Validation of contour-driven thin-plate splines for tracking fraction-to-fraction changes in anatomy and radiation therapy dose mapping

Abstract

The goal of this study is to validate a deformable model using contour-driven thin-plate splines for application to radiation therapy dose mapping. Our testing includes a virtual spherical phantom as well as real computed tomography (CT) data from ten prostate cancer patients with radio-opaque markers surgically implanted into the prostate and seminal vesicles. In the spherical mathematical phantom, homologous control points generated automatically given input contour data in CT slice geometry were compared to homologous control point placement using analytical geometry as the ground truth. The dose delivered to specific voxels driven by both sets of homologous control points were compared to determine the accuracy of dose tracking via the deformable model. A 3D analytical spherically symmetric dose distribution with a dose gradient of approximately 10% per mm was used for this phantom. This test showed that the uncertainty in calculating the delivered dose to a tissue element depends on slice thickness and the variation in defining homologous landmarks, where dose agreement of 3-4% in high dose gradient regions was achieved. In the patient data, radio-opaque marker positions driven by the thin-plate spline algorithm were compared to the actual marker positions as identified in the CT scans. It is demonstrated that the deformable model is accurate (approximately 2.5 mm) to within the intra-observer contouring variability. This work shows that the algorithm is appropriate for describing changes in pelvic anatomy and for the dose mapping application with dose gradients characteristic of conformal and intensity modulated radiation therapy.

Performance of commercially available deformable image registration platforms for contour propagation using patient‐based computational phantoms: A multi‐institutional study

“…In this scenario, characterized by low image contrast, the regularization term of the algorithms failed to preserve the anatomy of the ROIs adjacent to the bladder, extending the deformation well beyond its support. Accuracy values proximal to the more reliable situation depicted by DVF1 have been found in mono‐institutional studies on self‐made software …”

“…In recent years, DIR has been extensively implemented in multiple RT applications: contour propagation, dose summation in IGART, [33][34][35][36] organ motion modeling on 4D scans 26,27,37 and multimodal image registration. 38,39 Although many commercial platforms are available, there is a lack of solid methods to provide DIR QA, resulting in fuzzy knowledge concerning the accuracy and reproducibility of these systems in typical clinical settings.…”

3-D Conformal radiotherapy of localized prostate cancer within an Austrian–German multicenter trial: a prospective study of patients' acceptance of the rectal balloon during treatment

“…Such studies, which aim to increase doses, further increase the need for optimal dose conformation, requiring accurate target localization and reproducibility of patient set-up. Accurate localization of the prostate using ultrasound-based systems [11][12][13], implanted radio-opaque markers or catheters [14][15][16] and corrections of prostate displacement at daily treatment using repeated CT-scans [17,18] are approaches to minimize the safety margins.…”

A multi-organ biomechanical model to analyze prostate deformation due to large deformation of the rectum

“…al., performed research using a contour-driven alignment and thin-plate splines for interpolation. 2 The algorithm assumed negligible in and out of plane rotations of the prostate. The accuracy, approximately 2.5 mm, was determined from implanted gold markers.…”