Tumour volume delineation in prostate cancer assessed by [11C]choline PET/CT: validation with surgical specimens

A Tumor Volume Segmentation Algorithm Based on Radiomics Features in FDG-PET in Lung Cancer Patients, Validated Using Surgical Specimens

BACKGROUND

Although the integration of positron emission tomography into radiation therapy treatment planning has become part of clinical routine, the best method for tumor delineation is still a matter of debate. In this study, therefore, we analyzed a novel, radiomics-feature-based algorithm in combination with histopathological workup for patients with non-small-cell lung cancer.

METHODS

A total of 20 patients with biopsy-proven lung cancer who underwent [18F]fluorodeoxyglucose positron emission/computed tomography (FDG-PET/CT) examination before tumor resection were included. Tumors were segmented in positron emission tomography (PET) data using previously reported algorithms based on three different radiomics features, as well as a threshold-based algorithm. To obtain gold-standard results, lesions were measured after resection. Pathological volumes and maximal diameters were then compared with the results of the segmentation algorithms.

RESULTS

A total of 20 lesions were analyzed. For all algorithms, segmented volumes correlated well with pathological volumes. In general, the threshold-based volumes exhibited a tendency to be smaller than the radiomics-based volumes. For all lesions, conventional threshold-based segmentation produced coefficients of variation which corresponded best with pathologically based volumes; however, for lesions larger than 3 ccm, the algorithm based on Local Entropy performed best, with a significantly better coefficient of variation (p = 0.0002) than the threshold-based algorithm.

CONCLUSIONS

We found that, for small lesions, results obtained using conventional threshold-based segmentation compared well with pathological volumes. For lesions larger than 3 ccm, the novel algorithm based on Local Entropy performed best. These findings confirm the results of our previous phantom studies. This algorithm is therefore worthy of inclusion in future studies for further confirmation and application.

Target Volume Optimization for Localized Prostate Cancer

PURPOSE

To provide a comprehensive review of the means by which to optimize target volume definition for the purposes of treatment planning for patients with intact prostate cancer with a specific emphasis on focal boost volume definition.

METHODS

Here we conduct a narrative review of the available literature summarizing the current state of knowledge on optimizing target volume definition for the treatment of localized prostate cancer.

RESULTS

Historically, the treatment of prostate cancer included a uniform prescription dose administered to the entire prostate with or without coverage of all or part of the seminal vesicles. The development of prostate magnetic resonance imaging (MRI) and positron emission tomography (PET) using prostate-specific radiotracers has ushered in an era in which radiation oncologists are able to localize and focally dose-escalate high-risk volumes in the prostate gland. Recent phase 3 data has demonstrated that incorporating focal dose escalation to high-risk subvolumes of the prostate improves biochemical control without significantly increasing toxicity. Still, several fundamental questions remain regarding the optimal target volume definition and prescription strategy to implement this technique. Given the remaining uncertainty, a knowledge of the pathological correlates of radiographic findings and the anatomic patterns of tumor spread may help inform clinical judgement for the definition of clinical target volumes.

CONCLUSION

Advanced imaging has the ability to improve outcomes for patients with prostate cancer in multiple ways, including by enabling focal dose escalation to high-risk subvolumes. However, many questions remain regarding the optimal target volume definition and prescription strategy to implement this practice, and key knowledge gaps remain. A detailed understanding of the pathological correlates of radiographic findings and the patterns of local tumor spread may help inform clinical judgement for target volume definition given the current state of uncertainty.

A Novel Radiomics-Based Tumor Volume Segmentation Algorithm for Lung Tumors in FDG-PET/CT after 3D Motion Correction—A Technical Feasibility and Stability Study

