ESTRO 37 Abstract book

S1189

ESTRO 37

3 University of Newcastle, School of Mathematical and Physical Sciences, Newcastle, Australia 4 Royal Brisbane Hospital, Australian e-Health Research Centre- CSIRO, Herston, Australia 5 University of Wollongong, Centre for Medical Radiation Physics, Wollongong, Australia 6 Sir Charles Gairdner Hospital, Radiation Oncology, Nedlands, Australia 7 Liverpool and Macarthur Cancer Therapy Centres, Department of Radiation Oncology, Liverpool, Australia 8 Calvary Mater Newcastle Hospital, Radiation Oncology, Newcastle, Australia 9 University of Western Australia, School of Physics and Astrophysics- Faculty of Science, Crawley, Australia Purpose or Objective Development of a probabilistic prostate atlas can allow for secondary analysis of the large RADAR patient dataset. This study investigated whether clinical target volume (CTV) contouring variations for prostate cancer could be a predictor for local disease progression, overall survival and rectal toxicity. Material and Methods Five prostate cancer patient datasets each had CTV contoured on planning CT by ten observers, with probability maps constructed using observer contours. Patient scans were used to construct a pelvic atlas for retrospective analysis of the larger RADAR dataset, containing 711 patients that underwent external-beam radiotherapy for prostate cancer treatment. RADAR patients without prostate only CTV contours were excluded from the study. Remaining RADAR patients each had a single atlas patient, selected based off prior clustering work, undergo rigid and deformable (Demons non-rigid) registration to allow propagation of probability maps onto the RADAR patient. Probability maps were thresholded at 50% observer agreement, and spatial overlap of probability maps and RADAR CTVs were assessed using Dice similarity coefficient (DSC). Correlations with time to local progression and overall survival were calculated using Cox proportional hazards regression. Correlations with grade 2 and higher rectal bleeding were assessed using Wilcoxon signed-rank test. Results A total of 461 patients from the RADAR dataset contained prostate only CTV contours. Mean, median, and standard deviation DSC across these patients were 0.595, 0.621, and 0.158 respectively. Mean time to local progression for these patients was 76.48 months. Following Cox regression, a statistically significant difference (p = 0.0444) for local progression was found for RADAR patients with DSC > 0.55, with b = 3.521 and hazard ratio of 33.819. Figure 1 illustrates hazard rate estimates for local progression between patients stratified by DSC = 0.55. No statistically significant relationships between DSC and overall survival were found. Within the RADAR subset 214 patients experienced no rectal bleeding following radiotherapy treatment. 122, 80, 35, and 6 patients experienced grade 1, 2, 3, and 4 rectal bleeding respectively. Wilcoxon signed-rank analysis of DSC between patients with and without rectal bleeding (grade >= 2; grade < 2) revealed no statistically significant difference between DSC medians (p = 0.2531).

femur (left and right) the corrCBCT had the lowest EMD in four out of six cases, and were 31% lower than rawCBCT and 33% lower than VarianCBCT across the scans.

Conclusion In this study we found that the scatter correction algorithm overall improved the HU correctness compared to the clinical/commercial reconstruction. However, in a few cases, both the raw reconstruction and the clinical/commercial reconstruction performed better than the scatter correction. The scatter correction may be further improved by taking air and weight-loss better into account. EP-2150 Can contouring probability maps be a predictor for prostate cancer treatment outcome and toxicity? D. Roach 1,2 , J.A. Dowling 1,3,4,5 , A. Kennedy 6 , M. Jameson 2,7 , P. Greer 3,8 , M. Ebert 5,6,9 , L. Holloway 1,2,5,7 1 University of New South Wales, Faculty of Medicine, Sydney, Australia 2 Ingham Institute for Applied Medical Research, Medical Physics, Liverpool, Australia

Figure 1: Hazard function for local progression for RADAR patients containing prostate CTV contours.