Highlights
- •In order to estimate patient’s doses around the metallic shield for electron treatment.
- •Use of 3D scanner and printer to fabricate patient’s specific dummy shields.
- •The dummy shields were used to generate metal artifact-free CT images.
- •TPS and Monte Carlo dose calculations on the metal artifact-free CT images and film measurements.
Abstract
Patient’s CT images taken with metallic shields for radiotherapy suffer from artifacts.
Furthermore, the treatment planning system (TPS) has a limitation on accurate dose
calculations for high density materials. In this study, a Monte Carlo (MC)-based method
was developed to accurately evaluate the dosimetric effect of the metallic shield.
Two patients with a commercial tungsten shield of lens and two patients with a custom-made
lead shield of lip were chosen to produce their non-metallic dummy shields using 3D
scanner and printer. With these dummy shields, we generated artifact-free CT images.
The maximum CT number allowed in TPS was assigned to metallic shields. MC simulations
with real material information were carried out. In addition, clinically relevant
dose-volumetric parameters were calculated for the comparison between MC and TPS.
Relative dosimetry was performed using radiochromic films. The dose reductions below
metallic structures were shown on MC dose distributions, but not evident on TPS dose
distributions. The differences in dose-volumetric parameters of PTV between TPS and
MC for eye shield cases were not clearly shown. However, the mean dose of lens from
TPS and MC was different. The MC results were in superior agreement with measured
data in relative dosimetry. The lens dose could be overestimated by TPS. The differences
in dose-volumetric parameters of PTV between TPS and MC were generally larger in lip
cases than in eye cases. The developed method is useful in predicting the realistic
dose distributions around the organs blocked by the metallic shields.
Keywords
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Article info
Publication history
Published online: June 16, 2020
Accepted:
June 1,
2020
Received in revised form:
May 10,
2020
Received:
December 14,
2019
Identification
Copyright
© 2020 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
