engleski

Dose profiles measurements for leksell Gamma- knife model C using automatic positioning system with stereotactic diode detector

Gamma-Knife radiosurgery is highly precise method for treatment of small intracranial lesions with high single radiation dose [1]. For Leksell Gamma-Knife unit (LGK) Model C (Elekta AB, Stockholm, Sweden) radiosurgery uses 201 convergent narrow Co-60 photon beams, collimated with the 18, 14, 8 and 4 mm helmet collimator. The quality assurance program (QA) for Gamma- Knife includes periodical checks of size and position of single collimator helmet dose distributions from which complex clinical distributions are composed [2]. This is done by measuring dose distributions profiles in a three orthogonal planes (usually along x, y and z - axis of Gamma-Knife unit) and comparing them against the profiles measured during commissioning of Gamma-Knife or calculated by the treatment planning system (TPS). A method was proposed for high resolution dose profiles measurements for LGK Model C using the Automatic positioning system (APS) - a motorized system for positioning of the patient head and stereotactic frame into the target coordinates [7], with p-type stereotactic diode detector. Measurements were performed in a non- reference geometry where spherical phantom with detector was moved from one measuring point to another using APS. The method was validated by comparison of profiles simulated in a non- reference geometry of phantom against the profiles simulated in a reference geometry using the Leksell Gamma Plan (LGP) TPS and by comparison of profiles measured with EBT3 film with phantom in reference geometry against the profiles measured with the Diode SRS in a non- reference geometry. Diode SRS PTW60018 detector represent good choice for the Gamma-Knife dosimetry because of high spatial resolution and good signal response and in conjunction with the Automatic positioning system it can provide high resolution and volume averaging free dose profile measurement for the Leksell Gamma-Knife Model C. In addition, less noise in a measured signal and simpler workflow represent one advantage over the radiochromic film. However, EBT3 radiochromic film remains the detector of choice for the 2D dosimetry because of high spatial resolution and tissue equivalence.

Gamma-Knife radiosurgery ; Dose profiles ; Quality assurance ; Diode detector ; Radiochromic film

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