Blood oxygenation level-dependent MRI at 3T for differentiating prostate cancer from benign tissue: a preliminary experience

OBJECTIVE

Blood oxygenation-level dependent (BOLD) MRI may identify or quantify the regional distribution of hypoxia within a tumor. We aimed to evaluate the feasibility of BOLD MRI at 3 T in differentiating prostate cancer from benign tissue.

METHODS

A total of 145 patients with biopsy-proven prostate cancer underwent BOLD MRI at 3 T. BOLD MRI was performed using a multiple fast field echo sequence to acquire 12 T₂*-weighted images. The R2* value (rate of relaxation, s^-1) was measured in the index tumor, and benign peripheral (PZ) and transition zone (TZ), and the results were compared. The variability of R2* measurements was evaluated.

RESULTS

Tumor R2* values (25.95 s^-1) were significantly different from the benign PZ (27.83 s^-1) and benign TZ (21.66 s^-1) (p < 0.001). For identifying the tumor, the area under the receiver operating characteristic of R2* was 0.606, with an optimal cut-off value of 22.8 s^-1 resulting in 73.8% sensitivity and 52% specificity. In the Bland-Altman test, the mean differences in R2* values were 8.5% for tumors, 13.3% for benign PZ, and 6.8% for benign TZ. No associations between tumor R2* value and Gleason score, age, prostate volume, prostate-specific antigen, or tumor size.

CONCLUSION

BOLD MRI at 3 T appears to be a feasible tool for differentiating between prostate cancer and benign tissue. However, further studies are required for a direct clinical application.

ADVANCES IN KNOWLEDGE

The R2* values are significantly different among prostate cancer, benign PZ, and benign TZ.

T2*-weighted imaging and diffusion kurtosis imaging (DKI) of rectal cancer: correlation with clinical histopathologic prognostic factors

PURPOSE

Histopathologic prognostic factors of rectal cancer are closely associated with local recurrence and distant metastasis. We aim to investigate the feasibility of T2*WI in assessment of clinical prognostic factors of rectal cancer, and compare with DKI.

METHODS

This retrospective study enrolled 50 out of 205 patients with rectal cancer according to the inclusion criteria. The following parameters were obtained: R2* from T2*WI, mean diffusivity (MD_k), mean kurtosis (MK), and mean diffusivity (MD_t) from DKI using tensor method. Above parameters were compared by Mann-Whitney U-test or students' t test. Spearman correlations between different parameters and histopathological prognostic factors were determined. The diagnostic performances of R2* and DKI-derived parameters were analyzed by receiver operating characteristic curves (ROC), separately and jointly.

RESULTS

There were positive correlations between R2* and multiple prognostic factors of rectal cancer such as T category, N category, tumor grade, CEA level, and LVI (P < 0.004). MD_k and MD_t showed negative correlations with almost all the histopathological prognostic factors except CRM and TIL involvement (P < 0.003). MK correlated positively with the prognostic factors except CA19-9 level and CRM involvement (P < 0.006). The AUC ranges were 0.724-0.950 for R2* and 0.755-0.913 for DKI-derived parameters for differentiation of prognostic factors. However, no significant differences of diagnostic performance were found between T2*WI, DKI, or the combined imaging methods in characterizing rectal cancer.

CONCLUSION

R2* and DKI-derived parameters were associated with different histopathological prognostic factors, and might act as noninvasive biomarkers for histopathological characterization of rectal cancer.

Integrative Radiogenomics Approach for Risk Assessment of Postoperative and Adjuvant Chemotherapy Benefits for Gastric Cancer Patients

Gastric cancer (GC) is a typical heterogeneous malignant tumor, whose insensitivity to chemotherapy is a common cause of tumor recurrence and metastasis. There is no doubt regarding the effectiveness of adjuvant chemotherapy (ACT) for GC, but the population for whom it is indicated and the selection of specific options remain the focus of present research. The conventional pathological TNM prediction focuses on cancer cells to predict prognosis, while they do not provide sufficient prediction. Enhanced computed tomography (CT) scanning is a validated tool that assesses the involvement of careful identification of the tumor, lymph node involvement, and metastatic spread. Using the radiomics approach, we selected the least absolute shrinkage and selection operator (LASSO) Cox regression model to build a radiomics signature for predicting the overall survival (OS) and disease-free survival (DFS) of patients with complete postoperative gastric cancer and further identifying candidate benefits from ACT. The radiomics trait-associated genes captured clinically relevant molecular pathways and potential chemotherapeutic drug metabolism mechanisms. Our results of precise surrogates using radiogenomics can lead to additional benefit from adjuvant chemotherapy and then survival prediction in postoperative GC patients.

