SU‐FF‐T‐134: Segmented Field Electron Conformal Therapy with An Electron Multi‐Leaf Collimator

Purpose: To investigate the potential of a prototype electron multi‐leaf collimator (eMLC) to deliver segmented‐field electron conformal therapy (ECT) and to improve dose homogeneity to the planning target volume (PTV) by feathering the abutting edge of the higher energy electron fields. Method and Materials: Electron beams (6–20 MeV) using a prototype eMLC were commissioned for the pencil beam dose algorithm in the Pinnacle treatment planning system. A discrete Gaussian edge spread function was used to match electron dose penumbras of differing energies at a specified depth in a water phantom. The effect of edge feathering on dose homogeneity was computed for a segmented‐field ECT treatment plan for a cylindrical, 2‐step PTV in a water phantom (depths = 2.5 and 4 cm). Results: For abutting 9 and 16 MeV fields, Gaussian edge feathering reduced the standard deviation of dose in the PTV from 5.6% to 3.5%. The treatment plan with edge feathering delivered 90% of the prescription dose to 94% of the PTV, while the treatment plan with no feathering delivered 90% of the dose to 88% of the PTV. Conclusions: An eMLC was found to improve dose homogeneity in the 2‐step PTV for segmented‐field ECT through 1D edge feathering of the leaf positions for the higher energy electron field.