eISSN: 2081-2841
ISSN: 1689-832X
Journal of Contemporary Brachytherapy
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2/2021
vol. 13
 
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abstract:
Original paper

Individualized mould-based high-dose-rate brachytherapy for perinasal skin tumors: technique evaluation from a dosimetric point of view

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

1.
Department of Radiation Oncology, University Hospital, Goethe University, Frankfurt, Germany
J Contemp Brachytherapy 2021; 13, 2: 179–187
Online publish date: 2021/04/14
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Introduction
Dosimetric treatment planning evaluations concerning patient-adapted moulds for iridium-192 high-dose-rate brachytherapy are presented in this report.

Material and methods
Six patients with perinasal skin tumors were treated with individual moulds made of biocompatible epithetic materials with embedded plastic applicators. Treatment plans were optimized with regard to clinical requirements, and dose was calculated using standard water-based TG-43 formalism. In addition, retrospective material-dependent collapsed cone calculations according to TG-186 protocol were evaluated to quantify the limitations of TG-43 protocol for this superficial brachytherapy technique.

Results
The dose-volume parameters D90, V100, and V150 of the planning target volumes (PTVs) for TG-43 dose calculations yielded 92.2% to 102.5%, 75.1% to 93.1%, and 7.4% to 41.7% of the prescribed dose, respectively. The maximum overall dose to the ipsilateral eyeball as the most affected organ at risk (OAR) varied between 8.9 and 36.4 Gy. TG-186 calculations with Hounsfield unit-based density allocation resulted in down by –6.4%, –16.7%, and –30.0% lower average D90, V100, and V150 of the PTVs, with respect to the TG-43 data. The corresponding calculated OAR doses were also lower. The model-based TG-186 dose calculations have considered reduced backscattering due to environmental air as well as the dose-to-medium influenced by the mould materials and tissue composition. The median PTV dose was robust within 0.5% for simulated variations of mould material densities in the range of 1.0 g/cm³ to 1.26 g/cm³ up to 7 mm total mould thickness.

Conclusions
HDR contact BT with individual moulds is a safe modality for routine treatment of perinasal skin tumors. The technique provides good target coverage and OARs’ protection, while being robust against small variances in mould material density. Model-based dose calculations (TG-186) should complement TG-43 dose calculations for verification purpose and quality improvement.

keywords:

brachytherapy, perinasal skin cancer, individual moulds, TG-43, TG-186

 
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