Accuracy of manual and automated rectal contours using helical tomotherapy image guidance scans during prostate radiotherapy.

Abstract

94 Background: Prostate radiotherapy can be delivered using daily image-guided helical tomotherapy. Previous work has shown that contouring the rectum on the kV planning CT scan has a Jaccard conformity index (JCI) of 0.78 for different oncologists (inter-observer variability) and 0.82 for a single oncologist (intra-observer variability) (Lutgendorf-Caucig C et al. Feasibility of CBCT-based target and normal structure delineation in prostate cancer radiotherapy: multi-observer and image multi-modality study. Radiother Oncol. 2011;98(2):154-61.). Using the daily image guidance MV CT scan we have developed automated methods to contour the rectum in order to investigate the dose delivered over a course of treatment. We sought to quantify the accuracy of MV manual and automated contours. Methods: A single oncologist (JES) contoured the rectum on 370 MV scans for 10 participants treated with helical tomotherapy to prostate and pelvic lymph nodes. Accuracy of MV manual contours was tested using a scalar algorithm to enlarge and reduce the contours and intra-observer re-contouring at a 3-month interval. Automated contouring, incorporating the Chan-Vese algorithm, was developed and outputs were compared with manual contours. Results: JES could identify differences in MV manual contour size at the level of ±2.2 mm, equivalent to 1.7 pixels. The median JCI for MV re-contouring was 0.87 with inter-quartile range (IQR) 0.78 to 0.90. When compared with manual contours, automated outputs had a median JCI of 0.79 (IQR 0.74 to 0.79). These results were obtained after 3 iterations, each taking less than 10 seconds. Conclusions: Manual contouring using MV scans was accurate, at a level of approximately 2 mm, and reproducible, with JCI of 0.87. The time taken to contour was approximately 20 minutes per scan. Automated contouring was also reproducible with JCI of 0.79 and, in contrast, took less than a minute per scan. Both manual and automated methods produced results comparable to those for contouring using kV scans. We plan to use auto-contouring to calculate accumulated dose to the rectum in an initial cohort of 100 participants. These doses will be correlated with toxicity as part of the VoxTox Study.

Accumulated dose to the rectum, measured using dose–volume histograms and dose-surface maps, is different from planned dose in all patients treated with radiotherapy for prostate cancer

“…We have previously investigated interobserver contouring of this part of the rectum using deliberately extended image guidance scans. 59 We found that median Jaccard conformity index above the superior pelvic muscles was 0.84, interquartile range (IQR) 0.80–0.87. The corresponding value below the muscles was 0.62, IQR 0.53–0.72.…”

Associations between voxel-level accumulated dose and rectal toxicity in prostate radiotherapy

“…For daily MVCT scans, the rectum was identified using a locally developed autosegmentation system based on the Chan-Vese algorithm [32]. Manual contouring of the 4174 MVCT scans (over 62,000 slices) in this study would not have been practicable, and the autosegmentation system has previously been shown to fall within an acceptable range for intra-and inter-observer variability [33]. Dose was calculated directly from the MVCT images (and recalculated for kVCT images) using CheckTomo, an independent ray-tracing dose calculation algorithm [34,35].…”

A Two-stage Classification Method for High-dimensional Data and Point Clouds

“…[26,35,11,39,26,48,49,58,5] and references therein. Moreover, various applications were put forward for instance in optical flow [19], tomographic imaging [3], and medical imaging [59,14,15,12,51,20].…”