Needle Insertion and Radioactive Seed Implantation in Human Tissues: Simulation and Sensitivity Analysis<Fall 2001 ~ Present>
Abstract:
To facilitate training and planning for medical procedures such as prostate brachytherapy, we are developing an interactive simulation of needle insertion and radioactive seed implantation in soft tissues. We describe a new 2D dynamic FEM model based on a reduced set of scalar parameters such as needle friction, sharpness, and velocity, where the mesh is updated to maintain element boundaries along the needle shaft and the effect of needle tip and frictional forces are simulated. The computational complexity of our model grows linearly with the number of elements in the mesh and achieves 24 frames per second for 1250 triangular elements on a 750MHz PC. We use the simulator to characterize the sensitivity of seed placement error to physician-controlled and biological parameters. Results indicate that seed placement error is highly sensitive to physician-controlled parameters such as needle position, sharpness, and friction, and less sensitive to patient-specific parameters such as tissue stiffness and compressibility.
Human surgery is increasingly based on minimally invasive procedures that operate inside the body through narrow openings, reducing disturbance to healthy tissue, minimizing risk of infection, and speeding recovery.
Permanent seed brachytherapy is a minimally invasive medical procedure that has rapidly gained popularity for treating prostate cancer due to the excellent long-term outcomes. During the procedure, physicians use needles to permanently implant seeds inside the prostate that irradiate surrounding tissue over several months. The radioactive dose delivered should minimize healthy tissue damage while maximizing the destruction of cancerous cells. The success of this procedure depends on the accurate placement of radioactive seeds within the prostate gland.
Unfortunately, inserting and retracting needles causes the surrounding soft tissues to displace and deform: ignoring these deformations during the implantation results in misplaced seeds, as demonstrated above. A dynamic simulation can facilitate procedure planning by allowing a physician or optimizing planner to determine how physician-controlled and patient-specific parameters will affect seed placement.
In June 2002, a needle insertion procedure was performed in the operating room at the UCSF Medical Center on a patient undergoing brachytherapy treatment for prostate cancer. The procedure was recorded using an ultrasound probe in the sagittal plane. The first frame of the ultrasound video was used to manually generate the mesh and texture map for the simulator. Unknown simulation parameters were set so that the simulation output closely matched the ultrasound video. Snapshots from the simulation output can be compared with frames from the ultrasound video, and are available here. Although it is difficult for non-specialists to identify gland boundaries in ultrasound, UCSF medical experts comparing the two image sequences judged them as remarkably similar. We plan to perform controlled experiments to further evaluate simulation accuracy across multiple patients.
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