Procedures which involve invasive surgery, radiation therapy or other procedures preformed on the brain or other intracranial structures are especially difficult for the patient. While significant advances have been made in stereotactic equipment and procedures to reduce the discomfort and stress suffered by a patient, most procedures still require the use of invasive stereotactic appliances both in the diagnostic and in the surgical or treatment procedures. For example, referring to FIG. 1, there is shown a "BRW"/"CRW"-type stereotactic head ring 10 disposed around the outside of a patient's head 11. The head ring 10 comprises an annular base 12 formed of metal. Four vertical brackets 13 extend upward from the inside diameter of the base 12. Four adjustable skull pins 14 are threadedly engaged with the upper portions of the brackets 13. The skull pins 14, when rotated relative to the brackets 13, extend inwardly to engage the patient's skull, or retract outwardly to disengage from the patient's skull. The skull pins 14 have pointed tips or ends 15 which, when the skull pins are extended inwardly, penetrate the outer tissue of the patient's head 11 and engage the bone of the skull so as to rigidly and invasively affix the head ring 10 to the patient's head.
The head ring 10 includes recessed ball sockets 16 into which the ball type connectors of compatible stereotactic devices may be received. For example, the head ring 10 is illustrated as supporting a localizing device, that is, a fiducial localizer, 17 used for establishing a coordinate system and measurement reference for diagnostic procedures. The localizing device 17 includes six vertical bars 18 and three inclined bars 19. When diagnostic scanning procedures such as magnetic resonance imaging ("MRI") or computerized axial tomography ("CAT scan") or the like are performed on a patient's head with the localizing device 17 in place, the vertical and inclined bars 18, 19 provide fixed indicia (fiducials) against which measurements can be made and relative to which a coordinate system can be established for the cranium and the intracranial areas. In conjunction with existing computer software developed for the system, the diagnostic images produced from the CAT scan performed with the localizing ring 17 in place will provide X, Y and Z coordinates or, in some applications, polar coordinates, for any portion of the patient's skull, brain or other tissue within the cranium which is to be investigated or treated. Such systems make it possible for example, to identify the location of a target, for example, a tumor, or the like, within the patient's brain, by X, Y and Z coordinates which define the position of the tumor, as well as its point of greatest extension within the brain tissue, etc. Since the localizing device 17 is rigidly attached to the head ring 10, which in turn is rigidly attached to the patient's head 11, the coordinates of diagnostic measurements made utilizing the localizing device 17, may be used directly as coordinates for later surgical, or other treatment, procedures performed, utilizing other appliances or instruments rigidly attached to the head ring 10 as long as the head ring remains attached in its position to the patient's head. As used in this patent, the term "diagnostic procedure" is used broadly and encompasses imaging, visualizing and localizing procedures used for diagnosis and/or treatment of cranial and/or intracranial structures. With the above procedures, the head ring 10 is applied prior to the diagnostic procedure and is continuously maintained on the patient's head during the diagnostic, surgical planning and surgical procedures. The procedures may require eight or more hours to fully complete. The continued application of the head ring to the patient during that entire time causes significant discomfort and stress to the patient.
To disconnect the imaging and treatment procedures in time which makes it possible to administer the treatments repeatedly over days and also reduces the patient's discomfort and stress, a noninvasive stereotactic adapter known as the "LAITINEN STEREOADAPTER" has been developed and is generally known and used. The "LAITINEN STEREOADAPTER" incorporates fiducial markers which can be related to CAT scans, magnetic resonance images, DSA or other images to establish an intracranial coordinate system. That coordinate system is used to relate the position of a target with respect to an isocenter or origin of the Stereotactic adapter. The "LAITINEN STEREOADAPTER" is noninvasive and is removably attached in an exactly reproducible position to the patient's head by reference to the patient's nose bridge and ear canals. Since the device also can be applied, removed and reapplied with accuracy and precision, stereotactic coordinates obtained during preoperative scanning procedures can be reproduced later during surgery with full confidence that the position of the patient's head is exactly where it was relative to the preoperative imaging studies.
The "LAITINEN STEREOADAPTER" is compatible with a "LAITINEN" head ring or arc which is used for surgical or treatment procedures and is affixed to the skull by invasive skull pins. However, the stereotactic adapter is not directly compatible with other known and widely used surgical headrings for stereotactic systems, for example, the Radionics Brown-Roberts-Wells ("BRW") stereotactic system, the Cosman, Roberts and Wells ("CRW") system, the Elekta Instruments Leksell stereotactic system and the Fischer stereotactic system. To resolve the physical incompatibility of the stereotactic adapter with other headrings, a positioning apparatus was developed which is described in the Gildenberg U.S. Pat. No. 5,423,832.
