A technique that facilitates an accurate comparison between stereotactic and IMRT plans

A non-invasive localization and immobilization method that facilitates tomographic intensity-modulated radiation treatment (IMRT) of intracranial tumors with accuracy comparable to that achieved with invasive methods were developed. This method combines coordinate systems of Linac based radiosurgery (RS), stereotactic radiotherapy (SRT), and tomographic IMRT treatment planning systems (TPSs). In this method, stereotactic localization frame (BRW-LF) with the NOMOS CT pointer attached to its top is used for CT scanning. Patient is scanned from the tip of the CT Pointer to the bottom ring of the localization frame. Thus, CT slices contain fiducial marks for RS, SRT, and tomographic IMRT. Contouring of patient anatomy and target(s) is done on imaging system that can communicate with both RS and NOMOS-IMRT TPSs. Treatment planning is concurrently done for both stereotactic and IMRT methods using the same study set. This provides more accurate comparison of competing treatment plans. Same patient immobilization system is used for both treatment techniques. For IMRT patient localization, a modified Target Box replaced the original NOMOS Target Box. This Target Box is attached to the Linac Target Localization Frame when a patient is in a treatment position. For fractionated IMRT treatments, the accuracy of frame repositioning is checked before every fraction using the stereotactic Depth Helmet. This method of immobilization and localization method was clinically tested. Based on the comparison of developed SRT and IMRT treatment plans, the IMRT method was selected. Depth Helmet measurements verified that an accurate (∼1mm) repositioning of the patient was achieved.