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An Operator-Free Inverse Planning Algorithm Using a Self-Adjusting Weighting Method for High Dose Rate (HDR) Brachytherapy

S Cui

S Cui1,2*, P Despres1,2 , L Beaulieu1,2 , (1) Centre hospitalier universitaire de Quebec, Quebec City, QC, (2) Universite Laval, Quebec City, QC


WE-AB-605-3 (Wednesday, August 2, 2017) 7:30 AM - 9:30 AM Room: 605

Purpose: To present an operator-free inverse planning algorithm (OF-IPA) for HDR brachytherapy, and compare it to a standard inverse planning algorithm (S-IPA) for prostate HDR brachytherapy cases.

Methods: An OF-IPA was developed based on a research version of Inverse Planning Simulated Annealing (IPSA, Elekta Brachy, Veenendaal, The Netherlands). The objective function was formulated based on a class solution. However, to simulate the trade-off process of finding a suitable objective function, additional organ-specific weighting factors (OWF) were introduced. Plans with OWF limit values for each organ and a plan with equally emphasis of all organs (class solution) were computed as anchor plans. With the dosimetric parameters obtained from anchor plans, the minimal limit of OWF to obtain a clinical plan (Target: V100>=95%, Bladder/Rectum: V75<=1cc, Urethra: D10<=120%) was estimated using a polynomial curve fit for each organ. These analytical relationships were previously extracted by studying the Pareto surface with a multi-criteria optimization tool for 140 prostate cases (training set). Ten plans were uniformly generated from the minimum to the maximum of OWF. From the plan pool, one plan was chosen and compared with the physician-approved plan obtained using a S-IPA (IPSA in Oncentra) for 236 new prostate cases (testing set).

Results: Compared with S-IPA, the number of plans not reaching clinically relevant parameters can be significantly reduced with OF-IPA from 120 (51%) to 78 (33%) cases. On average, OF-IPA led to similar target coverage and better urethra protection (-1.954% on D10). The results of V75 for bladder and rectum were comparable for S-IPA and OF-IPA. Single core computation time for OF-IPA is 3.9 mins (or 23 s/plan).

Conclusion: The presented approach significantly increases the frequency of plans meeting all criteria, even without manual adjustment of weighting factors by an operator. It is also generalizable to any HDR sites.

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