μPF, σPF) and (μE, σE) and individual weights (wF, wPF and wE) representing full (F), partially full (PF) and empty (E) rectum states, respectively. In our study, the pooled standard deviation of the rectal deviation obtained from published data was based on three different techniques; CT scans, implanted seeds and bone anatomy. These two pdf functions were convolved with a correlation coefficient in the range from -1 to 1.
Results: A mathematical algorithm based on the rectal geometric deviations using a 2D pdf function integrating the variability of the rectal motion and wall thickness was developed. In additional, possible correlation between pdfWT and pdfM is graphically presented. The new 2D pdf function can be described as a product-mixture of the 2D pdfM&TW function for a single anatomic direction. For the new function, 14 specific mean values (μ), standard deviations (σ) and weights (w) are required. Arbitrary correlation factors are used to show the tendency of the modification of the pdfM&TW function profile and projection of contours in the equi-probability levels.
Conclusion: The 2D profile of the pdfM&TW function was found depending significantly on the correlation between the pdfM and pdfTW functions. Further investigation of the correlation over the rectal toxicity has an impact on prostate IMRT.
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