Positron emission tomography (PET) provides important additional information when applied in radiation therapy treatment planning. However, the optimal way to define tumors in PET images is still undetermined. As radiomics features are gaining more and more importance in PET image interpretation as well, we aimed to use textural features for an optimal differentiation between tumoral tissue and surrounding tissue to segment-target lesions based on three textural parameters found to be suitable in previous analysis (Kurtosis, Local Entropy and Long Zone Emphasis). Intended for use in radiation therapy planning, this algorithm was combined with a previously described motion-correction algorithm and validated in phantom data. In addition, feasibility was shown in five patients. The algorithms provided sufficient results for phantom and patient data. The stability of the results was analyzed in 20 consecutive measurements of phantom data. Results for textural feature-based algorithms were slightly worse than those of the threshold-based reference algorithm (mean standard deviation 1.2%—compared to 4.2% to 8.6%) However, the Entropy-based algorithm came the closest to the real volume of the phantom sphere of 6 ccm with a mean measured volume of 26.5 ccm. The threshold-based algorithm found a mean volume of 25.0 ccm. In conclusion, we showed a novel, radiomics-based tumor segmentation algorithm in FDG-PET with promising results in phantom studies concerning recovered lesion volume and reasonable results in stability in consecutive measurements. Segmentation based on Entropy was the most precise in comparison with sphere volume but showed the worst stability in consecutive measurements. Despite these promising results, further studies with larger patient cohorts and histopathological standards need to be performed for further validation of the presented algorithms and their applicability in clinical routines. In addition, their application in other tumor entities needs to be studied.

Pilot study comparing dominant intraprostatic lesion volume using Ga-68 prostate-specific membrane antigen PET-computed tomography and multiparametric MRI

PURPOSE

The standard imaging used for delineation of dominant intraprostatic lesion (DIL) is multiparametric MRI (mpMRI). The use of biologic imaging such as Ga-68 prostate-specific membrane antigen (PSMA) PET-computed tomography (PET-CT) for this purpose is being explored in view of increased sensitivity of this modality and the associated ease of delineation.

MATERIALS AND METHODS

The primary objective of the study was to compare the autogenerated volumes of the DIL in Ga-68 PSMA PET-CT with the standard volume delineated in mpMRI. Twenty patients with biopsy-proven untreated prostatic adenocarcinoma were included. Multiple percentages of the maximum standardized uptake value (%SUVmax) were used to autogenerate DIL volumes in Ga-68 PSMA PET-CT and these volumes were numerically matched with the consensus DIL volume in mpMRI. PSMA tumor volume (PSMA-TV) and total lesion PSMA (TL-PSMA) were also calculated for each lesion.

RESULTS

Median volume of DIL in mpMRI was 4 cm (interquartile range, IQR = 2.5-7.6 cm). The IQR for interobserver variability was 0.5-2.5 cm. Median SUVmax of the DIL was 14.1 (IQR = 10.2-22.3). Median %SUVmax corresponding to mpMRI volume was 41% of SUVmax (IQR = 34-55%). There was a strong negative correlation between MRI volume and %SUVmax (r = -0.829, P < 0.001). There was a significant correlation between TL-PSMA and prostate-specific antigen (r = 0.609, P = 0.004).

CONCLUSIONS

The median DIL volume was 4 cm and median %SUVmax corresponding to MR volume of DIL was 41%. A strong inverse relationship is found between mpMRI-defined DIL volume and the %SUVmax which generates similar volume in Ga-68 PSMA PET-CT. TL-PSMA could be a quantitative biomarker for tumor load and prognosis.

The Evolving Role of 18F-FDG PET/CT in Diagnosis and Prognosis Prediction in Progressive Prostate Cancer

Positron emission tomography/computed tomography (PET/CT) is widely used in prostate cancer to evaluate the localized tumor burden and detect symptomatic metastatic lesions early. ¹⁸F-FDG is the most used tracer for oncologic imaging, but it has limitations in detecting early-stage prostate cancer. ⁶⁸Ga-PSMA is a new tracer that has high specificity and sensibility in detecting local and metastatic tumors. But with the progression of prostate cancer, the enhancement of glucose metabolism in progressive prostate cancer provides a chance for ¹⁸F-FDG. This review focuses on PET/CT in the detection and prognosis of prostate cancer, summarizing the literature on ¹⁸F-FDG and ⁶⁸Ga-PSMA in prostate cancer and highlighting that ¹⁸F-FDG has advantages in detecting local recurrence, visceral and lymph node metastases compared to ⁶⁸Ga-PSMA in partial progressive prostate cancer and castration-resistant prostate cancer patients. We emphasize ¹⁸F-FDG PET/CT can compensate for the weakness of ⁶⁸Ga-PSMA PET/CT in progressive prostate cancer.

