Prostate cancer: localization with three-dimensional proton MR spectroscopic imaging--clinicopathologic study

Does local recurrence of prostate cancer after radiation therapy occur at the site of primary tumor? Results of a longitudinal MRI and MRSI study

PURPOSE

To determine if local recurrence of prostate cancer after radiation therapy occurs at the same site as the primary tumor before treatment, using longitudinal magnetic resonance (MR) imaging and MR spectroscopic imaging to assess dominant tumor location.

METHODS AND MATERIALS

This retrospective study was HIPAA compliant and approved by our Committee on Human Research. We identified all patients in our institutional prostate cancer database (1996 onward) who underwent endorectal MR imaging and MR spectroscopic imaging before radiotherapy for biopsy-proven prostate cancer and again at least 2 years after radiotherapy (n = 124). Two radiologists recorded the presence, location, and size of unequivocal dominant tumor on pre- and postradiotherapy scans. Recurrent tumor was considered to be at the same location as the baseline tumor if at least 50% of the tumor location overlapped. Clinical and biopsy data were collected from all patients.

RESULTS

Nine patients had unequivocal dominant tumor on both pre- and postradiotherapy imaging, with mean pre- and postradiotherapy dominant tumor diameters of 1.8 cm (range, 1-2.2) and 1.9 cm (range, 1.4-2.6), respectively. The median follow-up interval was 7.3 years (range, 2.7-10.8). Dominant recurrent tumor was at the same location as dominant baseline tumor in 8 of 9 patients (89%).

CONCLUSIONS

Local recurrence of prostate cancer after radiation usually occurs at the same site as the dominant primary tumor at baseline, suggesting supplementary focal therapy aimed at enhancing local tumor control would be a rational addition to management.

Measurements of T(1) -relaxation in ex vivo prostate tissue at 132 μT

The proton T(1) was measured at 132 μT in ex vivo prostate tissue specimens from radical prostatectomies of 35 patients with prostate cancer. Each patient provided two specimens. The NMR and MRI measurements involved proton repolarization, a field of typically 150 mT and detection of the 5.6-kHz signal with a superconducting quantum interference device. Values of T(1) varied from 41 to 86 ms. Subsequently, the percentages of tissue types were determined histologically. The theoretical image contrast is quantified for each case by δ = [1 - T(1) (more cancer)/T(1) (less cancer)]. A linear fit of δ versus difference in percentage cancer yields T(1) (100% cancer)/T(1) (0% cancer) = 0.70 ± 0.05 with correlation coefficient R(2) = 0.30. Two-dimensional T(1) maps for four specimens demonstrate variation within a single specimen. These results suggest that MR images with T(1) contrast established at ultra-low fields may discriminate prostate cancer from normal prostate tissue in vivo without a contrast agent.

Imaging in prostate cancer staging: present role and future perspectives

Despite recent improvements in detection and treatment, prostate cancer continues to be the most common malignancy and the second leading cause of cancer-related mortality. Thus, although survival rate continues to improve, prostate cancer remains a compelling medical health problem. The major goal of prostate cancer imaging in the next decade will be more accurate disease characterization through the synthesis of anatomic, functional, and molecular imaging information in order to plan the most appropriate therapeutic strategy. No consensus exists regarding the use of imaging for evaluating primary prostate cancer. However, conventional and functional imaging are expanding their role in detection and local staging and, moreover, functional imaging is becoming of great importance in oncologic management and monitoring of therapy response. This review presents a multidisciplinary perspective on the role of conventional and functional imaging methods in prostate cancer staging.

Effect of gold marker seeds on magnetic resonance spectroscopy of the prostate

PURPOSE

Magnetic resonance stereoscopic imaging (MRSI) of the prostate is an emerging technique that may enhance targeting and assessment in radiotherapy. Current practices in radiotherapy invariably involve image guidance. Gold seed fiducial markers are often used to perform daily prostate localization. If MRSI is to be used in targeting prostate cancer and therapy assessment, the impact of gold seeds on MRSI must be investigated. The purpose of this study was to quantify the effects of gold seeds on the quality of MRSI data acquired in phantom experiments.

METHODS AND MATERIALS

A cylindrical plastic phantom with a spherical cavity 10 centimeters in diameter wss filled with water solution containing choline, creatine, and citrate. A gold seed fiducial marker was put near the center of the phantom mounted on a plastic stem. Spectra were acquired at 1.5 Tesla by use of a clinical MRSI sequence. The ratios of choline + creatine to citrate (CC/Ci) were compared in the presence and absence of gold seeds. Spectra in the vicinity of the gold seed were analyzed.

RESULTS

The maximum coefficient of variation of CC/Ci induced by the gold seed was found to be 10% in phantom experiments at 1.5 T.

CONCLUSION

MRSI can be used in prostate radiotherapy in the presence of gold seed markers. Gold seeds cause small effects (in the order of the standard deviation) on the ratio of the metabolite's CC/Ci in the phantom study done on a 1.5-T scanner. It is expected that gold seed markers will have similar negligible effect on spectra from prostate patients. The maximum of 10% of variation in CC/Ci found in the phantom study also sets a limit on the threshold accuracy of CC/Ci values for deciding whether the tissue characterized by a local spectrum is considered malignant and whether it is a candidate for local boost in radiotherapy dose.

Single blind randomized phase III trial to investigate the benefit of a focal lesion ablative microboost in prostate cancer (FLAME-trial): study protocol for a randomized controlled trial

Background

The treatment results of external beam radiotherapy for intermediate and high risk prostate cancer patients are insufficient with five-year biochemical relapse rates of approximately 35%. Several randomized trials have shown that dose escalation to the entire prostate improves biochemical disease free survival. However, further dose escalation to the whole gland is limited due to an unacceptable high risk of acute and late toxicity. Moreover, local recurrences often originate at the location of the macroscopic tumor, so boosting the radiation dose at the macroscopic tumor within the prostate might increase local control. A reduction of distant metastases and improved survival can be expected by reducing local failure. The aim of this study is to investigate the benefit of an ablative microboost to the macroscopic tumor within the prostate in patients treated with external beam radiotherapy for prostate cancer.