Hypoxia and the phenomenon of immune exclusion

Over the last few years, cancer immunotherapy experienced tremendous developments and it is nowadays considered a promising strategy against many types of cancer. However, the exclusion of lymphocytes from the tumor nest is a common phenomenon that limits the efficiency of immunotherapy in solid tumors. Despite several mechanisms proposed during the years to explain the immune excluded phenotype, at present, there is no integrated understanding about the role played by different models of immune exclusion in human cancers. Hypoxia is a hallmark of most solid tumors and, being a multifaceted and complex condition, shapes in a unique way the tumor microenvironment, affecting gene transcription and chromatin remodeling. In this review, we speculate about an upstream role for hypoxia as a common biological determinant of immune exclusion in solid tumors. We also discuss the current state of ex vivo and in vivo imaging of hypoxic determinants in relation to T cell distribution that could mechanisms of immune exclusion and discover functional-morphological tumor features that could support clinical monitoring.

Early Prediction of Breast Cancer Therapy Response using Multiresolution Fractal Analysis of DCE-MRI Parametric Maps

We aimed to determine whether multiresolution fractal analysis of voxel-based dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) parametric maps can provide early prediction of breast cancer response to neoadjuvant chemotherapy (NACT). In total, 55 patients underwent 4 DCE-MRI examinations before, during, and after NACT. The shutter-speed model was used to analyze the DCE-MRI data and generate parametric maps within the tumor region of interest. The proposed multiresolution fractal method and the more conventional methods of single-resolution fractal, gray-level co-occurrence matrix, and run-length matrix were used to extract features from the parametric maps. Only the data obtained before and after the first NACT cycle were used to evaluate early prediction of response. With a training (N = 40) and testing (N = 15) data set, support vector machine was used to assess the predictive abilities of the features in classification of pathologic complete response versus non-pathologic complete response. Generally the multiresolution fractal features from individual maps and the concatenated features from all parametric maps showed better predictive performances than conventional features, with receiver operating curve area under the curve (AUC) values of 0.91 (all parameters) and 0.80 (K^trans), in the training and testing sets, respectively. The differences in AUC were statistically significant (P < .05) for several parametric maps. Thus, multiresolution analysis that decomposes the texture at various spatial-frequency scales may more accurately capture changes in tumor vascular heterogeneity as measured by DCE-MRI, and therefore provide better early prediction of NACT response.

Effect of granulocyte colony-stimulating factor on bone marrow: evaluation by intravoxel incoherent motion and dynamic contrast-enhanced magnetic resonance imaging

OBJECTIVE

To report our experience with the use of intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI) and dynamic contrast-enhanced (DCE)-MRI in bone marrow before and after administration of granulocyte colony-stimulating factor (GCSF). Moreover, a small series of patients with bone metastases from breast cancer have been evaluated by IVIM DW-MRI and DCE-MRI before and after GCSF administration.

MATERIALS AND METHODS

We studied with IVIM-MRI and DCE-MRI 14 patients with rectal or uterine cervix cancer studied before and 4-18 days after administration of GCSF; the second MR examination was obtained after three chemotherapy courses. IVIM perfusion fraction (f), pseudo-diffusion coefficient (D*), true diffusion coefficient (D) and apparent diffusion coefficient (ADC) as well area under the curve at 60 s (AUC60) were calculated for bone marrow before and after GCSF administration. Moreover, two different IVIM parametric maps (i.e., ADC and ADC_low) were generated by selecting two different intervals of b values (0-1000 and 0-80, respectively). Furthermore, four patients affected by pelvic bone metastases from breast adenocarcinoma who received GCSF administration were also qualitatively evaluated for evidence of lesions on ADC maps, ADC_low maps and DCE-MRI.

