Generating prostate models by means of geometric deformation with application to computerized training of cryosurgery

Abstract

Purpose As a part of an ongoing effort to develop computerized training tools for cryosurgery, this study presents a scheme to geometrically deform a 3D organ template in order to generate clinically relevant prostate models. The objective for creating deformed models is to develop a database for computerized training. This study further presents compiled literature data on the likelihood of cancer tumor growth in the prostate and its relationship to the prostate shape. Methods Cryosurgery is typically performed on patients with localized prostate cancer, found in stages T3 or earlier. The analysis is restricted to cancer originating from the peripheral zone of the prostate as majority of cancer cases are found within this region. The distribution of geometric features, likely to be found in prostates at stage T3, is determined using tumor growth patterns that attribute to changes in the prostate surface. The extended free-form deformation (EFFD) method is applied on a 3D prostate template to create localized surface changes that resemble cancerous prostates. Results Deformed prostate models were generated using the process of: (1) selecting the desired deformation parameters—extra capsular extension (ECE) range and location, and (2) manipulating the lattice control points until the deformed prostate model's ECE length and transverse span fall within the pre-selected ranges. Conclusions EFFD is an efficient method to rapidly generate prostate models for the application of computerized training of cryosurgery. While the selected criteria for deformation do not lead to a unique shape, since the contours of the deformed body are randomly selected, they do lead to shapes resembling cancer growth, as various growth histories can lead to different ECE shapes of the same maximum extension.

Simulation-Based Cryosurgery Intelligent Tutoring System Prototype

“…For each case, the trainee was presented with a prostate and urethra model and asked to use ten cryoprobes to plan a layout. Each case used a different geometrical model of the prostate and the urethra, which was generated by means of geometrical deformation, based on ultrasound-reconstructed organs (28). All cases were limited to a uniform insertion depth for cryoprobes (29), where the trainee can only select the x and y coordinates for each probe (follow-on studies are planned to address multi-depth configurations, which presents a higher level of planning complexity in 3D).…”

Simulation-Based Cryosurgery Training

“…While ten cryoprobes were found appropriate for the trainee’s first layout in the context of the current investigation, future studies will attempt to optimize the number of cryoprobes in this new strategy. Prostate models were generated by geometrically deforming base prostate shapes, reconstructed from preclinical ultrasound scanning, as described previously (18). …”

Development of a computational simulation tool to design a protocol for treating prostate tumours using transurethral laser photothermal therapy

“…The given dimensions of an ellipsoid with a height of 46 mm, a width of 50 mm, and a depth of 45 mm were based on simplifications of typical human prostates and the prostatic urethra [1]. A PC3 tumour was modelled as a sphere with a diameter of 10 mm and its centre was located 10 mm below the urethral path.…”

“…As shown in Figure 1, the prostate is located below the bladder, surrounding the urethra. A normal prostate is slightly larger than a walnut [1]. In the absence of complications, the prostate will remain the same size for the duration of a lifespan [2].…”