Prostate Imaging Reporting and Data System (PI-RADS), Version 2: A Critical Look

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1 Genitourinary Imaging Opinion Rosenkrantz et al. ritical Look at Prostate Imaging Reporting and Data System, Version 2 Genitourinary Imaging Opinion FOUS ON: ndrew. Rosenkrantz 1 ytekin Oto 2 aris Turkbey 3 ntonio. Westphalen 4 Rosenkrantz, Oto, Turkbey, Westphalen Keywords: guidelines, MRI, PI-RDS, prostate biopsy, prostate cancer, Prostate Imaging Reporting and Data System DOI: /JR Oto,. Turkbey, and.. Westphalen contributed equally to this work. Received October 29, 2015; accepted after revision January 2, The opinions and assertions contained herein are the private views of the authors and are not to be construed as official or as representing the views of the National Institutes of Health. 1 Department of Radiology, enter for iomedical Imaging, New York University School of Medicine, New York University Langone Medical enter, 660 First ve, 3rd Fl, New York, NY ddress correspondence to.. Rosenkrantz (ndrew.rosenkrantz@nyumc.org). 2 Department of Radiology, University of hicago, hicago, IL. 3 Molecular Imaging Program, National ancer Institute, National Institutes of Health, ethesda, MD. 4 Department of Radiology, University of alifornia, San Francisco, San Francisco,. JR 2016; 206: X/16/ merican Roentgen Ray Society Prostate Imaging Reporting and Data System (PI-RDS), Version 2: ritical Look OJETIVE. The purpose of this article is to highlight the potential challenges associated with the Prostate Imaging Reporting and Data System, version 2 (PI-RDS v2), and to offer, when possible, suggestions and ideas for improvement. ONLUSION. PI-RDS v2 offers clear improvements to its earlier version and will greatly benefit the prostate MRI community. Nonetheless, caution remains on the basis of early user experience, and potential ambiguities and gaps of PI-RDS v2 are noted. ontinued data-driven clarification and refinement of the guidelines will be invaluable for PI-RDS v2 to achieve its goal of improving patient care. T he Prostate Imaging Reporting and Data System, version 1 (PI-RDS v1), which was released in the form of a 12-page peer-reviewed article in 2012, provided recommendations for standardizing the acquisition, interpretation, and reporting of prostate MRI [1]. lthough PI-RDS v1 served an important purpose, its adoption was limited because of potential weaknesses in the proposed reporting system and ongoing evolution in the field. PI-RDS, version 2 (PI-RDS v2), which was released online in the form of a 55- page document in December 2014 [2], addresses many of the shortcomings associated with PI-RDS v1. The primary improvement associated with the newer version is its provision of a specific algorithm for deriving an overall assessment on the basis of a lesion s individual scores on T2-weighted imaging (T2WI), DWI, and dynamic contrast-enhanced MRI (DE-MRI); such an algorithm was lacking in PI-RDS v1. Indeed, various methods for deriving an overall score with the use of PI-RDS v1 have been reported, thereby undermining its aim of standardizing MRI interpretation [3]. PI-RDS v2 also simplifies interpretation, modifying earlier criteria for the individual sequence scores to achieve greater clarity. In particular, the interpretation of DE-MRI was greatly simplified and is now a binary assessment of the presence or absence of focal early enhancement. Kinetic curves, pharmacokinetic analysis, and any assessment for contrast washout are no longer included. lso, specific criteria are provided for assigning T2WI and DWI scores of 3 (rather than reserving a score of 3 for lesions that do not meet the criteria for other scores), and a size threshold of 15 mm is suggested for differentiating between T2WI and DWI scores of 4 and 5. Finally, MR spectroscopic imaging, which is an optional parameter in PI-RDS v1, no longer influences the assessment of lesions in PI-RDS v2. PI-RDS v2 is anticipated to be of tremendous benefit to the prostate MRI community and, ultimately, to improve patient care. y standardizing MRI interpretation, PI-RDS v2 may reduce the gap in performance between radiologists and centers with varying experience in prostate MRI. lso, its more uniform reporting structure should improve communication between radiologists and referring physicians. In addition, the PI-RDS v2 framework may facilitate initial training for radiologists learning to interpret prostate MRI and may ease interpretation for less experienced readers. Despite the improvements in and value of PI-RDS v2, we believe that some degree of caution is warranted. The precise details of the scoring system reflect a combination of the most relevant published data, supplemented by the experience of the developers of the system. Thus, further studies are required to validate the system and highlight potential continued limitations. For instance, although the current system for weighing the JR:206, June