RESULTS

ADC, D, D*, f and AUC60 values were significantly higher in hyperplastic bone marrow than in untreated bone marrow (p values < 0.0001, < 0.0001, < 0.001, < 0.001, < 0.0001, respectively). All bone metastases were clearly differentiable from hyperplastic bone marrow on ADC_low maps, but not on ADC maps and DCE-MRI.

CONCLUSION

MR functional imaging techniques, such as DW-, IVIM DW- and DCE-MRI are effective tools in assessing the response of bone marrow to the administration of growth factors. Although an overlap between signal of hyperplastic bone marrow and lytic bone metastases can occur on ADC maps and DCE-MRI, evaluation of ADCl_ow maps by IVIM DW-MRI could permit to differentiate hyperplastic bone marrow from lytic bone metastases. Further studies are needed to confirm our data.

Value of blood oxygenation level-dependent MRI for predicting clinical outcomes in uterine cervical cancer treated with concurrent chemoradiotherapy

OBJECTIVES

To investigate the value of blood oxygenation level-dependent (BOLD) MRI as a predictor of clinical outcomes in cervical cancer patients treated with concurrent chemoradiotherapy (CCRT).

METHOD

Enrolled 92 patients with stage IB2-IVB cervical cancer who received CCRT underwent 3-T BOLD MRI before treatment. The R2* value (rate of spin dephasing, s^-1) was measured in the tumor. Cox regression analysis was used to evaluate the associations of imaging and clinical parameters with progression-free survival (PFS) and cancer-specific survival (CSS). Inter-reader reliability for the R2* measurements was evaluated using an intraclass correlation coefficient (ICC).

RESULTS

Tumor R2* values were significantly different between patients with and without disease progression (p < 0.001). Multivariate analysis demonstrated that tumor R2* value was significantly independent factor for PFS (hazard ratio [HR] = 5.746, p < 0.001) and CSS (HR = 12.878, p = 0.001). Additionally, squamous cell carcinoma antigen (HR = 1.027, p = 0.001) was significantly independent factor for PFS. Inter-reader reliability for the R2* measurements was good (ICC = 0.702).

CONCLUSION

Pretreatment 3-T BOLD MRI may be useful for predicting clinical outcomes in uterine cervical cancer patients treated with CCRT, with good inter-reader reliability.

KEY POINTS

• Tumor R2* values are different between patients with and without disease progression. • The R2* value is an independent factor for treatment outcomes in cervical cancer. • Inter-reader reliability for R2* measurements using BOLD MRI is good.

Mapping Hypoxia in Renal Carcinoma with Oxygen-enhanced MRI: Comparison with Intrinsic Susceptibility MRI and Pathology

Purpose To cross-validate T1-weighted oxygen-enhanced (OE) MRI measurements of tumor hypoxia with intrinsic susceptibility MRI measurements and to demonstrate the feasibility of translation of the technique for patients. Materials and Methods Preclinical studies in nine 786-0-R renal cell carcinoma (RCC) xenografts and prospective clinical studies in eight patients with RCC were performed. Longitudinal relaxation rate changes (∆R1) after 100% oxygen inhalation were quantified, reflecting the paramagnetic effect on tissue protons because of the presence of molecular oxygen. Native transverse relaxation rate (R2*) and oxygen-induced R2* change (∆R2*) were measured, reflecting presence of deoxygenated hemoglobin molecules. Median and voxel-wise values of ∆R1 were compared with values of R2* and ∆R2*. Tumor regions with dynamic contrast agent-enhanced MRI perfusion, refractory to signal change at OE MRI (referred to as perfused Oxy-R), were distinguished from perfused oxygen-enhancing (perfused Oxy-E) and nonperfused regions. R2* and ∆R2* values in each tumor subregion were compared by using one-way analysis of variance. Results Tumor-wise and voxel-wise ∆R1 and ∆R2* comparisons did not show correlative relationships. In xenografts, parcellation analysis revealed that perfused Oxy-R regions had faster native R2* (102.4 sec-1 vs 81.7 sec-1) and greater negative ∆R2* (-22.9 sec-1 vs -5.4 sec-1), compared with perfused Oxy-E and nonperfused subregions (all P < .001), respectively. Similar findings were present in human tumors (P < .001). Further, perfused Oxy-R helped identify tumor hypoxia, measured at pathologic analysis, in both xenografts (P = .002) and human tumors (P = .003). Conclusion Intrinsic susceptibility biomarkers provide cross validation of the OE MRI biomarker perfused Oxy-R. Consistent relationship to pathologic analyses was found in xenografts and human tumors, demonstrating biomarker translation. Published under a CC BY 4.0 license. Online supplemental material is available for this article.

