[1067] An in vitro study of secondary shielding to reduce breast dose during radiation therapy for pediatric Hodgkin's disease. Shaves M, Gray A, Priola G, Plemmons J. Eastern Virginia Medical School, Norfolk, VA INTRODUCTION: Girls and female adolescents treated with radiation for Hodgkin's disease are at a significantly increased risk for subsequent breast cancer. A linear dose response relationship without a threshold has been described for the induction of radiation-induced cancers. Using an in vitro model, we examined the effect of secondary breast shielding on breast dose during a standard radiation therapy technique for Hodgkin's disease. MATERIALS AND METHODS: Simulated breast tissue was fabricated from bolus material (Superflab, Fluke Biomedical) and placed on an anthropomorphic phantom. Two calibrated thermoluminescent detectors (TLDs) were placed at four depths within each simulated breast: at skin surface and at depths of 0.5 cm 1.0 and 1.5cm. A standard mantle field was designed using cerrobend blocks. A 2mm thick secondary lead shield was placed over the skin within the “shadow” of the mantle field's lung blocks. The phantom was then treated five times with the secondary shielding and five times without. Each iteration consisted of 180 cGy to midplane. Following the completion of the fifth iteration, the TLDs were then removed for annealment and readings. The exposure reading of each TLD was divided by 5 for an effective per treatment radiation exposure measurement. Additional TLDs were placed within the phantom to determine whether the secondary shields affected the dose delivered to the mediastinum. RESULTS: At the surface of the simulated breasts, an average dose reduction of 45.0% was observed with the secondary shielding in place. Average dose reductions of 21.1%, 15.7% and -2.4% were observed at depths of 0.5cm, 1.0cm and 1.5cm, respectively, in the shielded breasts compared with the unshielded breasts. The reduction at 1.5 cm was within the TLD calibration uncertainty (+/- 3%). There was no measurable effect from the secondary breast shielding on dose within the phantom's mediastinum. CONCLUSIONS: This in vitro model demonstrates that secondary breast shielding further reduces radiation dose to portions of the breasts which are incidentally shielded by lung blocks during mantle irradiation. The magnitude of dose reduction declines rapidly as a function of depth within the breast and is essentially absent beyond 1.5 cm. The secondary shielding utilized is inexpensive, easy to construct and does not interfere with the intended dose to target tissues. The reduction in dose demonstrated here may decrease the incidence of secondary breast cancers in young females treated with radiation for Hodgkin's disease. San Antonio Breast Cancer Symposium, 12/06 Remember we are NOT Doctors and have NO medical training. This site is like an Encylopedia - there are many pages, many links on many topics. Support our work with any size DONATION - see left side of any page - for how to donate. You can help raise awareness of CAM.