Planning Benchmark Study for Stereotactic Body Radiation Therapy of Liver Metastases: Results of the DEGRO/DGMP working group stereotactic radiotherapy and radiosurgery

PURPOSE: Our purpose was to investigate whether liver stereotactic body radiation therapy 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 intersystem and interuser differences. We provide best practice guidelines for all used techniques.

METHODS AND MATERIALS: A multiparametric specification of target dose (gross target volume [GTV] D50%, GTV D0.1cc, GTV V90%, planning target volume [PTV] V70%) with a prescription dose of GTV D50% = 3 × 20 Gy and organ-at-risk (OAR) limits were distributed with computed tomography and structure sets from 3 patients with liver metastases. 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 (PTV Dmin, PTV D98%, PTV D2%, PTV Dmax). The resulting 660 treatments plans were evaluated regarding target doses to study the effect of dose renormalization to different prescription methods. A relative scoring system was used for comparisons.

RESULTS: GTV D50% prescription can be performed in all systems. Treatment plan harmonization was overall successful, with standard deviations for D max, PTV D98%, GTV D98%, and PTV Dmean of 1.6, 3.3, 1.9, and 1.5 Gy, respectively. Primary analysis showed 55 major deviations from clinical goals in 132 plans, whereas in only <20% of deviations GTV/PTV dose was traded for meeting OAR limits. GTV D50% prescription produced the smallest deviation from target planning objectives and between techniques, followed by the PTV Dmax, PTV D98%, PTV D2%, and PTV Dmin prescription. Deviations were significant for all combinations but for the PTV Dmax prescription compared with GTV D50% and PTV D98%. Based on the various dose prescription methods, all systems significantly differed from each other, whereas GTV D50% and PTV D98% prescription showed the least difference between the systems.

CONCLUSIONS: This study showed the feasibility of harmonizing liver stereotactic body radiation therapy treatment plans across different treatment planning systems and delivery techniques when a sufficient set of clinical goals is given.