Published in:
01-07-2013 | Original article
Dosimetric properties and commissioning of cone-beam CT image beam line with a carbon target
Authors:
Y. Dzierma, F.G. Nuesken, N.P. Licht, C. Ruebe
Published in:
Strahlentherapie und Onkologie
|
Issue 7/2013
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Abstract
Background and purpose
Accurate patient positioning before radiotherapy is often verified using advanced imaging techniques such as cone-beam computed tomography (CBCT). Even for dedicated imaging beam lines, the applied dose is not necessarily negligible with respect to the treatment dose and should be considered in the treatment plan.
Materials and methods
This study presents measurements of the beam properties of the Siemens kView (Siemens AG, Munich, Germany) image beam line (IBL) and the commissioning in the Philips Pinnacle3 treatment planning system (TPS; Philips, Amsterdam, Netherlands).
Results
The percent depth dose curve reaches its maximum at a depth of 10 mm, with a surface dose of 44 %. The IBL operates in flattening filter-free mode, showing the characteristic dose falloff from the central axis. Stability over several days to months is within less than 2 % dose deviation or 1 mm distance-to-agreement. Modelling of the IBL beam line was performed using the Pinnacle3 automatic modelling routine, with absolute dosimetric verification and film measurements of the fluence distribution.
Conclusion
After commissioning of the IBL beam model, the dose from the imaging IBL CBCT can be calculated. Even if the absolute dose deposited is small, repeated imaging doses may sum up to significant amounts and can shift the position of the dose maximum by several centimetres.