Abstract
Diffusion-weighted imaging quantified using the mono-exponential model has shown great promise for monitoring treatment response in prostate cancer bone metastases. The aim of this prospective study is to evaluate whether non-mono-exponential diffusion models better describe the water diffusion properties and may improve treatment response assessment. Diffusion-weighted imaging data of 12 treatment-naïve patients with 34 metastases acquired before and at one, two, and three months after initiation of antiandrogen treatment are analysed using the mono-exponential, the intravoxel incoherent motion, the stretched exponential, and the statistical model. Repeatability of the fitted parameters and changes under therapy are quantified. Model preference is assessed and correlation coefficients across times are calculated to delineate the relationship between the prostate-specific antigen levels and the diffusion parameters as well as between the diffusion parameters within each model. There is a clear preference for non-mono-exponential diffusion models at all time points. Particularly the stretched exponential is favoured in approximately 60% of the lesions. Its parameters increase significantly in response to treatment and are highly repeatable. Thus, the stretched exponential may be utilized as a potential optimal model for monitoring treatment response. Compared with the mono-exponential model, it may provide complementary information on tissue properties and improve response assessment.
Highlights
Several studies have demonstrated the potential of diffusion-weighted imaging (DWI) quantified by the apparent diffusion coefficient (ADC) from the mono-exponential diffusion model for evaluating response to therapy in bone metastases from prostate cancer[11,12,13,14,15]
Inter-patient variability of the parameters was below 20% for all diffusion parameters with the exception of σ* from the statistical model, and f, f·D*, and D* from the intravoxel incoherent motion (IVIM) model (Table 1)
Osteoblastic bone metastases without associated soft tissue, such as those commonly encountered in prostate cancer, are classified as non-measurable according to RECIST7
Summary
Several studies have demonstrated the potential of diffusion-weighted imaging (DWI) quantified by the apparent diffusion coefficient (ADC) from the mono-exponential diffusion model for evaluating response to therapy in bone metastases from prostate cancer[11,12,13,14,15]. The ADC is a simple and robust quantitative biomarker but it draws an incomplete picture of the molecular motion in both healthy and pathological tissue since signal attenuation in DWI is not completely described by a mono-exponential process For this reason, several studies have recently investigated the use of more complex non-mono-exponential diffusion models for the characterization of tumour masses[17,18,19,20,21,22,23,24,25,26,27,28] and the evaluation of treatment response[29, 30]. Model preference is investigated by evaluating the Bayesian information criterion (BIC)
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