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Current Directions in Biomedical Engineering

Joint Journal of the German Society for Biomedical Engineering in VDE and the Austrian and Swiss Societies for Biomedical Engineering

Editor-in-Chief: Dössel, Olaf

Editorial Board: Augat, Peter / Buzug, Thorsten M. / Haueisen, Jens / Jockenhoevel, Stefan / Knaup-Gregori, Petra / Kraft, Marc / Lenarz, Thomas / Leonhardt, Steffen / Malberg, Hagen / Penzel, Thomas / Plank, Gernot / Radermacher, Klaus M. / Schkommodau, Erik / Stieglitz, Thomas / Urban, Gerald A.


CiteScore 2018: 0.47

Source Normalized Impact per Paper (SNIP) 2018: 0.377

Open Access
Online
ISSN
2364-5504
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Distance-dependent penumbra and MLC-width: new insights in determinants of healthy tissue sparing in stereotactic irradiation

Arguments in favor of a virtual isocenter

Klaus Bratengeier
  • Corresponding author
  • University of Würzburg, Department of Radiation Oncology, Josef-Schneider-Str. 11, 97080 Würzburg, Germany
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  • De Gruyter OnlineGoogle Scholar
/ Sonja Wegener / Barbara Herzog
Published Online: 2017-09-07 | DOI: https://doi.org/10.1515/cdbme-2017-0166

Abstract

For stereotactic irradiation, both, penumbra and MLC leaf width make an impact on the sparing of healthy tissue around the target. Mostly, MLC design is regarded as the one influenceable parameter. However, also penumbra can be varied by choosing different distances between the source of radiation and the patient. The authors investigate the distance- dependent penumbra effects of idealized collimators as well as for real 5 mm MLCs. Test objects are small spherical targets of varying diameters to be irradiated under differing prescription conditions. A method to calculate exact stereotactic radial dose distributions from beam profiles or 2D dose distributions of single beams is developed for circular and MLC shaped targets. Also, a planning study is performed using a Pinnacle3™ planning system. Also, in a theoretical analysis perfect top hat profile beams and beams with varying penumbra are compared for better understanding of penumbra effects with respect to radial dose distributions. It is shown, that the penumbra changes for small targets are more relevant than the beam shaping by 5 mm MLCs. Quasi-isotropic irradiated MLC shaped (quadratic) beams at virtual SAD 700 mm produce steeper radial dose decrease than ideal circular beam shapes with a penumbra typical for SAD 1000 mm. A reduced source-to-patient distance allows better sparing of healthy tissue because of two reasons: The smaller effective leaf width but even more due to steeper penumbra. First, the authors suggest for future recommendations on stereotactic irradiations to specify not only MLC widths but also penumbra characteristics. Second, a so-called “virtual isocentre” could be useful to take advantage of the penumbra effect: Dependent on gantry angle and isocentric couch angle, the couch should be steered automatically in a way that the central axes of all beams always intersect in the same point at the same distance from the source.

Keywords: Stereotactic Irradiation; Multi-leaf Collimator; Penumbra; Virtual Isocentre; Robotic Table Motion; Planning Study; Radiotherapy

About the article

Published Online: 2017-09-07


Citation Information: Current Directions in Biomedical Engineering, Volume 3, Issue 2, Pages 787–790, ISSN (Online) 2364-5504, DOI: https://doi.org/10.1515/cdbme-2017-0166.

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©2017 Klaus Bratengeier et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License. BY-NC-ND 4.0

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