Determination of accurate dosimetric parameters for beveled intraoperative electron beam applicators

Intraoperative electron beam therapy requires accurate dose maximum/monitor unit ( D max / MU) values for both flat and beveled ended applicators (cones). Measurement of D max /MU values with either solid or nontilting scanning water systems may give rise to inaccuracies due to the difficulty in locating an accurate position for d max , since the ionization chamber usually cannot be scanned along the central axis of the beveled intraoperative applicator. A linear one‐dimensional scanner (which permits ionization measurements to be made as a function of water depth) has been modified to provide scanning along a line up to 30° from the perpendicular to the phantom surface. This modification has proven helpful in improving the accuracy of certain dosimetric parameters (e.g., D max /MU) of beveled applicators. For example, we found inaccuracies which arose when we measured D max /MU of beveled intraoperative radiation therapy cones in either solid or other scanning water systems were greatly reduced, especially for the lower electron beam energies (e.g., 6 and 9 MeV).