Brass Eye Shields for Total-Skin Electron Therapy
Abstract
Purpose
To confirm leaded brass as a shielding alternative to Cerrobend for eye shields during total-skin electron (TSE) radiotherapy treatments.
Methods
1.5cm thick leaded-brass inserts were fashioned from patient-specific lung blocks from .decimal. Inserts were placed inside of swimming goggles as eye shields for TSE treatments utilizing 2.5MeV electrons. With a density of 8.4g/cm3, the electron range in the brass is expected to be 1.5mm. With an effective attenuation coefficient of 0.0392cm2/g, the half value layer of the brass is approximately 2.10cm, reducing the photon contamination to 61%. The goggles were placed on a RANDO head-and-neck phantom and positioned with clinical setup. Gafchromic EBT4 film was placed (1) on the front goggle face, (2) between the goggles and the brass, and (3) behind the brass. The phantom was irradiated under treatment conditions: six orientations with two gantry angles for each orientation, 70° and 110°, to a total of 120cGy to the patient’s skin. This irradiation was repeated three times and the films in locations 1 through 3 were compared to reference film (4) that was irradiated on the phantom without shielding. Films were read after 24 hours with both prescan and background subtraction.
Results
Average dose for film location 1 was 108cGy, location 2 was 114cGy, location 3 was 13cGy, and location 4 was 94cGy. The shielding reduced the dose to film 3 by 86% relative to the reference film. Experimental measurements showed a greater reduction than the calculations as the calculations assumed perpendicular incidence, an infinitely wide shield of uniform thickness, a monoenergetic beam, and did not account for air attenuation.
Conclusion
This work shows the viability of reusing brass from lung blocks as eye shields for TSE treatments. Using brass instead of Cerrobend for TSE treatments increases safety for therapists and patients while also limiting waste.