Timo Soeterik

15 General Introduction and Thesis Outline MAGNETIC RESONANCE IMAGING Introduction of magnetic resonance imaging in risk prediction The first generation of prediction models and risk classification systems for prostate cancer, based on baseline PSA, biopsy Gleason score and cT have substantially improved risk stratification and disease prognostication. 25,26 However, the utility of these tools can be further improved by incorporating additional specific tumour characteristics, such as tumour size, location and EPE. Novel prognostic indicators can be collected using advanced imaging modalities such as magnetic resonance imaging (MRI). Moreover, improved visualization of the prostate cancer lesion at initial diagnosis can also lead to more accurate estimation of the predictor variables. For example, targeting MRI- identified suspicious lesions using MRI-guided target biopsy can reduce the risk of tumour sampling error, resulting in a more accurate estimation of the prostate cancer Gleason grade. Prostate cancer detection Since its first application for prostate cancer imaging in the mid-1980s, MRI has evolved from a promising technique into a mature prostate imaging modality. 27 MRI can provide functional tissue information along with anatomic information. To increase the accuracy, anatomic T2-weighted MRI and imaging techniques such as dynamic contrast agent- enhanced imaging and diffusion-weighted imaging can be combined in an integrated multiparametric magnetic resonance (mpMRI) examination. 28 Use of mpMRI has increased substantially in the last decade, fulfilling the unmet need of a non-invasive accurate screening tool for prostate cancer in men with elevated PSA. 29 MpMRI-visualized lesions can be targeted using mpMRI-guided biopsy, decreasing the risk of sampling error compared with traditional transrectal ultrasonography guided systematic biopsy. Studies on this subject, including the PROMIS, PRECISION, and 4M study, have shown that use of prebiopsy MRI and subsequent target biopsy leads to higher detection rates of clinically significant prostate cancer, and lower detection rates of clinically insignificant prostate cancer. 30–32 The current EAU guidelines therefore recommend that mpMRI should be performed before prostate biopsy. 17 In case of a positive mpMRI (PI-RADS ≥3), MRI target and systematic biopsies should be combined. In case of a negative mpMRI, combined with a low clinical suspicion for prostate cancer, biopsy may be omitted based on shared decision-making with the patient. 17 Local tumour staging Besides prostate cancer detection, MRI can be used for local staging of the tumour. Information regarding the localization, diameter and presence of extraprostatic extension (EPE) is crucial for determining the optimal treatment strategy. For instance, 1