Stopping power and radial dose distribution for 42 MeV bromine ions

Linear energy transfer restricted in radius (LETr) and total linear energy transfer (LET infinity) were determined for 42 MeV bromine ions in tissue-equivalent gas. A variable pressure cylindrical ionisation chamber was used. Dose as a function of distance from the ion's path was also determined using a mesh wall ionisation chamber placed inside the cylindrical chamber. The range of distances studied was from 5 to 710 A in simulated tissue of unit density. Experimentally obtained values of radial dose were compared with calculations made using Paretzke's program. Stopping power for these ions in tissue-equivalent gas was extrapolated from proton stopping power in constituent gases. In this calculation the effective charge of the ions was obtained from the formula given by Dimitriev and Nikolaev. This calculated value was 6.3 x 10(4) MeV g-1 cm2. The experimentally determined value was 7.3 x 10(4) MeV g-1 cm2. The discrepancy between calculated and experimental values may be due to uncertainty in the determination of the effective charge of the incident ions. Uncertainty on the experimental value of LET infinity was estimated to be +/- 5% (one standard deviation).