- Wed Mar 01, 2023 5:49 pm
Some questions concerning initially correct couch LNG value. We are starting tattooless in certaint patient group in breast.
All the linacs are not yet equipped with SGRT, so this happens slowly. However, our policy in this breast group is to check the value on the side of the breast board at the CT at the mamilla level for reference level, some of you use SSN for this. This value of the fixation is marked down at the CT. Our breast boards are indexed identically at the linacs (H2), meaning that certain side value on the breast boards in the reference level indicates reliable couch LNG value at the linac. Typically, additional (1-8 cm) planned LNG shift is done during the dose planning process and this LNG shift from reference level to isocenter level is added to achieve initially adequate couch LNG value. During the first fraction this workflow guides the actual couch LNG value with TrueBeam automatic drive inside 1-2 cm from the correct one, based on AlignRT. On the first fraction, the couch values (VRT, LNG, LAT) are saved after image guidance. Is there some other way that hospitals are using to record couch LNG values at the CT for the first fraction setup than using scale of the breast board for this? How is this done in the pelvis cases for example, if there is no fixation with side values under pelvic region? I know several hospitals are doing manual couch shifts at the first fraction with moving the patient to near correct isocenter and use AlignRT for the finetuning at the time it begins to see where the patient should locate, but I think it would be great if we could use automation for this from the start for pretty much all the patients. Is someone having scale at CT couch or is this fiducial at the reference level at the CT slices used somehow to this...? Thank you, I would appreciate your answer.
Best regards Marko