Changes to dose at surface and shifts of dose distributions at depth through dry and wet wound dressings for photon and electron beam radiotherapy.

Wound dressings are used during patient radiotherapy treatments, particularly in cases of radiation induced lesions. Potentially, the presence of a dressing may increase the dose to the skin, further aggravating the skin reaction and decrease the dose at depth. The changes are dependent on linear accelerator beam type and beam quality and were determined for 4 and 10 MV photon energies and 6 and 15 MeV electron energies using a slab phantom and fixed separation parallel plate chambers. Since these dressings have been designed to be used on exuding wounds, measurements were taken under eight different wound dressings in both dry and wet state. Irradiations with photon energies increased the skin dose significantly (max. increase: 68.1 %; average increase: 48 %) with little or no change to dose at depth. Electron beam energies showed little or no change to doses at the surface, but the dose distribution was shifted towards the surface. The maximum decrease in dose at depth was 3.6 % for 6 and 15 MeV through all dressings except one and was therefore considered to be clinically insignificant. A change in dose at surface of 9.7 % and at R(50) of 25.9 %, equivalent to a shift of dose towards the surface of 7.5 mm, was measured for one dressing. This demonstrates that it is possible for a wet dressing to significantly alter electron beam dosimetry.