1. A method for medical imaging comprising: a) performing a multi-detector computed tomography (MDCT) scan of a patient to produce MDCT scan data; b) reconstructing MDCT image slices from the MDCT scan data; c) performing a cone-beam computed tomography (CBCT) scan of the patient using a CBCT beam source to produce CBCT scan data, wherein performing the CBCT scan comprises positioning a patterned lead sheet between the CBCT beam source and the patient to partially block x-rays from the CBCT beam source; d) reconstructing CBCT image slices from the partially blocked CBCT scan data; e) performing 3D rigid registration of the MDCT image slices and the CBCT image slices to obtain fused reconstructed images of the patient for use in radiation treatment planning and dose calculation.