MEDRADSC 3S03 Lecture Notes - Lecture 4: Wicket-Keeper, Mouth, Ghost Hunting
4 Jan 2017
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Week 4 treatment of superficial malignancies with electrons (1) When depth of ptv exceeds 2. 0 cm. When skin is significantly sloping across field. When bone is closely underlying trt area. Electrons accelerated across waveguide to predetermined energy. Pencil beam is produced (not clinically useful at this point) Beam is widened to make clinically useful by: Pencil beam scatter or scan over the field. Week 4 treatment of superficial malignancies with electrons (2) Difference vs photon: very curved, rapid fall off on the side. Electrons scattered widely (spreads beam out to make clinically useful) using a high z material in head of machine: gold, silver, brass, steel or aluminum. Pencil beam scanned across opening by magnetic fields. Foil must be kept thin enough to minimize photon contamination in the process (mm thick) Interactions within foil degrade beam energy, resulting in a non- mono-energetic beam there is no material placed in the path of the beam.
