Supporting data
Figure S1: A more detailed material assignment with four metallic materials was also used for EGSnrc
MC dose calculations. The HU scale was split into five HU ranges and assigned to air [-1000; -950],
lithium [-950; 0], calcium [0; 1000], aluminum [1000; 2000], and titanium [2000, 3000]. The metallic
materials were chosen such as their electron densities were within the designated HU range.
Figure S2: Comparison of MC simulations with water (markers) and metal (solid lines) material
segmentation for the C5-2 probe in horizontal orientation for 6 MV (top row) and 15 MV (bottom row)
beams. The dose difference lines (water-metal) are within statistical uncertainties for the 6 MV beam. The
15 MV dose profiles taken at depths > 3cm are also within statistical uncertainties and the profile taken at
0.5 cm depth are within the ±4% line plotted for reference. We concluded that material segmentation did
not affect dose calculation results at depths beyond the depth of maximum dose deposition (d max).
Figure S3: Dose profiles (a, c) and 3%/3 mm gamma maps (b, d) for 6 MV (a, b) and 15 MV (c, d)
acquired with the 2D-Array at 5 cm depth comparing doses for the X6-1 probe in vertical orientation with
probe cable positioned to the left (squares) and to the right (circles). The maximum dose difference in the
profiles was 5.5% and 4.3% for the 6 MV and 15 MV beams, respectively. The failing pixels in the
gamma map in the shadow of the probe cable further support the difference between the presented
measurements and MC simulation results, in which the cable was not simulated in its full length.
Figure S4: In-plane and cross-plane modulation transfer function (MTF) for Tomotherapy MV CT
imaging was determined by imaging a high-density ball bearing. We determined that the in-plane spatial
resolution was 1.3 mm and the cross-plane spatial resolution was 3.6 mm (for MTF=0.05). The accuracy
of the US probe MC models was limited by the resolution of the MV CT scan.
Table S1: Gamma passing rates for dose comparison between MC simulations and film measurements for
3%/3mm and 5%/1mm criteria.
X6-1
3%/3mm
5%/1mm
Horizontal
6 MV
15 MV
98.0
97.9
99.0
99.6
Vertical
6 MV
96.4
98.1
15 MV
98.1
99.3
C5-2
Horizontal
6 MV
15 MV
99.9
97.7
100.0
100.0