ESTRO 2021 Abstract Book

S1174

ESTRO 2021

Università Cattolica del Sacro Cuore, Campobasso, Italy; 7 Medical Physics Unit, Gemelli Molise Hospital – Università Cattolica del Sacro Cuore, Campobasso, Italy; 8 Proton Therapy Center, Santa Chiara Hospital, Trento, Italy Purpose or Objective To evaluate outcomes in a large series of patients treated with neoadjuvant radiotherapy (RT) for primary localized soft tissue sarcomas (STS) of the extremities. Materials and Methods One-hundred and twelve patients (median age: 53 years, range: 16-87) with primary high grade STS treated with neoadjuvant external beam RT and surgery were retrospectively analyzed. Eighty-two patients (73.2%) with chemo-sensitive histological subtypes also received neoadjuvant and/or adjuvant chemotherapy. Selection criteria were localized high grade STS and bulky disease or tumor in close proximity of critical structures such as nerves or vessels. All patients underwent CT and MRI scan of the region of interest, chest CT +/- 18 F-FDG-PET-CT before, after RT and during the follow-up. Eight patients, treated in 2005, received 44 Gy to the PTV delivered in 22 daily fractions. Thirty-two patients treated between 2006 and 2009 received a dose of 46 Gy (23 daily fractions), while the prescribed dose was 50 Gy (25 daily fraction) in 72 patients treated between 2009 and 2019. Treatment was delivered with 3D-conformal multiple beams technique to achieve the best PTV coverage while reducing the dose to OaRs and avoiding contralateral limb irradiation. Results With a median follow-up of 47.9 months (range: 4-176), only five patients (4.5%) had local relapse, with 94.7% 5-year local control (LC). Twenty-six patients (23.2%) developed metastases and 5-year metastasis-free survival (MFS) and disease-free survival (DFS) were 73.9% and 70.5%, respectively. Seventeen patients died (15.2%) with 85.8% 5-year overall survival (OS) rate. Twenty patients (17.9%) received an adjuvant RT-boost due to marginal or intralesional margins. Nevertheless, a statistically significant impact of margin status was recorded being 5-year LC 95.2%, 96.6%, and 80.0% in patients with wide, marginal, and intralesional margins, respectively (p=0.021). Younger patients (< 53 years old) showed a trend for improved 5-year OS (88.0% vs 83.9%; p=0.066). Conclusion A high LC rate was recorded in this large series of patients treated with preoperative RT. Prospective studies in the STS neoadjuvant setting are still needed to improve LC in subjects with intralesional margins and MFS, DFS, and OS in the whole patients population. PO-1430 Radiotherapy in Pediatric Rhabdomyosarcoma: Validity of IRS Risk Classification for a Single Center S. Kamer 1 , M. Öztürk 1 , E. Ataseven 2 , B. Balci 1 , B. Kadioglu 3 , M. Kantar 2 , D. Kizmazoglu 4 , Y. Anacak 1 1 Ege University, Radiation Oncology, IZMIR, Turkey; 2 Ege University, Pediatric Oncology, IZMIR, Turkey; 3 Behcet Uz Childrens Hospital, Pediatric Oncology, IZMIR, Turkey; 4 Tepecik Childrens Research Hospital, Pediatric Oncology, IZMIR, Turkey Purpose or Objective Management of pediatric rhabdomyosarcoma (RMS) involves the use of surgery, radiotherapy and chemotherapy in an orchestrated manner. Treatment data obtained from the large, well-organized, multicentric series of the pediatric oncology groups does not necessarily fits in the data of a single center. In IRS studies of North America patients are classified into risk groupings to deliver optimum treatment. The aim of the present study was to evaluate the survival of pediatric RMS patients and to check the validity of IRS risk classification for the data of the Ege University Hospital. Materials and Methods 72 patients who underwent radiotherapy between 2001-2018 were analyzed retrospectively. 29 of them were girls and 43 were boys; girl/boy ratio was 0.67; their median age was 5 (1-18). Common sites were H&N 31 cases (43.1%) – orbita 8, parameningeal 16, non-parameningeal 7; GU 20 cases (27.8%) - bladder 12 cases, other GU 8; extremities 6 (8.3%) cases and other sites 15 cases (20.8%). The most frequent histologic subtype was embryonal 45 cases (62.5%), followed by alveolar 11 (15.3%), myxoid 9 (12.5%), undifferentiated 4 (5.6%), and spindle cell 3 (4.2%). At the time of diagnosis there were lymph node metastates in 13 (18.1%) and distant metastases in 15 (20.8%); lungs were the most common site (11 cases). According to IRS risk classification 13 patients were in low-risk group (LRG), 42 in were intermediate-risk group (IRG) and 16 were high-risk group (HRG). Tumor resection was performed in 50 (69.4%), all patients received radiotherapy and chemotherapy. Radiotherapy delivered as external irradiation (ERT) in 51 (70.8%) cases, brachytherapy (BRT) in 16 (22.2%) and ERT+BRT in 5 (6.9%). ERT doses were 36 – 54 Gy with 1.8 Gy daily fractions. BRT delivered in in 6-8 twice- daily fractions in 3-4 days with 2.5-3 Gy fraction doses. Results After a median follow-up of 44.5 months (2-220), tumor recurrence occurred in 20 patients (27.8%). Median time to recurrence was 31 months. Of those recurrences 7 (9.7%) were local, 4 (5.6%) were in regional nodes and 9 (12.5%) were distant – 5 in lungs. 5-y OS was 68.0% in the whole group, and it was 90.0% in LRG, 75.8% in IRG, and 28.6% in HRG (p<0.01). 5-y DFS was 68.2% in the whole group, and it was 90.9% in LRG, 69.1% in IRG, and 37.9% in HRG (p<0.05) Conclusion Radiotherapy is an important component of the RMS treatment. In our series of 72 patients treated with radiotherapy, relapse rates and survival was not different from the previous reports. IRS risk classification perfectly estimates the prognosis of the patients and our data strongly supports the use of IRS risk grouping in the management of pediatric rhabdomyosarcoma. Digital Poster: Paediatric tumours