(Tuesday, 7/31/2018) 10:00 AM - 10:30 AM
Room: Exhibit Hall | Forum 3
Purpose: Treatment planning of high-dose-rate brachytherapy (HDRBT) is typically performed under a high time pressure. A planner uses a dose-modification tool provided by a treatment planning system to generate a plan. The tool, however does not necessarily ensure optimality of the resulting plan. The purpose of this study is to perform a comprehensive analysis of previously treated cases to investigate the quality of these plans and potential of further dosimetric improvement and benefits in clinical outcome.
Methods: A total of 96 HDRBT plans with a tandem-and-ovoid applicator previously treated at our institution were collected. Each plan was fed to an in-house developed inverse treatment-planning tool that minimizes dose of critical organs subject to the same CTV coverage as in the original plan. The optimization tool was repeatedly launched for 1000 times with different organ weighting factors to generate a spectrum of competing plans. D2cc of the bladder, rectum, and sigmoid in the generated plans were compared against those of the original plan. Toxicity rate of organs were computed using published models and compared with that of the original plan.
Results: Compared with the original plan, relative D2cc reductions in the bladder, rectum, and sigmoid were 5.41%, 14.7%, and 5.21% with the largest reduction being 47.1%, 59.9%, and 45.9%, respectively. Correspondingly, toxicity rates of bladder, rectum, and sigmoid were reduced by 3.81%, 6.15%, and 5.27%, and the maximum relative reduction being 24.53%, 58.22%, and 69.54%, respectively.
Conclusion: Under the time pressure with a simple dose modification tool, the clinically delivered plans still have a relatively large room of improvement. This highlights the need for inverse optimization in HDRBT.
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