CASS Photon Knife System

The CASS PhotonKnife provides a non-invasive method of treating various brain lesions and arteriovenous malformations (AVMs) using a linear accelerator (LINAC).


CASS PhotonKnife RadioPlan Treatment Planning System 3-D radiosurgery treatment plan of an AVM (light blue) in the left amygdala with 80% isodose margin (red) around the lesion. The CASS whole brain mapping system is used to automatically display the volumetrically determined region of the left hippocampus (yellow).
The CASS PhotonKnife RadioPlan Treatment Planning System is a highly advanced 3-D graphical planning system for radiosurgery and fractionated radiotherapy. Computer optimization of isocenter and collimator size are automatically performed based on lesion location and shape. Integration of image data along with graphic renditions of volume and anatomic structures allows interactive assessment of a treatment plan. With the CASS PhotonKnife RadioPlan comes years of experience in stereotactic procedures and radiation therapy.

Advantages of the PhotonKnife RadioPlan Treatment Planning System include:

  • The CASS PhotonKnife RadioPlan allows modern imaging techniques, such as CT, MR, and angiography, to be used to precisely localize a target site within the brain.
  • The CASS PhotonKnife RadioPlan provides the flexibility to treat with small fields, large fields, fractionation, and conformal collimation.
  • Many institutions may already have the equipment necessary to perform stereotactic procedures, but do not yet have a system which can provide them stereotactic radiosurgery and fractionated radiotherapy. The CASS PhotonKnife RadioPlan can be used with most commercially available stereotactic frames, as well as being provided with the necessary stereotactic hardware for such procedures.
  • Installation of the LINAC hardware components and the gathering of beam data can be done by our team of physicists and engineers, allowing patient treatments to begin within a few weeks.
  • The CASS PhotonKnife RadioPlan is provided with both a mouse and keyboard interface and is available with other interfaces (infrared touch screen, joystick, etc.) as the user desires.
  • The size and description of the dose matrix can be modified on a case-by-case basis. This flexibility gives the user the opportunity to assess a treatment plan based on the prescribed isodose line as well as any of the surrounding isodose lines.
  • Many aspects of the procedure are automated, to allow the user to focus on the more important aspects of the procedure, such as the optimization of the treatment plan.
  • Fractionation allows the pre-planning of cases for treatment of multiple patients with only a minor reduction in the normal LINAC patient load.
  • Image fusion allows the integration of CT and MR data reducing the effects of distortion found in MR imaging.
  • User-defined library of treatment arc sets allows rapid definition of initial treatment plan.
  • User-defined couch and gantry for direct simulation of LINAC equipment coordinate systems.

The Treatment Procedure - Frame Based Radiosurgery

  • The neurosurgeon positions the stereotactic frame on the patient.
  • Imaging is performed and the images acquired into the CASS system. Stereotactic calibrations and automated surface contouring is done during this acquisition phase.
  • Treatment planning is interactively performed on the CASS system. Arcs can be positioned manually, from standard arc sets, or interactively with 2-D/3-D displays. Interactive arc positioning and collimator positioning is also possible using 3-D beams-eye view displays of the calculated dosimetry.
  • Before treatment, the couch is positioned at isocenter, the test ball is positioned at the isocenter coordinate using a stereotactic phantom then attached to the head holder of the couchmount. Test films are taken at standard couch and gantry angles and run through the Automated Test Target Calibration (ATTC) program for verification. If necessary, adjustments are made and a second set of films are taken.
  • The isocenter can also be set up and verified by the use of the CASS Laser Calibration System (Example) in conjunction with the CASS Precision Localizier Box.
  • Once the isocenter is verified, the patient is placed on the couch and the stereotactic head ring attached to the mount. A "dry run" of the gantry rotation is done, after which the treatment is performed. Steps 4 and 5 are repeated for all isocenters and beam arcs until treatment is complete.
  • Estimated time for imaging, treatment planning and treatment is 2 1/2 to 4 hours for a single isocenter.

The Treatment Procedure - Fractionated Radiotherapy

  • The neurosurgeon positions the Laitinen StereoAdapter. The positional readings are recorded for repeat positioning.
  • Imaging is performed, and the images acquired into the CASS System. Automatic surface contouring and image calibration is performed during this acquisition phase.
  • Treatment planning is interactively Cass RadioPlan Orbital Frontal Tumor
    performed on the CASS system. Arcs can be positioned manually, from standard arc sets, or interactively with 2-D/3-D displays. Interactive arc positioning and collimator positioning is also possible using 3-D beams-eye view displays of the calculated dosimetry.
  • Using the determined treatment coordinates, the patient is positioned for treatment. Arcs can be positioned and the treatment plan can be performed at the discretion of the physician. Treatment can begin immediately after treatment planning or at any convenient time thereafter.
  • For treatment, the patient is immobilized on the couch using the Laitinen StereoAdapter (Example) and the CASS couchmount. for rapid and efficient Fractionated Stereotactic Radiotherapy.
  • Estimated time for imaging, treatment planning and treatment is 2 1/2 to 4 hours for a single isocenter. Each subsequent fraction given does not require imaging or treatment planning and takes about 1/2 to 1 hour.

