It is a well-known fact that skin injuries after high-energy photon beam radiotherapy are attributed to the secondary electron emitted from acrylic shadow trays. We applied, as a shadow tray material, a high-impact nylon net used generally for tennis rackets, Comparative studies on surface doses in radiotherapy with Linac 10 MV (Toshiba) in conjuction with acrylic trays or the novel nylon net tray were carried out, with the facts being reparted below. In a clinical setting (i.e., source-to-chamber distance 90 cm, tray-to-surface distance 17 cm, field size 15x 15 cm^2), surface doses at a peak depth 25 mm were normalized to the value in the use of conventional trays (5 mm acrylic+10 mm acrylic) respectively in the following tray occasions. a) 5 mm acrylic-high-impact nylon. b) 7 mm lead-acrylic-high-impact nylon. c) hight-impct nylon + high-impact nylon. Normalized data clearly showed improved reduction in the secondary electron of a) 23.6% b) 37.3% c) 42.6% The dramatical reduction (42.6%) in the surface doses thus far obtained by use of the high-impact nylon net tray would greatly benefit clinical radiotherapy.