2 Rosenkrantz et al. various parameters is straightforward, it may not necessarily yield the highest diagnostic accuracy. It remains possible that subsequent data will show improved performance through refinements to the current weighting. Of note, two initial studies of PI-RDS v2 reported moderate interreader agreement among readers from the same center [4], in addition to limited performance in the assessment of tumors with a Gleason score of or higher and a volume of 0.5 ml or less, thereby suggesting a role for continued optimization [5]. Even if PI-RDS v2 is supported by early investigations from centers with expertise in prostate MRI, such results may not reflect the performance of the system when it is applied by the broader radiology community. Thus, multicenter studies that include smaller and nonacademic centers will be required to validate any initial positive results. Indeed, the inappropriate use of PI-RDS v2 by new users, who do not have sufficient training or experience, may be damaging to clinical care. For instance, the mere mention of PI-RDS v2 in a report may create an artificial sense of reader expertise that is not necessarily always present. In the coming years, potential inconsistent or suboptimal clinical use of PI-RDS v2 by readers who are not sufficiently trained in the system could undermine urologists recent overall acceptance of prostate MRI and hinder the continued growth of the technology. Finally, even if radiologists apply the system properly, concern remains if urologists base management decisions too strictly on the assessment categories provided. Outcome data derived from MRI-targeted biopsies are needed to develop new nomograms that define patients risk on the basis of clinical variables in combination with overall PI-RDS v2 assessment categories. The aforementioned concerns notwithstanding, the current reality is that PI-RDS v2 is increasingly being applied by the radiology community. Therefore, on the basis of our initial experiences in using the system, we seek to highlight potential weaknesses and to offer, when possible, suggestions for improvement. Suggestions for Improvement First, there continues to be ambiguity associated with some aspects of the criteria for individual sequence scores. For example, what constitutes mild-to-moderate versus marked signal abnormality on high-bvalue DWI is inherently subjective, yet this differentiation is critical in determining the DWI score (Fig. 1). The apparent degree of signal abnormality may vary depending on technical parameters, such as the exact b- value regimen. lthough PI-RDS v2 indicates that the signal intensity (SI) of a lesion on DWI should be visually compared with that of normal tissue in the same zone, it may be helpful to also incorporate explicit criteria for distinguishing the degree of any such signal abnormality. For instance, mild-to-moderate high-b-value hyperintensity may allow for the presence of other foci with similar SI, whereas marked hyperintensity would require the SI of the lesion to be higher than any other focus in the same zone. Other terms in the PI-RDS v2 lexicon are subjective, including focal shape, obscured margins, and definite invasive behavior. In PI-RDS v2, ppendix 3 provides verbal definitions of dozens of terms in the lexicon, and the Figures section provides a limited number of illustrative cases. Nonetheless, in our experience, it is not uncommon for even expert readers to encounter discrepancies in classifying such terms. The inclusion of an expanded pictorial atlas providing numerous illustrations of lesions that satisfy and do not satisfy these visual descriptors would be helpful in reducing such interreader variability when the PI-RDS v2 lexicon is used. Furthermore, if future studies cannot show consistent reproducibility of certain features, then removing them from a future version of PI-RDS should be