Clinical trials targeting hypoxia

The concept of tumour hypoxia as a cause of radiation resistance has been prevalent for over 100 years. During this time, our understanding of tumour hypoxia has matured with the recognition that oxygen tension within a tumour is influenced by both diffusion and perfusion mechanisms. In parallel, clinical strategies to modify tumour hypoxia with the expectation that this will improve response to radiation have been developed and tested in clinical trials. Despite many disappointments, meta-analysis of the data on hypoxia modification confirms a significant impact on both tumour control and survival. Early trials evaluated hyperbaric oxygen followed by a generation of studies testing oxygen mimetics such as misonidazole, pimonidazole and etanidazole. One highly significant result stands out from the use of nimorazole in advanced laryngeal cancer with a significant advantage seen for locoregional control using this radiosensitiser. More recent studies have evaluated carbogen and nicotinamide targeting both diffusion related and perfusion related hypoxia. A significant survival advantage is seen in muscle invasive bladder cancer and also for locoregional control in hypopharygeal cancer associated with a low haemoglobin. New developments include the recognition that mitochondrial complex inhibitors reducing tumour oxygen consumption are potential radiosensitising agents and atovaquone is currently in clinical trials. One shortcoming of past hypoxia modifying trials is the failure to identify oxygenation status and select those patient with significant hypoxia. A range of biomarkers are now available including histological necrosis, immunohistochemical intrinsic markers such as CAIX and Glut 1 and hypoxia gene signatures which have been shown to predict outcome and will inform the next generation of hypoxia modifying clinical trials.

Quantitative phase-filtered wavelength-modulated differential photoacoustic radar tumor hypoxia imaging toward early cancer detection

Overcoming the limitations of conventional linear spectroscopy used in multispectral photoacoustic imaging, wherein a linear relationship is assumed between the absorbed optical energy and the absorption spectra of the chromophore at a specific location, is crucial for obtaining accurate spatially-resolved quantitative functional information by exploiting known chromophore-specific spectral characteristics. This study introduces a non-invasive phase-filtered differential photoacoustic technique, wavelength-modulated differential photoacoustic radar (WM-DPAR) imaging that addresses this issue by eliminating the effect of the unknown wavelength-dependent fluence. It employs two laser wavelengths modulated out-of-phase to significantly suppress background absorption while amplifying the difference between the two photoacoustic signals. This facilitates pre-malignant tumor identification and hypoxia monitoring, as minute changes in total hemoglobin concentration and hemoglobin oxygenation are detectable. The system can be tuned for specific applications such as cancer screening and SO₂ quantification by regulating the amplitude ratio and phase shift of the signal. The WM-DPAR imaging of a head and neck carcinoma tumor grown in the thigh of a nude rat demonstrates the functional PA imaging of small animals in vivo. The PA appearance of the tumor in relation to tumor vascularity is investigated by immunohistochemistry. Phase-filtered WM-DPAR imaging is also illustrated, maximizing quantitative SO₂ imaging fidelity of tissues. Oxygenation levels within a tumor grown in the thigh of a nude rat using the two-wavelength phase-filtered differential PAR method.

Assessment of early treatment response to neoadjuvant chemotherapy in breast cancer using non-mono-exponential diffusion models: a feasibility study comparing the baseline and mid-treatment MRI examinations

OBJECTIVES

To assess the feasibility of the mono-exponential, bi-exponential and stretched-exponential models in evaluating response of breast tumours to neoadjuvant chemotherapy (NACT) at 3 T.

