Alasti H, et al. – Experts aspired to figure out whether the enhanced soft tissue contrast provided by high–dose volumetric CT (HDVCT) could reduce inter–observer variability in delineating prostate compared to helical conventional CT (CCT) scans and 3T MRI scans for patients undergoing radical prostate cancer radiotherapy, as well as, to quantify the potential PTV reduction with decreased inter–observer variability. Data emphasized that inter–observer variability in delineation remained an important source of systematic error. This error was reduced by HDCTV for treatment planning, without recourse to MRI. In addition, it allowed a PTV reduction of 2 mm at the apex.

Methods

• This study employed a 320 slice volumetric CT scanner.
• As per observations, the wide-detector coverage of 16 cm enabled volumetric image acquisition of prostate gland in one rotation.
• On ten patients, three imaging studies were performed.
• In addition, CCT and HDVCT were performed consecutively at the same coordinate system followed by MRI.
• The prostate was delineated by five radiation oncologists.

Results

• With the maximum at the apex region, the inter-observer variability was 2.0±0.6, 1.9±0.4 and 1.8±0.4 mm for CCT, HDVCT and MR.
• Moreover, comparing inter-observer difference variability between CCT and HDVCT with MR indicated that observers had larger variations in contouring using CCT than HDVCT especially at apex.
• Results revealed significantly higher Jaccard index of HDVCT than CCT with a mean difference of 0.03 (p=0.011).
• As compared to CCT, both MRI and HDVCT offered the opportunity for a 2 mm PTV margin reduction at the apex.