Abstract
The use of small volume ionization chamber has become required for the dosimetry of equipments that use small radiation fields such as the Gamma Knife® Perfexion (GKP) unit. In this work, a pinpoint ionization chamber was inserted into the dosimetry phantom and measurements were performed with the phantom in different positions, in order to verify if the change in the phantom positioning affects the dosimetry of the GKP. Four different phantom positions were performed. The variation in the result is within the range allowed for the dosimetry of a GKP equipment.
Highlights
The Gamma Knife® Perfexion (GKP) unit, introduced in 2006, is a fully automated unit for the stereotactic radiosurgery and the stereotactic radiotherapy of the brain lesions including certain extra-cranial lesions [1].It has 192 sealed sources of 60Co arranged on eight movable sectors such that each sector contains 24 sources
Quickly move out from their shielded home position at the extreme rear of the radiation cavity and slide over the tungsten ring and past the 8 mm collimators to park in the “off position” in shielded space between the 8 and 4 mm collimators
A dose-rate calibration of a GKP unit is performed using the largest size collimator (16 mm, shown in Figure 1) and an ionization chamber with small volume positioned at the geometric center of the phantom
Summary
The Gamma Knife® Perfexion (GKP) unit, introduced in 2006, is a fully automated unit for the stereotactic radiosurgery and the stereotactic radiotherapy of the brain lesions including certain extra-cranial lesions [1] It has 192 sealed sources of 60Co arranged on eight movable sectors such that each sector contains 24 sources. Quickly move out from their shielded home position at the extreme rear of the radiation cavity and slide over the tungsten ring and past the 8 mm collimators to park in the “off position” in shielded space between the 8 and 4 mm collimators. During this time, no beam is turned on and the treatment does not start to count. The beams from a sector may remain “blocked” if the sources in that sector remain parked in the off-position [1]
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