Extracting patterns of anatomical deformations in prostate patients undergoing proton beam irradiation with an endorectal balloon

External beam proton therapy (EBPT) treats cancer by delivering small daily fractions of ionizing radiation to a target volume. For prostate cancer, the target undergoes day-to-day geometrical variations in position, volume, and shape. Accurate treatment delivery requires management of daily variations. (Water-filled) Endorectal balloons (ERBs) can be used to limit these variations. However, patterns of variations for patients with ERB have not yet been investigated. We used point set non-rigid registration and statistical modeling to extract and model patterns of geometrical variations for patients with EBRs. Non-rigid registration was optimized to ensure high accuracy.