Planning benchmark study for SBRT of liver metastases: Results of the DEGRO/DGMP working group stereotactic radiotherapy and radiosurgery

PURPOSE: To investigate, if liver SBRT treatment planning can be harmonized across different treatment planning systems, delivery techniques and institutions by using a specific prescription method and to minimize the knowledge gap concerning inter-system and inter-user differences. To provide best practice guidelines for all used techniques. METHODS: A multiparametric specification of target dose (GTVD50%, GTVD0.1cc, GTVV90%, PTVV70%) with a prescription dose of GTVD50% = 3 × 20 Gy and OAR limits were distributed with CTs and structure sets from three liver metastases patients. Thirty-five institutions provided 132 treatment plans using different irradiation techniques. These plans were first analyzed for target and OAR doses. Four different renormalization methods were performed (PTVDmin, PTVD98%, PTVD2%, PTVDmax). The resulting 660 treatments plans were evaluated regarding target doses in order to study the effect of dose renormalization to different prescription methods. A relative scoring system was used for comparisons. RESULTS: GTVD50% prescription can be performed in all systems. Treatment plan harmonization was overall successful with standard deviations for Dmax, PTVD98%, GTVD98% and PTVDmean of 1.6 Gy, 3.3 Gy, 1.9 Gy and 1.5 Gy, respectively. Primary analysis showed 55 major deviations from clinical goals in 132 plans, while in only