considered. In the transition zone (TZ), a T2WI score of 1 denotes a normal appearance, whereas a T2WI score of 2 includes benign prostatic hypertrophy (PH). However, PH nodules are ubiquitous in the TZ of men who undergo prostate MRI. Therefore, although PI-RDS v2 states that such nodules do not require being assigned an assessment category, the criteria make it possible to identify a category 2 lesion in the TZ in the overwhelming majority of patients, when there is strict adherence to the guidelines. Rather, to receive a T2WI of 2, perhaps a nodule in the TZ should be required to have an appearance that is at least mildly atypical of PH, even if it is still favored to indeed represent PH. n example is a PH nodule for which there is a predominance of low signal, which is more likely to be associated with a preponderance of stromal tissue than with cancer. In the peripheral zone (PZ), a lesion that is interpreted as exhibiting markedly abnormal SI on just the apparent diffusion coefficient map or a high-b-value image, but not both, does not meet the criteria for a DWI score of either 3 (denoting mild-to-moderate abnormality on both image sets) or 4 (denoting marked abnormality on both image sets). This source of uncertainty can lead to variable interpretation of lesions of this nature, and clarification is therefore warranted. The applied criteria and overall suspicion scores are distinctly different for lesions in the PZ and TZ. However, some lesions, in particular those at the base and apex, can be difficult to reliably assign to one zone or the other (Fig. 2), or may legitimately involve both zones to a similar extent. ecause the overall PI-RDS v2 assessment category will vary depending on which zone is selected, it would be helpful to have further guidance in assigning lesions located in an anatomically uncertain location to a single zone (i.e., on the basis of the location of > 50% of the lesion or of the apparent center of the lesion). PI-RDS v2 criteria also do not fully account for the spectrum of lesions encountered. For instance, lesions within the anterior fibromuscular stroma and the central zone (Z) may not be optimally evaluated using current PZ and TZ criteria. DE-MRI has little effect on the assessment of TZ lesions with the use of PI-RDS v2, given the exceedingly common hypervascularity of PH. However, the anterior fibromuscular stroma, which is typically assessed using TZ criteria, is usually hypovascular, and DE-MRI may in fact be useful for evaluating this region (Fig. 3). lso, because the Z commonly exhibits restricted diffusion that is similar in extent to that of tumors, ancillary criteria (e.g., the degree of asymmetry, compared with the contralateral Z and DE-MRI findings) may assist in detecting tumors in the Z. The PZ in men with diffuse prostatitis or marked PH often exhibits diffusely altered signal characteristics on various sequences, which may pose a diagnostic challenge and potentially yield more false-positive or false-negative results. lthough it is not possible for any system to be comprehensive and encompass all possible cases, and although exceptions will invariably occur, it may be useful for some of these more commonly encountered potential pitfalls to be more clearly addressed in future updates to PI-RDS (rather than be briefly acknowledged, as in the current version). For contexts in which diagnostic performance may be lowered and for which any clear solution is lacking, standard language for providing a caveat within the report may be considered. n additional concern involves potential large shifts in the assigned overall PI-RDS 1180 JR:206, June 2016

3 ritical Look at Prostate Imaging Reporting and Data System, Version 2 assessment category when the criteria are strictly applied. These abrupt shifts result from elevations in the assessment category that occur only at certain levels of suspicion. For instance, for a PZ lesion for which DE-MRI findings are positive, a DWI score of 2 leads to an overall category of 2, whereas a DWI score of 3 leads to an overall category of 4. Similarly, for a TZ lesion that measures at least 15 mm, a T2WI score of 3 leads to an overall category of 3; whereas considering the lesion to fulfill criteria for a T2WI score of 4 would, instead, lead to a T2WI of 5, given lesion size greater than 15 mm, and, thus, an overall category of 5 (Fig. 4). In these contexts, a potentially subjective judgment