Reply To: SGRT and involuntary organ motion

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SGRT can obviously be used to “gate” the beam for patients who often experience large and small involuntary motions.

One of the more interesting things I like using the system for is its quality management characteristics as an optical observer. One unique thing that SGRT can be used for that other systems typically cannot is in its capacity as an optical tool for statistically evaluating the quality of the immobilization needed / made for a patient with these types of conditions rather than just as a separate method of simply treating them without immobilization.

By that I mean you can immobilize one of these patients in an open face mask for SRS / partial brain treatment or in a acuform cushion / vacloc with an extremity mask for an extremity sarcoma to limit the involuntary motion as best you can during simulation. Then you can bring the patient back during the planning process prior to treatment and set them up on the machine using a preplan DICOM surface in the custom immobilization and monitor them for the estimated duration of a treatment (i.e.10-15 minutes) while exporting the data for evaluation.

You can then use that data to plot probability distributions across all axes and statistically derive the proper treatment margins given the motion seen under the immobilization from simulation. This is something no other modality can do on a per patient or fabricated immobilization device specific basis making it a very useful tool.

Using this data, you can determine if further refinement of the immobilization technique is required in order to limit how much healthy tissue is treated or if a slight adjustment of the PTV margin is required to account for the motion seen during observation. It may be that the PTV margin you thought you needed is actually larger than what is required given the observed motion and it can be reduced to spare more healthy tissue in an intelligent way.

SGRT is well suited to answer these unique patient specific questions where no other “treatment” technique can. Maybe SGRT is more than just another treatment technique? You can tell us.