Purpose or Objective
Dual Energy Computed Tomography (DECT) captures images in different voltages, potentially allowing a better definition of organs due to different tissues densities (. The aim of this work is to evaluate the impact of DECT simulation in inter-observer variability (IOV) for prostate gland (PG) and organs at-risk (OARs) contouring.
Material and Methods
Five radiation oncologists, with different expertise in prostate cancer (PC) treatment, performed the contouring of PG and OARs of 10 patients who underwent DECT simulation. The contouring was carried out on basal CT scan and also on 80 kV, 140 kV, mixed and 55 KeV mono-energetic reconstructions. Consistency in target volume delineation was expressed by the IOV. Dice Similarity Index (DSI), center of mass distance (dCOM) and volumes were then calculated. Median values and accompanying ranges were used to describe the data, since not all variables were normally distributed. A Wilcoxon signed-rank test was performed to compare paired variables using R Core Team (2021).
Results
A total of 750 structures were collected: 250 clinical target volumes (CTV), 250 rectum and bladder volumes were included in the study. The analysis did not reach statistically significant differences in the variability between the different CT reconstructions. For CTVs the median DSI values were 0.17, 0.58, 0.99, 0.93, 0.47 for basal CT, 55 kV, 80 kV, 140 KeV and mixed reconstruction, respectively. For rectum and bladder the same values were 0.33, 0.43, 0.63, 0.39, 0.53. and 0.17, 0.58, 0.99, 0.93, .047 respectivly. The median percentage differences of the CTV volumes were 7.5%, 6.2%, 5.5%, 5.3%, 5.7% for basal CT, 80 kV, 140 kV, 55 KeV and mixed, respectively. Rectum differences accounted to 6.4%, 6.8%, 7.4%, 5.6%, 7.4%, whereas bladder variability were 1.6%, 1.3%, 2.1%, 1.7% and 1.6%. surprisingly, the data show how basal CT, used daily for the definition of targets, is associated with a greater IOV
Conclusion
Our data show that reconstruction at 55 KeV is the sequence that provides a lower IOV in the contouring of PG and OARs, although the difference is not statistically significant. The higher IOV is observed in the basal CT scan, while the integrated use of the additional DECT reconstructions could reduce the IOV even if with greater time consuming. To our knowledge, this is the first study evaluating the role of DETC in IOV for PC and highlights the potentialities of DECT in improving the contouring of the PG and OARs