ESTRO 2021 Abstract Book

S851

ESTRO 2021

National University College of Medicine, Department of Otorhinolaryngology, Seoul, Korea Republic of; 5 Seoul National University College of Medicine, Department of Internal Medicine, Seoul, Korea Republic of

Purpose or Objective This study aimed to evaluate outcome and prognostic factors of postoperative radiotherapy for differentiated

thyroid cancer (DTC). Materials and Methods

In this retrospective study, 80 patients who received postoperative radiotherapy for DTC from January 2000 to December 2019 were analyzed. The median follow-up duration was 7.5 years (range, 0.6-18.7 years). Results Thirty-three (41.3%) patients had recurrent tumor and 21 (26.3%) patients still had gross disease even after radical surgery. Cervical node metastasis was present in 54 (67.5%) patients, while 7 (8.75%) patients were presented with distant metastasis. The median total dose and fraction size were 63.0 Gy and 2.0 Gy, respectively. The 5-year locoregional recurrence free survival (LRFS) was 80.7% and the five-year overall survival (OS) was 89.1%. Multivariate analysis showed age ≥ 55 (HR 6.11; 95% CI 1.51-25.25), male (HR 3.22; 95% CI 1.02-11.11), gross residual disease after surgery (HR 2.80; 95% CI 1.01-7.77) and esophageal invasion (HR 5.50; 95% CI 1.38-21.93) were significantly associated with worse LRFS. However, only the age ≥ 55 (HR, 1.10; 95% CI, 1.03-1.18) and the presence of gross residual disease (HR, 4.56; 95% CI, 1.02-20.31) were significant prognostic factors for OS. No severe toxicity was reported. Conclusion Postoperative radiotherapy can be one of the feasible and safe modalities for advanced or recurrent DTC, since the locoregional control was comparable to other studies despite unfavorable clinicopathologic elements of the study population . The age ≥55 and gross residual disease significantly affect both locoregional control and overall survival. However, due to the lack of a control in this study, there is a limitation to definitely confirm the efficacy of adjuvant RT and therefore a further study is necessary to find those who can benefit from it. PO-1022 Local-control efficacy of EBRT on well-DTC bone metastases: single center real-life experience E. Lodi Rizzini 1 , D. Vallerossa 1,5 , C. Scampoli 1,5 , E. Tabacchi 2 , V. Laghi 1,5 , L. Cavallini 1,5 , E. Scirocco 1,5 , E. Deraco 1,5 , S. Cammelli 1,5 , M. Boriani 1 , A.L. Angelini 3 , F. Romani 3 , G.P. Frezza 4 , A.G. Morganti 1,5 , 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 Radiation Oncology, Radiotherapy Department, Ospedale Bellaria, Bologna, Bologna, Italy; 5 Department of Experimental, Diagnostic and Specialty Medicine - DIMES , Alma Mater Studiorum Bologna University, Bologna, Italy Purpose or Objective Well differentiated thyroid carcinoma (DTC) is associated with good-long-term prognosis and radioiodine therapy (RAIT) is the definitive treatment of choice; however, when bone metastases appear, disease is associated with a significant decrease of QoL and overall survival. We evaluated how the use of EBRT on metastatic bone (BM) lesions, associated with RAIT, can impact on disease control in terms of pain reduction and local response. Materials and Methods We retrospectively analyzed 30 patients (pts) treated with EBRT on one or more BM lesions from February 2012-October 2019 at Radiation Oncology Center of S. Orsola-Malpighi Hospital (Bologna). Contrast enhanced CT (ceCT) or 18F-FDG-PET/CT scans were performed before and at least 2 months after the end of EBRT. Local response to treatment was assessed according RECIST and PERCIST criteria; NRS scale was used for estimating subjective pain response. Results Of the 31 pts treated, BM lesions were diagnosed synchronously in 60% of pts (n=18) and metachronously in 40% of pts (n=12). All pts received at least one RAIT (mean cumulative dose:410mCi-range:900-100mCi). 22/31 pts received intravenous monthly bisphosphonates and 16/31 pts started TKI therapy. A total of 67 BM lesions were treated. EBRT was delivered in 1-25 fractions, with a median dose of 30 Gy (range:8-50 Gy). 5/67 BM lesions were reirradiated. 9/67 MB lesions were also treated with surgery (n=6) and embolization (n=3). Mean FU: 29,8 months (range: 3-82months). 4/30 pts were lost at FU. Acute EBRT adverse events were mild and rare. FU imaging was performed with 18F-FDG-PET/CT for 39/67 BM lesions (mean pre-treatment SUVmax:11;range:40,9-1,9) and with ceCT for 8/67 BM lesions; restaging for 20/67 BM lesions was not assessed with the same imaging exam, so local response data was missed. 18F-FDG PET/CT response assessment was: stable metabolic disease in 16/39 lesions (41%), partial metabolic response in 11/39 lesions (28%), complete metabolic response in 11/39 lesions (28%) and one lesion with metabolic progression. CeCT assessed stable disease in 8/8 lesions (100%). Pain was the most frequent clinical presentation and 15/26 pts (58%) were symptomatic; overall, 3/15 pts had mild pain (NRS score<5) and 12/15 pts had severe pain (NRS>=5). Pain decreased in all pts and completely disappeared in 9/15 pts (60%). Conclusion According to literature data, EBRT associated or not with other local therapies appears to contribute effectively to local control and to the improvement of QoL in pts with DTC bone metastases. PO-1023 Impact of 18F-FDG-PET/CT in the management of suspected RAI refractory DTC persistence/recurrence E. Lodi Rizzini 1 , L. Zanoni 2 , E. Tabacchi 2 , A. Repaci 3 , C. Scampoli 1,6 , D. Vallerossa 1,6 , V. Laghi 1,6 , L. Cavallini 4,6 , N. Razganiayeva 1,6 , R. Cardano 1,6 , E. Scirocco 1,6 , S. Cammelli 1,6 , G.P. Frezza 5 , A.G. Morganti 1,6 , S. Fanti 2,6 , F. Monari 1 1 Radiation Oncology, IRCSS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy; 2 Nuclear Medicine