Surface doses for acrylic versus lead acrylic blocking trays for Co-60, 8-MV, and 17-MV photons

Clear acrylic trays are commonly used on teletherapy units to support freehand and custom-molded blocks for photon beam irradiation. While these trays have many desirable physical characteristics, they have the disadvantage of degrading the buildup region by contribution of low-energy electrons to the patient's surface. Recently, clear leaded acrylic has been introduced and suggested as a replacement for acrylic. The effect of the lead acrylic on the buildup region was investigated for cobalt-60, 8-MV, and 17-MV x-ray beams. The lead acrylic was found to decrease the surface dose compared to acrylic. Except for cobalt-60, the lead acrylic results in a higher dose than an open wire tray.