Breast cancer patients are commonly treated after surgery using radiotherapy with the breast unconstrained, which leaves the technique susceptible to respiratory motion, deformations of the breast tissues and the ability to sustain setup posture. Continuously structured light projection from an interferometer system is used to generate a temporal sequence of height maps for one small and one large breast case in order to assess the nature of setup perturbations. The treatment position precludes full field operation and unwanted couch structures add to unavoidable shadowing to complicate scaled dynamic surface height measurement and display. The temporal sequence of partial field height maps is reduced to a stable mean surface height map and a residual surface sequence by the use of the standard deviation (SEM) of each surface point as an automated mask. For the large breast case the masked residual surfaces appear as flat laminae that barely flex or move more than a millimetre. For the small breast the mean surface height map clearly shows surgical scarring at the limits of sensor performance. The display of the masked residual surface series reveals centimeter scale displacements of a lamina that is flexing anisotropically. This is consistent with heavy chest breathing and a patient not at ease during the treatment.
