A frameless stereotactic radiosurgery system: utilization of a mobile CT, mask immobilization and micro-multileaf collimators

Abstract

We present frameless stereotactic radiotherapy (SRT) using mobile computed tomography (CT), thermal plastic mask fixation, a vacuum-form body immobilizer and micro-multileaf collimators. A linear accelerator (LINAC, Siemens Mevatron KD2 Primus, Germany) and a self-moving helical CT scanner gantry (Toshiba Xvision/GX, Japan) were installed in the same room. The Fischer CBI system (Leibinger, Germany) was used for stereotactic treatment planning with micro-multileaf collimators. Using a mobile CT gantry mounted on floor-embedded rails, CT scanning and LINAC irradiation can be performed on the same couch by rotating it. The isocenter of irradiation can also be aligned with the center of the CT gantry by rotating the couch. A thermal plastic mask and vacuum-form body immobilizer was used for registration and immobilization. The advantages of this system are as follows. (1) Accurate and painless frameless fractionated irradiation can be performed smoothly, as the patient's head is fixed without exchanging the couch from CT scanning to irradiation system. (2) This mask system can be applied to children, infants or adults with a previous craniotomy bone flap that must have a fixation pin placed into it. This system can be also used for fractionated radiosurgery without painful skull pin-fixed frame. (3) Micro-multileaf collimators of 1 mm enable irregular contour irradiation. (4) Image fusion (among CT, MRI, angiography and PET) and 3D images can be used for irradiation planning. (5) This system can be used on any part of the body. (6) This system can be installed in any irradiation room without any extension or new construction.