SU‐E‐T‐377: Evaluation of a Novel Transmission Detector as a Reference Chamber for Use in Beam Measurements

Purpose: To evaluate a new transmission chamber for use as a reference chamber in measurements of beam data Methods: We assessed the performance of a new transmission detector, the Stealth Chamber, manufactured by IBA (IBA Dosimetry). The chamber has an active volume of 249 cm3, with an attenuation equivalent of <0.5mm Al. We mounted the chamber to a TrueBeam linac (Varian Medical Systems, Palo Alto, CA) such that the active area is perpendicular to the beam direction. We performed PDD and profile measurements on field sizes from 1×1 cm2 to 10×10 cm2, as well as for a 4 mm cone. The field detector was either a CC-13 chamber (IBA Dosimetry) with an active volume of 0.13 cm3 or an Edge Detector (Sun Nuclear, Melbourne, FL) with an active volume of 0.019 cm3. For comparison we repeated all measurements using a CC-13 or CC-01 (active volume 0.01 cm3 ) chamber as reference detectors (IBA Dosimetry).All scans were acquired using a Blue Phantom2 (IBA Dosimetry) and IBA OmniPro-Accept v7.4.24 software. Results: All measurements with the Stealth Chamber were identical to those with ion reference chambers. For both regular and filter free 6MV beams there was agreement in PDDs and profiles, including the penumbra region, for all field sizes. This was true for the 4mm cone measurement, as well. The deviation between the Stealth and ion chamber measurements was on average 0.3%. Conclusion: The Stealth Chamber gives identical beam data as a conventional ion chamber for all field sizes. The advantage of the Stealth chamber over ion chambers is its efficiency. Once mounted, there is no need to reposition the chamber with varying field sizes. This translates into a huge savings in measurement time, as well as a reduction in potential errors due to reference chamber mispositioning.