ESTRO 2021 Abstract Book

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ESTRO 2021

lesions), controlled by increasing the dose of steroids. Three pts had less than three months of follow-up, and one patient was lost to follow-up. Median follow-up after re-irradiation in 20 evaluable patients was 9 (3.6- 36.6) months. Radionecrosis occurred in only one patient (GTV>1cc). He underwent two previous VMAT SRT (prescribed dose 30 Gy in 5 fractions and 21 Gy in 3 fractions) and presented seizures. He was treated with steroids and levetiracetam. Local control was: complete response (CR) in one patient, partial response (PR) in 8 pts, stable disease (SD) in four pts, and progressive disease (PD) in 7 pts. Nine pts were dead at the last follow up (one for systemic progression and 8 with intracranial progressions). Six- and twelve-months OS were 65% and 25% respectively. Conclusion SRT for re-irradiation is feasible, with only one case of radionecrosis registered. The treatment is effective with local control registered in 65% of pts. An accurate patient selection is warranted in order to avoid toxicity and a longer follow-up is needed to confirm the low radionecrosis rate. PO-1026 Re-irradiation with concurrent Nivolumab in locally recurrent Head and Neck Cancer J. von der Grün 1,2,3,6 , A. Altay-Langguth 1 , P. Balermpas 4 , C. Brandts 5,2,3,6 , S. Balster 7 , S. Ghanaati 8 , R. Winkelmann 9 , I. Burck 10 , F. Rödel 1,2,3,6 , D. Martin 1,2,3,6 , C. Rödel 2,3,1,6 1 University Hospital Frankfurt, Department of Radiotherapy, Frankfurt, Germany; 2 German Cancer Research Center, DKFZ, Heidelberg, Germany; 3 German Cancer Consortium, DKTK, Frankfurt/Mainz, Germany; 4 University Hospital Zurich, Department of Radiation Oncology, Zurich, Switzerland; 5 University Hospital Frankfurt, Department of Medicine, Hematology and Oncology, Frankfurt, Germany; 6 University Hospital Frankfurt, Frankfurt Cancer Institute, Frankfurt, Germany; 7 University Hospital Frankfurt, Department of Otorhinolaryngology, Frankfurt, Germany; 8 University Hospital Frankfurt, Department of Oral, Maxillofacial and Facial Plastic Surgery, Frankfurt, Germany; 9 University Hospital Frankfurt, Senckenberg Institute of Pathology, Frankfurt, Germany; 10 University Hospital Frankfurt, Department of Diagnostic and Interventional Radiology, Frankfurt, Germany Purpose or Objective The rate of loco-regional recurrences for locally advanced head and neck squamous cell carcinoma (HNSCC) following standard treatment reaches up to 50%, accompanied by a probability of 20% to develop a second primary tumor in the head and neck region. Materials and Methods Ten patients with inoperable, in-field recurrence of HNSCC following previous primary or adjuvant radiotherapy (RT) in combination with concurrent platinum-based chemotherapy were re-irradiated with 60 Gray in 30 fractions between December 2017 and January 2020 with concurrent and maintenance nivolumab administration. Data were retrospectively collected and compared with patients who underwent re-irradiation (ReRT) with concurrent cisplatin following propensity score matching (PSM). Local progression-free survival (LPFS) and overall survival (OS) were visualized using Kaplan-Meier method (log-rank test). Results All patients completed ReRT. Median number of applied courses of nivolumab was 12 (range, 3-38). OS rate was 50% at 12 months and the median OS was 11 (range, 2-23) months. Six and 12 month LPFS rates were 60% and 30%, respectively. Median LPFS was 8 (range, 2-19) months. OS and LPFS rates were not inferior to those of patients treated with concurrent cisplatin. No unexpected radiation-related toxicity occurred. A total of four patients developed any-grade immune-related adverse events of which two presented with grade 3 toxicities. One patient died within 3 weeks after ReRT. Higher blood levels of CRP (p=0.004), lower levels of hemoglobin (p=0.029) and higher neutrophil/lymphocyte ratio (p=0.004) were associated with impaired LPFS. Higher recursive portioning analysis (RPA) class was associated with impaired LPFS (p=0.022) and OS (p=0.024). Conclusion The combination of ReRT and nivolumab for locally recurrent HNSCC was feasible without occurrence of unexpected toxicities. Combined radioimmunotherapy might offer an effective treatment option for carefully selected pre-irradiated patients ineligible for salvage surgery. PO-1027 Radioiodine therapy guided by 124I-PET/CT in metastatic DTC: long-term follow-up data E. Lodi Rizzini 1 , V. Allegri 2 , L. Zanoni 2 , E. Tabacchi 2 , V. Laghi 1,6 , L. Strigari 3 , A. Repaci 4 , C. Scampoli 1,6 , D. Vallerossa 1,6 , E. Deraco 1,6 , L. Cavallini 1,6 , F. Bertini 1,6 , S. Cammelli 1,6 , G.P. Frezza 5 , A.G. Morganti 1,6 , S. Fanti 2,7 , F. Monari 1 1 Radiation Oncology, IRCSS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy; 2 Nuclear Medicine Unit, IRCSS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy; 3 Medical Physics, IRCSS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy; 4 Endocrinology Center, IRCSS Azienda Ospedaliero- Universitaria di Bologna, Bologna, Italy; 5 Radiotherapy Department, Ospedale Bellaria, Bologna, Italy; 6 Department of Experimental, Diagnostic and Specialty Medicine - DIMES , Alma Mater Studiorum Bologna University, Bologna, Italy; 7 Department of Experimental, Diagnostic and Specialty Medicine - DIMES , Department of Experimental, Diagnostic and Specialty Medicine - DIMES Alma Mater Studiorum Bologna University, Bologna, Italy Purpose or Objective Although RAIT was used for over 80 years in the metastatic-DTC management, number, frequency and optimal administrated 131I activity remain matter of debate. 124I-PET/CT can be a useful tool to identify lesions still iodine-avid with higher detection rate compared to post-treatment I-131scan (RxWBS) and to perform personalized dosimetry to the lesions, particularly in the case of potentially curative RAIT. The aim of this study is to confirm with long-term follow-up (FU) data the utility of 124I-PET/CT in RAIT planning of metastatic-DTC. Materials and Methods We collected long-term FU data of 30 patients (pts) affected by metastatic DTC and recruited in a prospective