Editorial for “Metastatic Diffusion Volume Based on Apparent Diffusion Coefficient as a Prognostic Factor in Castration‐Resistant Prostate Cancer”

Abstract

Editorial for “Metastatic Diffusion Volume Based on Apparent Diffusion Coefficient as a Prognostic Factor in Castration-Resistant Prostate Cancer” The management of advanced castration-resistant prostate cancer (CRPC) patients has evolved continuously in the past decades with the increasing availability of cutting-edge imaging technologies. Whole-body multiparameter MRI and positron emission tomography (PET) with specific tracers, such as prostate-specific membrane antigen (PSMA), fluciclovine, fluorodeoxyglucose (FDG), and so on, has demonstrated promising clinical value for treatment response monitoring of patients with metastatic CRPC. Because of its operational complexity and abundant information from large number of images, the growing adoption of whole-body MRI necessities a delicate combination of streamlined workflow, structured reporting mechanism, and identification of reliable biomarkers. The clinical interpretation of wholebody MRI is a comprehensive approach demanding a systematic evaluation of multiple contrast mechanisms, including diffusionweighted imaging (DWI), T1 and T2, which is detailed in the guideline for MET-RADS-P scoring process. Among all MRI contrasts, DWI is regarded to be most sensitive in detecting metastatic lesions. In addition to MRI, it is notable that, with the recent surge of molecular imaging-based theragnostic approach for treating late-stage prostate cancer, such as PSMA-labeled 177Lu/68Ga pair, PET/CT is rapidly gaining clinical favorability as it features as a direct measurement of biochemical markers of metastatic lesions. Recent clinical adoption of PET/MR also offers an opportunity to achieve a one-stop-shop solution for acquiring metabolic, molecular, functional, and anatomical information of patients with CRPC. With the fast development of radiomics and artificial intelligence (AI), many imaging phenotypes are being thoroughly evaluated by super computing power. These technologies analyze multimodal or multiparametric images and leverage existing clinical data as a gold standard for model training. The comprehensive analysis of image features would undoubtedly increase the sensitivity and efficacy in monitoring CRPC progression and offer great insights into appropriate adjustment of treatment plan. However, AI or radiomics also face unique challenges, such as (1) the homogeneous nature of clinical data for model training may render it susceptible to variability across different imaging platforms; and (2) the requirement of complete multimodal data makes it difficult to disseminate to broader sites where imaging hardware might not be state of the art. Therefore, advanced DWI remains the main-stream imaging modality for the management of CRPC because of its accessibility and lack of ionizing radiation. Diffusion volume is a widely used quantitative derivative from DWI, which features intuitive summation of all voxels within a certain range of apparent diffusion coefficient (ADC). Diffusion volume has demonstrated applications in the follow-up of multiple types of cancers, including cervical cancer and primary prostate cancer. However, it still lacks clinical evidence how fully automatic diffusion volume calculation predicts patient prognosis in CRPC in comparison with more imperial approach such as MET-RADS-P. The authors meticulously evaluate the clinical significance of the widely used DWI images. The quantitative metrics employed by the authors are not based on AI or radiomics but rather on a threshold-based total volume calculation. Total diffusion volume is a straightforward quantitative derivative from clinical DWI, which is readily available across different imaging platforms including 1.5 T and 3 T MRI. Future work on the long-term follow-up of these patients will be crucial and such data will be important to systematically evaluate the clinical impact of DWI on the management of patients with CRPC. There are also a few potential caveats regarding diffusion volume. For example, many therapy procedures can lead to confusing alternation of ADC in lesions. For those patients receiving targeted peptide receptor radionuclide therapy (PRRT), radiation therapy, or other novel treatments, extra caution should be taken in the interpretation of diffusion value and volume.