Session Item

Oligometastasis concept was proposed for patients with 1 to 5 metastases with intermediate prognosis. Randomized phase 3 trial STEREO-OS (NCT03143322) assess interest for stereotactic radiotherapy in addition with systemic treatment for oligometastatics patients. The effectiveness of treament is related to the quality of radiotherapy. In this context, quality controle with a dummy-run (DR) was established before the activation of participating centers.

2 prescription schedules were accepted, 35Gy/5 fractions/3 fractions per week or 27Gy/3 fractions/3 fractions per week. A double DR was performed with an analysis of recaluation and contouring and an analysis of planification (realized from each own center planification software). The two dummy-run were realized independently. The contouring dummy-run consisted on a vertebral metastasis with provision of a CT-scan and an RMN T2. They should contouring GTV, CTV, PTV and spinal cord. The material was then returned on Aquishare plateform software for evaluation of correlation index and dosimetric constraints analysis.

For contouring DR, Kappa index (KI) for GTV was highly correlated (mean=0,76 [0,7-1]), KI for CTV was almost perfect (mean=0,89 [0,83-1]) such as KI for PTV (mean=0,89 [0,83-1]). For GTV, 13 centres had an acceptable KI whereas for CTV and PTV all centers had an excellent KI. Concerning planification DR, of the 19 centers, 17 were able to hold dose constraints, 2 had inacceptable deviations requiring respectively 1 and 2 corrective planifications.

This DR shown a high correlation for target volumes between centers. This has shown a good knowledge of American recommendations published in 2012 and used internationally. Despite the use of different planification softwares, 89% of the centers had the ability to follow dose constraints of protocol. This quality assurance is essential to expect an efficient protocol and a rigorous interpretation of the results.