Recommendations for Post-Operative Radiotherapy after complete resection of Thymoma - a French DELPHI consensus initiative

Background Thymomas are rare intrathoracic malignancies that can relapse after surgery. Whether or not Post-Operative Radiotherapy (PORT) should be delivered after surgery remains a major issue. RADIORYTHMIC is an ongoing, multicenter, randomized phase 3 trial addressing this question in patients with completely R0 resected Masaoka-Koga stage IIb/III thymoma. Experts in the field met to develop recommendations for PORT. Methods A scientific committee from the RYTHMIC network identified key issues regarding the modalities of PORT in completely resected thymoma. A DELPHI-method was used to question 24 national experts, with 115 questions regarding: 1/ Imaging techniques, 2/ Clinical Target Volume (CTV) and margins, 3/ Dose constraints to Organs At Risk, 4/ Dose and fractionation, 5/ Follow-up and records. Consensus was defined when opinions reached ≥ 80% agreement. Results We established the following recommendations: pre-operative contrast-enhanced CT-scan is recommended (94% agreement); optimization of radiation delivery includes either a 4D-CT based planning (82% agreement), a breath-holding inspiration breath-hold-based planning, or daily control CT-imaging (81% agreement); imaging fusion based on cardiovascular structures of pre-operative and planning CT-scan is recommended (82% agreement); right coronary and left anterior descending coronary arteries should be delineated as cardiac substructures (88% agreement); rotational RCMI/VMAT is recommended (88% agreement); total dose is 50Gy (81% agreement) with 1.8-2Gy per fraction (94% agreement); cardiac evaluation, and follow-up for patients with history of cardiovascular disease is recommended (88% agreement) with EKG and evaluation of LVEF at 5 years and 10 years. Conclusion This is the first consensus for PORT in thymoma. Implementation will help to harmonize practices.