Evaluation of segmentation algorithms for generation of patient models in radiofrequency hyperthermia

Abstract

Time-efficient and easy-to-use segmentation algorithms (contour generation) are a precondition for various applications in radiation oncology, especially for planning purposes in hyperthermia. We have developed the three following algorithms for contour generation and implemented them in an editor of the HyperPlan hyperthermia planning system. Firstly, a manual contour input with numerous correction and editing options. Secondly, a volume growing algorithm with adjustable threshold range and minimal region size. Thirdly, a watershed transformation in two and three dimensions. In addition, the region input function of the Helax commercial radiation therapy planning system was available for comparison. All four approaches were applied under routine conditions to two-dimensional computed tomographic slices of the superior thoracic aperture, mid-chest, upper abdomen, mid-abdomen, pelvis and thigh; they were also applied to a 3D CT sequence of 72 slices using the three-dimensional extension of the algorithms. Time to generate the contours and their quality with respect to a reference model were determined. Manual input for a complete patient model required approximately 5 to 6 h for 72 CT slices (4.5 min/slice). If slight irregularities at object boundaries are accepted, this time can be reduced to 3.5 min/slice using the volume growing algorithm. However, generating a tetrahedron mesh from such a contour sequence for hyperthermia planning (the basis for finite-element algorithms) requires a significant amount of postediting. With the watershed algorithm extended to three dimensions, processing time can be further reduced to 3 min/slice while achieving satisfactory contour quality. Therefore, this method is currently regarded as offering some potential for efficient automated model generation in hyperthermia. In summary, the 3D volume growing algorithm and watershed transformation are both suitable for segmentation of even low-contrast objects. However, they are not always superior to user-friendly manual programs for contour generation. When the volume growing algorithm is used, the contours have to be postprocessed with suitable filters. The watershed transformation has a large potential if appropriately developed to 3D sequences and 3D interaction features. After all, the practicality and feasibility of every segmentation method critically depend on various details of the user software as pointed out in this article.

Online feedback focusing algorithm for hyperthermia cancer treatment

“…As shown in Figures 4 and 5A, the initial focus was lost in the first few iteration steps and then regained in subsequent iterations. The use of an idealized initial model relieves the burden of building an accurate and detailed patient model (1 to 2 days if built manually [59] and ∼4h. if built semi-automatically [59,60]) and the associated time-intensive numerical simulations.…”

“…The use of an idealized initial model relieves the burden of building an accurate and detailed patient model (1 to 2 days if built manually [59] and ∼4h. if built semi-automatically [59,60]) and the associated time-intensive numerical simulations. Depending on the initial model used, when the maximum eigenvector was used as the first heating vector Figure 6(a), the feedbackfocusing algorithm successfully raised approximately 90-99% of the tumor temperature ≥ 43°C and only about 25% of normal tissue temperature ≥ 41°C.…”

“…To characterize the effect of such an error, the actual patient position was assumed to be shifted by 2 cm in the +y direction (see Figure 2) from the position assumed in the initial model. Moreover, since building a detailed patient model can require 1 to 2 days if built manually [59] or ∼4h if built semi-automatically [59,60], a simple idealized model was considered instead. The simple model consisted of a homogeneous, muscle equivalent tissue volume, with the same external geometry as the actual patient leg.…”

Thermal Therapy, Part IV: Electromagnetic and Thermal Dosimetry

“…An extensive set of visualization and evaluation tools must complete a treatment planning system. 162 For treatment planning or post-treatment evaluation of completed therapy, a more detailed study of the dielectric parameters, anatomical structures, and blood perfusion mechanism is necessary. Monitoring and control of temperatures during treatment requires advanced thermal imaging.…”

Connectivity-based local adaptive thresholding for carotid artery segmentation using MRA images

“…Validation is typically performed using one of two different types of truth models. The most straightforward approach to validation is by comparing the automated segmentations with manually obtained segmentations [41][42]. This approach, besides suffering from the drawbacks outlined (complex and time consuming), does not guarantee a perfect truth model since an operator's performance can also be flawed.…”