J. zu Münster
we are treating Lung SBRT with SGRT, also in free breathing. Our current tolerances for this indication are 2 mm. Meaning in our SGRT System Align RT the patient can breathe 2 mm in any direction, before the system stops the treatment via the beamhold function. Most patients have a higher breathing amplitude/range during our 4D-CTs that are used for the treatment plans. Still our MPEs would like to not reach the max. registered breathing range during the treatment itself. So we instruct the patients beforehand accordingly to take calm and slow breaths. If a beamhold is triggered we usually first wait a little while, to see if the patient regains that breathing rythm and position. Sometimes we also advise the patient to take more shallow or deeper breaths. If that does not work, we re-do the CBCT. But that is only very rarely to the case.
During the starting phase, we also initially took a second CBCT post-treatment to verify our methods.
We also verify, that our PTV is large enough to accomondate every breathing phase, with a Motion View imaging before the first treatment.