Machined brass skin collimation with variable thickness for electron therapy

Skin collimation in electron therapy ensures sharper penumbra and maximal protection to adjacent critical structures. It also provides a better clinical dose to the target and avoids recurrences at the periphery. The thickness of the electron skin collimation must be adequate for shielding purposes, not too thick to cause discomfort to the patient and be conformal to the skin. This study assessed the clinical potential of machined brass skin collimation with variable thickness. Brass transmission factors for 6, 9, and 12 MeV electron beams were measured and used to determine the skin collimation clinically acceptable thickness. Dosimetric performance of the variable thickness skin collimation was evaluated for 9 MeV electrons within a rectilinear water-equivalent phantom and a water-filled head phantom. Results showed the variable thickness skin collimation is dosimetrically equivalent to the uniform thickness collimation. Favorable dosimetric advantages for brass skin collimation for small electron fields were achieved.