The Effect of Different Density Coverings on the Superficial
Objective To investigate the effect of different density coverings on superficial dose during radiation therapy.Methods With the application of Monte Carlo program(EGSnrc)to simulate the accelerator 6 MV photon beam,at the center of the accelerator beam and the source skin distance 100 cm,30 cm×30 cm×30 cm water phantom was set to verify the accuracy of the percentage dose depth of the accelerator beam;Afterwards,with the construction of a tissue phantom simulating the human body(with a size of 30 cm×30 cm×30 cm),common covering materials(paraffin,wet gauze,commercial compensation film Bolus,and thermoplastic film)for radiation therapy with a thickness of 5 mm were covered on the surface of the tissue phantom.Meanwhile,with the simulation of the process of accelerator photon beam irradiation on the phantom,the percentage depth dose of the beam center axis below the surface of the tissue mold was collected and analyzed.To eliminate the impact of adding 0.5 cm of built-up area,the covering material with the same material for the tissue phantom was covered on the surface of the tissue phantom,and the irradiation results under the same conditions were collected and compared with the above results.Results The difference between the percentage depth dose of the 6 MV beam simulated by EGSnrc in the water model and the actual measured value of the accelerator was less than 1%;Compared with no cover,all four cover with different densities could increase the superficial dose of the phantom to varying degrees,and the magnitude of dose increase gradually decreased with the increase of phantom depth;Under different coverings,the maximum dose increase was at the surface of the tissue phantom.The magnitude of increase for paraffin,wet gauze,commercial compensation film Bolus and thermoplastic film were 36.45%,42.42%,43.23% and 54.79%,respectively.The magnitude of increase in dose showed a decreasing trend with the increase in covering density,the dose at the maximum dose point varied by-0.49%,-0.59%,-0.65%,and-1.15%,respectively;At the same depth and under the mold surface depth<1 cm,the depth dose of different coverings was significantly correlated with the material density(P<0.05).Compared with the density of the tissue phantom,as the difference in coverage density increased,the dose effect on the tissue phantom became greater.The magnitude of dose increase of the thermoplastic film with the largest density difference from the tissue model was 7.54%,and the magnitude of increase of water with the smallest density difference was about 1%.Conclusions The surface coverings with different densities increase the superficial dose of the tissue mold to different degrees,and the influence decreases with the increase of depth;The depth dose of different coverings is significantly correlated with its density;There are differences in the impact of different material coverings on superficial dose.The larger the density difference between the cover and the tissue phantom has a greater impact on the shallow dose of the contact surface.However,for common epidermal coverings,there was little difference in relative density,and the dose effect was mainly due to the predictable increase in built-up area depth caused by the coverings.
EGSnrcMonte Carlo programDensityCovering materialSuperficial dosePercentage depth dose
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