The influence of various vascular access ports on MV photon beam uniformity examined on the PMMA phantom
The presence of a high-density material object such as the vascular access port made of titanium, can affect the homogeneity of dose distribution in underlying tissues. This influence depends on numerous factors but in the first place on the composition material of such an object and its geometry. In this work an influence of the various titanium-made vascular ports, placed in the 6 MV photon field, have been analyzed. The vascular ports of various sizes were placed on the top of thepolymethyl-methacrylate (PMMA) phantom which is then scanned on a computed tomography (CT) simulator to generate the digitized 3-dimensional images for the purpose of treatment planning. The treatment plans were prepared in matRad treatment planning toolkit. The beam profiles and the percentage depth doses have been analyzed. The observed maximum dose values, for ports A, B, C and D, relatively to the maximum dose value in PMMA phantom alone, were 102.25%, 100.62%, 101.78% and 102.48%, respectively. The titanium edges of the ports reduce the dose below them in amount of 8.52%, 8.64%, 10.01% and 10.04% observed for ports A, B, C and D, respectively, in comparison to the central axis dose value obtained in PMMA phantom for the port-free case. The established changes in PDD curves and beam profiles depend on the vascular access port dimensions, reservoir volumes as well as of the amount of titanium content.