ESTRO 2021 Abstract Book

S1219

ESTRO 2021

Conclusion The TwiCs design was accepted by the majority of patients who had served as control without explicit notification in TwiCs. Their opinion did not vary by underlying condition, type of intervention and trial outcome. Most patients did not remember their informed consent 2-8 years after cohort enrollment. Actively reminding cohort participants of the possibility of serving as control without explicit notification, might further reduce negative opinions on the TwiCs design. PO-1489 Radiotherapy in benign pathology: treatment of lymphorrheas V. Cañón 1 , J. Anchuelo 1 , I. Diaz de Cerio 1 , J. Cardenal 1 , M. Ferri 1 , A. Garcia Blanco 1 , U. Corro 1 , P. Navarrete 1 , P. Galdós 1 , A.L. Rivero 1 , J. Albendea 1 , R. Astudillo 1 , M. Gutierrez 1 , J. Alonso 1 , L. Alonso 2 , H. Vidal 3 , S. Velasco 1 , R. Fabregat 1 , S. Ruiz 1 , M. Garnacho 1 , A.I. Aviles 1 , M.T. Pacheco 1 , P.J. Prada 1 1 Hospital Universitario Marqués de Valdecilla, Radiation Oncology, Santander, Spain; 2 Hospital Universitario Marqués de Valdecilla, Medical Oncology, Santander, Spain; 3 Hospital Universitario Marqués de Valdecilla, Radiology, Santander, Spain Purpose or Objective To aim of the study is to determine the efficacy and safety of treatment with low-dose 3D external beam radiotherapy (EBRT) in patients with inguinal lymphorrhea. Materials and Methods We retrospectively analysed a total of 53 patients with persistent lymphorrhea (figure 1) after conservative treatment between 2008 and 2018. All patients were treated with 3D EBRT with photons of 6 - 18 MeV. The most common schedules were 7.5 Gy in 5 fractions (90.7%). The treated area included the vessels under the scar and the seroma, if still present (CTV). A safety margin was considered (PTV) between 0.5 and 1 cm depending on the immobilization and image system for positioning (EPID or CONEBEAM). Protection of the nearby organs was provided. Conformal RT (3D) was used for all patients (figure 2). The efficacy of the treatment was evaluated clinically as no response or complete response (complete closure of the fistula). We measured acute toxicity according to toxicity scales of RTOG cancer treatments. All patients were reviewed at the end of treatment and a month later in the Radiation Oncology Service. If the treatment was not satisfactory, the patients were referred back to our Service for a new evaluation. Subsequently, further follow-ups were done by their referral service Figure 1: Persistent lymphocutaneous fistula (FLC) and persistent lymphorrhea.

Figure 2: External Beam Radiotherapy. Axial dose distribution