The Stealth Detector is a transmission detector with a circular active area with a diameter of 72
mm. The active detecting area is constructed of carbon fiber and has a total attenuation equivalent of less
than 0.5mm Al. The detector is attached to a Varian TrueBeam using the interface mount which is 57.4
cm from the source. With the maximum detector width of 70mm at a distance of 1.75 cm (detector
thickness) below the interface mount, the largest field measurable with this detector is 8.44 cm x 8.44 cm.
The Stealth detector is held at a negative bias voltage of -420 V. Central axis point measurements,
percent depth dose, and profile data are acquired using a Blue Phantom 2 scanning system (IBA
Dosimetry) with a TN60019 microDiamond detector (PTW-Freiberg). For scans using an in-field
reference detector, another TN60019 detector is used. This is waterproof solid-state detector with a 0.004
mm
sensitive volume. This detector is irradiation axially with its effective point of measurement being 1
mm from the detector tip. When used as a reference detector, the TN60019 is placed at 15 degrees above
the horizontal, exposing the effective point of measurement by allowing the detector to physically
protrude into the field. The TN60019 serves well as a reference chamber because of three major design
aspects: it is nearly water-equivalent, it has a small collecting volume, and it produces a large signal. All
data are acquired using a Varian TrueBeam (Varian Medical Systems, Palo Alto, CA) Version 1.6 using a
6 MV beam. The software used to acquire data is IBA OmniProAccept v7.4.18C, which as an important
feature (vital required for the current application) which allows separate bias voltages to be set for
different detector channels.