A dose-volume histogram based optimization algorithm for ultrasound guidedprostate implants

The task of treatment planning for prostate implants is to find an optimal seed configuration, comprising the target coverage and dosimetric considera tion of critical structures such as the rectum and urethra. An efficient me thod to accomplish this is to use an inverse planning technique that derive s the optimized solution from a prescribed treatment goal. The goal can be specified in the voxel domain as the desired doses to the voxels of the tar get and critical structures, or in the dose volume representation as the de sired dose volume histograms (DVHs) of the target and critical structures. The DVH based optimization has been successfully used in plan optimization for intensity-modulated radiation therapy (IMRT) but little attention has b een paid to its application in prostate implants. Clinically, it has long b een known that some normal structure tolerances are more accurately assesse d by volumetric information. Dose-volume histograms are also widely used fo r plan evaluation. When working in the DVH domain for optimization one has more control over the final DVHs. We have constructed an objective function sensitive to the DVHs of the target and critical structures. The objective function is minimized using an iterative algorithm, starting from a random ly selected initial seed configuration. At each iteration step, a trial pos ition is given to a randomly selected source and the trial position is acce pted if the objective function is decreased. To avoid being trapped in a le ss optimal local minimum, the optimization process is repeated. The final p lan is selected from a pool of optimized plans obtained from a series of ra ndomized initial seed configurations. (C) 2000 American Association of Phys icists in Medicine. [S0094-2405(00)01210-4].