The impact of the co-registration technique and analysis methodology in comparison studies between advanced imaging modalities and whole-mount-histology reference in primary prostate cancer

Comparison studies using histopathology as standard of reference enable a validation of the diagnostic performance of imaging methods. This study analysed (1) the impact of different image-histopathology co-registration pathways, (2) the impact of the applied data analysis method and (3) intraindividually compared multiparametric magnet resonance tomography (mpMRI) and prostate specific membrane antigen positron emission tomography (PSMA-PET) by using the different approaches. Ten patients with primary PCa who underwent mpMRI and [¹⁸F]PSMA-1007 PET/CT followed by prostatectomy were prospectively enrolled. We demonstrate that the choice of the intermediate registration step [(1) via ex-vivo CT or (2) mpMRI] does not significantly affect the performance of the registration framework. Comparison of analysis methods revealed that methods using high spatial resolutions e.g. quadrant-based slice-by-slice analysis are beneficial for a differentiated analysis of performance, compared to methods with a lower resolution (segment-based analysis with 6 or 18 segments and lesions-based analysis). Furthermore, PSMA-PET outperformed mpMRI for intraprostatic PCa detection in terms of sensitivity (median %: 83-85 vs. 60-69, p < 0.04) with similar specificity (median %: 74-93.8 vs. 100) using both registration pathways. To conclude, the choice of an intermediate registration pathway does not significantly affect registration performance, analysis methods with high spatial resolution are preferable and PSMA-PET outperformed mpMRI in terms of sensitivity in our cohort.

Use of Imaging to Optimise Prostate Cancer Tumour Volume Assessment for Focal Therapy Planning

PURPOSE OF REVIEW

Rapid advances in imaging of the prostate have facilitated the development of focal therapy and provided a non-invasive method of estimating tumour volume. Focal therapy relies on an accurate estimate of tumour volume for patient selection and treatment planning so that the optimal energy dose can be delivered to the target area(s) of the prostate while minimising toxicity to surrounding structures. This review provides an overview of different imaging modalities which may be used to optimise tumour volume assessment and critically evaluates the published evidence for each modality.

RECENT FINDINGS

Multi-parametric MRI (mp-MRI) has become the standard tool for patient selection and guiding focal therapy treatment. The current evidence suggests that mp-MRI may underestimate tumour volume, although there is a large variability in results. There remain significant methodological challenges associated with pathological processing and accurate co-registration of histopathological data with mp-MRI. Advances in different ultrasound modalities are showing promise but there has been limited research into tumour volume estimation. The role of PSMA PET/CT is still evolving and further investigation is needed to establish if this is a viable technique for prostate tumour volumetric assessment. mp-MRI provides the necessary tumour volume information required for selecting patients and guiding focal therapy treatment. The potential for underestimation of tumour volume should be taken into account and an additional margin applied to ensure adequate treatment coverage. At present, there are no other viable image-based alternatives although advances in new technologies may refine volume estimations in the future.

Molecular Imaging in Photon Radiotherapy

Nowadays, more than ever before, the treatment of cancer patients requires an interdisciplinary approach more than ever. Radiation therapy (RT) has become an indispensable pillar of cancer treatment early on, offering a local, curative treatment option and symptom control in palliative cases.

