DOSIMETRIC CONSIDERATIONS OF COMMERCIALLY FABRICATED ESOPHAGEAL APPLICATORS

Two commercially fabricated esophageal applicators for low dose rate i ntraluminal brachytherapy were compared using the dose non-uniformity ratio (DNR). One of the applicators has a single afterloading catheter while the other applicator has six afterloading catheters to accommod ate low dose rate Ir-192 ribbon or wire sources. Five sets of source c onfigurations, each with a different ribbon length in the range of 5-1 7 cm were analysed using the DNR. The DNR shows the delivery of relati vely higher total doses at higher dose rates to tissues closer to the applicators. The difference in the inhomogeneity of dose rates and the treatment volume exposed to higher dose rates than the prescribed dos e rate between the two applicators are minimal. The dose homogeneity i s better for the single-source applicator while the worst dose homogen eity for the six-source applicator is caused by the placement of each source closer to the surface of the applicator. The implications of hi gher dose rates were discussed using the alpha/beta model.