ESTRO 2021 Abstract Book

S1070

ESTRO 2021

PO-1301 THE ROLE OF 18F-FDG PET/CT AND PELVIC MRI AFTER CONCURRENT CHEMO-RADIOTHERAPY V. Lancellotta 1 , R. Autorino 2 , M. Campitelli 2 , A. Nardangeli 2 , B. Gui 2 , V. Rufini 3 , G. Ferrandina 4 , N. Bizzarri 4 , L. Tagliaferri 2 , V. Valentini 2 , G. Macchia 5 , M.A. Gambacorta 2 1 Fondazione Policlinico Universitario “A. Gemelli” IRCCS, UOC Radioterapia Oncologica, Roma, Italy, Dipartimento di Diagnostica per Immagini, Radioterapia Oncologica ed Ematologia, , Rome, Italy; 2 Fondazione Policlinico Universitario “A. Gemelli” IRCCS, UOC Radioterapia Oncologica, Roma, Italy, Dipartimento di Diagnostica per Immagini, Radioterapia Oncologica ed Ematologia, Rome, Italy; 3 UOC di Medicina Nucleare, Fondazione Policlinico Universitario A. Gemelli IRCCS, Rome, Italy., Dipartimento di Diagnostica per Immagini, Radioterapia Oncologica ed Ematologia, Rome, Italy; 4 Department of Health of Woman and Child , Gynecologic Oncology Unit, Catholic University of Sacred Heart , Rome , Italy., Gynecologic Oncology Unit, Rome, Italy; 5 Gemelli Molise Hospital, Università Cattolica del Sacro Cuore, Campobasso, Italy., Radiation Oncology Unit, Campobasso, Italy Purpose or Objective There is no agreement on the standard imaging to evaluate the cervix cancer (CC) response after definitive treatment with concurrent chemo-radiotherapy followed by interventional radiotherapy (IRT, brachytherapy). Magnetic resonance imaging (MRI) and 18-Fluorodeoxyglucose positron emission tomography (18F-FDG PET/CT) represent the most frequently used imaging techniques: MRI for assessing the response of the primary tumor and 18F-FDG PET/CT for the assessment of the metastases. Considering the uncertainty of current evidence, we retrospectively compared the diagnostic results of 18F-FDG PET/CT and MRI in the response evaluation after concurrent chemo-radiotherapy followed by IRT in 57 advanced CC. Materials and Methods We retrospectively analyzed the clinical data of all patients with CC between January 2019 and December 2020. The selected patients with advanced CC treated by external beam radiotherapy+chemotherapy followed by IRT. Inclusion criteria were (a) histologically proven squamous cell cervical cancer and adenocarcinoma; b) a pre-treatment pelvic MRI and total body 18F-FDG PET/CT and post-treatment pelvic MRI and whole-body 18F-FDG PET/CT. We documented the patient status at baseline with pelvic MRI and whole-body 18F-FDG PET/CT and treatment response three months after the end of IRT in the same tomographs. Results We observed agreement between MRI and 18F-FDG PET/CT in the evaluation response to therapy of lymph nodes in 48/57 (84.2%) of cases. The number of false-positive findings and false-negative was 5 (8.7%) and 4 (7%) for pelvic MRI. In assessing the primary tumor volume regression at three months, we observed an agreement in 36/57 patients (63.2%). In 21/57 (36.8%) cases, MRI and 18F-FDG PET/CT showed different responses: in 8 (14%) patients, MRI reported residual disease, and 18F-FDG PET/CT complete remission. In 12 (21%) patients, MRI showed complete remission and 18F-FDG PET/CT partial response. There were an agreement in 21 (58.3%) patients at six months and a disagreement in 15 (41.7%) patients. The number of false-positive findings was 10 (24.7%) for 18F-FDG PET/CT and 5 (13.8%) for pelvic MRI. We detected no false negatives with both imaging techniques. Conclusion Regarding loco-regional lymph-nodes assessment, MRI and 18F-FDG PET/CT are comparable. For primary tumor response, pelvic MRI seems to be superior to 18F-FDG PET/CT. Further studies need to confirm if 18F-FDG PET/CT or pelvic MRI should be the standard option at the end of concurrent chemo-radiotherapy in advanced CC to evaluate the treatment response. These studies may suggest that potentially we should favor one of the two techniques to assess the residual or progressive disease. PO-1302 Intraoperative electron radiation after salvage surgery in gynecological cancers and sarcomas G. oses gonzalez 1 , D. Muñoz-Guglielmetti 1 , C. Cases 1 , A. Biete 1 , T.D. Barreto 1 , A. Rovirosa 1 , A. Herreros 1 , J. Saez 1 , M. Mollà 1 1 Hospital Clinic of Barcelona, Radiation Oncology, Barcelona, Spain Purpose or Objective Salvage surgery is considered the curative option for isolated recurrences of retroperitoneal and pelvic tumors, in patients who have undergone previous radiotherapy. However, in order to increase local control Intra Operative Electron Radiation Therapy (IOERT) can be used in these patients to administer additional radiation dose. We evaluated the outcomes and adverse effects in patients with retroperitoneal sarcoma and gynecologic tumors after salvage surgery and IOERT. Materials and Methods Twenty patients treated between January 2014 and February 2019 were retrospectively analyzed: 23 IOERT treatments were performed after surgery. Of 20 patients, 6 (30%) were sarcoma and 14 (70%) were gynecological carcinoma. One (5%) patient in the sarcoma group was primary sarcoma and the other 5 patients (25%) were sarcoma relapse. In the gynecological group, 4 (20%) were primary locally advanced cervix carcinoma, 5 (25%) were cervix carcinoma recurrence, 4 (20%) endometrial carcinoma recurrence and one (5%) was a recurrence of ovarian carcinoma. IOERT was administered with a dedicated mobile electron linear accelerator installed in the operating theatre. Administered dose depended on previous dose received with External Beam Radiotherapy (EBRT) and proximity to critical structures. The median administered dose was 10Gy (range 8-20). The toxicities were scored using the Common Terminology Criteria for Adverse Events version 4.0. The statistical analysis was carried out through the IBM SPSS version 25.0. Results The median age of the patients (p) was 51 years (range 34-70). After a median follow-up of 32 months (range 1- 68), in the sarcoma group, local recurrence (LR) was observed in 2 p, regional recurrence (RR) in 2 p and distant recurrence (DR) in 2 p; while in the gynecological group LR was observed in 5 p, RR in 5 p and DR in 4 p. Salvage surgery was performed in 5 p (3 from sarcoma group and 2 from gynecologic group). In relation to late toxicity, one patient had a grade 2 vesicovaginal fistula, and one patient presented grade 4 enterocolitis and enteric intestinal fistula. These last two patients had previously been treated with EBRT. At the end of