Dose delivered by secondary electrons radiated by metallic objects implanted in human tissue during radiation therapy using high energy photons.

Abstract

This abstract summarizes the results of a research project undertaken during 1983 to 1985 to evaluate the dose to the surrounding tissue contributed by secondary electrons originating from metallic surgical sutures and total hip prosthesis implanted in human tissue, upon interaction with high energy photons during radiation therapy. To date, no such work, has been undertaken on metallic prostheses or sutures but the effect of breast prosthesis made of silicone gel, during radiation therapy with high energy photons and electrons has been reported in two research papers. In this investigation, film and TLD methods of dosimetry are used to evaluate the dose due to these secondary electrons in a polystyrene phantom. Two types of films are used: they are Dupont 7L and Dupont 6 PLUS. Calibrated beams of X-ray photons of 4 MeV and electrons of 8.6 MeV energy are used as the sources of X-ray photons and electrons. The difference in optical density with film and the difference in response in the case of TLDs with and without the metallic objects is a measure of the dose contributes by the secondary electrons. This dose is taken off from the corresponding calibration curves for film and TLDs and this dose varies from 2.5% to 6.72% to soft tissue and the dose to bone varies from 4% to 12% approximately. In certain clinical situations, this amount of dose could be quite significant. Knowing such contribution, a more effective course of radiation therapy can be planned.