Methods/Design

The FLAME-trial (Focal Lesion Ablative Microboost in prostatE cancer) is a single blind randomized controlled phase III trial. We aim to include 566 patients (283 per treatment arm) with intermediate or high risk adenocarcinoma of the prostate who are scheduled for external beam radiotherapy using fiducial markers for position verification. With this number of patients, the expected increase in five-year freedom from biochemical failure rate of 10% can be detected with a power of 80%. Patients allocated to the standard arm receive a dose of 77 Gy in 35 fractions to the entire prostate and patients in the experimental arm receive 77 Gy to the entire prostate and an additional integrated microboost to the macroscopic tumor of 95 Gy in 35 fractions. The secondary outcome measures include treatment-related toxicity, quality of life and disease-specific survival. Furthermore, by localizing the recurrent tumors within the prostate during follow-up and correlating this with the delivered dose, we can obtain accurate dose-effect information for both the macroscopic tumor and subclinical disease in prostate cancer. The rationale, study design and the first 50 patients included are described.

Trial registration

This study is registered at ClinicalTrials.gov: NCT01168479

Metabolite detection of pancreatic carcinoma by in vivo proton MR spectroscopy at 3T: initial results

PURPOSE

The authors sought to identify metabolic features of pancreatic carcinoma by in vivo proton magnetic resonance (MR) spectroscopy at 3 Tesla.

MATERIALS AND METHODS

Forty healthy volunteers and 40 patients with pancreatic carcinoma confirmed by histopathology underwent T2-weighted imaging for localisation of the single voxel. Respiration-triggered (1)H MR spectroscopy was used to detect metabolites in normal pancreas and cancerous tissue. All spectral data were processed with SAGE software. Unsuppressed water at 4.7 ppm was used as an internal reference to determine metabolite concentrations. Each ratio among the different peak areas was statistically evaluated between normal pancreas and pancreatic carcinoma.

RESULTS

The following five groups of spectra were detected: unsaturated fatty acids (-CH = CH-) at 5.4 ppm; residual water at 4.7 ppm; choline metabolites at 3.2 ppm; unsaturated fatty acids (-CH2-CH = CH-) or a combination of N-acetylaspartate (NAA), N-acetylaspartylglutamate (NAAG), glutamine, glutamate, macromolecules and unsaturated fatty acids (-CH2-CH = CH-) at 2.0 ppm and lipids at 1.3 ppm. Ratio of lipids to unsuppressed water in normal pancreas was statistically greater than that in pancreatic cancer (p=0.004). Ratio of choline to unsuppressed water in normal pancreas was statistically greater than that in pancreatic cancer (p=0.0001). Ratio of fatty acids (-CH = CH-) to lipids in normal pancreas was statistically lower than that in pancreatic cancer (p=0.006).

CONCLUSIONS

Compared with normal pancreas, pancreatic carcinoma has a higher ratio of fatty acids (-CH = CH-) to lipids and lower ratios of lipids to unsuppressed water and choline to unsuppressed water at 3T.

Prostate cancer: multiparametric MR imaging for detection, localization, and staging

This review presents the current state of the art regarding multiparametric magnetic resonance (MR) imaging of prostate cancer. Technical requirements and clinical indications for the use of multiparametric MR imaging in detection, localization, characterization, staging, biopsy guidance, and active surveillance of prostate cancer are discussed. Although reported accuracies of the separate and combined multiparametric MR imaging techniques vary for diverse clinical prostate cancer indications, multiparametric MR imaging of the prostate has shown promising results and may be of additional value in prostate cancer localization and local staging. Consensus on which technical approaches (field strengths, sequences, use of an endorectal coil) and combination of multiparametric MR imaging techniques should be used for specific clinical indications remains a challenge. Because guidelines are currently lacking, suggestions for a general minimal protocol for multiparametric MR imaging of the prostate based on the literature and the authors' experience are presented. Computer programs that allow evaluation of the various components of a multiparametric MR imaging examination in one view should be developed. In this way, an integrated interpretation of anatomic and functional MR imaging techniques in a multiparametric MR imaging examination is possible. Education and experience of specialist radiologists are essential for correct interpretation of multiparametric prostate MR imaging findings. Supportive techniques, such as computer-aided diagnosis are needed to obtain a fast, cost-effective, easy, and more reproducible prostate cancer diagnosis out of more and more complex multiparametric MR imaging data.

Effect of Prostate Biopsy Hemorrhage on MRDW and MRS Imaging

Purpose

To retrospectively evaluate the effect of post-prostate-biopsy hemorrhage on the interpretation of magnetic resonance diffusion-weighted (MRDW) and magnetic resonance spectroscopic (MRS) imaging in the detection of prostate cancer. We also investigated the optimal timing for magnetic resonance examination after prostate biopsy.

Materials and Methods

We reviewed the records of 135 men. All patients underwent prostate magnetic resonance imaging (MRI). The prostate was divided into eight regions according to the biopsy site. Subsequently, we measured hemorrhage on apparent diffusion coefficient (ADC) values and (choline+creatinine)/citrate ([Cho+Cr]/Cit) ratios in the same regions on the MRI. We investigated the effect of hemorrhage at ADC values and (Cho+Cr)/Cit ratios on MRI and the relationship between prostate biopsy results and MRI findings.

Results

The mean patient age was 68.7 years and the mean time between biopsy and MRI was 23.5 days. The total hemorrhagic score demonstrated no significant associations with intervals from biopsy to MRI. Higher hemorrhagic scores were associated with higher ADC values, prostate cancer, and noncancer groups, respectively (p<0.001). ADC values were lower in tumors than in normal tissue (p<0.001), and ADC values were inversely correlated with tumor Gleason score in biopsy cores (p<0.001). However, (Cho+Cr)/Cit ratios did not exhibit any association with prostate biopsy results and hemorrhage.

Conclusions

Hemorrhage had no significant associations with the interval from biopsy to MRI. ADC values may help to detect prostate cancer and predict the aggressiveness of cancer; however, it is important to consider the bias effect of hemorrhage on the interpretation of MRDW imaging given that hemorrhage affects ADC values.

Reproducibility of 3D 1H MR spectroscopic imaging of the prostate at 1.5T

PURPOSE

To determine the reproducibility of 3D proton magnetic resonance spectroscopic imaging ((1)H-MRSI) of the human prostate in a multicenter setting at 1.5T.

