ESTRO 2021 Abstract Book

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ESTRO 2021

[1] Olsson et al. PhIRO 2019:11:88 [2] Gay et al. IJROBP 2012:83:e353 [3] Salembier et al. RO 2018:127:49

Materials and Methods DICOM-RT datasets for 19 patients extracted from the Eclipse TM treatment planning system ( Varian Medical Systems; version 15.6) at one institution in Sweden was used. The patients were treated for prostate cancer in 2018-2019 using 15 MV photon beams to total doses of 50-70Gy@2-3Gy/fraction. Rectal volumes were defined on planning CT images clinically ( clinical ), according to proposed standard ( reference ), and auto-contoured using the existing version of the MVision software ( MVision Segmentation Service; version 1.1). The degree of variation between volumes was investigated. Statistics included dose volume histogram metrics, the Jaccard index, and the Dice similarity coefficient with comparisons between groups based on hypothesis testing with a two-sided P-value≤0.05 indicating a statistically significant difference. Results The clinical and the MVision DVH points were in general closer to each other than to the points of the reference DVH (Figure 1). Clinical and MVision volumes were also somewhat larger than the reference volume (83cc and 84cc versus 80cc; p>>0.05; Table 1). Overall, mean doses were 0.8/0.9Gy lower for clinical / MVision compared with the reference (p>>0.05; Table 1) whilst maximum doses were similar for all. Both overlap metrics were similar for volume comparisons between MVision and reference and for MVision and clinical but somewhat higher for clinical and reference (Jaccard index/Dice coefficient: 0.74/0.85 versus 0.73/0.83 versus 0.90/0.95, respectively). Differences were primarily found in cranio-caudal direction between any two data sets.

Figure 1. Averaged dose-volume histograms for clinical, MVision and reference rectal volumes.

Table 1. Clinical and MVision rectal volumes compared to reference rectal volumes.