S2143
Physics - Inter-fraction motion management and daily adaptive radiotherapy
ESTRO 2026
which limits their implementation in clinical settings [4]. To overcome these challenges, we implemented a dose prediction-based automated planning solution to investigate the potential benefits of daily replanning. Material/Methods: A retrospective dataset of 28 left-sided breast cancer patients treated with volumetric modulated arc therapy (VMAT) under deep inspiration breath hold (DIBH) was analyzed. Clinical treatment plans were dose-accumulated to daily anatomy using deformed CT images, generated through deformable image registration (DIR), corresponding to the anatomy observed in daily cone beam CTs (CBCTs).Automated adaptive plans were created using a customized deep learning-based U-net model for dose prediction. Fraction-specific dose distributions predicted by the model were condensed into dose volume histogram (DVH) curves and converted into Monaco® (Elekta AB) treatment plan templates. An in-house script was developed to automate VMAT plan optimization. Dose- accumulated clinical plans and automated adaptive plans were compared using DVH metrics for planning target volume (PTV) and organs at risk (OARs), including the heart and lungs. Results: PTV coverage increased with adaptation (Figure 1). Daily adaptation achieved a median PTV D95% of 96.0% (range: 92.2%–97.1%) compared to 93.4% (range: 91.1%–97.2%) of dose-accumulated clinical plans (Table 1). Additionally, the goal of D95% > 95% for PTV coverage was met by 93.6% of adaptive fractions and 23.3% of dose-accumulated clinical plans. The adapted plans also retained the intended PTV mean dose.Daily replanning demonstrated OAR sparing benefits, although the magnitude of improvement varied between patients. The most notable benefits were seen in the ipsilateral lung, where V16Gy decreased in 78.8% of the fractions and by a median of 2.1 percentage points (pp) (Table 1). In contrast, the heart V4Gy and contralateral lung V2.5Gy increased slightly by 0.6 pp and 0.2 pp, respectively, along with their mean doses (Table 1).
Conclusion: For ART decision-making, greater emphasis should be placed on Δ D than on Δ V. The improved CUSUM charts are valuable for monitoring dose metric variations during treatment and may guide adaptive radiotherapy in individual patients. References: Xiao Q, Li G. Application and Challenges of Statistical Process Control in Radiation Therapy Quality Assurance. Int J Radiat Oncol Biol Phys. 2024 Jan 1;118(1):295-305. Gan Y, Langendijk JA, Oldehinkel E, Lin Z, Both S, Brouwer CL. Optimal timing of re- planning for head and neck adaptive radiotherapy. Radiother Oncol. 2024 May;194:110145. Li G, Xiao Q, Dai G, Wang Q, Bai L, Zhang X, Zhang X, Duan L, Zhong R, Bai S. Guaranteed performance of individual control chart used in gamma passing rate-based patient- specific quality assurance. Phys Med. 2023 May;109:102581. Keywords: nasopharyngeal carcinoma, cumulative sum chart Digital Poster Highlight 2858 Automated CBCT-based daily adaptation for breast cancer radiotherapy Nina Pesonen 1,2 , Tuomas Virén 2 , Mikko Mankinen 3 , Akseli Leino 2,4 , Janne Heikkilä 2 , Hiran Maladenige 1,2 , Jan Seppälä 2 , Henri Korkalainen 1,2 1 Department of Technical Physics, University of Eastern Finland, Kuopio, Finland. 2 Cancer Center, Kuopio University Hospital, Kuopio, Finland. 3 Department of Radiotherapy, Päijät-Häme Central Hospital, Lahti, Finland. 4 Department of Nuclear Medicine, Satasairaala, Pori, Finland Purpose/Objective: Daily anatomical variations can affect treatment accuracy and quality in modern radiotherapy [1,2]. Adaptive radiotherapy (ART) aims to address these variations by adjusting the treatment plan according to the patient’s daily anatomy [2,3]. ART techniques, however, can be time-consuming and labor-intensive,
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