ESTRO 2023 - Abstract Book

S606

Monday 15 May 2023

ESTRO 2023

for 8/10 patients. Allowing individual template changes, a clinically acceptable fast optimization plan was achieved for all 10 patients. The end-to-end dummy runs took on average 55 minutes. The average on-table time for the first four actually delivered fractions is 68 minutes. Figure 1 shows the percentage of time each individual workflow step accounted for. In only 1 delivered fraction a minor violation in PTV coverage (98.8%) was observed. Conclusion This study is the first step towards safely treating PCa patients with UHF when the whole SV needs to be treated and shows that online adaptive treatment on the CyberKnife is technically feasible, which was clinically demonstrated by the first patient treatment. We expect the total treatment time will reduce with ongoing experience in the UPRATE trial.

PD-0742 Accuracy of four models and update strategies to estimate liver tumor motion from external motion P. Samadi Miandoab 1,2 , E. Worm 1 , R. Hansen 1 , B. Weber 1,3 , M. Høyer 3 , P. Poulsen 1,3 1 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 2 Amirkabir University of Technology, Department of Energy Engineering and Physics, Tehran, Iran Islamic Republic of; 3 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus, Denmark Purpose or Objective This study investigates the accuracy of four models for estimating internal liver tumor motion based on continuous monitoring of external marker motion combined with four strategies for sparse intrafractional imaging of the internal tumor position. Materials and Methods The study includes 15 patients with liver tumors previously treated in free breathing with three-fraction SBRT. At all fractions the 3D internal tumor motion (INT) was monitored by implanted electromagnetic transponders (Calypso) while the vertical external motion (EXT) of a marker block on the patient’s abdomen was monitored by a camera. The ability of the following four external-internal motion correlation models (ECM) to estimate INT as function of EXT was investigated: (1) a simple linear model, (2) an augmented linear model, (3) an augmented quadratic model, and (4) an extended quadratic model (Fig 1.a). First, the ECM was constructed by fitting the internal and external motion during the first 60s of each fraction, and the fit accuracy was calculated as the root-mean-square error (RMSE) between ECM estimated and actual internal motion. Next, the following four strategies for updating each ECM during the remaining part of the fraction were simulated, and the RMSE of the estimated tumor motion was calculated: (A) no ECM update, (B) sampling the internal tumor position every 3s and continuously update all ECM parameters based on samples of the last 2 minutes, (C) sampling the internal tumor position every 3s and continuously updating the constant term of the ECM based on the five last samples, (D) sampling the internal tumor motion continuously for 20s before each field delivery and updating the entire ECM based on these samples.