Fifty-seventh annual meeting of the American association of physicists in medicine
TH-AB-BRA-06: Independent Automatic Catheter Digitization Algorithm for High Dose Rate (HDR) Brachytherapy Quality Improvement (QI) and Quality Assurance (QA)
Individual-user and inter-user variability during manual catheter digitization for interstitial HDR brachytherapy can be significant since the process can time consuming and error prone. We present an algorithm and workflow for catheter digitization that can be used for independent verification of manual digitization (QA) or automatic digitization (QI).
After DICOM CT images are imported into the TPS, this proximal end of each catheter is located and numbered on a single slice near the needle template. The DICOM RP and CT files are then exported for digitization. Each transverse CT slice is smoothed with a Gaussian filter, then a convolution kernel finds the Laplacian of the CT image. This process highlights regions of rapid density change. A sliding window filter is applied to the image afterwards to locate each catheter center. The catheter is traced and geometry digitized from the needle template to the tip slice by slice, similar to the manual procedure. All the contour points are written into the original DICOM RP file and imported back into the TPS for planning. The difference between the manual digitization and the automatic digitization was quantified with a RMS calculation of the deviation between the manual and automatic catheter geometries for 11 clinical cases.
The RMS difference between the automatic and manual digitization was 0.50±0.04mm. Execution time for automatic digitization is ∼3 minutes (analysis ∼2 min; DICOM export/import ∼1 minute).
This automatic catheter digitization method can be used as both a QA and QI tool. As a QI it is executed instead of manual catheter digitization. The algorithmic nature ensures reduced individual- and intra-user variability and reduces digitization time. As a QA tool, the algorithm can be used to validate the manually generated catheter pattern to ensure digitization integrity.