Apparatus and method for therapeutically irradiating a chosen area using a diagnostic computer tomography scanner

In combination with a diagnostic computer tomography scanner that uses a radiant energy beam for imaging purposes, an apparatus for therapeutically irradiating a chosen area with the radiant energy beam comprising:

• a masking member fabricated from a material that partially attenuates the radiant energy passing therethrough, but transmits a sufficient amount of the radiant energy for imaging purposes and having an aperture therein adapted for passing an unattenuated portion of the radiant energy beam therethrough;
• means for fastening said masking member to the scanner interposing said masking member in the radiant energy beam intermediate the source of the radiant energy beam and the chosen area for passing said unattenuated portion of the radiant energy beam to irradiate the chosen area;
• means for selectively varying the cross-sectional shape of said masking member aperture in a predetermined manner as a function of the location of the chosen area and the position of the source of the radiant energy beam;
• means for selectively varying the spatial position of said masking member aperture in a predetermined manner as a function of the location of the chosen area and the position of the source of the radiant energy beam;
• and,
• a post-masking member aligned with said masking aperture and fabricated of a material that attenuates the radiant energy passing therethrough to an energy level essentially uniform with that of the radiant energy passing through said masking member.

A method for using a diagnostic computer tomography scanner that uses a radiant energy beam for imaging purposes for therapeutically irradiating a chosen area with the radiant energy beam comprising the steps of:

• positioning a patient in the scanner using positioning restraints to prevent patient motion with respect to the scanner;
• performing a diagnostic scan of said patient;
• determining an area chosen for therapeutic irradiation;
• repositioning said patient as necessary to move said chosen area to a selected predetermined location;
• measuring the spatial dimensions of said chosen area;
• choosing a masking member fabricated from a material that attenuates the radiant energy passing therethrough and having an aperture therein adapted for passing an unattenuated portion of the radiant energy beam therethrough with a cross-sectional beam area essentially equal to that of said chosen area;
• interposing said masking member in the radiant energy beam intermediate the source of the radiant energy beam and the chosen area so that said unattenuated portion of the radiant energy beam irradiates the chosen area;
• and
• scanning the chosen area through multiple cycles to irradiate the chosen area to a desired exposure level.