Purpose: With the advent of multi-detector scanners, z-axis collimations have increased up to 160mm. In addition, Image Guided Radiotherapy (IGRT) based on Cone-Beam CT (CBCT) with collimations up to 400mm is often used for patient's positioning in highly accurate radiotherapy treatments. The litterature shows that for collimations greater than 40mm, the 100mm pencil ionization chamber does not consider a large part of the primary and scattered radiation and several methods have been proposed to overcome this problem but because of the limitation of the available tools, dosimetric quality controls are rarely performed on these wide collimations. This study introduce a new method and device in order to overcome these limitations and perform accurate dosimetric quality control on wide collimations and CBCT.
Methods: Fibermetrix® has developed a measurement method and associated device (IVIscan®: based on a scintillating fiber placed on the CT scan's couch) allowing to integrate the dose even on wide collimations. The CTDI100, CTDIw and CTDIvol are measured and calculated on a Siemens definition EDGE and a Canon Aquilion ONE Genesis for thinnest, largest and clinical collimations. The same measurements and calculations are done on the CBCT of a Varian Truebeam linear accelerator. We compared the results between the ionization chamber of 100mm, 300mm and the IVIscan® device for the calculated CTDI100, CTDIW for wide CT collimations and for CBCT collimations.
Results: IVIscan® detector showed comparable performances to currently used methods for small and large collimations with differences of less than 5% compared to the reference calculation methods for CTDIw and CTDIvol
Conclusion: IVIscan is a easy to use tool and can be used routinely for regulatory quality control including large collimations and radiotherapy CBCT.
Funding Support, Disclosures, and Conflict of Interest: This work is part of a PhD supported by the FIBERMETRIX company.
Cone-beam CT, Quality Control, Dosimetry