ESTRO 2020 Abstract Book

S485 ESTRO 2020

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 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 sacral chordoma. An analysis was also performed to compare the toxicities obtained by the combination of conventional proton therapy and Tomotherapy vs. Tomotherapy alone. Material and Methods Patient treated for sacral chordoma between November 2005 and June 2018 were included. Qualitative data were compared using Chi-2 or Fischer’s exact test. Continuous variables were compared by Student’s t-test or Wilcoxon sum rank test. Local relapse (LR) and OS, were defined as the time between the end of treatment and the local relapse or death respectively. OS was estimated using Kaplan-Method method. The cumulative incidence of local relapse was displayed by the Fine-Gray method for competing risks. Patients without any event were censored at their date of last news. Results Median tumor size at presentation was 255 cm 3 , interquartile range [IQR]: 136-525. Thirty patients have been operated with a macroscopic residue for 15 of them (residue median size: 241 cm 3 , IQR: 46–643). Among the 41 patients included, 13 of them received Tomotherapy alone whereas 28 received proton therapy and a boost in Tomotherapy (Proton – Tomo). The mean prescribed dose in the high risk PTV was 69.5 Gy RBE (52.2 Gy RBE proton and 21.6 Gy photon for the 28 patients treated with the association). After a median follow-up of 46 months (range, 0–125 months), there were 8 local relapses and 7 patients had developed distant metastasis (particularly bone and lung). The 2 and 5- years LR rate were 11.4% CI95% [0.65–22.2 %] and 29% [10.5–47.4%], respectively. Over the follow-up period, 10 patients (24.4%) have died for an estimated 2 and 5-year OS of 91.4% CI95%[82.5– 100%] and 74.5% [59.4–93.5%], respectively. Univariate analysis revealed that the post-surgical tumour volume was significantly bigger when patient had LR (p=0.043). Fibrosis, cauda equina syndrome and pain were the most common late toxicities. Comparison between patients treated with Tomotherapy alone vs. Proton – Tomo revealed that cystitis and fibrosis toxicity were significantly more frequent in Tomotherapy group: 38% and 15% vs. 0% and 3 %, respectively ( p=0.001 ). Proctitis, late cauda equina syndrome, and pain seemed also to be more frequent in the group Tomotherapy alone than in the Proton – Tomo group: 38.5% vs. 14.3%, 61.5% vs. 35.7% and 81.8% vs. 53.8%, respectively. Conclusion Radiation therapy remains essential to improve local control in sacral chordoma. A combination of proton and photon allowed improving organ at risks, such as bladder, rectum, and spine sparing and indeed to decrease the risk of late toxicities.