S. Heijmink

Multi-center validation of prostate tumor localization using multi-parametric MRI and prior knowledge.

Purpose: Tumor localization provides crucial information for radiotherapy dose differentiation treatments, such as focal dose escalation and dose painting by numbers, which aim at achieving tumor control with minimal side effects. Multiparametric (mp‐)MRI is increasingly used for tumor detection and localization in prostate because of its ability to visualize tissue structure and to reveal tumor characteristics. However, it can be challenging to distinguish cancer, particularly in the transition zone. In this study, we enhance the performance of a mp‐MRI‐based tumor localization model by incorporating prior knowledge from two sources: a population‐based tumor probability atlas and patient‐specific biopsy examination results. This information typically would be considered by a physician when carrying out a manual tumor delineation. Materials and methods: Our study involves 40 patients from two centers: 23 patients from the University Hospital Leuven (Leuven), Leuven, Belgium and 17 patients from the Netherlands Cancer Institute (NKI), Amsterdam, the Netherlands. All patients received a mp‐MRI exam consisting of a T2‐weighted, diffusion‐weighted, and dynamic contrast‐enhanced MRI before prostatectomy. Thirty‐one features were extracted for each voxel in the prostate. Among these, 29 were from the multiparametric‐MRI, one was from the population‐based tumor probability atlas and one from the biopsy map. T2‐weighted images of each patient were registered to whole‐mount section pathology slices to obtain the ground truth. The study was validated in two settings: single‐center (training and test sets were from the same cohort); and cross‐center (training and test sets were from different cohorts). In addition, automatic delineations created by our model were compared with manual tumor delineations done by six different teams on a subset of Leuven cohort including 15 patients. Results: In the single‐center setting, mp‐MRI‐based features yielded area under the ROC curves (AUC) of 0.690 on a pooled set of patients from both cohorts. Including prevalence into mp‐MRI‐based features increased the AUC to 0.751 and including all features achieved the best performance with AUC of 0.775. Using all features always showed better results when varying the size of the training set. In addition, its performance is comparable with the average performance of six teams delineating the tumors manually. The error rate using all features was 0.22. The two prior knowledge features ranked among the top four most important features out of the 31 features. In the cross‐center setting, combining all features also yielded the best performance in terms of the mean AUC of 0.777 on the pooled set of patients from both cohorts. In addition, the difference in performance between the single‐center setting and cross‐center setting was not significant. Conclusions: The results showed significant improvements when including prior knowledge features in addition to mp‐MRI‐based features in both single‐ and cross‐center settings.

Performance of a fast and high‐resolution multi‐echo spin‐echo sequence for prostate T2 mapping across multiple systems

To evaluate the performance of a multi‐echo spin‐echo sequence with k‐t undersampling scheme (k‐t T2) in prostate cancer.

Impact of contrast agent injection duration on dynamic contrast-enhanced MRI quantification in prostate cancer

The volume transfer constant Ktrans, which describes the leakage of contrast agent (CA) from vasculature into tissue, is the most commonly reported quantitative parameter for dynamic contrast‐enhanced (DCE‐) MRI. However, the variation in reported Ktrans values between studies from different institutes is large. One of the primary sources of uncertainty is quantification of the arterial input function (AIF). The aim of this study is to determine the influence of the CA injection duration on the AIF and tracer kinetic analysis (TKA) parameters (i.e. Ktrans, kep and ve).

PO-0772: Multi-center validation of a model for prostate tumor delineation using multi-parametric MRI

PO-0772 Multi-center validation of a model for prostate tumor delineation using multi-parametric MRI C. Dinh, K. Haustermans, P. Steenbergen, G. Ghobadi, E. Lerut, R. Oyen, H.V.D. Poel, J.D. Jong, S. Heijmink, U.V.D. Heide The Netherlands Cancer Institute, Department of Radiation Oncology, Amsterdam, The Netherlands University Hospitals Leuven, Department of Oncology KU Leuven, Leuven, Belgium University Hospitals Leuven, Department of Imaging & Pathology, Leuven, Belgium The Netherlands Cancer Institute, Department of Radiology, Amsterdam, The Netherlands The Netherlands Cancer Institute, Department of Pathology, Amsterdam, The Netherlands

4 Relatie tussen de preoperatieve dikte van de periprostatische fascie op MRI en erectiele functie na zenuwsparende RALP bij patiënten met prostaatcarcinoom

SamenvattingDe studie had tot doel de relatie tussen de preoperatieve periprostatische fasciedikte (FD) op de MRI-scan en postoperatieve erectiele functie (EF) na zenuwsparende robotgeassisteerde laparoscopische prostatectomie (RALP) te onderzoeken bij patiënten met prostaatcarcinoom (PCa).

MRI en active surveillance voor laagrisicoprostaatkanker

SamenvattingDe methoden voor de risico-inschatting van prostaatcarcinoom dienen te worden verbeterd. Dit reviewartikel bespreekt 15 artikelen waarin de waarde van de MRI in een active surveillance (AS) situatie werd geanalyseerd. Bij patiënten met laagrisicoziekte is de MRI ook meestal niet-verdacht, wat van nut zou kunnen zijn bij AS-selectie en follow-up. Hoogrisicoziekte is echter niet altijd op een MRI te zien. De plaats van de MRI in de diagnostiek en behandeling van prostaatcarcinoom zal nog verder moeten worden bepaald.SummaryMRI and active surveillance for low risk prostate cancer.Methods for risk-stratifying prostate cancer should be improved. This review-article includes 15 articles assessing the value of MRI in an active surveillance (AS) setting. In patients with low risk disease, the MRI generally is non-suspicious, which may be used within AS selection and follow-up. Higher risk disease is however not always detected with MRI. The place of MRI within prostate cancer diagnostics and treatment should still be determined.