MATERIALS AND METHODS

Fourteen subjects were measured twice with 3D point-resolved spectroscopy (PRESS) (1)H-MRSI using an endorectal coil. MRSI voxels were selected in the peripheral zone and combined central gland at the same location in the prostate in both measurements. Voxels with approved spectral quality were included to calculate Bland-Altman parameters for reproducibility from the choline plus creatine to citrate ratio (CC/C). The repeated spectroscopic data were also evaluated with a standardized clinical scoring system.

RESULTS

A total of 74 voxels were included for reproducibility analysis. The complete range of biologically interesting CC/C ratios was covered. The overall within-voxel standard deviation (SD) of the CC/C ratio of the repeated measurements was 0.13. This value is equal to the between-subject SD of noncancer prostate tissue. In >90% of the voxels the standardized clinical score did not differ relevantly between the measurements.

CONCLUSION

Repeated measurements of in vivo 3D (1)H-MRSI of the complete prostate at 1.5T produce equal and quantitative results. The reproducibility of the technique is high enough to provide it as a reliable tool in assessing tumor presence in the prostate.

Multiparametric 3T prostate magnetic resonance imaging to detect cancer: histopathological correlation using prostatectomy specimens processed in customized magnetic resonance imaging based molds

PURPOSE

We determined the prostate cancer detection rate of multiparametric magnetic resonance imaging at 3T. Precise one-to-one histopathological correlation with magnetic resonance imaging was possible using prostate magnetic resonance imaging based custom printed specimen molds after radical prostatectomy.

MATERIALS AND METHODS

This institutional review board approved prospective study included 45 patients (mean age 60.2 years, range 49 to 75) with a mean prostate specific antigen of 6.37 ng/ml (range 2.3 to 23.7) who had biopsy proven prostate cancer (mean Gleason score of 6.7, range 6 to 9). Before prostatectomy all patients underwent prostate magnetic resonance imaging using endorectal and surface coils on a 3T scanner, which included triplane T2-weighted magnetic resonance imaging, apparent diffusion coefficient maps of diffusion weighted magnetic resonance imaging, dynamic contrast enhanced magnetic resonance imaging and spectroscopy. The prostate specimen was whole mount sectioned in a customized mold, allowing geometric alignment to magnetic resonance imaging. Tumors were mapped on magnetic resonance imaging and histopathology. Sensitivity, specificity, positive predictive value and negative predictive value of magnetic resonance imaging for cancer detection were calculated. In addition, the effects of tumor size and Gleason score on the sensitivity of multiparametric magnetic resonance imaging were evaluated.

RESULTS

The positive predictive value of multiparametric magnetic resonance imaging to detect prostate cancer was 98%, 98% and 100% in the overall prostate, peripheral zone and central gland, respectively. The sensitivity of magnetic resonance imaging sequences was higher for tumors larger than 5 mm in diameter as well as for those with higher Gleason scores (greater than 7, p <0.05).

CONCLUSIONS

Prostate magnetic resonance imaging at 3T allows for the detection of prostate cancer. A multiparametric approach increases the predictive power of magnetic resonance imaging for diagnosis. In this study accurate correlation between multiparametric magnetic resonance imaging and histopathology was obtained by the patient specific, magnetic resonance imaging based mold technique.

Fine-tuning robot-assisted radical prostatectomy planning with MRI

OBJECTIVES

Robot-assisted radical prostatectomy (RARP) has now become the most common surgical treatment option for prostate cancer (CaP). Clinicopathologic data (i.e., biopsy, digital rectal exam, prostate specific antigen level) and patient-specific factors (e.g., age, erectile function, co-morbidities) are the primary sources of information that urologists use for counseling and treatment decision making. Magnetic resonance imaging (MRI) has evolved along a similar temporal arc to RARP, with increased utilization and precision over the past decade. MRI prior to RARP provides multifaceted adjunctive information, including enhancement of locoregional staging, delineation of spatial anatomic information, and identification of aberrant anatomy, all of which aid in patient treatment counseling and operative planning. This article is designed for urologic surgeons who perform RARP, with the aim of providing a review of prostate MRI imaging and highlighting findings which may specifically alter the operation.

METHODS AND MATERIALS

A review of the literature was performed, focusing on the most recent publications.

RESULTS

MRI imaging of the prostate has become increasing accurate for the identification, localization, and characterization of CaP lesions. In addition to tumor-specific information, a number of intra- and extra-prostatic findings are consistently identified on MRI which may impact RARP.

CONCLUSIONS

MRI provides important information which may alter RARP.

Usefulness of prebiopsy multifunctional and morphologic MRI combined with free-to-total prostate-specific antigen ratio in the detection of prostate cancer

OBJECTIVE

The purpose of the study was to assess the predictive value for prostate cancer of MRI using morphologic (T2-weighted imaging [T2WI]) and functional (MR spectroscopy [MRS], diffusion-weighted imaging [DWI], and dynamic contrast-enhanced [DCE] MRI) sequences and the free-to-total prostate-specific antigen (PSA) ratio, alone and combined.

MATERIALS AND METHODS

This retrospective study included 70 patients (PSA level, > 4 ng/mL; free-to-total PSA ratio, < 20%) who underwent endorectal 1.5-T MRI before biopsy. We graded the likelihood of cancer on a 5-point scale. Imaging data were compared with histologic results on biopsy or prostatectomy. Accuracies were estimated from the area under receiver operating characteristic using the hemiprostate as the unit of analysis. A p value less than 0.05 denoted statistical significance.

RESULTS

The model combining all variables was more accurate than each variable alone (95.2% vs 73.5% for T2WI, 76.0% for MRS, 81.8% for DWI, 75.6% for DCE-MRI, and 78.8% for free-to-total PSA ratio). The complete model had accuracy similar to that of combining two imaging variables with free-to-total PSA ratio, especially free-to-total PSA ratio, T2WI, and DWI (94.0%); and free-to-total PSA ratio, DWI, and MRS (93.8%); with negative predictive values of 91.0% and 89.5%, respectively. The best models combining two imaging variables (MRS and DWI, 85.8%; T2WI and DWI, 84.8%) had accuracy that was similar to that of the combination of all imaging variables (87.3%) and higher than that of the best individual imaging variable (DWI, 81.8%), but lower than that of the complete model.

CONCLUSION

The combination of at least one functional technique with free-to-total PSA ratio is more accurate than combining only imaging variables in cancer detection. The use of more than two imaging variables does not increase the detection rate. Functional MRI has the potential to help avoid a large number of negative biopsies.

