Imaging for early stage breast cancer

CBCT guidance for APBI

20 patients with CBCT after skin-mark setup and before treatment delivery

image registraton using ipsilateral lung and external contours

random and systematic error were calculated and compared

Setup errors in mm

skin-mark setup

CBCT guidance*

RL AP SI

RL

AP SI

systematic

2.7 1.7 2.4 0.8 0.7 0.8

random

2.4 2.2 2.9 1.5 1.5 1.6

isotropic CTV-PTVmargin

8.8

3.6

RL: right-left, AP: anterior-posterior, SI: superior-inferior, *3 mm action level (shifts > 3 mm are executed)

skin-mark setup for APBI patients is sufficient for 1 cm CTV-PTV margins

CBCT guidance may permit a reduction of CTV-PTV margin by a factor of 2

White et al. IJROBP 68:547-554. 2007