ESTRO 2024 - Abstract Book

S4869

Physics - Quality assurance and auditing

ESTRO 2024

A planning and dosimetric intercomparison of radiosurgery for multiple brain metastasis (BM) was conducted in most Swiss radiation oncology centres. In the current study, we evaluated the results for the treatment planning of multiple BM.

Material/Methods:

A scan of on anthropomorphic patient derived phantom (RTsafe Prime) was delivered to each centre, see Figure 1. The CT contained three BM defined by their gross tumour volume (GTV), three planning target volumes (PTV) were generated by expanding the GTV by 1mm isotropically. All the critical organs at risk were also defined on the CT. Each centre was asked to plan these BM as they would do for a clinical patient. The dose distribution obtained from each centre was then exported to the evaluating centre. The dose distribution was evaluated based on the PTV volume covered by the prescribed dose (V100%(PTV)), dose to 95% of the GTV (D95%(GTV)), maximal dose to the PTV (Dmax), conformity index (CI), brain volume receiving 100%, 83.3%, 66.6%, 50%, 33.3% and 16.6% of the prescribed dose (VXX%(brain)).The dose to the other OARs was not evaluated since being far below dose of complication due to the

large distance between the PTV and OAR.

Results:

At the time of evaluation, 24 centres participated in this study, encompassing 30 treatment units. 2 centres were separately evaluated since the dose was normalized to the mean PTV dose and 3 centres were excluded since one of the three PTV was not taken into consideration during the plan optimisation. Plans were optimized on various treatment platforms, including 21 Varian Truebeam machines equipped with the Eclipse Treatment Planning System (TPS), two Elekta Synergy machines employing the Monaco TPS, one Elekta machine utilizing the Raystation TPS, three Cyberknife systems with the Precision TPS, one Cyberknife system integrated with the Raystation TPS, and two Radixat machines using RayStation TPS. The V100%(PTV) was ranging between 95% and 97% for 1% of the PTVs, between 97% and 99% for 20% of the PTVs, 99% and 100% for 79% of the PTVs. The maximal dose was between 110% and 117% of the prescribed dose in 3% of the PTVs, 117% - 133% in 69% of the PTVs and 133% - 150% in 28% of the PTVs. The mean GTV dose was ranging from 110% - 120% in 38% of the GTVs, 120%-130% in 47% of the GTVs and 130%-135% in 15% of the GTVs. 81% of the GTVs had the D95% between 110%-120% and in 9.5% of the GTVs the dose was <110% and 9.5% of the GTVs the dose was >120%. In 71% of the plans, the CI was < 1.1, in 17% the CI was between 1.1 and 1.2, in 8% the CI was between 1.2 and 1.25 and in 4% the CI > 1.25. The V16.6% - 100%(brain) is displayed on Figure 2.