S Aftab , M Barnes*, J Lehmann , Calvary Mater Hospital Newcastle, Newcastle, NSW

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  M Barnes

(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: In the Sun Nuclear 3D scanning water tank the horizontal metallic drive rail is in close proximity to the detector. This study investigates the impact of this proximity on reference dosimetry for MV photons, MeV electrons and kV photons.

Methods: Two experiments have been performed. In experiment 1 reference dosimetry measurements were compared between standard measurements in the 3D scanner and both measurements in the same tank, but with the addition of a 3D printed spacer that increases the chamber to rail separation, and measurements in a Standard Imaging 1D tank which does not have a rail. All measurements were performed three times on three different dates. In a second experiment, using an additional holder, the distance of the rail from the chamber was incrementally altered and the effect on chamber readings was recorded. Both experiments were performed for kV photons, MV photons and MeV electrons.

Results: Experiment 1: Agreement in measured absolute dose between all tank setups was within measurement uncertainty for all beams. However, the measurement uncertainty, assessed in a detailed uncertainty budget, was relatively large for kV photons due to setup uncertainty and short SSD, and the measured differences of up to -1.2 % are clinically significant if real.Experiment 2: For all beams, reducing the rail to chamber separation resulted in a measurable change in chamber readings. At the standard chamber-rail distance there was no significant change in reading compared to a large distance (25 cm) where the effect of the rail will be minimized for megavoltage photons and electrons. For kV photons a 0.5% change was recorded.

Conclusion: Within experimental uncertainty the proximity of the horizontal metallic drive rail was not found to have significant impact on megavoltage reference dosimetry measurements. However, some caution is warranted when using the tank with kV photon beams.

Keywords

Backscatter, Dosimetry, 3D

Taxonomy

TH- Radiation dose measurement devices: Phantoms for dosimetric measurement

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