Diagnostic accuracy of surface coil magnetic resonance imaging at 1.5 T for local staging of elevated risk prostate cancer

INTRODUCTION

Preoperative prostate cancer stage predicts prognosis and affects treatment decisions. The purpose of this study was to estimate the sensitivity and specificity of surface coil magnetic resonance imaging (MRI) for prostate cancer stage using surgical pathologic data as the reference standard.

METHODS

High-risk patients (>/=cT3 or PSA >/=20 ng/mL or Gleason >/=8) and selected intermediate-risk patients (clinically bulky disease on exam or biopsy, cT2b/c, or Gleason 7 with >/=3 of 5 biopsy cores positive in a lobe) routinely received a pelvic MRI at our institution. The images of identified patients were reviewed by one radiologist who was blinded to clinical information. The radiologist reported presence or absence of tumour within each lobe of the prostate. Extraprostatic extension (EPE), seminal vesicle (SV) invasion and pelvic lymph node (PLN) metastasis were also reported. Radiological findings were compared with prostatectomy pathology reports.

RESULTS

During the study period, about 320 radical prostatectomies were performed. Of these, 32 had a preoperative surface coil pelvic MRI adequate for analysis. Pathologically, 53 of 64 (82.8%) prostate lobes contained tumour, 17 (26.6%) lobes had associated EPE, 12 (18.8%) had SV involvement and 7 (10.9%) sets of PLNs contained cancer. Magnetic resonance imaging sensitivity and specificity were, respectively, 94.3% and 81.8% for tumour location, 82.4% and 87.2% for EPE, 83.3% and 92.3% for SV invasion and 71.4% and 94.7% for PLN involvement.

INTERPRETATION

Surface coil MRI accurately stages many prostate cancer patients with elevated risk of extraprostatic disease. This mode of imaging may be reasonable at centres that do not have endorectal coil MRI.

State-of-the-art uroradiologic imaging in the diagnosis of prostate cancer

In the diagnostic process of prostate cancer, several radiologic imaging modalities significantly contribute to the detection and localization of the disease. These range from transrectal ultrasound (TRUS) and magnetic resonance imaging (MRI) to positron emission tomography (PET). Within this review, after evaluation of the literature, we will discuss the advantages and disadvantages of these imaging modalities in clarifying the patient's clinical status as to whether he has prostate cancer or not and if so, where it is located, so that therapy appropriate to the patient's disease may be administered. TRUS, specifically with the usage of intravenous contrast agents, provides an excellent way of directing biopsy towards suspicious areas within the prostate in the general (screening) population. MRI using functional imaging techniques allows for highly accurate detection and localization, particularly in patients with prior negative ultrasound guided biopsies. A promising new development is the performance of biopsy within the magnetic resonance scanner. Subsequently, a proposal for optimal use of radiologic imaging is presented and compared with the European and American urological guidelines on prostate cancer.

Investigating the Clinical Aspects of Using CT vs. CT-MRI Images during Organ Delineation and Treatment Planning in Prostate Cancer Radiotherapy

In order to apply highly conformal dose distributions, which are characterized by steep dose fall-offs, it is necessary to know the exact target location and extension. This study aims at evaluating the impact of using combined CT-MRI images in organ delineation compared to using CT images alone, on the clinical results. For 10 prostate cancer patients, the respective CT and MRI images at treatment position were acquired. The CTV was delineated using the CT and MRI images, separately, whereas bladder and rectum were delineated using the CT images alone. Based on the CT and MRI images, two CTVs were produced for each patient. The mutual information algorithm was used in the fusion of the two image sets. In this way, the structures drawn on the MRI images were transferred to the CT images in order to produce the treatment plans. For each set of structures of each patient, IMRT and 3D-CRT treatment plans were produced. The individual treatment plans were compared using the biologically effective uniform dose ([Formula: see text]) and the complication-free tumor control probability ( P+) concepts together with the DVHs of the targets and organs at risk and common dosimetric criteria. For the IMRT treatment, at the optimum dose level of the average CT and CT-MRI delineated CTV dose distributions, the P+ values are 74.7% in both cases for a [Formula: see text] of 91.5 Gy and 92.1 Gy, respectively. The respective average total control probabilities, PB are 90.0% and 90.2%, whereas the corresponding average total complication probabilities, PI are 15.3% and 15.4%. Similarly, for the 3D-CRT treatment, the average P+ values are 42.5% and 46.7%, respectively for a [Formula: see text] of 86.4 Gy and 86.7 Gy, respectively. The respective average PB values are 80.0% and 80.6%, whereas the corresponding average PI values are 37.4% and 33.8%, respectively. For both radiation modalities, the improvement mainly stems from the better sparing of rectum. According to these results, the expected clinical effectiveness of IMRT can be increased by a maximum Δ P+ of around 0.9%, whereas of 3D-CRT by about 4.2% when combined CT-MRI delineation is performed instead of using CT images alone. It is apparent that in both IMRT and 3D-CRT radiation modalities, the better knowledge of the CTV extension improved the produced dose distribution. It is shown that the CTV is irradiated more effectively, while the complication probabilities of bladder and rectum, which is the principal organs at risk, are lower in the CT-MRI based treatment plans.

Initial results of 3-dimensional 1H-magnetic resonance spectroscopic imaging in the localization of prostate cancer at 3 Tesla: should we use an endorectal coil?

PURPOSE

The purpose of this study was to compare the diagnostic performance of 3 Tesla, 3-dimensional (3D) magnetic resonance spectroscopic imaging (MRSI) in the localization of prostate cancer (PCa) with and without the use of an endorectal coil (ERC).

MATERIALS AND METHODS

Our prospective study was approved by the institutional review board, and written informed consent was obtained from all patients. Between October 2004 and January 2006, 18 patients with histologically proven PCa on biopsy and scheduled for radical prostatectomy were included and underwent 3D-MRSI with and without an ERC. The prostate was divided into 14 regions of interest (ROIs). Four readers independently rated (on a 5-point scale) their confidence that cancer was present in each of these ROIs. These findings were correlated with whole-mount prostatectomy specimens. Areas under the receiver-operating characteristic curve were determined. A difference with a P < 0.05 was considered significant.

