S182
Clinical - Biomarkers of clinical response
ESTRO 2026
Proffered Paper 577
the CCRT series show an increase in PDFF over time, starting around 1 week from the first fraction (Figure 1A), except for L5, which acts as a within-subject low- dose control. Despite the higher fraction dose, we did not observe a change in PDFF during the SCRT (figure 1B).
Multiparametric quantitative MRI: Prospective characterization of soft tissue sarcomas and prediction of radiotherapy response Benoît Allignet 1,2 , Benjamin Leporq 2 , Floriane Izarn 3 , Amine Bouhamama 4,2 , Frank Pilleul 4,2 , Alexandra Meurgey 5 , Aline Baltres 5 , Gualter Vaz 6 , Alexandre Beige 1 , Waisse Waisse 1 , Olivier Beuf 7 1 Radiation Oncology, Centre Léon Bérard, Lyon, France. 2 CREATIS, CNRS UMR 5220, Inserm U1294, INSA-Lyon, Université Claude Bernard Lyon 1, Villeurbanne, France. 3 Medical Oncology, Centre Léon Bérard, Lyon, France. 4 Radiology, Centre Léon Bérard, Lyon, France. 5 Biopathology, Centre Léon Bérard, Lyon, France. 6 Surgical Oncology, Centre Léon Bérard, Lyon, France. 7 CREATIS, CNRS UMR 5220, Inserm U1294, INSA-Lyon, Université Claude Bernard Lyon 1, Lyon, France Purpose/Objective: Soft tissue sarcomas (STS) are rare and heterogeneous tumors with few predictive factors for response to neoadjuvant radiotherapy (nRT). Hypoxia is a major prognostic factor but its assessment with nitroimidazole PET-CT is not frequently performed due to lack of availability. Our trial (NCT05684874) evaluates the feasibility of a quantitative multiparametric MRI (mpqMRI) to measure the relative oxygen extraction fraction (rOEF) without contrast agent injection. Material/Methods: Sixteen adult patients with STS of the limbs or trunk were prospectively enrolled. The mpqMRI protocol (14 minutes, Siemens MAGNETOM Vida 3T) included three sequences:(1) A chemical-shift encoded 3D fast low- angle shot multi-echo gradient-echo sequence (3D FLASH CSE-MRI, 10 echoes, echo spacing 1.2 ms) to separate fat/water signals and measure R2*, magnetic susceptibility, and proton density fat fraction (PDFF) values. R2*-value was corrected for chemical shift and B0 inhomogeneity. (2) A 2D turbo spin-echo multi- echo sequence (10 echoes, 8–80 ms) used to estimate R2-value with mono-exponential fitting after discarding the first echo; (3) a multi-b-value diffusion- weighted sequence (10 b-values, 0–800 s/mm ² ) for Bayesian inference of IVIM parameters. Relative blood volume (rBV) was approximated from the perfusion fraction (f) of the IVIM model, corrected for T2 and normalized by water fraction (1–PDFF). rOEF and SvO2 were derived using a quantitative BOLD (qBOLD) method adapted from Toth et al. All sequences shared identical geometry to avoid registration artifacts. Results: The protocol was completed in 100% of cases without significant artifacts.
Figure 2. Dose-response.For CCRT treatments, we found a significant correlation between planned dose and observed PDFF, with higher planned doses leading to larger increases in PDFF across structures (Pearson’s r=0.67, p=1.1e-04; Figure 2). Conclusion: Our results show that the increase in PDFF occurs gradually over time, starting from around 1 week from first irradiation. Higher planned doses do not seem to accelerate this process, with the SCRT showing no increase in PDFF in 5 days. Long-term follow-up imaging is necessary to assess the changes in PDFF and compare these between groups; the relationship with lymphopenia should be supported with blood sample testing. In conclusion, we found a significant correlation between dose and PDFF increase, highlighting potential for bone marrow sparing. References: [1] Damen et al.; Int J Radiat Oncol Biol Phys 2021; https://doi.org/10.1016/j.ijrobp.2021.07.1695[2] Corbeau et al.; Radiotherapy and Oncology 2025; https://doi.org/10.1016/j.radonc.2025.111089.[3] Corbeau et al.; Physics and Imaging in Radiation Oncology 2024; https://doi.org/10.1016/j.phro.2024.100651.[4] Wasserthal et al., Radiol Artif Intell (2023); https://doi.org/10.1148/ryai.230024 Keywords: lymphopenia, bone marrow sparing, MRI
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