The corresponding "fine-tuning" of internal organs was required to avoid overlapped surfaces. It is necessary to restore the deformed NURBS surface to the mesh-type surface, because of the consistency of the attributes of the derived surface and indiscernibility of NURBS surfaces by Monte Carlo codes. The operation involving surface deformation should be carried out on the NURBS-type surface, so the mesh-type surface should be converted into the NURBS-type surface first. The specific operation was to reduce the height and increase the volume of places where fat is easy to accumulate (e.g., abdomen, back and buttocks). A total of 84 mesh-type surfaces were segmented, and then reassembled to form new MRCPs according to their relative positions. Each tissue or organ of the standard phantom was reconstructed by gray threshold division and mesh reconstruction based on CT images with a resolution of 0.2 mm × 0.2 mm. Relevant changes (organ scaling and local subtraction methods) in MRCPs were determined on the basis of a standard MRCP with a height of 160 cm and a weight of 55 kg ( Fig. The patient weighed 60 kg with a height of 1.55 m. Phantom construction included body-size adjustment and phantom simplification. In both directions, irradiation fields were 10 cm × 10 cm with a center aimed at the heart. In the PA direction, X-rays were generated by a point source right below the patient's heart, 60 cm away from the couch, while in the LAO direction, the source was rotated 30 ° about the axis of the heart. The influence of surrounding shielding layers including lead curtain and lead glass on the dose absorbed by the patient was also considered. To determine the actual exposure scenario, dose distributions were calculated in both PA and LAO directions. According to the recollection of the attending physician, the patient was mainly irradiated in the direction of PA during the procedure. Irradiation was conducted in the posteroanterior (PA) and left anterior oblique (LAO) directions. Lead curtain 60 cm × 27 cm and lead glass 60 cm × 20 cm with a lead equivalent of 0.5 mm, were placed 5 cm to the right of the patient. The distance from the X-ray source to the couch was 60 cm, and from the couch to the detector 50 cm. 1, restored from an on-the-spot photograph of the operating room. The exposure scenario simulated by Monte Carlo codes was shown in Fig.
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