Highlights
- •Shows inconsistency of prescribing to lung PTV volumes for Monte Carlo calculations.
- •Provides data showing that Dose Mass Histograms do not offer a solution either.
- •The suggested solution is to abandon the PTV concept.
Abstract
Purpose
The goal of this study is to show that the PTV concept is inconsistent for prescribing
lung treatments when using type B algorithms, which take into account lateral electron
transport. It is well known that type A dose calculation algorithms are not capable
of calculating dose in lung correctly. Dose calculations should be based on type B
algorithms. However, the combination of a type B algorithm with the PTV concept leads
to prescription inconsistencies.
Methods
A spherical isocentric setup has been simulated, using multiple realistic values for
lung density, tumor density and collimator size. Different prescription methods are
investigated using Dose-Volume-Histograms (DVH), Dose-Mass-Histograms (DMH), generalized
Equivalent Uniform Dose (gEUD) and surrounding isodose percentage.
Results
Isodose percentages on the PTV drop down to 50% for small tumors and low lung density.
When applying the same PTV prescription to different patients with different lung
characteristics, the effective mean dose to the GTV is very different, with factors
up to 1.4. The most consistent prescription method seems to be the (PTV) DMH point, but is also limited to tumors with size over 1 cm.
Conclusions
Even when using the different prescription methods, the prescription to the PTV is
not consistent for type B-algorithm based dose calculations if clinical studies should
produce coherent data. This combination leads to patients’ GTV with low lung density
possibly receiving very high dose compared to patients with higher lung density. The
only solution seems to remove the classical PTV concept for type B dose calculations
in lung.
Abbreviations:
MC (Monte Carlo), PTV (Planning Target Volume), DVH (Dose-Volume Histogram), DMH (Dose-Mass Histogram), gEUD (generalized Equivalent Uniform Dose), FFF (Flattening Filter Free)Keywords
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Article info
Publication history
Published online: March 30, 2017
Accepted:
March 18,
2017
Received in revised form:
March 16,
2017
Received:
December 14,
2016
Identification
Copyright
© 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
