Measured Radial Distributions of Dose and LET for Alpha and Proton Beams in Hydrogen and Tissue-Equivalent Gas

Experimental measurements of the radial distribution of dose and radially restricted linear energy transfer (L/sub r/) are reported for alpha and proton beams of 1 to 3 MeV from a Van de Graaff accelerator. The method employs a large cylindrical ionization chamber filled with tissue-equivalent gas (or hydrogen) at variable low pressure for L/sub r/ measurement. For radial dose determination, a small movable ionization chamber of transparent mesh located inside the large cylinder is used to measure ionization by secondary electrons around the charged particle beam. Results are presented for simulated tissue radii from about 10 A to a few thousand angstroms. Comparison of the measured dose distributions with recent calculations by H. G. Paretzke indicates fair agreement except for large radii, where the local energy deposition is a small part of the total. (auth)