METHODS

Thirty-six female patients (median age 53, range 32-75 years) with invasive breast cancer undergoing NACT were enrolled for diffusion-weighted MRI (DW-MRI) prior to the start of treatment. For assessment of early response, changes in parameters were evaluated on mid-treatment MRI in 22 patients. DW-MRI was performed using eight b values (0, 30, 60, 90, 120, 300, 600, 900 s/mm2). Apparent diffusion coefficient (ADC), tissue diffusion coefficient (D t), vascular fraction (ƒ), distributed diffusion coefficient (DDC) and alpha (α) parameters were derived. Then t tests compared the baseline and changes in parameters between response groups. Repeatability was assessed at inter- and intraobserver levels.

RESULTS

All patients underwent baseline MRI whereas 22 lesions were available at mid-treatment. At pretreatment, mean diffusion coefficients demonstrated significant differences between groups (p < 0.05). At mid-treatment, percentage increase in ADC and DDC showed significant differences between responders (49 % and 43 %) and non-responders (21 % and 32 %) (p = 0.03, p = 0.04). Overall, stretched-exponential parameters showed excellent repeatability.

CONCLUSION

DW-MRI is sensitive to baseline and early treatment changes in breast cancer using non-mono-exponential models, and the stretched-exponential model can potentially monitor such changes.

KEY POINTS

• Baseline diffusion coefficients demonstrated significant differences between complete pathological responders and non-responders. • Increase in ADC and DDC at mid-treatment can discriminate responders and non-responders. • The ƒ fraction at mid-treatment decreased in responders whereas increased in non-responders. • The mono- and stretched-exponential models showed excellent inter- and intrarater repeatability. • Treatment effects can potentially be assessed by non-mono-exponential diffusion models.

Assessment of Early Therapeutic Changes to Concurrent Chemoradiotherapy in Uterine Cervical Cancer Using Blood Oxygenation Level-Dependent Magnetic Resonance Imaging

OBJECTIVE

This study aimed to investigate blood oxygenation level-dependent magnetic resonance imaging (MRI) in assessing early therapeutic changes in cervical cancers to concurrent chemoradiotherapy (CCRT).

METHODS

Fifteen consecutive patients with cervical cancer treated with CCRT were evaluated with blood oxygenation level-dependent MRI at 3 T. Magnetic resonance imaging examinations were performed before treatment (preTx), 1 week after treatment (postT1) and 4 weeks after treatment (postT2). At each time, the rate of spin dephasing (R2*) values were measured in tumor and in normal uterus.

RESULTS

Tumor R2* increased from preTx to postT2 (P < 0.01). In pairwise comparisons of tumor R2*, postT2 was significantly higher than preTx or postT1 (P < 0.01), whereas postT1 was not significantly different from preTx (P > 0.05). A significant difference in R2* was found between the tumors and normal uterus at preTx (P = 0.001), postT1 (P < 0.001), and postT2 (P < 0.001).

CONCLUSIONS

Blood oxygenation level-dependent MRI may demonstrate early therapeutic changes of cervical cancers to CCRT.

Targeting T1 and T2 dual modality enhanced magnetic resonance imaging of tumor vascular endothelial cells based on peptides-conjugated manganese ferrite nanomicelles

Tumor angiogenesis plays very important roles for tumorigenesis, tumor development, metastasis, and prognosis. Targeting T₁/T₂ dual modality magnetic resonance (MR) imaging of the tumor vascular endothelial cells (TVECs) with MR molecular probes can greatly improve diagnostic sensitivity and specificity, as well as helping to make an early diagnosis of tumor at the preclinical stage. In this study, a new T₁ and T₂ dual modality nanoprobe was successfully fabricated. The prepared nanoprobe comprise peptides CL 1555, poly(ε-caprolactone)-block-poly(ethylene glycol) amphiphilic copolymer shell, and dozens of manganese ferrite (MnFe₂O₄) nanoparticle core. The results showed that the hydrophobic MnFe₂O₄ nanoparticles were of uniform spheroidal appearance and narrow size distribution. Due to the self-assembled nanomicelles structure, the prepared probes were of high relaxivity of 281.7 mM⁻¹ s⁻¹, which was much higher than that of MnFe₂O₄ nanoparticles (67.5 mM 1 s⁻¹). After being grafted with the targeted CD105 peptide CL 1555, the nanomicelles can combine TVECs specifically and make the labeled TVECs dark in T₂-weighted MR imaging. With the passage on, the Mn²⁺ ions were released from MnFe₂O₄ and the size decreased gradually, making the signal intensity of the second and third passage of labeled TVECs increased in T₁-weighted MR imaging. Our results demonstrate that CL-poly(ethylene glycol)-MnFe₂O₄ can conjugate TVECs and induce dark and bright contrast in MR imaging, and act as a novel molecular probe for T₁- and T₂-enhanced MR imaging of tumor angiogenesis.