RESULTS

A total of 504 ROIs were rated for the presence and absence of PCa. Localization of PCa with MRSI with the use of an ERC had a significantly higher areas under the receiver-operating characteristic curve (0.68) than MRSI without the use of an ERC (0.63) (P = 0.015).

CONCLUSION

The use of an ERC in 3D MRSI in localizing PCa at 3 Tesla slightly but significantly increased the localization performance compared with not using an ERC.

Endorectal MRI after radiation therapy: questioning the sextant analysis

PURPOSE

To evaluate whether the information gained by three coregistration systems (sextant, hemi-prostate, and whole gland) differs significantly, suggesting that one approach should be routinely favored over the others. Despite its known limitations, sextant is the generally accepted standard for magnetic resonance imaging (MRI) and biopsy coregistration; nevertheless, depending on the magnitude of localization errors, other options may be adequate.

MATERIALS AND METHODS

Institutional Review Board approval was obtained and the study was Health Insurance Portability and Accountability Act (HIPAA)-compliant. We identified 70 patients who underwent 1.5 T endorectal MRI of the prostate between 1999 and 2008 after external beam radiotherapy for prostate cancer. A single reader reviewed all T2-weighted images for the presence or absence of tumor. The performance of each approach was quantified using receiver operating characteristic (ROC) curve analysis. Transrectal ultrasound-guided sextant biopsies were used as a standard of reference.

RESULTS

The areas under the ROC curve indicating accuracy for each MRI approach were 0.63 (sextant), 0.68 (hemi-prostate), and 0.71 (whole gland). There was no statistically significant difference among these approaches.

CONCLUSION

As expected, the point estimate was higher for the whole-gland approach, but not significantly. Reliable assessment of locally recurrent prostate cancer after external beam radiotherapy by endorectal MRI may be made using a sextant, hemi-prostate, or whole gland approach. The option for one or another approach should not be solely based on estimations of imaging accuracy, but on the purpose of the procedure.

Discriminating cancer from noncancer tissue in the prostate by 3-dimensional proton magnetic resonance spectroscopic imaging: a prospective multicenter validation study

OBJECTIVES

A prospective multicenter validation of the ability of 1H magnetic resonance spectroscopic imaging (MRSI) to distinguish cancer from noncancer tissues throughout the prostate with histopathology of the resected organ as the standard of reference.

MATERIALS AND METHODS

Institutional review board approval was obtained for all centers and all participating patients and volunteers provided written informed consent. Ninety-nine patients and 10 age-matched volunteers from 8 participating centers underwent magnetic resonance imaging and 3-dimensional MRSI with an endorectal coil at 1.5 T. Selected MRSI voxels were assigned to the peripheral zone (PZ), the central gland (CG), the periurethral area, and cancer tissue. Signal ratios of choline + creatine to citrate (CC/C) in spectra of these voxels were automatically calculated. Receiver operating characteristic curves were constructed to assess the accuracy by which this ratio can discriminate cancer from noncancer tissue.

RESULTS

A total of 70% of voxels in noncancer tissue and 90% of voxels in cancer tissue passed the quality check of the automatically fitted spectra. The median CC/C was significantly different between any noncancer and cancer tissue (P < 0.0001), but not between the different contributing centers. CC/C increased with cancer focus size (P =0.0008) and certainty of voxel mapping to histopathologic cancer site (P 0.0001). The area under the receiver operating characteristic curve for discriminating voxels of cancer tissue from noncancer tissue was 0.88 (confidence interval: 0.84-0.92) in the PZ and 0.76 (confidence interval: 0.71- 0.81) in the CG.

Detection of fully refocused polyamine spins in prostate cancer at 7 T

(1)H MRSI is often used at 1.5 or 3 T to study prostate cancer, where the ratio of choline + creatine to citrate is taken as a marker for tumour presence. Recently, the level of polyamines (mainly spermine) has been shown to improve specificity even further. However, the in vivo detection of these polyamines (at 3.1  ppm) is hampered by signal cancellation as a result of J-coupling effects and signal overlap with choline (3.2  ppm) and creatine (3.0  ppm) resonances. At higher magnetic field strengths, the chemical shift dispersion will increase, which allows the use of very selective radiofrequency pulses to refocus J-coupled spins. In this work, we added selective refocusing pulses to a semi-LASER (localisation based on adiabatic selective refocusing) sequence at 7 T, and optimised the inter-pulse timings of the sequence for fully refocused detection of spermine spins, whilst maintaining optimised detection of choline, creatine and the strongly coupled spin system of citrate.

A pilot study of endorectal magnetic resonance imaging and magnetic resonance spectroscopic imaging changes with dutasteride in patients with low risk prostate cancer

OBJECTIVE

•To evaluate the effects of dutasteride on treatment-naïve prostate cancer in men using serial magnetic resonance imaging (MRI) and magnetic resonance spectroscopic imaging (MRSI) in this pilot study.

PATIENTS AND METHODS

•This investigator-initiated prospective single-arm study was approved by the institutional committee on human research ethics board. •The target accrual was 10 patients. Newly diagnosed prostate cancer patients with low risk disease either with symptomatic benign prostatic hypertrophy or deemed to require pre-brachytherapy androgen suppression therapy were eligible. In the latter group, dutasteride was used to achieve cytoreduction. •All patients received 6 months of dutasteride 3.5 mg daily and underwent baseline blood work, health-related quality of life indices and MRI/MRSI, which were repeated at 1, 3 and 6 months. •MRSI spectra were examined and scored as healthy or cancerous. The change in cancerous volumes over time was evaluated.

RESULTS

•Of the 10 patients enrolled, nine patients completed the entire study. One patient withdrew after 3 months because of drug-related toxicity. •Because a significant decrease in citrate and polyamines on MRSI spectra was noted at 1 month compared with baseline, healthy tissue appeared to be more like cancer and thus created a false impression that the cancer had grown after 1 month. To reduce this bias, comparisons were made between the 1-month and 6-month scans. •The median MR cancer volumes at 6 months and 3 months were 100% and 101% of the 1-month value, respectively. Three of the nine patients had a 30-45% decrease in cancer volume at 6 months relative to 1-month measures. Of the others, two had no change in cancer volume and four had an increase (range 65-167% of the 1-month value). •The median cancer volume (range) at baseline was only 0.5 (0.1-5.6) mL.

