Interobserver variation of prostate delineation on CT and MR by radiation oncologists, radiologists and urologists at the Universitas annex oncology department
Introduction and aim: In recent years advances in delivery of radiation to clinically localised prostate volume has enabled dose escalation and greater sparing of organs at risk. At our department a significant proportion of prostate cancer patients are treated with curative radiation therapy and targets are defined through manual delineation. In this study we evaluate and quantify the variation of prostate contouring between radiation oncologists, radiologists and urologists respectively on CT and MR images and we determine the regions of significant concordance in segmented contours. Materials and methods: CT and MR image sets of 5 prostate cancer patients were presented separately for prostate delineation in a blinded and independent fashion to each subgroup of specialists from various hospitals and included 7 radiation oncologists, 6 radiologists and 3 urologists. Variations were first analysed visually. In house tools and dedicated software was developed to automatically analyse various metrics in terms of volumes, volume centroids, maximum volume ratios (MVR), apex/base locations & diameters, ratio of scan encompassing volume (SEC), ratio of scan common volume (SCV), mean values & coefficient of variations and also to calculate the concordance index for each patient & each subgroup of specialists. Results: Significant differences were observed between the subgroups of specialists. The volumes were significantly larger on CT than the corresponding MR image sets in all cases. The average prostate volumes were 28,3cm3 larger on CT than on MRI for oncologists with the MVR of 2.24; followed by radiologists with the average prostate volume of 18,1cm3 larger on CT than on MRI with the MVR of 1.57 and lastly the urologists had an average volume of 16,8cm3 larger on CT than on MRI with the MVR of 1.51. Furthermore the p-value was significant for oncologists vs radiologists (p=0.02) and for oncologists vs urologists (p=0.01) with regards to the maximum volume ratios (MVR). Variations in base positions were small and the base contours drawn were within 5mm of the defined base location on both CT and MRI where as for the apex position, the variations were significant and the apex contours drawn were mainly >5mm in relation to defined apex and varied more for CT than MRI. The inter-scan variation was similar (2.22) in both CT and MRI for radiologists demonstrating that they were more homogenous compared to other specialists. For the oncologists the variation on CT (1.72) was less than for MRI (1.82) whereas for the urologists the variation on CT (1.75) was larger than for the MRI (1.69). The conformity index (CI) for all the patients for combined images (CT and MR) were 0.45+/-0.04 for urologists; 0.56+/-0.08 for oncologists and 0.58+/-0.05 for radiologists which corresponds to poor concordance. Volume centroids provided useful interpretation of three dimensional spread of prostate volumes and uncovered larger CT derived prostate volumes delineated by radiologists and oncologists compared to urologists. Conclusion: Major discordances were observed between radiation oncologists, urologists and radiologists delineations and areas of disagreements were identified indicating that this step needs to be improved. MRI images proved to be critical when delineating the prostate and thus making use of such an imaging technique provides a useful contribution in overcoming this difficult delineation. The urologists produced the most comparable delineations, followed by the radiologists and lastly the oncologists. The radiologists were more homogenous compared to other specialists. A better training of radiation oncologists in prostate imaging and the collaboration between radiation oncologists, radiologists and urologists should decrease this variability and ensure consistency in the delineation within the department.