Radiation Therapy : Brachytherapy


Treatment Planning Algorithm for Implanting Radioactive Seeds During Brachytherapy

UW–Madison researchers have developed a non-iterative treatment planning algorithm for implant brachytherapy. The algorithm builds off the previous invention to create a faster and more accurate treatment planning algorithm.

The method starts by determining what doses are required for specific locations in the area of interest. An importance function is developed based on the match between the original dose pattern and a hypothetical seed moved through the different locations in the pattern. The locations then are ranked and reserved for a seed in the order of importance. Every time a seed is reserved, the original dose pattern is updated to show the difference between the current dose pattern and the dose provided by seeds at the reserved locations. This difference then is used to update the importance function.  These steps are repeated until a predetermined criterion is met.

Directionally Emitting Radioactive Sources for Brachytherapy

UW-Madison researchers have developed radioactive seeds that emit radiation in a directional pattern for improved treatment of diseased tissue at the interface between diseased and healthy tissue. Each seed has a shield that partially blocks the radiation, controlling the direction of the emission. They are placed in diseased tissue by a needle and anchored so that they cannot rotate. These radiation sources are particularly useful in permanent-implant brachytherapy for the treatment of prostate cancer.

Device for Placement of Needles and Seeds in Radiotherapy

UW-Madison researchers have now developed an automated stage that allows the insertion of needles at freely selected, rather than fixed, locations within the prostate and at optimum insertion angles. Under the control of a computer program, the automated stage guides the insertion needle, loaded with seeds, to a selected position. Once positioned, the needle is either automatically inserted into the prostate or the surgeon inserts it by hand, receiving tactile feedback from the device when the proper depth has been reached. Next, the device pushes a seed through the needle and into the tissue, and a wire holds the seed in place as the needle is withdrawn. Once the needle has been withdrawn, the wire is also retracted.

Method and Device for Planning Treatment with Implanted Radioactive Seeds

A team of UW-Madison medical physicists has now developed an extremely rapid optimization algorithm for planning the placement of radioactive seeds in prostate tissue. The technique is based on a “greedy” algorithm and an adjoint function for a tissue region-of-interest (ROI). The adjoint function is defined as the sensitivity of the dose in the ROI to the placement of a single seed at any arbitrary position. For each seed position, a ratio is computed that is the sum of the adjoint values for sensitive structures (e.g., urethra) divided by the adjoint value for the target tumor in the ROI. An optimization process then follows in which the greedy algorithm inspects the ratios and ranks the seed positions based on their ability to irradiate the tumor while sparing sensitive tissue. The greedy algorithm then designs the overall seed pattern by choosing the most favorable seed positions.