Fractionated Gamma Knife surgery (FGKS) has recently been used to treat large brain metastases. However, little is known about specific volume changes of lesions during the course of treatment. The authors investigated short-term volume changes of metastatic lesions during FGKS.
The authors analyzed 33 patients with 40 lesions who underwent FGKS for intracranial metastases of non–small-cell lung cancer (NSCLC; 25 patients with 32 lesions) and breast cancer (8 patients with 8 lesions). FGKS was performed in 3–5 fractions. Baseline MRI was performed before the first fraction. MRI was repeated after 1 or 2 fractions. Adaptive planning was executed based on new images. The median prescription dose was 8 Gy (range 6–10 Gy) with a 50% isodose line.
On follow-up MRI, 18 of 40 lesions (45.0%) showed decreased tumor volumes (TVs). A significant difference was observed between baseline (median 15.8 cm3) and follow-up (median 14.2 cm3) volumes (p < 0.001). A conformity index was significantly decreased when it was assumed that adaptive planning was not implemented, from baseline (mean 0.96) to follow-up (mean 0.90, p < 0.001). The average reduction rate was 1.5% per day. The median follow-up duration was 29.5 weeks (range 9–94 weeks). During the follow-up period, local recurrence occurred in 5 lesions.
The TV showed changes with a high dose of radiation during the course of FGKS. Volumetric change caused a significant difference in the clinical parameters. It is expected that adaptive planning would be helpful in the case of radiosensitive tumors such as NSCLCs or breast cancer to ensure an adequate dose to the target area and reduce unnecessary exposure of normal tissue to radiation.
ABBREVIATIONSBSM = Basic Score for Brain Metastases; CI = conformity index; dsGPA = diagnosis-specific graded prognostic assessment; FGKS = fractionated GKS; GKS = Gamma Knife surgery; KPS = Karnofsky Performance Scale; NSCLC = non–small-cell lung cancer; OR = odds ratio; PIV = prescription isodose volume; RPA = recursive partitioning analysis; SIR = Score Index for Radiosurgery; TV = tumor volume.
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