open access

Vol 22, No 5 (2017)
Original research articles
Published online: 2017-09-01
Submitted: 2016-10-13
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The accuracy of treatment planning system dose modelling in the presence of brass mesh bolus

Neil Richmond
DOI: 10.1016/j.rpor.2017.06.004
·
Rep Pract Oncol Radiother 2017;22(5):354-359.

open access

Vol 22, No 5 (2017)
Original research articles
Published online: 2017-09-01
Submitted: 2016-10-13

Abstract

Aim

This work assesses the dosimetric accuracy of three commercial treatment planning system (TPS) photon dose calculation algorithms in the presence of brass mesh used as a bolus.

Background

Bolus material is used in radiotherapy to provide dose build-up where superficial tissues require irradiation. They are generally water equivalent but high density materials can also be used.

Materials and methods

Dose calculations were performed on Monaco and Masterplan TPS (Elekta AB, Sweden) using phantoms defined by the three DICOM CT image sets of water equivalent blocks (no bolus, 1 layer and 2 layers of brass mesh) exported from the CT scanner. The effect of the mesh on monitor units, build-up dose, phantom exit dose and beam penumbra were compared to measured data.

Results

Dose calculations for 6 and 15[[ce:hsp sp="0.25"/]]MV photon beams on plain water equivalent phantoms were seen to agree well with measurement validating the basic planning system algorithms and models. Dose in the build-up region, phantom exit dose and beam penumbra were poorly modelled in the presence of the brass mesh. The beam attenuation created by the bolus material was overestimated by all three calculation algorithms, at both photon energies, e.g. 1.6% for one layer and up to 3.1% for two layers at 6[[ce:hsp sp="0.25"/]]MV. The poor modelling of the physical situation in the build-up region is in part a consequence of the high HU artefact caused by the mesh in the CT image.

Conclusions

CT imaging is not recommended with the brass mesh bolus in situ due to the poor accuracy of the subsequent TPS modelling.

Abstract

Aim

This work assesses the dosimetric accuracy of three commercial treatment planning system (TPS) photon dose calculation algorithms in the presence of brass mesh used as a bolus.

Background

Bolus material is used in radiotherapy to provide dose build-up where superficial tissues require irradiation. They are generally water equivalent but high density materials can also be used.

Materials and methods

Dose calculations were performed on Monaco and Masterplan TPS (Elekta AB, Sweden) using phantoms defined by the three DICOM CT image sets of water equivalent blocks (no bolus, 1 layer and 2 layers of brass mesh) exported from the CT scanner. The effect of the mesh on monitor units, build-up dose, phantom exit dose and beam penumbra were compared to measured data.

Results

Dose calculations for 6 and 15[[ce:hsp sp="0.25"/]]MV photon beams on plain water equivalent phantoms were seen to agree well with measurement validating the basic planning system algorithms and models. Dose in the build-up region, phantom exit dose and beam penumbra were poorly modelled in the presence of the brass mesh. The beam attenuation created by the bolus material was overestimated by all three calculation algorithms, at both photon energies, e.g. 1.6% for one layer and up to 3.1% for two layers at 6[[ce:hsp sp="0.25"/]]MV. The poor modelling of the physical situation in the build-up region is in part a consequence of the high HU artefact caused by the mesh in the CT image.

Conclusions

CT imaging is not recommended with the brass mesh bolus in situ due to the poor accuracy of the subsequent TPS modelling.

Get Citation

Keywords

Treatment planning; Bolus; Radiotherapy

About this article
Title

The accuracy of treatment planning system dose modelling in the presence of brass mesh bolus

Journal

Reports of Practical Oncology and Radiotherapy

Issue

Vol 22, No 5 (2017)

Pages

354-359

Published online

2017-09-01

DOI

10.1016/j.rpor.2017.06.004

Bibliographic record

Rep Pract Oncol Radiother 2017;22(5):354-359.

Keywords

Treatment planning
Bolus
Radiotherapy

Authors

Neil Richmond

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