Abstract
Specialized beam splitting breast blocks are being used in radiation therapy of breast cancer to treat the chest wall with tangential 60Co fields. Some of these breast blocks have a permanently attached lucite end plate which reduces skin sparing effects. The relative surface dose was measured on a 60Co irradiator utilizing a breast block with and without the lucite plate. A parallel plate extrapolation chamber was used. The surface dose was measured as a function of the distance from the end of the breast block, the position in the field and the angle of incidence for typical chest wall fields. These results are used to compare the dose to the skin of the chest wall for several treatment regimes. Using an attached lucite end plate without a bolus is comparable to using a bolus for half of the treatment and no bolus with no lucite plate for the remainder.