Mathematical Models of Contrast Transport Kinetics for Cancer Diagnostic Imaging: A Review

Angiogenesis plays a fundamental role in cancer growth and the formation of metastasis. Novel cancer therapies aimed at inhibiting angiogenic processes and/or disrupting angiogenic tumor vasculature are currently being developed and clinically tested. The need for earlier and improved cancer diagnosis, and for early evaluation and monitoring of therapeutic response to angiogenic treatment, have led to the development of several imaging methods for in vivo noninvasive assessment of angiogenesis. The combination of dynamic contrast-enhanced imaging with mathematical modeling of the contrast agent kinetics enables quantitative assessment of the structural and functional changes in the microvasculature that are associated with tumor angiogenesis. In this paper, we review quantitative imaging of angiogenesis with dynamic contrast-enhanced magnetic resonance imaging, computed tomography, and ultrasound.

Dynamic contrast-enhanced ultrasound parametric maps to evaluate intratumoral vascularization

OBJECTIVES

The purposes of this study were to assess the reliability of parametric maps from dynamic contrast-enhanced ultrasound (DCE-US) to reflect the heterogeneous distribution of intratumoral vascularization and to predict the tissue features linked to vasculature. This study was designed to compare DCE-US parametric maps with histologic vascularity measurements.

MATERIALS AND METHODS

Dynamic contrast-enhanced ultrasound was performed on 17 melanoma-bearing nude mice after a 0.1-mL bolus injection of SonoVue (Bracco SPA, Milan, Italy). The parametric maps were developed from raw linear data to extract pixelwise 2 semiquantitative parameters related to perfusion and blood volume, namely, area under the curve (AUC) and peak intensity (PI). The mathematical method to fit the time-intensity curve for each pixel was a polynomial model used in clinical routine and patented by the team. Regions of interest (ROIs) were drawn on DCE-US parametric maps for whole tumors and for several local areas of 15 mm within each tumor (iROI), the latter reflecting the heterogeneity of intratumoral blood volume. As the criterion standard correlation, microvessel densities (MVDs) were determined for both ROI categories. In detail, for all iROI of 15 mm, MVD and maturity were divided separately for vessels of 0 to 10 μm, 10 to 40 μm, and greater than 40 μm in diameter, and the results were correlated with the ultrasound findings.

RESULTS

Among the 17 studied mice, a total of 64 iROIs were analyzed. For the whole-tumor ROI set, AUC and PI values significantly correlated with MVD (rAUC = 0.52 [P = 0.0408] and rPI = 0.70 [P = 0.0026]). In the case of multiple iROI, a strong linear correlation was observed between the DCE-US parameters and the density of vessels ranging in their diameter from 0 to 10 μm (rAUC = 0.68 [P < 0.0001]; rPI = 0.63 [P < 0.0001]), 10 to 40 μm (rAUC = 0.98 [P = 0.0003]; rPI = 0.98 [P = 0.0004]), and greater than 40 μm (rAUC = 0.86 [P = 0.0120]; rPI = 0.92 [P = 0.0034]), respectively. However, the DCE-US parameter values of perfusion and blood volume were not significantly different according to the diameters (AUC: P = 0.1731; PI: P = 0.2918) and maturity of blood vessels.

CONCLUSIONS

Parametric maps of DCE-US can be reliably established from raw linear data and reflect the heterogeneous histological measures of vascularization within tumors. In contrast, the values of DCE-US parametric maps (AUC, PI) do not allow deduction of heterogeneous tissue features such as the diameters and maturity of vascular networks.