of a single feature can increase the final assessment category by two levels. Thus, we suggest that the assessment categories not be regarded as overly strict but, rather, that some flexibility be allowed when deriving the overall category on the basis of reader discretion and experience. Such flexibility may improve the performance of PI-RDS v2 in assessing cases that appear to represent exceptions to the current scoring schemes or that do not seem to clearly conform to the criteria provided. Furthermore, flexibility in scoring may encourage adoption of PI-RDS v2 by expert readers who are already accustomed to existing in-house scoring systems. One particular aspect of PI-RDS v2 for which we have noted particular variability in reader interpretations is scoring of DE-MRI. For example, what exactly constitutes early enhancement and enhancement that is focal and that matches an abnormality on other sequences is unclear. Furthermore, a positive interpretation of DE-MRI is defined as the observation of either early or contemporaneous enhancement, whereas a negative interpretation is defined as the absence of early enhancement, leading to uncertainty regarding how to handle contemporaneous enhancement. lso, although PI-RDS v2 states that diffuse enhancement should be considered a negative finding, it remains unclear how to handle widespread multifocal, albeit nondiffuse, early background enhancement. ontinued standardization of the technical aspects of the acquisition, postprocessing, and interpretation of DE-MRI, as well as more rigorous definitions of positive and negative DE-MRI findings, may help address these challenges. PI-RDS v2 states that the system should not be applied for the detection of tumor recurrence after therapy, because the MRI findings of greatest concern are different in this context. However, the lack of any alternative approach creates a risk that radiologists may apply the existing scoring criteria for this purpose, leading to potential inappropriate risk assessments. Future updates may address this need by aiming to develop similar structured criteria to guide evaluation for recurrences. eyond the aforementioned practical concerns and pitfalls regarding the application of PI-RDS v2 for clinical reporting, a wide range of questions remain to be answered regarding how to apply PI-RDS v2 in directing patient management. For instance, for which overall PI-RDS assessment categories is targeted biopsy warranted? Do all lesions warrant biopsy or does only the single most suspicious lesion warrant biopsy? an monitoring of the PI-RDS assessment category on serial MRI examinations of patients with prostate cancer managed by active surveillance be used as a safe and effective surveillance strategy? lso, from a practical standpoint, do meaningful differences regarding patient care exist between PI-RDS v2 categories 1 and 2 (for which biopsy typically is not advised) as well as between PI-RDS v2 categories 4 and 5 (for which biopsy typically is advised), to support the current five-tiered system? ddressing such questions requires concrete data on the actual implications of each of the PI-RDS v2 categories, which in turn requires that PI-RDS v2 be shown to be reproducible across institutions. Once PI-RDS v2 can be applied in a consistent fashion across practices, the system will provide a powerful mechanism for accumulating multicenter data to optimally address these important questions that may change current paradigms for prostate cancer management. onclusion PI-RDS v2 represents an important step in the integration of prostate MRI into clinical practice. Ongoing needs at this time include addressing potential ambiguities and gaps in the system that may be revealed by early user experience, expanding the availability of pictorial atlases of possibly challenging scenarios to guide new users in learning the criteria, promoting intense educational efforts to ensure proper usage, and conducting largescale testing and validation. Rigorous data from academic and community centers will be needed to guide continued revisions of the system. Such a multifaceted effort will be invaluable for PI-RDS v2 to achieve its ultimate goal of improving the clinical care of patients with prostate cancer. References 1. arentsz JO, Richenberg J, lements R, et al. ESUR prostate MR guidelines Eur Radiol 2012; 22: merican ollege of Radiology. Prostate Imaging Reporting and Data