Management Of More Than 10 Brain Metastases Using The Leksell Gamma Knife Perfexion: Dosimetry And Practice

Keywords: brain metastasis, gamma knife, dosimetry, technique, radiosurgery

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     The purpose of this study was to evaluate dosimetry and practice data for patients with 10 or more brain metastases irradiated on the Leksell Gamma Knife Perfexion (LGK PFX) over a two year period.
     64 procedures for patients with 10 and more brain metastases were performed on the LGK PFX. Primary histology for these patients was: melanoma 18 (28%), NSC lung CA 18 (28%), breast 16 (25%) and other 12 (19%). In 42 cases (66%) patient received WBRT. The mean number of brain metastases was 13 (range: 10-23, median 12) with a total tumor volume of 0.10-40.21 cm3 (median 3.87 cm3, mean 7.27 cm3) per patient.
     The mean volume per metastasis was 0.02-3.7 cm3 (median 0.32 cm3, mean 0.63 cm3). Minimal prescription dose to the tumor margin varied from 12-20 Gy (median 16 Gy, mean 16 Gy) using the 40-90 % prescription isodose lines. Because of the typically small individual target volumes we were able to reduce treatment times by prescribing to isodose volumes above 50% if feasible. In this study the median prescription isodose was 74 % (mean 72%). Whole brain volume was contoured and the following dosimetry parameters were used to assess the dose delivered: 1) brain mean dose (including dose to target volumes), 2) brain integral dose (including dose to target volumes) and 3) total 12 Gy volume delivered to brain. Total treatment time and number of runs was also recorded.
     Mean dose to brain varied from 0.8-6.3 Gy (median 2.2 Gy, mean 2.3 Gy). Integral dose to brain was 1.1-8.8 J (median 3.4 J, mean 3.6 J). Total volume of 12 Gy delivered to brain varied from 1.3-111.5 cm3 (median 16.3 cm3, mean 20.3 cm3). Every procedure could be completed without any collision issues in one or two runs. Typically one run was used. Total treatment time on LGK PFX varied from 62-142 min (median 95 min, mean 95 min).
     This is a retrospective study.
     LGK PFX was an efficient tool for multiple brain metastases radiosurgery.
     Even for high number of tumors irradiation could usually be completed within two hours. Total brain irradiation was generally very low.


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