AbstractIntroduction Despite existing radiotherapy contouring guidelines for Ewing's sarcoma (ES), important gaps remain for certain anatomical sites. The Euro-Ewing Consortium radiotherapy committee collaborated with QUARTET to identify and address ambiguities through consensus statements. Material and methods Between September 2023 and March 2025, a series of delineation workshops were held using two previously treated cases: a pelvic ES treated with radical radiotherapy and a chest wall ES treated post-operatively. The requested structures included GTVpPre, GTVpPost, CTVpPre₄500 and CTVpPost₅400 for both cases; as well as CTVpPost₆000 for pelvic case and CTVpLung₁500 for chest wall case. Visual and quantitative analyses were performed. Results For the pelvic case, substantial variability was observed in the CTVpPre₄500, CTVpPost₅400, and CTVpPost₆000 volumes. As differences were primarily related to adjustments at anatomical barriers, participants agreed to consider compartmental fascia as natural barriers in the absence of infiltration, and to apply a 0. 5-cm margin beyond the barrier when the ES was in direct contact. For the chest wall case, variability in GTVpPre and GTVpPost were related to changes between pre- and post-operative anatomy and reflected in CTVpPre₄500 and CTVpPost₅400 delineation. It was therefore agreed that non-infiltrated surfaces in contact with the tumour before surgery should be included in the GTVpPre. Standard margins should be applied to generate CTVpPre₄500, which should then be edited to avoid the skin, lungs, and heart while ensuring inclusion of the surgical bed. Conclusions The delineation workshops highlighted significant inter-clinician variability in target definition for ES. The resulting consensus statements will be used to supplement existing resources and support clinicians.
Greco et al. (2026) studied this question.