Influence Of Dose Distribution From Hip Prosthesis During Radiotherapy Simulated By MCNP

With the rapid development of modern medical technology, more and moremedical metal materials was used in the surgery, when a cancer patients whose bodycontains a metal implant during radiation therapy, Metal implants which have high Zand high density characters relative to human tissues and organs can make impact ondose distribution in the body according to scattering and absorption. Studies haveshown that this influence is objective existence and this influence is mainlycharacterized by dose enhancement at the incident surface of metal implants causedby backscattering of scattered electron and dose attenuation at the target region due tothe block of metal implants.This article selects the hip prosthesis as metal implants, prostate cancerradiotherapy as an example. Building a virtual human body model which containsspecific metal implants and specific tumor information and Using the Monte Carlomethod (MCNP5) simulation the influence of dose distribution from hip prosthesis.Before do this job, a model with a metal block inside a water-filled phantom isestablished to analyze the influence factors of back scattering factor and the law offunction, which provide theoretical support to specific metal implants (hip prosthesis)influence on the dose in later simulation. The study found that BSDF is more sensitiveto the metal implant material, thickness, distance measurement point apart from themetal surface, energy, angle of incident beam, and less sensitive to the depth of metalimplants in the tank, width, irradiation area.For human dose simulation, creating a virtual human body model is a veryimportant job. Virtual human model types used in this paper is a hybrid model, whichis conducted by3D human model through Rhinoceros software converted into anon-uniform rational B-spline model (NURBS model), then obtained from theBINVOX and READVOX procedures. It includes both the flexibility of mathematicalmodel, and the authenticity of the voxel model, is the development direction of futureresearch of human body model. The model in this paper with a resolution of0.2cm×0.2cm×0.4cm, total8,407,350voxels. Using MCNP software to calculate the influence of dose distribution about targetand the incident surface of hip prosthesis stem from Co, Cr, Mo alloy when irradiatedby X ray in different angles (0°,5°,8°,15°).It can be seen that when the incidentbeam path through the hip prosthesis cause much attenuation to the clinical targetdose, at15.35%, And target dose inhomogeneity increased, tumor center differencedegree above20%, however, adjust the radiation field path to avoid hip prosthesis canbe effective to reduce their impact on the target dose, at the same time, angledincident ray makes the normal tissue in front of the hip prosthesis suffer moreabsorbed dose, at above10%. Thus, more attention should be paid to increasing ofsecondary cancer risk because normal organs suffer additional dose due to scatteringparticles.