Clinical implications of PET/CT in prostate cancer management

Several imaging modalities exist for the investigation of prostate cancer (PCa). From ultrasound to computed tomography (CT) and magnetic resonance imaging (MRI), the role of imaging in detecting lesion foci, staging, and localizing disease after biochemical recurrence (BCR) is expanding. However, many of the conventional imaging modalities are suboptimal, particularly in the detection of metastasis. Positron emission tomography (PET) has recently emerged as a promising tool in PCa management. The ability to develop radiolabeled tracers for functional imaging based on characteristics of PCa cells can potentially provide more insight into management by utilizing key features of those cells, such as metabolic activity, increased proliferation, and receptor expression. 18-flurodeoxyglucose (FDG) is one of the earliest tracers used in PET imaging that takes advantage of increased metabolism of glucose. Its role in PCa has been somewhat limited due to poor resolution and confounders including noise resulting from the proximity of the prostate to the bladder. Choline, a precursor molecule for a major component of the cell membrane, phosphatidylcholine, shows increased uptake in cells with rapid proliferation. When compared to metabolic based imaging techniques with FDG, choline PET/CT was superior. Nevertheless, choline PET/CT was not equivocal to MRI in detection of local disease, but was superior to conventional imaging in localizing metastasis and lymph node metastasis (LNM). Fluciclovine is another novel marker that utilizes the increased proliferation seen in tumor cells. Studies have shown it to be superior to choline PET/CT in PCa management, particularly in patients with BCR. As with choline PET/CT, studies that have assessed the impact of fluciclovine on clinical practice have highlighted the impact of these new tracers on clinical decision making. Most recently, the newest molecular probe targeting prostate specific membrane antigen (PSMA) was developed. It offers higher detection rates compared to choline PET/CT and conventional imaging modalities and has shown promise in LNM and BCR. With the wide range of available PET tracers, this review aims to highlight the role of each in lesion foci detection, primary staging, disease recurrence and explore the potential clinical impact.

Multimodal imaging for radiation therapy planning in patients with primary prostate cancer

Implementation of advanced imaging techniques like multiparametric magnetic resonance imaging (mpMRI) or Positron Emission Tomography (PET) in radiation therapy (RT) planning of patients with primary prostate cancer demands several preconditions: accurate staging of the extraprostatic and intraprostatic tumor mass, robust delineation of the intraprostatic gross tumor volume (GTV) and a reproducible characterization of the prostate cancer's biological properties. In the current review we searched for the currently available imaging techniques and we discussed their ability to fulfill these preconditions. We found that current pretreatment imaging was mainly performed with mpMRI and/or Prostate-specific membrane antigen PET imaging. Both techniques offered an accurate detection of the extraprostatic and intraprostatic tumor burden and had a major impact on RT concepts. However, some studies postulated that mpMRI and PSMA PET had complementary information for intraprostatic GTV detection. Moreover, interobserver differences for intraprostatic tumor delineation based on mpMRI were observed. It is currently unclear whether PET based GTV delineation underlies also interobserver heterogeneity. Further research is warranted to answer whether multimodal imaging is able to visualize biological processes related to prostate cancer pathophysiology and radiation resistance.

Imaging of Prostate Cancer Using 11C-Choline PET/Computed Tomography

This article reviews the role of ¹¹C-choline-PET/computed tomography (CT) in patients with prostate cancer for diagnosis, staging, and restaging the disease in case of biochemical recurrence after primary treatment. The main application of this imaging procedure is restaging of the disease in case of biochemical recurrence. ¹¹C-Choline-PET/CT proved its value for metastases-directed salvage therapies and for monitoring therapy response in castration-resistant patients. Prostate-specific antigen and prostate-specific antigen kinetics values confirmed their correlation with ¹¹C-choline PET/CT sensitivity.¹¹C-CholinePET/CT, despite low sensitivity to stage disease or in case of biochemical failure with low PSA levels, has an important impact on the management of patients with prostate cancer.

[PET-CT and PET-MRI of the prostate : From 18F-FDG to 68Ga-PSMA]

CLINICAL/METHODICAL ISSUE

In the last few years nuclear medical diagnostics have experienced a unprecedented renaissance in the diagnostics of prostate cancer, due to the availability of hybrid imaging with positron emission tomography computed tomography (PET/CT), PET magnetic resonance imaging (PET/MRI) and single photon emission computed tomography (SPECT) CT as well as the development of prostate-specific radiopharmaceuticals.

METHODICAL INNOVATIONS

The use of fluorodeoxyglucose (FDG), which has been successfully implemented for many years in PET diagnostics, is only helpful in dedifferentiated tumors due to the biological characteristics of prostate cancer. New specific radiopharmaceuticals, such as choline-derivatives, which are incorporated into the prostate cancer cell and built into the cell membrane as well as the recently developed highly specific ligands for prostate-specific membrane antigen (PSMA) are revolutionizing prostate cancer imaging and (re-) staging.

