SU‐E‐T‐288: A Finite‐Element Model to Predict Prostate Displacement and Deformation Due to Bladder Filling, Rectal Distension and Patient Posture during Prostate Brachytherapy

Abstract

Purpose: Noninvasive determination of the location and deformation of pelvic organs in different stages of organs fullness and patient‐related situations encountered during the post‐implant prostate irradiation period. To help perform a more realistic treatment planning, a biomechanical finite‐element (FE) model is presented which provides prospective information on individual patients based on their initial MRI. Methods: Three patients with different prostate sizes (mean 54.6 g, range 32–71 g) were studied. Sequential MR images at different stages of bladder and rectal filling and patient positions (supine and left decubitus) were acquired. The geometry of pelvic organs was 3D reconstructed using MR images of supine patients and then transferred to the ABAQUS software for FE modeling. To tune the FE model, the tissue mechanical properties, distension forces and boundary conditions were adjusted to find the optimum combinations of these parameters, to individually produce the best match with images of each patient in all positions and stages. Finally, the model was tested in a predictive mode, in which the averaged coefficients were used to predict prostate displacement and deformation following bladder and rectal filling for supine and left‐decubitus positions. Results: The tuned model showed prostate displacements/deformations that matched the measurements to within 1 mm. In the supine position, modeling the same bladder and rectal volumes as their image‐based measurements, mean prediction discrepancy for bladder‐filling prostate displacement was 1.5 mm, and 2.9 mm for bladder filling plus rectal distension. The corresponding left‐decubitus discrepancies were 4.3 mm and 4.1 mm. Mean prostate deformation discrepancies due to large rectal distension were 1.0 mm in both supine and left‐decubitus positions. Conclusions: The model predicts prostate displacement and deformation with reasonable accuracy and offers the potential to provide more representative dose distributions. This model can potentially be used to improve organs dosimetry in brachytherapy.