Beam Data

TruTaper Collimators Radiosurgery treatment planning requires the gathering of an extensive amount of data for each of the collimators and linear accelerators which are to be used for radiosurgery/radiotherapy treatments. The minimal characteristics of small fields necessary for dosimetric calculations are: a) relative output factors (total scatter factors); b) dose profiles (OAR or off axis ratio); and c) central axis attenuation of the beams (TMR or tissue maximum ratio).

The gathering of beam data can be performed in-house by the physicists at the institution, or can be done by MIDCO's team of physicists during hardware installation and training. Having our team of qualified and experienced physicists gather the data is both reliable and efficient. You should be ready to begin treating patients in a matter of weeks.

Accuracy and Reliability (for the Frame-Based System)

The overall accuracy of the mechanical movements and positioning of a given LINAC radiosurgery system is of primary importance in the accurate delivery of a radiation dose to a target structure. For this reason, it is important to test the geometric accuracy of the LINAC to be used for radiosurgery. The initial accuracy of the LINAC should be < 1.10 mm for gantry rotational intersection with the rotational axis of the couch in all gantry/couch positions. The CASS collimators and couchmount system are then positioned according to the guidelines in the CASS Radiosurgery Hardware Setup Manual. It is possible to configure a system with a high degree of accuracy in the range of 0.5 mm ± 0.3 mm.

Components of the CASS Couchmount System

Couchmount System
MIDCO has a quality Couchmount System (Patient Head Support System) for use in radiosurgery. This couchmount system complements the CASS Collimator set, and enables MIDCO to provide its customers with a full set of instrumentation necessary for radiosurgery. The design of this couchmount is such that it will fit most linear accelerators with only slight modifications to the couchmount adapter assembly.

Couchmount Adapter Assembly

The Couchmount Adapter Assembly is designed for quick attachment and disconnection to the end of the couch table of the linear accelerator. It affixes to the T-rails of the couch with thumb screws on each side for tightening the unit to the table once it is properly positioned. Repeat alignment is achieved with dowel pin stops which ensure proper position along the T-rails. The lower portion of the adapter assembly contains a fixation plate for the Couchmount Head Holder and Precision Positioner Unit.

Couchmount Head Holder and Precision Positioner

Most commercially available stereotactic headrings can be mounted to the CASS Couchmount System by the use of a stereotactic frame holder made specifically for the headring. Although most headrings are similar, each has a slightly different adapter plate which rigidly holds the headring.

The CASS Couchmount System has six axes of adjustment which allows for easy setup with the LINAC couch/gantry system. An additional feature of the system is a unique laser measurement apparatus for precisely measuring an isocenter of a target volume for LINAC-based radiosurgery/stereotactic radiotherapy. These two features also allow for the correction of alignment errors during treatment planning setup, such as errors inherent in the use of room lasers and errors due to couch shifts during patient positioning. It will also give an index of gantry sag or misalignment.

Couchmount Precision Localization Box (Example)

The Couchmount Precision Localization Box has sides and is substantially the same in size to that of the angiographic localizer provided with your stereotactic frame. This localization box has millimeter etchings around the edges and corners which correspond to your stereotactic frame's coordinate system. In addition, the sides of the box have angiographic markers similar to the angiographic localizer provided with your stereotactic frame. The precision localization box is capable of three means of target determination or confirmation, which include:

  • Use of the ruled millimeter etchings around the corners of the box in conjunction with the room laser lights for setup and/or confirmation of the target isocenter by checking the reflection position of the laser lights on the sides of the precision box.
  • Use of the angiographic-type localizer fiducials embedded in the sides of the localization box for the determination of the collimator alignment to the target point by the performance of AP and lateral X-rays with the circular field collimators in place, and the LINAC primary collimators set at approximately 25 x 25.
  • Use of the sides of the precision box in conjunction with the CASS Laser Measuring System to precisely measure the position of the localization box within the couch/gantry system. This method is used to measure the position of the isocenter after your system has been set up and calibrated.

Couchmount Laser Measurement Apparatus (Example)

The Couchmount Laser Measuring Apparatus consists of a power supply and fuzzy logic unit connected to a laser measuring sensor attached to a plate which attaches to the collimator housing. The system is equipped with a digital read-out meter set to four decimal places. The laser beam emitted from the laser measuring device is reflected off the surface of the Precision Localization Box to measure the distance of a given side of the Precision Localization Box from its fixed attachment point on the LINAC gantry. This system is used as an in vivo verification system to measure and/or confirm isocenter setup.

Couchmount Test Target Assembly (Optional)

The couchmount test target assembly consists of a test target pointer and 6 mm sphere with a small X-ray film holder with attachments to the collimator housing. This system is used for in vitro set up and target alignment in conjunction with CASS ATTC.