A high-precision system for conformal intracranial radiotherapy

Purpose: Currently, optimally precise delivery of intracranial radiotherapy is possible with stereotactic radiosurgery and fractionated stereotactic r adiotherapy. We report on an optimally precise optically guided system for three-dimensional (3D) conformal radiotherapy using multiple noncoplanar fi xed fields. Methods and Materials: The optically guided system detects infrared Light e mitting diodes (IRLEDs) attached to a custom bite plate linked to the patie nt's maxillary dentition, The IRLEDs are monitored by a commercially availa ble stereo camera system, which is intel faced to a personal computer. An I RLED reference is established with the patient at the selected stereotactic isocenter, and the computer reports the patient's current position based o n the location of the IRLEDs relative to this reference position. Using thi s readout from the computer, the patient may be dialed directly to the desi red position in stereotactic space. The patient is localized on the first d ay and a reference file is established for 5 different couch positions. The patient's image data are then imported into a commercial convolution-based 3D radiotherapy planning system, The previously established isocenter and couch positions are then used as a template upon which to design a conforma l 3D plan with maximum beam separation. Results: The use of the optically guided system in conjunction with noncopl anar radiotherapy treatment planning using fixed fields allows the generati on of highly conformal treatment plans that exhibit a high degree of dose h omogeneity and a steep dose gradient. To date, this approach has been used to treat 28 patients. Conclusion: Because IRLED technology improves the accuracy of patient local ization relative to the linac isocenter and allows real-time monitoring of patient position, one can choose treatment-field margins that only account for beam penumbra and image resolution without adding margin to account for larger and poorly defined setup uncertainty. This approach enhances the no rmal tissue sparing, high degree of conformality, and homogeneity character istics possible with 3D conformal radiotherapy, (C) 2000 Elsevier Science I nc.