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The importance of collimator angle error in volumetric-modulated arc therapy

Published online by Cambridge University Press:  26 May 2015

Vicente Puchades-Puchades ,
Alfredo Serna-Berná ,
Fernando Mata-Colodro ,
David Ramos-Amores  and
Miguel Alcaraz-Baños
Vicente Puchades-Puchades*
Affiliation:
Department of Medical Physics, Hospital Universitario Santa Lucia, Cartagena, Spain
Alfredo Serna-Berná
Affiliation:
Department of Medical Physics, Hospital Universitario Santa Lucia, Cartagena, Spain
Fernando Mata-Colodro
Affiliation:
Department of Medical Physics, Hospital Universitario Santa Lucia, Cartagena, Spain
David Ramos-Amores
Affiliation:
Department of Medical Physics, Hospital Universitario Santa Lucia, Cartagena, Spain
Miguel Alcaraz-Baños
Affiliation:
Departamento de radiología y medicina física, Universidad de Murcia, Murcia, Spain
*
Correspondence to: Vicente Puchades Puchades, Department of Medical Physics, Hospital Universitario Santa Lucia, c/Mezquita S/n Paraje Los arcos 30202 Murcia, Spain. Tel: +34 968128600; E-mail : Vicente.puchades2@carm.es
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Abstract

Purpose

To evaluate the dosimetric errors associated with the effect of the collimator angle error in volumetric-modulated arc therapy (VMAT) treatments.

Methods and materials

Four patients with different planning target volume (PTV) and localisations treated using VMAT were analysed (high-risk prostate, low-risk prostate, head and neck (H&N) and holocranial with hippocampus protection) in terms of dosimetric variations when errors in the collimator angle were introduced. Original plans underwent modifications of the planned collimator angles of ±0·5°, ±1° and ±1·5°. These modified plans were re-calculated using the same original plan fluencies, and the resulting dose–volume histograms and homogeneity index (HI-ICRU) were compared.

Results

For the high-risk prostate case, there was a noticeable loss of PTV dose coverage for collimator angle errors larger than ±1°, with HI-ICRU relative variations up to 75% in the range analysed. The low-risk prostate case did not present significant changes in organs at risk or PTV dose coverage. For the H&N case, the spinal cord presented changes around 4% for D0·1 cc. In the holocranial case, optic lens showed dose variations up to 5% for collimator angle errors larger than ±1°.

Conclusions

The effect of the collimator error in VMAT increased as the PTV increased.

For selecting the position of the isocentre, one should be cautious, and whenever possible choose a position close to the geometrical centre of the PTVs in order to avoid or minimise errors from the calibration of the collimator angle.

Keywords

collimator angle errorvolumetric modulated arc therapy (VMAT)dosimetric impact
Type
Technical Note
Information
Journal of Radiotherapy in Practice , Volume 14 , Issue 3 , September 2015 , pp. 323 - 330
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Copyright
© Cambridge University Press 2015 

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