Dosimetric Impact of Surgical Clips in Electron Beam Treatment of Breast Cancer

Titanium clips are commonly used to delineate the location of the tumor bed during breast cancer surgery. Electron beams are frequently used to boost radiation dose to the breast cavity. This research investigated the effect on such boost treatments as a result of metallic clip perturbation potentially exhibited through attenuation and scatter processes using measurements with Gafchromic film and treatment planning simulation with both generalized Gaussian pencil beam and electron Monte Carlo algorithms. Results showed that the potential effect of clip interference is unidentifiable from both algorithms. Dosimetry with Gafchromic external beam therapy film did detect dose perturbations caused by the titanium clips in proximal plane, 0.23 mm away, resulting in 3.0% backscatter and 2.4% attenuation at 6 MeV and 2.0% backscatter and 6.7% attenuation at 9 MeV. The noise contribution of the film scanner is estimated to be about 0.4% and nearly 2% uncertainty in film calibration. As a result, we conclude that the magnitude of dose perturbations from clip is negligible for clinical findings.