The positioning apparatus disclosed in the Gildenberg '832 patent utilizes the repositioning capability of the "LAITINEN STEREOADAPTER" to reapply and accurately position an invasive headring, for example, a "BRW"/"CRW" type headring to a patient's skull. For example, during the diagnostic procedures, the stereotactic adapter is mounted on the patient's head, and the scanning is performed. Surgical planning can then be done at a later time convenient to the persons required for planning and consultation; and a surgical procedure can be scheduled at a time and date that matches the schedules of the persons involved and the availability of the surgical facilities. At the time of surgery, the "LAITINEN STEREOADAPTER" is mounted on the patient's head in the same position that it was in during the preoperative scanning procedure. The surgical headring to be used is then mounted to the Gildenberg positioning apparatus; and the Gildenberg positioning apparatus is aligned with the "LAITINEN STEREOADAPTER", thereby positioning the surgical headring with respect to the noninvasive stereotactic adapter and the previously scanned data associated therewith. The Gildenberg positioning apparatus is designed to position its isocenter in a predetermined relationship with respect to the isocenter of the surgical headring, so that the isocenters of the surgical headring and the noninvasive stereotactic adapter coincide. To facilitate the alignment process, the positioning apparatus of the Gildenberg '832 patent is mounted with skull pins to the patient's skull to secure its aligned position while the skull pins of the surgical headring are tightened to mount and secure the surgical headring to the patient. When the pins of the surgical headring have been advanced and are firmly engaged in the patient's skull, the Gildenberg positioning apparatus and the noninvasive stereotactic adapter are removed and the patient is ready for surgery. In all stereotactic systems, the arcs or headrings used for stereotactic surgery are secured on the patient's skull using skull pins.
The positioning apparatus of the Gildenberg '832 patent provides significant advantages in, first permitting the diagnostic procedures to be conducted with noninvasive appliances and, second, permitting the diagnostic procedures to be separated in time from the surgical planning and surgery. However, the use of the Gildenberg device of the '832 patent is limited to invasive surgery, and it is not applicable to radiosurgery. If radiosurgery is being considered, the prior techniques must be used which require that the invasive headring be applied prior to the diagnostic scanning procedures and left in place during the scanning, surgical planning and surgical procedures.
As practiced today, radiosurgery uses a linear accelerator to focus a massive dose of radiation at a target or lesion in the brain. The radiation is not tissue sensitive and will damage all tissue through which it passes. Therefore, to minimize damage to healthy tissue and to target all the radiation at the lesion or tumor, as the radiation is applied, the collimator on the linear accelerator rotates through an arc having its isocenter or axis of rotation at the target, that is, the location of the lesion or tumor. The beam of radiation, therefore, sweeps through a slice of healthy tissue which exposes more tissue to the radiation, but for a shorter period of time. It is believed that even though more healthy tissue is exposed to radiation, because the time of exposure is shorter, the damage to the healthy tissue is less. Therefore, the tissue recovers more quickly and fully.
While the above radiosurgery has been shown effective, it is considered desirable to further minimize damage to healthy tissue with even less exposure to the radiation. Therefore, the radiation treatments are given over successive periods of time. Further, with each successive treatment the collimator projecting the radiation beam is rotated through a different plane with respect to the patient's head and, therefore, through different tissue with each successive arc. However, all of the axes of rotation intersect at a common point or isocenter which is the target point and location of the lesion or tumor. Therefore, the exposure of healthy tissue to the radiation is less and minimized to one treatment, whereas the target or lesion which is located at the isocenter receives the accumulation of all radiation dosages. This treatment is referred to as fractionated stereotactic radiotherapy. However, using known devices, the invasive skull pins of the surgical arc or headring must be attached to the patient and a scanning procedure and dose calculation performed with the series of treatments. While it is desirable to further stretch out the treatments over a longer period of time so that individual doses are less, the discomfort and stress of the repetitive application of the invasive skull pins of known appliances make that process impractical; and such extended and repetitive treatment procedures are not used. Therefore, there is a need to further reduce and eliminate, where possible, the discomfort and stress to a patient caused by invasive appliances, so that fractionated radiotherapy treatments extending over disconnected periods of time are practical, cost effective and acceptable.