Comparison of ionisation measurements in water and polystyrene for electron beam dosimetry

• Published in: Physics in medicine & biology Vol. 30; no. 10; pp. 1043 - 1053
• Main Authors: Bruinvis, I A D, Heukelom, S, Mijnheer, B J
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.10.1985; Institute of Physics
• Subjects: Biological and medical sciences; Biological effects of radiation; Electrons; Fundamental and applied biological sciences. Psychology; Ionizing radiations; Models, Anatomic; Particle Accelerators; Polystyrenes; Radiation Dosage; Radiometry - instrumentation; Scattering, Radiation; Tissues, organs and organisms biophysics; Water; Water; Absorbed dose; Ionization; Measurement result; Electron beam; Styrene polymer; Correction factor; Linear accelerator; Dosimetry; Comparative study
• ISSN: 0031-9155; 1361-6560
• DOI: 10.1088/0031-9155/30/10/003

For the determination of absorbed dose to water in electron beams, dosimetry protocols advocate ionisation measurements in plastic phantoms instead of water for practical reasons. The chamber readings in polystyrene at the depth of maximum ionisation must be corrected for the difference in physical properties between the two materials. This correction factor was determined for a Farmer 0.6 cm3 graphite-walled chamber in electron beams with mean energies at the phantom surface between 6 and 19 MeV. Experiments with white polystyrene yielded corrections for the measured ionisation ranging from 0.3 to 2.4%. For clear polystyrene, 0.6-1% higher corrections were found. For beams with the same mean energy at the phantom surface, but with different beam-flattening and collimation systems, variations in this correction up to 1.2% were observed. In contrast to recent reports on electrical charge storage in polystyrene due to electron irradiation, our experiments do not show differences in the chamber readings any larger than 0.5%.