A comparative study of three small-field detectors for patient specific stereotactic arc dosimetry


This paper examines the difference in patient specific dosimetry using three different detectors of varying active volume, density and composition, for quality assurance of stereotactic treatments. A PTW 60017 unshielded electron diode, an Exradin W1 scintillator, and a PTW 31014 PinPoint small volume ionisation chamber were setup in a Lucy 3D QA phantom, and were positioned at the isocentre of an Elekta Axesse, with beam modulator collimator, using Exactrac and a HexaPODTM couch. Dose measurements were acquired for 43 stereotactic arcs, and compared to BrainLAB iPlan version 3.0.0 treatment planning system (TPS) calculations using a pencil beam algorithm. It was found that for arcs with field sizes \(>15\) mm, the properties of a detector have minimal impact on the measured doses, with all three detectors agreeing with the TPS (to within 5%). However, for field sizes \(<15\) mm, only the scintillator was found to yield results to within 5% of the TPS. The dose discrepancies were found to increase with decreasing field size. It is recommended that for field sizes \(<15\) mm, a water equivalent dosimeter like the Exradin W1 scintillator be used in order to minimise detector composition perturbations in the measured doses.

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Correspondence to Luke K. Webb.

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The authors declares that we have no conflicts of interest.

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This study was performed using phantoms, as per my compliance with ethical standards there were no human or animal participants and therefore the study did not require ethics approval.

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This article does not contain any studies with human participants or animals performed by any of the authors.

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Webb, L.K., Inness, E.K. & Charles, P.H. A comparative study of three small-field detectors for patient specific stereotactic arc dosimetry. Australas Phys Eng Sci Med 41, 217–223 (2018). https://doi.org/10.1007/s13246-018-0622-2

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  • Scintillator
  • Stereotactic radiotherapy
  • Small fields
  • Patient dose verification