Ion-beam mask for cancer patient therapy

Claim 1

A radiation mask for mitigating the surface tissue effects of a radiotherapeutic treatment of embedded tumors in a patient by means of a beam of fast ions from a beam source, comprising: a block of radiation shielding material positioned in said beam intermediate the patient and said beam source, said block having a surface area larger than the cross section of said beam and a thickness greater than the range of ions of said beam in said shielding material, said shielding material block having a plurality of circular cross section apertures extending therethrough in a direction parallel to the rays of said beam and arranged in an orderly, evenly spaced array, each of said apertures having a diameter (d) and spaced with a wall thickness (w) therebetween defined by d w F sigma e, with f being in the range of from 1 to 2 and where sigma e is the effective dispersion of the ions passing through said apertures at the depth of said embedded tumor to attain sufficient overlap of discrete beam portions passing through adjacent ones of said apertures at the depth of the Bragg peak for said beam source coincident with the tumor region, thereby providing a lateral uniformity of radiation dose over the irradiated area of said tumor while shielding a substantial are of skin and intervening tissue.