Forums › SGRT – Best Practice › Determination of HU threshold to generate the DICOM reference surface › Reply To: Determination of HU threshold to generate the DICOM reference surface
Finally, I combine some results to my answer and think what this means from our side. I would like to say that I think it is worth somehow on the first fractions to achieve zero systematic error to the sternum VRT or tangential image ribs VRT in the images, as is your goal Jose. Based on the results, random error for the sternum VRT with SGRT only (without daily IGRT corrections) in the 20 patients DIBH group in our latest offline data is only 1.4 mm (group mean value of the patientspecific SDs for the daily sternum VRT in image acquisition position). With RPM here, with daily IGRT online match couch corrections, random error in the recent data (patient n=20) is 1.1 mm (p=0.01). Thereby daily 2D/2D IGRT and couch corrections based on online match still improves the accuracy also concerning this sternum VRT topic when compared to AlignRT only data (without image guidance). 1.4 mm SD in sternum VRT with AlignRT only (without IGRT corrections), seems however good enough for its part to proceed mostly with verification tangential images only, without online match couch corrections. As mentioned, this calls for that systematic error in sternum VRT or tangential image ribs VRT is in practice zero in the first fractions with the used setup reference surfaces without online match couch corrections. +- 2 mm BH window was used in both groups.