eISSN: 2081-2841
ISSN: 1689-832X
Journal of Contemporary Brachytherapy
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1/2022
vol. 14
 
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abstract:
Original article

Effects of iodinated contrast agent on HU-based dose calculation and dose delivered in iridium-192 high-dose-rate brachytherapy

Christian Scherf
1
,
Ulla Ramm
1
,
Thomas Stein
2
,
Martin Trommel
1
,
Nikolaos Tselis
1
,
Georgios Chatzikonstantinou
1
,
Markus Diefenhardt
1
,
Claus Rödel
1
,
Janett Köhn
1
,
Jörg Licher
1

  1. Department of Radiation Oncology, University Hospital, Goethe University, Frankfurt, Germany
  2. University of Applied Sciences Ansbach, Ansbach, Germany
J Contemp Brachytherapy 2022; 14, 1: 80–86
DOI: https://doi.org/10.5114/jcb.2022.113551
Online publish date: 2022/02/18
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Purpose
This study compares the effect of iodinated contrast agent on Hounsfield unit (HU)-based TG-186 dose calculation vs. delivered dose for high-dose-rate (HDR) iridium-192 brachytherapy using a phantom model.

Material and methods
A reservoir filled with a diluted contrast agent was placed inside a water phantom. A single steel needle applicator was centrally positioned inside the reservoir. Computed tomography (CT) datasets of five different contrast agent dilutions (25 to 300 mg/ml iodine concentration) were acquired, and dose calculations were performed with TG-186 ACE dose calculation formalism of Oncentra®Brachy (Elekta). The dose was measured with a PinPoint® ionization chamber (PTW) inside the contrast agent. ACE calculated and measured data were compared.

Results
For the different contrast agent dilutions, averaged Hounsfield units from 453 ±21 to 2623 ±221 were obtained. Electron densities derived from CT data were significantly higher than corresponding electron densities calculated from chemical compositions. Consequently, the measured dose was higher than corresponding HU-based calculated dose. Relative deviation ranged from 2.5% to 7% per 10 mm penetration depth, depending on contrast agent concentration.

Conclusions
The application of HU-based TG-186 dose formalisms in the presence of high-Z contrast agent bulks overestimates electron densities. Consequently, HU-based dose calculations result in a higher delivered dose than expected from the treatment planning system.

keywords:

dose calculation, contrast agent, TG-186, Hounsfield unit, electron density

  
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