RADIATION-DOSE DISTRIBUTIONS FOR ELECTRON ARC THERAPY USING ELECTRONS OF 6-20 MEV

Radiation dose distributions in electron arcs depend in a complicated manner on electron energy, collimation width and depth of isocentre and cannot easily be deduced from the dose distributions in stationary beams. In the present work the method of measuring dose distributions for electron arcs using film is discussed. The changes in the arc dose distribution produced by changes in electron energy, radiation field width and radius of curvature (i.e., depth of isocentre) are investigated. The change in radial percentage depth-dose with changes in radius of curvature or source-surface distance of the target volume is minimal whereas changes in radiation field size produce changes in percentage depth-dose and bremsstrahlung contamination at the isocentre. Several options available for treatment planning are presented and discussed.