Reducing scatter radiation to the contralateral breast with a mobile, conformal shield during breast cancer radiotherapy

During a standard course of breast radiotherapy, the contralateral breast g enerally receives similar to 2.5 to 6.0 Gy of scattered radiation. Although most studies have not found an overall increase in metachronous contralate ral breast cancers in patients undergoing radiotherapy, a cohort of younger women may be genetically more susceptible to radiation-induced breast canc ers and may thus be adversely affected by the scattered radiation. We are a ttempting to develop a simple, convenient, effective mechanism for minimizi ng the scattered radiation to the contralateral breast during the process o f clinical breast radiotherapy. We therefore designed a conformal, platform -based breast shield consisting of 2.5 cm of molded lead in a mobile counte rweighted polystyrene casing. This shield was intended to serve as a physic al barrier to prevent both low and high energy scattered photons from the m edial and lateral tangential fields. We conducted a prospective trial of 20 women, each woman serving as her own control. Each woman received breast r adiotherapy with and without shield, and an array of thermoluminescent dosi meters was positioned acres's the contralateral breast to evaluate the in v ivo dosimetry and the impact of the breast shield on surface absorption of scattered radiation. We found that the use of the breast shield reduced the median dose of scattered radiation by similar to 60% (p < 0.0001). This re presented a median dose reduction of similar to 300 cGy at the nipple. The shield was easily positioned and added <1 min to daily setup time. We concl ude that the use of this sort of surface barrier shielding technique was fe asible, effective, and practical for clinical use. The degree of scatter re duction accomplished through the use of this breast shield may be biologica lly significant, especially for those patients with biologic or epidemiolog ic risk factors that may predispose them to the development of radiogenic b reast cancers.