PRACTICAL RECOMMENDATIONS

The ⁶⁸ Ga-labeled PSMA ligands for PET-CT and PET-MRI are highly specific tracers for primary diagnostics and detection of metastases of prostate carcinoma. In risk patients, which includes patients with intermediate and high-risk tumors, they have largely replaced choline-based PET-CT, especially in the case of very low PSA values <0.5 ng/ml in the diagnostics of recurrence. The use in the primary diagnostics as PET-MRI, also in combination with multiparametric MRI (mpMRI), is promising with respect to early diagnostics and image fusion-assisted biopsy as well as surgery and irradiation planning.

Biological imaging for individualized therapy in radiation oncology: part II medical and clinical aspects

Positron emission tomography and multiparametric MRI provide crucial information concerning tumor extent and normal tissue anatomy. Moreover, they are able to visualize biological characteristics of the tumor, which can be considered in the radiation treatment planning and monitoring. In this review we discuss the impact of biological imaging positron emission tomography and multiparametric MRI for radiation oncology, based on the data of the literature and on the experience of our own institution in this field.

Evaluation of tumor hypoxia prior to radiotherapy in intermediate-risk prostate cancer using 18F-fluoromisonidazole PET/CT: a pilot study

Purpose

Hypoxia is a major factor in prostate cancer aggressiveness and radioresistance. Predicting which patients might be bad candidates for radiotherapy may help better personalize treatment decisions in intermediate-risk prostate cancer patients. We assessed spatial distribution of ¹⁸F-Misonidazole (FMISO) PET/CT uptake in the prostate prior to radiotherapy treatment.

Materials and Methods

Intermediate-risk prostate cancer patients about to receive high-dose (>74 Gy) radiotherapy to the prostate without hormonal treatment were prospectively recruited between 9/2012 and 10/2014. Prior to radiotherapy, all patients underwent a FMISO PET/CT as well as a MRI and ¹⁸F-choline-PET. ¹⁸F-choline and FMISO-positive volumes were semi-automatically determined using the fuzzy locally adaptive Bayesian (FLAB) method. In FMISO-positive patients, a dynamic analysis of early tumor uptake was performed. Group differences were assessed using the Wilcoxon signed rank test. Parameters were correlated using Spearman rank correlation.

Results

Of 27 patients (median age 76) recruited to the study, 7 and 9 patients were considered positive at 2.5h and 3.5h FMISO PET/CT respectively. Median SUV_max and SUV_max tumor to muscle (T/M) ratio were respectively 3.4 and 3.6 at 2.5h, and 3.2 and 4.4 at 3.5h. The median FMISO-positive volume was 1.1 ml.

Conclusions

This is the first study regarding hypoxia imaging using FMISO in prostate cancer showing that a small FMISO-positive volume was detected in one third of intermediate-risk prostate cancer patients.

The use of PET/CT in prostate cancer

BACKGROUND

Positron emission tomography/computed tomography (PET/CT) has recently emerged as a promising diagnostic imaging platform for prostate cancer. Several radiolabelled tracers have demonstrated efficacy for cancer detection in various clinical settings. In this review, we aim to illustrate the diverse use of PET/CT with different tracers for the detection of prostate cancer.

METHODS

We searched MEDLINE using the terms 'prostate cancer', 'PET', 'PET/CT' and 'PET/MR'). The current review was limited to ¹⁸F-NaF PET/CT, choline-based PET/CT, fluciclovine PET/CT and PSMA-targeted PET/CT, as these modalities have been the most widely adopted.

RESULTS

NaF PET/CT has shown efficacy in detecting bone metastases with high sensitivity, but relatively low specificity. Currently, choline PET/CT has been the most extensively studied modality. Although having superior specificity, choline PET/CT suffers from low sensitivity, especially at low PSA levels. Nevertheless, choline PET/CT was found to significantly improve upon conventional imaging modalities (CIM) in the detection of metastatic lesions at biochemical recurrence (BCR). Newer methods using fluciclovine and PSMA-targeted radiotracers have preliminarily demonstrated great promise in primary and recurrent staging of prostate cancer. However, their superior efficacy awaits confirmation in larger series.

