Emerging technology in cancer treatment: radiotherapy modalities.

This is a period of rapid developments in radiotherapy for malignant disease. New methods of targeting tumors with computed tomography (CT) virtual simulation, magnetic resonance imaging (MRI), and positron-emission tomography (PET) fusion provide the clinician with information heretofore unknown. Linear accelerators (linacs) with multileaf collimation (MLC) have replaced lead-alloy blocks. Indeed, new attachments to the linacs allow small, pencil beams of radiation to be emitted as the linac gantry rotates around the patient, conforming to three-dimensional (3D) targets as never before. Planning for these delivery systems now takes the form of "inverse planning," with CT information used to map targets and the structures to be avoided. In the area of brachytherapy, techniques utilizing the 3D information provided by the new imaging modalities have been perfected. Permanent seed prostate implants and high-dose-rate (HDR) irradiation techniques targeting bronchial, head and neck, biliary, gynecologic, and other anatomic targets are now commonplace radiotherapy tools. CT-guided permanent seed implants are being investigated, and a new method of treating early breast cancer with HDR brachytherapy via a balloon catheter placed in the lumpectomized cavity is coming to the forefront. Newer modalities for the treatment of malignant and benign disease using stereotactic systems and body radiosurgery are being developed. Targeted radionuclides using microspheres that contain radioemitters and other monoclonal antibody systems tagged with radioemitters have been recently approved for use by the Food and Drug Administration.