System version 2.0. merican ollege of Radiology website. Safety/Resources/PIRDS. Published ccessed January 24, arrett T, Turkbey, hoyke PL. PI-RDS version 2: what you need to know. lin Radiol 2015; 70: Muller G, Shih JH, Sankineni S, et al. Prostate cancer: interobserver agreement and accuracy with the revised prostate imaging reporting and data system at multiparametric MR imaging. Radiology 2015; 277: Vargas H, Hotker M, Goldman D, et al. Updated prostate imaging reporting and data system (PIRDS v2) recommendations for the detection of clinically significant prostate cancer using multiparametric MRI: critical evaluation using whole-mount pathology as standard of reference. Eur Radiol 2015 Sep 22 [Epub ahead of print] (Figures start on next page) JR:206, June

4 Rosenkrantz et al. Fig year-old man with prior negative prostate biopsy., xial T2-weighted MR image shows focal decreased T2 signal (arrow) in left peripheral zone. and, pparent diffusion coefficient (D) map () and high-b-value (1500 s/mm 2 ) DW image () show corresponding focal decreased hypointensity (arrow, ) and hyperintensity (arrow, ). lthough Prostate Imaging Reporting and Data System, version 2 (PI-RDS v2), advises comparing signal of lesion on D map and high-b-value DW image with signal of normal tissue in same histologic zone, differentiation between mild-to-moderate and marked signal abnormality remains subjective, which in turn leads to potential variation in whether both lesion s DWI score and overall PI-RDS assessment category is 3 or 4. Fusion-guided biopsy revealed lesion to be benign. Fig year-old man with prostate-specific antigen level of 12.9 ng/ml and no history of prior prostate biopsy., xial T2-weighted MR image shows T2-hypointense thickening (dashed arrows) by junction of peripheral and transition zones bilaterally. and, pparent diffusion coefficient (D) map () and high-b-value (1500 s/mm 2 ) DW image () show corresponding focal decreased hypointensity (arrow, ) and hyperintensity (arrow, ) by region of thickening on right. Definitive assignment of lesion to single zone (peripheral zone or transition zone) is challenging, in turn affecting selection of which Prostate Imaging Reporting and Data System, version 2, assessment criteria to apply for lesion evaluation. Fusion-guided biopsy revealed lesion to represent Gleason score of JR:206, June 2016

5 ritical Look at Prostate Imaging Reporting and Data System, Version 2 D Fig year-old man with prior negative prostate biopsy., xial T2-weighted MR image shows crescentic decreased T2 signal (arrow) along anterior fibromuscular stroma (FMS). and, pparent diffusion coefficient (D) map () and high-b-value (1500 s/mm 2 ) DW image () show corresponding mild hypointensity (arrow, ) and hyperintensity (arrow, ). Diagnostic considerations include tumor and benign thickening of FMS. D, Early dynamic contrast-enhanced (DE) MR image shows corresponding focal early enhancement (arrow), which increases level of suspicion for tumor, given normal hypovascularity of FMS. However, FMS is typically assessed using transition zone criteria, which do not incorporate DE-MRI findings in Prostate Imaging Reporting and Data System, version 2 (including for FMS lesions). Fusion-guided biopsy revealed lesion to represent Gleason score of Fig year-old man with prior negative prostate biopsy., xial T2-weighted MR image (T2WI) shows approximately 25-mm hypointense area of moderately decreased T2 signal (solid arrow) within left anterior transition zone. Lesion shows slight heterogeneity, with small foci of mildly increased T2 signal (arrowhead) centrally and possible encapsulation (dashed arrows) along its anterior aspect. and, pparent diffusion coefficient (D) map () and high-b-value (1500 s/mm 2 ) DW image () show corresponding hypointensity (arrow, ) and hyperintensity (arrow, ). With use of Prostate Imaging Reporting and Data System, version 2, if lesion is considered to meet description for T2WI score of 3 (presence of heterogeneous signal intensity with obscured margins), then large size does not affect further assessment of lesion on T2WI. However, if lesion is considered to meet description for T2WI score of 4 (presence of noncircumscribed homogeneous moderate hypointensity), then it automatically is raised by two levels to T2WI score of 5 given lesion size of 15 mm or greater. Fusion-guided biopsy revealed lesion to represent Gleason score of tumor. JR:206, June