ESTRO 2023 - Abstract Book

S723

Monday 15 May 2023

ESTRO 2023

Conclusion SMI evaluated at T12 is an independent prognostic factor for OS in non-metastatic OC patients treated with dCRT. SMI provides additional prognostic value over BMI and PS. Patients with low BMI and low SMI experienced the worst outcomes. At higher BMI the prognostic nature of low SMI was removed, emphasising the importance of close nutritional support in this population. Although external validation is required, this work suggests that a full understanding of body composition, over BMI alone, is needed for prognostic models in OC. MO-0876 BIOGUIDE-X: A First-in-Human Study of the Performance and Safety of Biology-Guided Radiotherapy L. Vitzthum 1 , M. Surucu 2 , M. Gensheimer 2 , N. Kovalchuk 2 , B. Han 2 , D. Pham 2 , D. Chang 3 , S. Shirvani 4 , D. Aksoy 4 , A. Maniyedath 4 , M. Narayanan 5 , A. Da Silva 5 , S. Mazin 6 , K. Al Feghali 4 , P. Iyengar 7 , T. Dan 7 , A. Pompos 7 , R. Timmerman 7 , O. Öz 8 , B. Cai 7 , A. Garant 7 1 Stanford University School of Medicine , Radiation Oncology, Stanford, USA; 2 Stanford University School of Medicine, Radiation Oncology, Stanford, USA; 3 University of Michigan School of Medicine, Radiation Oncology, Ann Arbor, USA; 4 RefleXion Medical, Clinical and Medical Affairs, Hayward, USA; 5 RefleXion Medical, Research and Development,, Hayward, USA; 6 RefleXion Medical, Corporate, Hayward, USA; 7 UT Southwestern Medical Center, Radiation Oncology, Dallas, USA; 8 UT Southwestern Medical Center, Radiology, Dallas, USA Purpose or Objective Biology-guided radiotherapy (BgRT) is a novel tracked dose delivery modality that uses real-time positron emission tomography (PET) to guide radiotherapy beamlets. Human subject data demonstrating accurate targeting with BgRT has not yet been presented. The BIOGUIDE-X study was performed with sequential cohorts of participants to (1) Identify the fluorodeoxyglucose (FDG) dose for BgRT on the RefleXion® X1 system and (2) Confirm that the emulated dose distribution of BgRT at delivery timepoints was consistent with a physician-approved radiotherapy plan. Materials and Methods This single-arm, open-label, prospective study included participants with at least 1 FDG-avid targetable primary or metastatic tumor ( ≥ 2cm and ≤ 5cm) in the lung or bone. For Cohort I, a modified 3 + 3 design was used to determine the FDG dose that would result in adequate FDG activity for BgRT functioning. For Cohort II, PET imaging data were collected on the X1 before the first and last fractions among patients undergoing conventional stereotactic ablative body radiotherapy. BgRT dose distributions were modeled on the patient’s CT anatomy using the collected PET data at each fraction, a process termed ‘emulated delivery’. A dose distribution was scored as accurate if 95% of dose volume histogram (DVH) points in the emulated delivery fell within the boundaries of the BgRT plan’s bounded DVH. Secondary endpoints included the deliverability of emulated fluence, safety of multiple FDG administrations, and BgRT workflow feasibility. Results Cohort I study results demonstrated that adequate FDG activity was achieved in 6/6 (100.0%) of evaluable participants with the first injected dose level of 15 mCi FDG. In Cohort II, 4 patients with lung tumors and 5 with bone tumors were enrolled, and evaluable emulated delivery data points were collected for 17 treatment fractions. Sixteen of the 17 emulations resulted in BgRT dose distributions that were accurate with respect to the approved BgRT plan. The 17th data point was just below the 95% threshold for accuracy (DVH Score = 94.6%). All emulated fluences were physically deliverable. No toxicities were attributed to multiple FDG administrations.