Measurements of absorbed dose distributions in air from low-energy electron point sources

Abstract

The growing use of internally deposited radionuclides in radioimmunotherapy has established the need for accurate information about the energy deposition by low-energy electrons at the cellular level. To the present time only theoretical calculations are available, and the theory has been tested only by indirect experimental methods. The present work contains an implementation of computer programs (based on current theoretical knowledge) that allow rapid dosimetry calculations at a cellular scale needed to estimate the usefulness of radionuclei that decay by emission of any combination of β particles, γ or x rays, or internal conversion electrons. As a test of the theory, a set of measurements using point sources of discrete-energy (internal conversion and Auger process) electrons as well as β-particle emissions is described. A finite detector correction that accounts for effective detector size and detector position displacement is included. The experimental results reported here indicate a significant disagreement with the theoretical data, specifically in the shape of the dose distribution (point kernel) functions at distances from the source in air below 15 mg/cm 2.