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ORIGINAL RESEARCH article

Front. Phys.
Sec. Medical Physics and Imaging
Volume 12 - 2024 | doi: 10.3389/fphy.2024.1433208
This article is part of the Research Topic Development of Task Specific Phantoms and Test Objects for Medical Imaging View all 3 articles

A phantom for 2D dose measurements in the vicinity of metal implants for photon and proton beams

Provisionally accepted
Wolfgang Lechner Wolfgang Lechner 1*Barbara Knäusl Barbara Knäusl 1Jacob Brunner Jacob Brunner 1,2Dietmar Georg Dietmar Georg 1Peter Kuess Peter Kuess 1
  • 1 Clinic for Radiation Oncology, Medical University of Vienna, Vienna, Austria
  • 2 MedAustron, Wiener Neustadt, Austria

The final, formatted version of the article will be published soon.

    This work aimed to characterize a dedicated phantom for assessing the dose near metal implants for radiotherapy with photons and protons. A dosimetry audit phantom was redesigned to position a Gafchromic EBT-3 film within a bisected titanium pedicle screw (6.5 mm diameter). The mass density and the water equivalent thickness (WET) of the phantom material were determined. The phantom was irradiated using a photon arc and a horizontal proton beam in combination with a couch rotation of 20°, with three repeated measurements each. Treatment plans utilizing a single field covering the screw and the EBT-3 film were optimized to deliver a physical dose of 2 Gy using a collapsed cone and Monte Carlo dose engine for photons and protons, respectively. The mass density and the WET of the phantom were determined as (1.033 ± 0.010) g cm−3 and (1.022 ± 0.013), respectively. Ionisation chamber measurements agreed within 1 % (photons) and 0.5 % (protons) with the calculated dose values. Relative photon dosimetry measurements using EBT-3 films revealed an agreement between measured and calculated horizontal profiles within the confidence interval for areas beyond 5 mm from the center. For photon plans, significant deviations of more than 10 % were found at the interfaces between phantom material and screw. The proton measurements showed a gradual decrease of 3 % across both profiles. In contrast to photon plans, no dose increase was measured within the screw, but significant dose fluctuations (>5 %) in the beam’s exit region. This study showed that the behavior of dose engine is affected by metal implants and thus dosimetric measurements are highly recommended. The presented phantom can serve as foundation for dedicated end-2-end phantoms.

    Keywords: proton and photon radiotherapy, Radiation Oncology, Dosimetry, Phantom design, Metal implants, Dose calculation accuracy

    Received: 15 May 2024; Accepted: 12 Jul 2024.

    Copyright: © 2024 Lechner, Knäusl, Brunner, Georg and Kuess. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

    * Correspondence: Wolfgang Lechner, Clinic for Radiation Oncology, Medical University of Vienna, Vienna, Austria

    Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.