CONCLUSIONS

•The inclusion of only men with low volume disease may have limited our ability to accurately assess response rates after dutasteride due to the background effects on normal prostate metabolism. Despite this, one-third of patients had a 30-45% reduction in cancer volume at 6 months. •Future studies including men with larger volume disease may enable estimates of response rates to be made more accurately.

MRI of the prostate: interobserver agreement compared with histopathologic outcome after radical prostatectomy

BACKGROUND

The purpose of this study was to evaluate interobserver agreement of prostatic MRI in assessing the performance of staging prostate carcinoma in comparison with histopathologic step section prostate specimens.

METHODS

We retrospectively evaluated 46 patients who underwent prostatic MRI examination at 1.5 T MRI and "subsequently" radical prostatectomy. All MR-images were reevaluated by two different experienced radiologists (15 and 1.5 years of experience) with special focus on T2/T3 differentiation. Both radiologists were not aware of the patient's clinical data, except that the patient had prostate cancer. These findings were compared with histopathologic whole mount step section prostate specimens, which served as the "gold standard". Fourfold tables were created to calculate sensitivity, specificity, positive and negative predictive values and efficiency for T2/T3 differentiation. Cohen's kappa was calculated to measure inter-rater agreement.

RESULTS

Twenty-eight patients were diagnosed with organ defined cancer (T2), 18 patients were staged with extracapsular extension (T3), and thereof 7 patients were staged with seminal vesicle invasion (T3b) by the pathologists. The experienced reader reached a sensitivity of 77.78% (95%-CI 52.36%; 93.59%) and specificity of 92.86% (95%-CI 76.50%; 99.12%) for T2/T3 differentiation, the less experienced reader however achieved a sensitivity of 33.33% (95%-CI 13.34%; 59.01%) and specificity of 71.43% (95%-CI 51.33%; 86.78%). The Cohen's kappa for inter-rater reliability for differentiation between T2 and T3 stage was κ=0.0129.

CONCLUSIONS

Evaluation of prostatic MR imaging requires lengthy experience for accurate interpretation and staging. While a highly experienced reader can achieve good correlation with histopathology even without utilization of functional MR imaging, a less experienced reader with theoretical knowledge falls short of expectation.

MRI for men undergoing active surveillance or with rising PSA and negative biopsies

The role of imaging in treatment decision-making for patients with prostate cancer is to characterize the cancer already diagnosed on biopsy, to determine tumor location, to assess tumor volume, and to exclude more-extensive disease. MRI is currently the most established imaging modality for this purpose, with the highest sensitivity and specificity for detection and staging of prostate tumors. The development and wider adoption of active surveillance and focal treatment approaches would also benefit from accurate localization of cancer. As such, 3 T MRI and multiparametric approaches are being developed as tools for the localization and staging of prostate cancer. Men wishing to commence or remain on active surveillance might benefit by having larger cancers identified before embarking on this management strategy. MRI might have its greatest role in patients where there is a discrepancy between PSA and biopsy results suggesting a potential missed prostate tumor.

Metabolomics: a novel approach to early and noninvasive prostate cancer detection

Prostate cancer (PCa) is the most commonly diagnosed visceral cancer in men and is responsible for the second highest cancer-related male mortality rate in Western countries, with increasing rates being reported in Korea, Japan, and China. Considering the low sensitivity of prostate-specific antigen (PSA) testing, it is widely agreed that reliable, age-independent markers of the presence, nature, and progression of PCa are required to facilitate diagnosis and timely treatment. Metabolomics or metabonomics has recently emerged as a novel method of PCa detection owing to its ability to monitor changes in the metabolic signature, within biofluids or tissue, that reflect changes in phenotype and function. This review outlines the physiology of prostate tissue and prostatic fluid in health and in malignancy in relation to metabolomics as well as the principles underlying the methods of metabolomic quantification. Promising metabolites, metabolic profiles, and their correlation with the presence and stage of PCa are summarized. Application of metabolomics to biofluids and in vivo quantification as well as the direction of current research in supplementing and improving current methods of detection are discussed. The current debate in the urology literature on sarcosine as a potential biomarker for PCa is reviewed and discussed. Metabolomics promises to be a valuable tool in the early detection of PCa that may enable earlier treatment and improved clinical outcomes.

Comparison of qualitative and quantitative approach to prostate MR spectroscopy in peripheral zone cancer detection

OBJECTIVE

To compare the diagnostic performance of a qualitative (pattern recognition) and a quantitative (numerical assessment) approach to magnetic resonance spectroscopy (MRS) in the diagnosis of peripheral zone prostate cancer.

METHODS

185 patients (131 with histopathologically proven cancer, 54 normal/benign after at least 12 months follow-up) were prospectively evaluated with qualitative MRS using a 4-point scale between 3/2004 and 1/2008, and retrospectively reassessed using a prototype quantitative postprocessing software in April 2008. Based on pathology and follow-up data, diagnostic performance parameters were calculated.

RESULTS

The qualitative and quantitative approaches were concordant in 78.9% (146/185) of cases. The difference between the areas under the ROC curve (0.791 versus 0.772, respectively) was not statistically significant. The sensitivity, specificity and accuracy were 55.7%, 94.4% and 67.0% for the qualitative approach, and 55.0%, 83.3% and 63.2% for the quantitative approach. The sensitivity for high grade tumours (Gleason 4+3 or higher) was 85.2% (23/27) for both approaches. All cancers missed on either one approach separately (31/31) and 91% of cancers missed on both approaches together (23/27) were of lower grade (Gleason 3+4 or lower).

CONCLUSIONS

Qualitative and quantitative approaches to MRS yield similar diagnostic results. Discordances in tumour detection only occurred in lower grade cancers.

Interactive, multi-modality image registrations for combined MRI/MRSI-planned HDR prostate brachytherapy

Purpose

This study presents the steps and criteria involved in the series of image registrations used clinically during the planning and dose delivery of focal high dose-rate (HDR) brachytherapy of the prostate.

Material and methods

Three imaging modalities – Magnetic Resonance Imaging (MRI), Magnetic Resonance Spectroscopic Imaging (MRSI), and Computed Tomography (CT) – were used at different steps during the process. MRSI is used for identification of dominant intraprosatic lesions (DIL). A series of rigid and nonrigid transformations were applied to the data to correct for endorectal-coil-induced deformations and for alignment with the planning CT. Mutual information was calculated as a morphing metric. An inverse planning optimization algorithm was applied to boost dose to the DIL while providing protection to the urethra, penile bulb, rectum, and bladder. Six prostate cancer patients were treated using this protocol.

