Extracranial Doses In Radiosurgery With Gamma Knife C: In-vivo Measurements In 1471 Patients And Relation With Dosimetric Parameters

F Desmedt1, Wagner A1, Devriendt D1, De Witte O1, Massager N1, Simon S.1

1Gamma Knife Center, University Hospital Erasme, Brussels, Belgium.

Keywords: gamma knife, Dose distribution, Dose, dosimetry, technique

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     Most patients treated with Gamma Knife have benign lesions and thus a long life expectancy. It is therefore essential to evaluate extracranial doses delivered during treatments.
     In this study with measurements performed on 1471 patients, the influence of different parameters on extracranial doses was analyzed. Treatments could be optimized with the results in a radioprotection way.
     Measurements were performed with thermoluminescent dosimeters (LiF:Mg,Ti), placed on patients and phantom (lateral cantus, thyroid, breasts and gonads).
     The influence of pathology, maximum prescribed dose, volume of prescribed isodose, integral dose, treatment time and distance between collimator and the organ were analyzed. The influence of plugs was also analyzed with the anthropomorphic phantom. Treatments with and without plugs with the same prescribed dose were simulated.
     Mean doses for lateral cantus, thyroid, breasts and gonads are respectively 28 cGy, 7.67 cGy, 3.3 cGy, and 0.6 cGy. No correlation was found between maximum dose, volume of prescribed isodose, integral dose and extracranial doses. A relation was found with treatment time, use of plugs, and distance to collimator. Measurements performed on phantom showed that the leakage component was more important than the scattered one and for each site of measurements. In comparison with in-vivo extracranial dosimetry performed with Gamma Knife Perfexion provided performed in studies
     This is a retrospective study.
     Extracranial doses for Gamma Knife treatments are relatively low. However, some benign lesions like meningioma can give more important doses, i.e. because of their complex shape. Extracranial doses are not dependant of the prescribed dose and the irradiated volume. It seems that the situation is comparable with that for IMRT treatments or Cyberknife and Tomotherapy treatments where doses outside treated site are not determined and only compared with prescribed dose.
     The use of multiple isocenters and plugs increases treatment time and thus has an influence on extracranial doses. It is therefore essential to take into account some parameters to minimize these doses, especially for young children. The major reduction of extracranial doses provided by the Leksell Gamma Knife Perfexion in comparison with Leksell Gamma Knife C represents an important issue in terms of radioprotection.


Project Roles:

F. Desmedt (), W. A (), D. D (), D. O (), M. N (), S. S. ()