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

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-...

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Bibliographic Details
Published in:Journal of radiotherapy in practice 2015-09, Vol.14 (3), p.323-330
Main Authors: Puchades-Puchades, Vicente, Serna-Berná, Alfredo, Mata-Colodro, Fernando, Ramos-Amores, David, Alcaraz-Baños, Miguel
Format: Article
Language:English
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Technical Note
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Summary: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 D 0·1 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.
ISSN:1460-3969
1467-1131
DOI:10.1017/S1460396915000217