Results

The morphing algorithm successfully modeled the probe-induced prostatic distortion. Mutual information calculated between the morphed images and images acquired without the endorectal probe showed a significant (p = 0.0071) increase to that calculated between the unmorphed images and images acquired without the endorectal probe. Both mutual information and visual inspection serve as effective diagnostics of image morphing. The entire procedure adds less than thirty minutes to the treatment planning.

Conclusion

This work demonstrates the utility of image transformations and registrations to HDR brachytherapy of prostate cancer.

Role of endorectal magnetic resonance spectroscopic imaging in two different Gleason scores in prostate cancer

OBJECTIVE

The major goal of the work was to record three-dimensional magnetic resonance spectroscopic imaging (MRSI) and to compare metabolite ratios between different Gleason scores (GS).

MATERIALS AND METHODS

MRSI localized by endorectal coil-acquired point-resolved spectroscopy was performed in 14 men with prostate cancer of GS 6 (n = 7) and 7 (n = 7) using a 1.5-tesla MRI scanner.

RESULTS

The ratio of (choline + creatine)/citrate was increased with an increase of GS, i.e. 0.590 ± 0.171 in the target lesion and 0.321 ± 0.157 in the contralateral region of patients with a GS of 6 as opposed to 1.082 ± 0.432 in the target lesion and 0.360 ± 0.243 in the contralateral region of patients with a GS of 7.

CONCLUSION

Our pilot results demonstrated that MRSI was an additional biochemical tool which is complementary to the current imaging modalities for early diagnosis and therapeutic management of prostate cancer.

Metabolomics and surgical oncology: Potential role for small molecule biomarkers

Metabolomics, the newest of the "omics" sciences, has brought much excitement to the field of oncology as a potential new translational tool capable of bringing the molecular world of cancer care to the bedside. While still early in its development, metabolomics could alter the scope and role of surgery in the multidisciplinary treatment of cancer. This review examines potential roles of metabolomics in areas of early cancer detection, personalized therapeutics and tumorigenesis.

Accuracy of MRI/MRSI-based transrectal ultrasound biopsy in peripheral and transition zones of the prostate gland in patients with prior negative biopsy

The purpose of the study was to evaluate the accuracy of transrectal ultrasound biopsy (TRUS-biopsy) performed on regions with abnormal MRI and/or MRSI for both the transition (TZ) and the peripheral (PZ) zones in patients with suspected prostate cancer with prior negative biopsy, and to analyze the relationship between MRSI and histopathological findings. MRI and MRSI were performed in 54 patients (mean age: 63.9 years, mean PSA value: 11.4 ng/mL) and the ability of MRI/MRSI-directed TRUS biopsy was evaluated. A three-point score system was used for both techniques to distinguish healthy from malignant regions. Descriptive statistics and ROC analyses were performed to evaluate the accuracy and the best cut-off in the three-point score system. Twenty-two out of 54 patients presented cancer at MRI/MRSI-directed TRUS biopsy, nine presented cancer only in PZ, eight both in PZ and TZ, and five exclusively in TZ. On a patient basis the highest accuracy was obtained by assigning malignancy on a positive finding with MRSI and MRI even though it was not significantly greater than that obtained using MRI alone (area under the ROC curve, AUC: 0.723 vs 0.676). On a regional (n = 648) basis the best accuracy was also obtained by considering positive both MRSI and MRI for PZ (0.768) and TZ (0.822). MRSI was false positive in 11.9% of the regions. Twenty-eight percent of cores with prostatitis were false positive findings on MRSI, whereas only 2.7% of benign prostatic hyperplasia was false positive. In conclusion, the accuracy of MRI/MRSI-directed biopsies in localization of prostate cancer is good in patient (0.723) and region analyses (0.768). The combination of both MRI and MRSI results makes TRUS-biopsy more accurate, particularly in the TZ (0.822) for patients with prior negative biopsies. Histopathological analysis showed that the main limitation of MRSI is the percentage of false positive findings due to prostatitis.

Magnetic resonance imaging in diagnosis, staging and radiotherapy planning for prostate cancer

T2-weighted magnetic resonance imaging (MRI), preferably using an endorectal coil, is able to clearly depict the normal prostatic anatomy and to identify prostate cancer with fair diagnostic accuracy. The latter can be further increased by using functional techniques such as spectroscopy (assessment of prostatic metabolism), dynamic contrast-enhanced MRI (assessment of angiogenesis) and diffusion-weighted imaging (assessment of cellular density). T2-weighted MRI is an important tool for local staging of prostate cancer in patients clinically staged as cT1 or cT2, because of its high specificity for macroscopic capsular extension or seminal vesicle invasion. Compared to CT-imaging, MRI depicts the internal prostatic anatomy, prostatic margins and the extent of prostatic tumours much more clearly. This benefit can be exploited to improve the accuracy of target delineations in radiotherapy planning.

Prostate cancer localization with multispectral MRI using cost-sensitive support vector machines and conditional random fields

Prostate cancer is a leading cause of cancer death for men in the United States. Fortunately, the survival rate for early diagnosed patients is relatively high. Therefore, in vivo imaging plays an important role for the detection and treatment of the disease. Accurate prostate cancer localization with noninvasive imaging can be used to guide biopsy, radiotherapy, and surgery as well as to monitor disease progression. Magnetic resonance imaging (MRI) performed with an endorectal coil provides higher prostate cancer localization accuracy, when compared to transrectal ultrasound (TRUS). However, in general, a single type of MRI is not sufficient for reliable tumor localization. As an alternative, multispectral MRI, i.e., the use of multiple MRI-derived datasets, has emerged as a promising noninvasive imaging technique for the localization of prostate cancer; however almost all studies are with human readers. There is a significant inter and intraobserver variability for human readers, and it is substantially difficult for humans to analyze the large dataset of multispectral MRI. To solve these problems, this study presents an automated localization method using cost-sensitive support vector machines (SVMs) and shows that this method results in improved localization accuracy than classical SVM. Additionally, we develop a new segmentation method by combining conditional random fields (CRF) with a cost-sensitive framework and show that our method further improves cost-sensitive SVM results by incorporating spatial information. We test SVM, cost-sensitive SVM, and the proposed cost-sensitive CRF on multispectral MRI datasets acquired from 21 biopsy-confirmed cancer patients. Our results show that multispectral MRI helps to increase the accuracy of prostate cancer localization when compared to single MR images; and that using advanced methods such as cost-sensitive SVM as well as the proposed cost-sensitive CRF can boost the performance significantly when compared to SVM.