Lobulated enhancement evaluation in the follow-up of liver metastases treated by stereotactic body radiation therapy

OBJECTIVE

The Response Evaluation Criteria in Solid Tumors (RECIST) can have limitations when used to evaluate local treatments for cancer, especially for liver malignancies treated by stereotactic body radiation therapy (SBRT). The aim of this study was to validate the relationship between the occurrence of lobulated enhancement (LE) and local relapse and to evaluate the utility of this relationship for predicting local progression.

PATIENTS AND METHODS

Imaging data of 59 lesions in 46 patients, including 281 computed tomographic (CT) scans, were retrospectively and blindly reviewed by 3 radiologists. One radiologist measured the lesion size, for each CT and overall, to classify responses using RECIST threshold criteria. The second studied LE occurrence. A third radiologist was later included and studied LE occurrence to evaluate the interobserver consistency for LE evaluation.

RESULTS

The mean duration of follow-up was 13.6 months. LE was observed in 16 of 18 progressive lesions, occurring before size-based progression in 50% of cases, and the median delay of LE detection was 3.2 months. The sensitivity of LE to predict progression was 89%, and its specificity was 100%. The positive predictive value was 100%, the negative predictive value was 95.3%, and the overall accuracy was 97%. The probability of local progression-free survival at 12 months was significantly higher for lesions without LE compared with all lesions: 0.80 (CI 95%: 0.65-0.89) versus 0.69 (CI 95%: 0.54-0.80), respectively. The overall concordance rate between the 2 readers of LE was 97.9%.

CONCLUSION

Response assessment of liver metastases treated by SBRT can be improved by including LE. This study demonstrates the diagnostic and predictive utility of LE for assessing local progression at a size still eligible for local salvage treatment.

MRI methods for the evaluation of high intensity focused ultrasound tumor treatment: Current status and future needs

Thermal ablation with high intensity focused ultrasound (HIFU) is an emerging noninvasive technique for the treatment of solid tumors. HIFU treatment of malignant tumors requires accurate treatment planning, monitoring and evaluation, which can be facilitated by performing the procedure in an MR-guided HIFU system. The MR-based evaluation of HIFU treatment is most often restricted to contrast-enhanced T1 -weighted imaging, while it has been shown that the non-perfused volume may not reflect the extent of nonviable tumor tissue after HIFU treatment. There are multiple studies in which more advanced MRI methods were assessed for their suitability for the evaluation of HIFU treatment. While several of these methods seem promising regarding their sensitivity to HIFU-induced tissue changes, there is still ample room for improvement of MRI protocols for HIFU treatment evaluation. In this review article, we describe the major acute and delayed effects of HIFU treatment. For each effect, the MRI methods that have been-or could be-used to detect the associated tissue changes are described. In addition, the potential value of multiparametric MRI for the evaluation of HIFU treatment is discussed. The review ends with a discussion on future directions for the MRI-based evaluation of HIFU treatment.

[Therapy monitoring of neoadjuvant therapy with MRI. RECIST and functional imaging]

CLINICAL/METHODICAL ISSUE

Neoadjuvant chemotherapy is increasingly being applied in patients with operable breast cancer. Thus, an early prediction of response to neoadjuvant chemotherapy is of high relevance.

STANDARD RADIOLOGICAL METHODS

The interobserver variability of clinical examination, mammography and ultrasonography in the assessment of response to neoadjuvant chemotherapy is high.

METHODICAL INNOVATIONS

Magnetic resonance imaging (MRI) allows the assessment of functional parameters in addition to changes in tumor size and morphology.

PERFORMANCE

A reliable therapy response monitoring aims at optimizing individualized patient care.

ACHIEVEMENTS

This paper summarizes current guidelines for the assessment of response to neoadjuvant chemotherapy in breast cancer according to the response evaluation criteria in solid tumors (RECIST). Furthermore, the technical principles of MRI-based therapy monitoring are described and an overview of the clinical studies that have assessed the feasibility of functional MRI in response to treatment evaluation is given.

