Radiation dose perturbation in the presence of permanent vascular-access injection ports.

Injection ports are commonly used to maintain permanent vascular access in patients with malignant disease. The injection ports allow blood sampling as well as infusion or injection of chemotherapeutic agents directly into the circulation. The access catheters are usually placed in the subclavian vein with the injection port being implanted in the intraclavicular area. These injection ports are entirely self-contained underneath the skin and may have been placed in an area which subsequently requires radiation treatment. A comprehensive study of the perturbation effects of the injection ports when placed in the path of the beam was carried out. All dose measurements were performed using stainless steel and titanium injection ports. The radiation beams were 6 MV and 10 MV X rays and 6, 9, 12, 15, and 18 MeV electrons. The data indicate that the presence of injection ports significantly alters the radiation dose and dose uniformity. For example, the dose underlying a stainless steel port is reduced by 47% when 18 MeV electrons are used. This paper presents the dosimetric data, discusses the clinical significance of the results, and provides recommendations for design modifications of the ports.