ESTRO 2020 Abstract book

S531 ESTRO 2020

A total of 68 patients with a median age of 61 years (range 34 – 84 years) were treated at the at the Heidelberg ion therapy facility. Primary treatment was performed in 52 patients (77%), while 16 patients (23%) received radiotherapy (RT) in the recurrent situation by using carbon-ions either as single-modality treatment or in combination with photons with a median radiation dose of 66 Gy RBE (range 60 – 74 Gy). In 40 patients (59%), RT was performed after tumor resection. The follow-up comprised regular pelvic MRI scans performed at 3-monthly intervals in the first year and at 6-monthly intervals for the following years. Local progress was defined as an increase of the maximum tumor diameter by 10 % or new tumor growth within the target volume. LC and OS were determined using the Kaplan-Meier method. The relevance of several prognostic factors for LC and OS were tested. Results The median follow-up was 60 months (range 1 – 96 months). The lost to follow-up rate was 15% after 5 years. The 5-year LC, metastasis-free-survival, disease-free survival and OS were 43%, 82%, 44% and 82%, respectively. Local recurrence was observed in 31 patients (46%), occurring after a median follow-up time of 24 months (range 2 – 72 months). Only 10% of local relapses occurred later than 5 years after RT. In the multivariate testing, borderline significance was evident when comparing primary and recurrent tumors (5-year LC rates 53% vs. 9%), while the tumor volume and applied radiation dose were unrelated to LC. There was no significant prognostic factor for OS in the multivariate analysis. The incidence of late toxicities ≥ grade 3 was 21% (14 patients). Sacral insufficiency fractures (SIFs) were by far the most common late side effect in our analysis accounting for 49 % of the patients (33 patients). Radiogenic damage to the peripheral nerves, intestinal tract and skin was much less frequently observed with incidence rates of 9% (6 patients), 3% (2 patients) and 9% (6 patients), respectively. Conclusion Our analysis showed moderate long-term local control rates after carbon-ion based RT, whereby sacral chordomas have a particularly poor prognosis in the recurrent situation. Future studies should take further dose escalation into account to optimize therapy outcomes. However, possible benefits of dose escalation must be weighed against the risks of therapy. In our study every fifth patient had grade 3 toxicities and every second patient a SIF. PO-0910 Efficacy and toxicity of infradiaphragmal radiotherapy fields in lymphoma patients L. Galunic Bilic 1 , F. Santek 1 , M. Soce 1 , J.J. Grah 2 , S. Basic Kinda 3 , I. Radman 3 , Z. Mitrović 4 , M. Martinović 5 , I. Aurer 3 1 University Hospital Center Zagreb, Department of oncology and radiotherapy, Zagreb, Croatia ; 2 Univ. Klinik für Strahlentherapie-Radioonkologie- LKH Graz, Department for radiotherapy, Graz, Austria ; 3 University Hospital Center Zagreb, Department of hematology, Zagreb, Croatia ; 4 University Hospital Dubrava, Department of hematology, Zagreb, Croatia ; 5 University Hospital Merkur, Department of hematology, Zagreb, Croatia Purpose or Objective Most studies of radiotherapy in lymphoma were performed in supradiaphrgamatic localizations. Data on efficacy and toxicity of irradiation of infradiaphragmatic fields are scarce. We therefore performed this retrospective study to analyze our experience with lymphoma patients receiving radiotherapy exclusively to infradiaphragmatic fields. Material and Methods Poster: Clinical track: Haematology

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. PO-0909 High-dose carbon-ion based radiotherapy of primary and recurrent sacrococcygeal chordomas T. Bostel 1,2 , M. Mattke 3 , N.H. Nicolay 2,4 , T. Welzel 3 , D. Wollschläger 5 , S. Akbaba 3 , T. Sprave 4 , J. Debus 2,3 , M. Uhl 3 1 University Medical Center Mainz, Radiation Oncology, Mainz, Germany ; 2 German Cancer Research Center DKFZ, Clinical Cooperation Unit Radiation Oncology, Heidelberg, Germany ; 3 Heidelberg University Hospital, Radiation Oncology, Heidelberg, Germany ; 4 Medical Center - University Hospital of Freiburg, Radiation Oncology, Freiburg, Germany ; 5 University Medical Center Mainz, Institute of Medical Biostatistics- Epidemiology and Informatics IMBEI, Mainz, Germany Purpose or Objective This retrospective study aimed to analyze the oncological long-term results and late toxicity of sacral chordoma patients after high-dose carbon-ion based radiation treatment and to identify prognostic factors for local control (LC) and overall survival (OS). Material and Methods