Inverse planning optimization for hybrid prostate permanent‐seed implant brachytherapy plans using two source strengths

The purpose is to demonstrate the ability to generate clinically acceptable prostate permanent seed implant plans using two seed types which are identical except for their activity. The IPSA inverse planning algorithms were modified to include multiple dose matrices for the calculation of dose from different sources, and a selection algorithm was implemented to allow for the swapping of source type at any given source position. Five previously treated patients with a range of prostate volumes from [Formula: see text] were re‐optimized under two hybrid scenarios: (1) using 0.32 and [Formula: see text] [Formula: see text] , and (2) using 0.64 and [Formula: see text] [Formula: see text]. Isodose lines were generated and dosimetric indices, [Formula: see text] , [Formula: see text] , [Formula: see text] , [Formula: see text] , [Formula: see text] , [Formula: see text] , and [Formula: see text] were calculated. The algorithm allows for the generation of single‐isotope, multi‐activity hybrid brachytherapy plans. By dealing with only one radionuclide, but of different activity, the biology is unchanged from a standard plan. All [Formula: see text] were within 2.3 percentage points for every plan and always above the clinically desirable 95%. All [Formula: see text] were identically zero, and [Formula: see text] is always below the clinically acceptable value of [Formula: see text]. Clinical optimization times for the hybrid plans are still under one minute, for most cases. It is possible to generate clinically advantageous brachytherapy plans (i.e. obtain the same quality dose distribution as a standard single‐activity plan) while incorporating leftover seeds from a previous patient treatment. This method will allow a clinic to continue to provide excellent patient care, but at a reduced cost. Multi‐activity hybrid plans were equal in quality (as measured by the standard dosimetric indices) to plans with seeds of a single activity. Despite the expanded search space, optimization times for these studies were still under two minutes on a modern day laptop and can be reduced to below one minute in a clinical setting. With the typical cost of a set of PPI seeds on the order of thousands of dollars, it is possible to reduce the cost of brachytherapy treatments by allowing for easier use of seeds left over from a previous patient or unused due to a cancelled treatment. PACS number: 87.55.D‐, 87.55.Kd, 87.55.ne