Every Single Time

The Winston-Lutz test is a standard in the industry to evaluate the isocenter of linear accelerators. This test is performed by meticulously placing a phantom on the treatment delivery table where the lasers meet, showing the central axis of the beam and where the point of dose delivery will eventually take place.

Numerous mechanical issues can cause this crucial point to be wobbly, from the table to the gantry, to the imagers or even the lasers themselves being slightly out of alignment; this defining point on a linear accelerator needs to be checked and double-checked routinely since this is the location on conventional accelerators the dose will ultimately be delivered when the patient is properly positioned.

What would you do if you were to place your Winston-Lutz phantom on the table, but prior to leaving the room you accidentally bumped into it? Your phantom is now off by 9mm’s to the left, 5 mm’s anterior, 6 mm’s superior with a .9-degree pitch, rolled slightly to the left and almost 3 degrees clockwise.

Without knowing you continued with the test and when you analyzed the results everything was perfect. Would you,

A.????? Re-run the test immediately after resetting the phantom.

B.????? Throw the phantom away because it is obviously defective.

C.???? Call your Field Service Engineer to do a complete recalibration.

D.???? Show everyone in the department the results while bragging how accurate a CyberKnife is.

I am hoping your answer will be D since the CyberKnife does not rely on an isocenter to treat. With a robotic arm that is accurate to sixty microns (less than a human hair), it paints dose to the lesion creating extreme conformality whether the lesion is wrapped around the spinal cord or surrounded by the bladder and bowel it will adjust the beam for even a tenth of a millimeter of motion in every plane and rotation, getting the dose exactly where it needs to be every single time.

So, in the Winston-Lutz scenario described above, even if the phantom is set up incorrectly the robot will make up the difference ensuring the beam is delivered correctly, thereby resulting in a perfect result. The same result that you will get for your patient.

This also holds true for lesions that move, like in the lung, liver, pancreas, or anywhere else motion is a concern. Every time the beam comes on it is delivered exactly where you intended it to treat regardless of the location or condition.

Imagine treating the outer portions of an irregularly shaped lesion with the same priority as the center. Only with a Knife can you be concerned about the edge, and in this case, it is a robotically manipulated, artificially intelligent CyberKnife.

Please feel free to reach out to me to find out more about how the CyberKnife makes whole body radiosurgery with absolute precision possible.

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*The statements on this site are my own and do not represent Accuray opinions or positions.

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