S139
Brachytherapy - Physics
ESTRO 2026
target robustness, and similar OAR robustness compared to the clinical plans. The target robustness of the RIP was better than for the IP, with the robustness for the OARs being greatly improved compared to both the clinical and the IP. Figure 2b illustrates the dwell time homogeneity. The IP and the RIP are, with a few exceptions, more homogeneous than the clinical plans. The dwell point resulting in the large outlier for the RIP is positioned in the HR-CTV with >12 mm to the closest OAR.
Proffered Paper 4192 Robust optimization accounting for organ motion uncertainty in brachytherapy Lovisa Byman, Tom Niessen, Rasmus Bokrantz, Erik Engwall Research and Development, RaySearch Laboratories, Stockholm, Sweden Purpose/Objective: To evaluate a new robust optimization technique for HDR brachytherapy accounting for organ motion uncertainties and compare it to non-robust inverse plans, as well as to clinical plans. Material/Methods: Five patients previously treated for cervical cancer with an intracavitary tandem-ovoid applicator and interstitial needles were retrospectively replanned using inverse planning in a research version of the RayStation treatment planning system augmented with the capability for robust optimization with respect to organ motion for brachytherapy. The inverse planning was for comparative purposes repeated without incorporation of robust optimization.The objective function used for the inverse plans (IP) and the robust inverse plans (RIP) was formulated to meet the soft and hard dose aims defined in the EMBRACE-II study [1]. For the RIP, the objective additionally contained the dose objectives for a set of simulated images generated by deforming the planning image, with the bladder, rectum, sigmoid or bowel individually driving the deformation through a 5 mm shift in the posterior, anterior, superior, inferior, left, and right directions, see Figure 1. The applicator and interstitial needles were modeled as fixed.Robustness was evaluated using the same simulated images as in the robust optimization.
Conclusion: Robust inverse planning with simulated organ motion is a feasible method to improve the robustness of brachytherapy plans. Keywords: Robustness, Organ motion, Inverse planning References: [1] Pötter R, Tanderup K, Kirisits C, de Leeuw A, Kirchheiner K, Nout R, Tan LT, Haie-Meder C, Mahantshetty U, Segedin B, Hoskin P, Bruheim K, Rai B, Huang F, Van Limbergen E, Schmid M, Nesvacil N, Sturdza A, Fokdal L, Jensen NBK, Georg D, Assenholt M, Seppenwoolde Y, Nomden C, Fortin I, Chopra S, van der Heide U, Rumpold T, Lindegaard JC, Jürgenliemk- Schulz I; EMBRACE Collaborative Group. The EMBRACE II study: The outcome and prospect of two decades of evolution within the GEC-ESTRO GYN working group and the EMBRACE studies. Clin Transl Radiat Oncol. 2018 Jan 11;9:48-60.
Results: The result of the robust evaluation is illustrated in Figure 2a. Evaluated on the nominal planning images, the IP, and the RIP had lower target dose than the clinical plans. The IP had similar or higher OAR doses; however, doses were within or close to the EMBRACE- II planning aims in all cases. The RIP had similar or lower OAR dose compared to both the clinical and the IP.When evaluated on the simulated images, the clinical plans showed a high level of target robustness. However, in many scenarios, the OARs received dose exceeding the hard constraints. The IP had worse
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