[MR spectroscopy of the prostate with external surface coils: clinical feasibility]

PURPOSE

To determine the clinical feasibility of MR spectroscopy (MRS) of prostate cancer using external multi-channel surface coils at 1.5T. Materials and methods. Retrospective study of 31 patients with prostate cancer who underwent MRS as part of the staging work-up prior to radical prostatectomy. The ratio of the three main metabolites ([choline + creatine]/citrate) were measured along with spectral analysis of different regions of interest (ROI) placed in areas of normal tissue and cancer using the surgical specimen as the standard of reference.

RESULTS

One hundred and eighty-three voxels were analyzed. Qualitative visual analysis identified pathological spectra in 88.5% of cancer ROI, 11.7% of normal transitional zone ROI and 1.6% of normal peripheral zone ROI. The ratios of normal prostate tissue were significantly more elevated (p<0.0001) in the transition zone (0.41 +/- 0.24) than in the peripheral zone (0.22 +/- 0.36). Tumor containing voxels had significantly higher ratios (2.84 +/- 2.74) than normal tissue containing voxels of the transition zone (p<0.0001) and peripheral zone (p<0.0001).

CONCLUSION

Prostate MRS using external surface coils appears routinely feasible at 1.5T, even though it presents some limitations.

MR Imaging of Prostate Cancer: Diffusion Weighted Imaging and (3D) Hydrogen 1 (H) MR Spectroscopy in Comparison with Histology

Purpose. To evaluate retrospectively the impact of diffusion weighted imaging (DWI) and (3D) hydrogen 1 (¹H) MR-spectroscopy (MRS) on the detection of prostatic cancer in comparison to histological examinations. Materials and Methods: 50 patients with suspicion of prostate cancer underwent a MRI examination at a 1.5T scanner. The prostate was divided into sextants. Regions of interest were placed in each sextant to evaluate the apparent diffusion coefficient (ADC)-values. The results of the DWI as well as MRS were compared retrospectively with the findings of the histological examination. Sensitivity and specificity of ADC and metabolic ratio (MET)—both separately and in combination—for identification of tumor tissue was computed for variable discrimination thresholds to evaluate its receiver operator characteristic (ROC). An association between ADC, MET and Gleason score was tested by the non-parametric Spearman ρ-test. Results. The average ADC-value was 1.65 ± 0.32mm²/s × 10⁻³ in normal tissue and 0.96±0.24 mm²/s × 10⁻³ in tumor tissue (mean ± 1 SD). MET was 0.418 ± 0.431 in normal tissue and 2.010 ± 1.649 in tumor tissue. The area under the ROC curve was 0.966 (95%-confidence interval 0.941–0.991) and 0.943 (0.918–0.968) for DWI and MRS, respectively. There was a highly significant negative correlation between ADC-value and the Gleason score in the tumor-positive tissue probes (n = 62, ρ = −0.405, P = .001). MRS did not show a significant correlation with the Gleason score (ρ = 0.117, P = .366). By using both the DWI and MRS, the regression model provided sensitivity and specificity for detection of tumor of 91.9% and 98.3%, respectively. Conclusion. The results of our study showed that both DWI and MRS should be considered as an additional and complementary tool to the T2-weighted MRI for detecting prostate cancer.

Tumor volume and metabolism of prostate cancer determined by proton magnetic resonance spectroscopic imaging at 3T without endorectal coil reveal potential clinical implications in the context of radiation oncology

PURPOSE

To determine whether a relationship exists between the tumor volume (TV) or relative choline content determined using magnetic resonance spectroscopy imaging (MRSI) at 3T and the clinical prognostic parameters for patients with localized prostate cancer (PCa).

METHODS AND MATERIALS

A total of 72 men (mean age, 67.8 ± 6.2 years) were stratified as having low-risk (n = 26), intermediate-risk (n = 24), or high-risk (n = 22) PCa. MRSI was performed at 3T using a phased-array coil. Spectra are expressed as the total choline/citrate, total choline plus creatine/citrate, and total choline plus polyamines plus creatine/citrate ratios. The mean ratio of the most pathologic voxels and the MRSI-based TV were also determined.

RESULTS

The mean values of the total choline/citrate, total choline plus creatine/citrate, and total choline plus polyamine plus creatine/citrate ratios were greater for Stage T2b or greater tumors vs. Stage T2a or less tumors: 7.53 ± 13.60 vs. 2.31 ± 5.65 (p = .018), 8.98 ± 14.58 vs. 2.56 ± 5.70 (p = .016), and 10.32 ± 15.47 vs. 3.55 ± 6.16 (p = .014), respectively. The mean MRSI-based TV for Stage T2b or greater and Stage T2a or less tumors was significantly different (2.23 ± 2.62 cm(3) vs. 1.26 ± 2.06 cm(3), respectively; p = .030). This TV correlated with increased prostate-specific antigen levels (odds ratio, 1.293; p = .012). Patients with high-risk PCa had a larger TV than did the patients with intermediate-risk PCa. A similar result was found for the intermediate-risk group compared with the low-risk group (odds ratio, 1.225; p = .041).

CONCLUSION

Biomarkers expressing the relative choline content and TV were significant parameters for the localization of PCa and could be helpful for determining the prognosis more accurately.

Molecular imaging of cancer: MR spectroscopy and beyond

Proton magnetic resonance spectroscopic imaging is a non-invasive diagnostic tool for the investigation of cancer metabolism. As an adjunct to morphologic and dynamic magnetic resonance imaging, it is routinely used for the staging, assessment of treatment response, and therapy monitoring in brain, breast, and prostate cancer. Recently, its application was extended to other cancerous diseases, such as malignant soft-tissue tumours, gastrointestinal and gynecological cancers, as well as nodal metastasis. In this review, we discuss the current and evolving clinical applications of proton magnetic resonance spectroscopic imaging. In addition, we will briefly discuss other evolving techniques, such as phosphorus magnetic resonance spectroscopic imaging, sodium imaging and diffusion-weighted imaging in cancer assessment.