Single versus multiples shorts dose planning for Gamma Knife radiosurgery of brain metastases.

Aims: Brain metastases (BMs) represent a significant medical concern in cancer patients. A valuable treatment option in selected patients with BMs is radiosurgery (RS), in particular using dedicated platforms such as the GammaKnife (GK). However, the impact on treatment response of different technical solutions, in particular use of multiple or single isocenters (shots), has not been established. The aim of our study is to evaluate differences in dosimetric parameters and clinical outcome among patients receiving multiple or single shot GammaKnife radiosurgery (GKRS) for BMs measuring less than 1 cm. Methods: Demographic, disease- and treatment-related features of 86 consecutive patients treated with the Leksell Gamma Knife® Perfexion™ for a total of 282 BMs were retrospectively collected. Each lesion was irradiated using one or two shots with a diameter of 4 and/or 8 mm. Selectivity Coverage and Gradient Index (GI) were examined for each lesion. Radiological response to RS treatment was observed according to RANO (Response Assessment in Neuro Oncology) criteria with MRI at 1, 3, 6 and 9 months. Results: Mean volume of metastases was 103.1 mm3 (2.4-721 mm3). Among treated BMs, 210 (74%) and 72 (25%) BMs were treated with one or two shots, respectively. Mean coverage of the plans executed with one shot was 99.9% (range: 92-100%) while it was 99.7% (range: 95-100%) using two shots. Mean selectivity and mean gradient were respectively 0,25 (range: 0.001-0.63) and 3.2 (range: 0.85-8.10) in single shot plans, and 0.35 (range: 0.07-0.78) and 3.2 (range: 2.11-9.8) in two shots plans. A statistically significant improvement in coverage was found in one shot plans (0.9995 vs 0.9968, p=0.0001), while selectivity was significantly better using two shots (0.2494 vs 0.3546, p=0.0001). Considering patient and disease-related characteristics, breast histology correlated with a poorer local control (p=0.0001) at 3 and 6months MRI, while a GPA (Graded Prognostic Assessment) < 3 was predictive of local failure (p=0.018) at 9months MRI. Concerning local control, overall local control rate at 1 month was 96%: patients treated with one shot had an improved local control at 1 (1.0% vs 11.6% p=0.0001) and 6months (5.9% vs 20.7%, p=0.026) as to two shots. Conclusion: Our study suggested that, in BMs with a diameter inferior to 1 cm receiving GKRS, the use of a single shot resulted in a better coverage and a better local control at one and three months. However, GPA score and histology affect clinical outcome of patients with BMs. [ABSTRACT FROM AUTHOR]