PRACTICAL RECOMMENDATIONS

The technology of functional MRI offers promising results concerning therapy response monitoring. However, the level of evidence is not sufficiently evaluated for the technologies of functional MRI presented here.

Use of diffusion-weighted, intravoxel incoherent motion, and dynamic contrast-enhanced MR imaging in the assessment of response to radiotherapy of lytic bone metastases from breast cancer

RATIONALE AND OBJECTIVES

To investigate the value of diffusion-weighted (DW), perfusion-sensitive, and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) techniques in assessing the response of bone metastases from breast cancer to radiotherapy, with particular emphasis on the role of intravoxel incoherent motion (IVIM)-DW parameters as a potential valuable imaging marker of tumor response.

MATERIALS AND METHODS

Fifteen women having breast cancer and bone metastases underwent MRI before and after radiotherapy (3 weeks [time 1], 2 months [time 2], and 4 months [time 3]), consisting of DW, perfusion-sensitive (IVIM), and DCE acquisitions. MR-based DW and perfusion parameters, including water diffusivity (D), perfusion fraction (f), pseudodiffusion (D*), total apparent diffusion coefficient (ADC-total), fractionated ADCs (ADC-high and ADC-low), and initial area under the gadolinium concentration curve after the first 60 seconds (IAUGC60), were determined. The morphologic MRI findings were also recorded. A one-way repeated measures analysis of variance was used to compare the value of MR-based parameters at the different time points.

RESULTS

A significant variation between pretreatment (time 0) and post-treatment (times 1, 2, and 3) was found for ADC-total and D parameters (P < .001). A statistically significant reduction was also found for IAUGC60 values between times 0 and 3 (P < .001). A significant change across the different time points was observed for D* and IAUGC60 parameters (P < .001). On the contrary, there was no statistically significant change over time for parameters ADC-total, D, f, and IAUGC60 comparing response between each metastasis, that is, the response to therapy was similar for each metastasis.

CONCLUSIONS

DW, IVIM, and DCE-MRI techniques show effectiveness in assessing the response to radiotherapy in bone metastases from breast cancer.

The clinical importance of assessing tumor hypoxia: relationship of tumor hypoxia to prognosis and therapeutic opportunities

Tumor hypoxia is a well-established biological phenomenon that affects the curability of solid tumors, regardless of treatment modality. Especially for head and neck cancer patients, tumor hypoxia is linked to poor patient outcomes. Given the biological problems associated with tumor hypoxia, the goal for clinicians has been to identify moderately to severely hypoxic tumors for differential treatment strategies. The "gold standard" for detecting and characterizing of tumor hypoxia are the invasive polarographic electrodes. Several less invasive hypoxia assessment techniques have also shown promise for hypoxia assessment. The widespread incorporation of hypoxia information in clinical tumor assessment is severely impeded by several factors, including regulatory hurdles and unclear correlation with potential treatment decisions. There is now an acute need for approved diagnostic technologies for determining the hypoxia status of cancer lesions, as it would enable clinical development of personalized, hypoxia-based therapies, which will ultimately improve outcomes. A number of different techniques for assessing tumor hypoxia have evolved to replace polarographic pO2 measurements for assessing tumor hypoxia. Several of these modalities, either individually or in combination with other imaging techniques, provide functional and physiological information of tumor hypoxia that can significantly improve the course of treatment. The assessment of tumor hypoxia will be valuable to radiation oncologists, surgeons, and biotechnology and pharmaceutical companies who are engaged in developing hypoxia-based therapies or treatment strategies.

Carbogen gas and radiotherapy outcomes in prostate cancer

Prostate cancer hypoxia is associated with inferior prognosis and resistance to treatment. The use of androgen deprivation therapy, both prior to and during radiotherapy, may exacerbate underlying hypoxia. Whilst larger radiation doses per fraction may achieve therapeutic gain, this is balanced by the reduced opportunity for re-oxygenation to take place during the course of treatment. Improving the underlying hypoxic tumour environment may therefore improve the treatment outcomes. Strategies to combat tumour hypoxia, with particular focus on the use of carbogen gas breathing concurrently with radiotherapy, is the subject of this review.