ESTRO 2020 Abstract book

S530 ESTRO 2020

The contrast clearance analysis present a novel model- independent approach providing efficient separation between tumor/nontumor tissues by adding a short MRI scan >1h post contrast injection. The methodology uses robust acquisition sequences, providing high resolution and easy to interpret maps with minimal sensitivity to susceptibility artifacts. The presented results provide histological validation of the analysis map and demonstrate their potential contribution to the management of brain tumor patients. PO-0907 Relationship Between Glioblastoma Dose- volume Parameters Measured by FET-PET and Clinical Outcomes M. Harat 1 , B. Malkowski 2 , I. Wiatrowska 3 , K. Roszkowski 4 , R. Makarewicz 4 1 The Franciszek Lukaszczyk Oncology Center, Radiotherapy, Bydgoszcz, Poland ; 2 Nuclear Medicine, Bydgoszcz, Poland ; 3 Medical Physics, Bydgoszcz, Poland ; 4 Bydgoszcz, Poland, Purpose or Objective Glioblastoma multiforme (GBM) is highly invasive. Despite irradiation with wide margins, GBM usually recurs in-field. Recent in vitro data have suggested that progression might be promoted by sublethal irradiation. FET-PET can be used to detect glioblastoma invasion not apparent on MRI. We therefore performed a retrospective analysis of a prospective clinical study to examine whether glioblastoma outcomes depend on dose-volume parameters measured by MRI and FET-PET Material and Methods Twenty-three patients were prospectively recruited to a study examining the role of dual time-point FET-PET in the treatment planning of GBM radiotherapy. The dose delivered to the site of recurrence was subdivided into suboptimal dose (SD) and high-dose (HD) areas. Types of progression were defined for correlation with dosimetric parameters including V100% of gross tumor volume (GTV) PET , GTV PETMRI and GTV MRI . Results The HD area did not cover the entire GTV PETMRI in any case. Recurrences were significantly more frequent in the SD area (chi-squared test, p=0.004). There was no relationship between increasing dose volume and progression. The V100% for GTV PET and PFS was positively correlated (Spearman’s rho 0.417; p=0.038). Conclusion Progression is more common in areas with suboptimal dosing. Dose heterogeneity within GTV PET may be responsible for shorter progression-free survival. PO-0908 Efficacy and Toxicity of Proton therapy and Tomotherapy combination in sacral chordoma patients A. Beddok 1,2 , C. Saint-Martin 3 , H. Mammar 1,2 , F. Goudjil 2 , S. Zefkili 1 , S. Helfre 1,2 , L. Feuvret 2,4 , S. Bolle 2,5 , S. Froelich 6 , M. Amessis 1 , D. Peurien 1 , R. Dendale 1,2 , C. Alapetite 1,2 , V. Calugaru 1,2 1 Curie Institute, Radiation Oncology, Paris, France ; 2 Curie Institute, Department of Proton therapy, Orsay, France ; 3 Curie Institute, Department of statistics, Saint Cloud, France ; 4 Pitié-Salpêtrière Hospital, Radiation Oncology, Paris, France ; 5 Gustave Roussy Institute, Radiation Oncology, Villejuif, France ; 6 Lariboisière Hospital, Neurosurgery, Paris, France Purpose or Objective Several recent studies have shown that radiation therapy (RT) can be used for the treatment of sacral chordoma, in combination with surgery, to improve local control and potentially overall survival (OS). Despite the use of intensity-modulated radiation therapy, such as Tomotherapy, the frequency of severe radiation induced toxicities is high. The goal of this study was to evaluate the efficacy and the toxicity of RT for the treatment of

Molecular changes were present in 20 patients (44%). At least one molecular characteristic changed over time in 89% of patients with primary grade III tumors. Gliomas with IDH wild-type and/or non-co-deleted were stable, but IDH1/2 mutation and/or co-deletion were sometimes lost at the time of recurrence. In a multivariate analysis, adjuvant radiotherapy alone was independently associated (p = 0.02) with changes in molecular profile. Conclusion Molecular biomarkers change in gliomas during the course of the disease, most often MGMT methylation status. These changes in genetic profiles are related to adjuvant treatment with radiotherapy alone, which might be important for individualized treatment planning over the disease course. PO-0906 MRI contrast clearance analysis for follow-up of brain tumors treated with VMAT and SRT A. Toutaoui 1 , T. Baroudi 1 , S. Mahmoudi 1 , R. Louelh 1 1 Hôpital Chahids Mahmoudi, Département de Radiothérapie et d'Imagerie Moléculaire, Tizi Ouzou, Algeria Purpose or Objective Treatment response assessment maps (TRAMs) based on contrast clearance analysis calculated from delayed- contrast MRI is a novel methodology that enables reliable differentiation between tumor and non-tumoral tissues in brain tumor patients. The contrast clearance analysis maps are calculated by subtracting 3D-T1-MRIs acquired 5min (early time point) post-contrast injection from those acquired 60-105min (late point) later. TRAMs maps differentiate between contrast clearance and accumulation and support clinicians in separating tumor progression and treatment effects, such as radiation necrosis. Clinical studies affirm high positive predictive values (PPV) and outstanding sensitivity to active tumor. We studied potential applications of this methodology for post-therapeutic follow-up of patients in conventional/stereotactic radiotherapy. Material and Methods A total of 7 patient treated in our department from April 2018 to February 2019 were included in this study. 5 patients with glioblastoma and 2 patients with germinoma were scanned by the contrast clearance analysis protocol (T1-MRIs acquired 5min and 60-105min post contrast injection). The first scan, for each patient, was performed 4 months after the end of treatment. For three patients, three additional scans were performed every three months. Two other patients had two more scans every three months. Tumor/treatment-effects volumes were calculated from the TRAMs within regions appearing enhanced on T1-MRIs. Results Overall, 20 TRAMs maps were calculated for 7 patients included in the study. Once the maps are validated to reliably depict tumor burden, and therefore also changes in tumor burden, they may be used to provide essential information for improved patient management. Detailed examples demonstrating the potential application of the TRAMs to the daily management of brain tumor patients are presented in this study. The potential application of the TRAMs for assessing the existence/absence of residual tumor after radiotherapy is demonstrated in the case of all patients with the first scan 4 months after the end of the treatment. The use of this technique for differentiating progression from treatment effects after a while is demonstrated in the case of patients with 4 and 3 contrast clearance analysis maps (5 patients). In the case 4 patients, significant increase in the red volume in the maps was indicative of necrosis. For one patient with 4 maps, the contrast clearance analysis favored pseudoprogression over progression. These evaluations are supported by the analysis of clinical signs and tumor markers. Conclusion