METHODS
Measurements were performed by placing BBs and VBs of
varying thicknesses and air gaps onto water and solid phantoms.
CT scans of the solid phantom mechanism were transferred
to TPS for dose calculation.
RESULTS
2.6%, 3.9% and 5.5% dose decreases were observed for 10, 15
and 20 mm plexiglass at 5 cm depth. Maximum dose decrease
was 1.5% for VB. TPS calculations were within 1% for both
systems. Skin dose increased in accordance with thickness. A
maximum 6.3% difference was found between calculation and
measurements for increasing air gaps, but the differences were
not statistically significant.
CONCLUSION
BB must be positioned so as to avoid beam entry. Otherwise,
it must be included into the CT scan for better calculation. If
using VBs, it must be considered that skin doses increase with
thickness.
Keywords: Breast board; air gaps; treatment planning algorithms; vacuum bed
