Features
• Radioactive check device replacement for constancy checks of ion chambers without the need for radiation source.
• Checks for proper functioning of the complete dosimetry system per IEC 60731
• Holders available for a variety of thimble-type ion chambers
Introduction
The Constancy Check Phantom provides the Medical Physicists with an easy way to check the constancy of response of thimble type ionization chambers. The phantom is more accurate than and replaces the 90Sr, Radioactive Check Source and is equivalent to ISO Class C43323. Chamber cavities can be drilled for a variety of ion chambers.
Application
Use of the Constancy Check Phantom is recommended for high precision dosimetry and is required by IEC 60731 - Dosimeters with ionization chambers as used in radiotherapy, 1977. A check measurement performed before each dose measurement will assure the ionization chamber is responding properly. The chamber volume is irradiated from all directions within the Constancy Check Phantom and secures the chamber for correct positioning and repositioning accuracy for any thimble type ion chamber including 0.6cc Farmer Type Chambers.
The Constancy Check Phantom replaces the need for a Radioactive Check Source. Unlike the Radioactive Check Source, 90Sr, 33 MBq (892 µCi) there is no radioactive material license required for purchase.
Results show the linear accelerator provides a more precise and efficient method for evaluating the stability of ionization chambers due to less positioning uncertainty. The external beam measurements are also more compatible with a variety of chambers, while the check source is limited by the size of the opening. Overall, this work provides a comparison to allow the clinician to make an informed decision on their methods for evaluation of chamber stability.