CONCLUSIONS

PET/CT has emerged as a promising staging modality for both primary and recurrent prostate cancer. Newer tracers have increased detection accuracies for small, incipient metastatic foci. The clinical implications of these occult PET/CT detected disease foci require organized evaluation. Efforts should be aimed at defining their natural history as well as responsiveness and impact of metastasis-directed therapy.

Comparison of PET/CT and whole-mount histopathology sections of the human prostate: a new strategy for voxel-wise evaluation

Background

Implementation of PET/CT in diagnosis of primary prostate cancer (PCa) requires a profound knowledge about the tracer, preferably from a quantitative evaluation. Direct visual comparison of PET/CT slices to whole prostate sections is hampered by considerable uncertainties from imperfect coregistration and fundamentally different image modalities. In the current study, we present a novel method for advanced voxel-wise comparison of histopathology from excised prostates to pre-surgical PET. Resected prostates from eight patients who underwent PSMA-PET/CT were scanned (ex vivo CT) and thoroughly pathologically prepared. In vivo and ex vivo CT including histopathology were coregistered with three different methods (manual, semi−/automatic). Spatial overlap after CT-based registration was evaluated with dice similarity (DSC). Furthermore, we constructed 3D cancer distribution models from histopathologic information in various slices. Subsequent smoothing reflected the intrinsically limited spatial resolution of PSMA-PET. The resulting histoPET models were used for quantitative analysis of spatial histopathology-PET pattern agreement focusing on p values and coefficients of determination (R²). We examined additional rigid mutual information (MI) coregistration directly based on PSMA-PET and histoPET.

Results

Mean DSC for the three different methods (ManReg, ScalFactReg, and DefReg) were 0.79 ± 0.06, 0.82 ± 0.04, and 0.90 ± 0.02, respectively, while quantification of PET-histopathology pattern agreement after CT-based registration revealed R² 45.7, 43.2, and 41.3% on average with p < 10⁻⁵. Subsequent PET-based MI coregistration yielded R² 61.3, 55.9, and 55.6%, respectively, while implying anatomically plausible transformations.

Conclusions

Creating 3D histoPET models based on thorough histopathological preparation allowed sophisticated quantitative analyses showing highly significant correlations between histopathology and (PSMA-)PET. We recommend manual CT-based coregistration followed by a PET-based MI algorithm to overcome limitations of purely CT-based coregistrations for meaningful voxel-wise comparisons between PET and histopathology.

Clinical PET Imaging in Prostate Cancer

Prostate cancer is the second most common cancer in men worldwide, with a wide spectrum of biologic behavior ranging from indolent low-risk disease to highly aggressive castration-resistant prostate cancer. Conventional imaging with computed tomography, magnetic resonance imaging, and bone scintigraphy is limited for the detection of nodal disease and distant bone metastases. In addition, advances in the available therapeutic options, both localized and systemic, drive the requirement for precise diagnostic and prognostic tools to refine the individual therapeutic approach at various times in the management of patients with prostate cancer. Positron emission tomography (PET) has a rapidly evolving role in the assessment of prostate cancer, particularly in the scenario of biochemical relapse. Fluorine 18 (¹⁸F) fluorodeoxyglucose, the most widely available PET tracer, has limitations, particularly in indolent prostate cancer. In the past decade, several PET tracers with specific molecular targets have reached the clinical domain. These tracers include ¹⁸F-sodium fluoride, which is a bone-specific biomarker of osteoblastic activity; ¹⁸F-choline and carbon 11-choline, which are directed at cell membrane metabolism; gallium 68-prostate-specific membrane antigen ligands; and, more recently, an amino acid analog, ¹⁸F-fluciclovine (anti-1-amino-3-¹⁸F-fluorocyclobutane-1-carboxylic acid; also known as FACBC), which is also directed at cell membrane turnover. The mechanisms of actions of the clinically available PET tracers are reviewed, as well as their role in the imaging of prostate cancer with reference to relevant guidelines and the technical and imaging pearls and pitfalls of these tracers. ^©RSNA, 2017.

PET Tracer 18F-Fluciclovine Can Detect Histologically Proven Bone Metastatic Lesions: A Preclinical Study in Rat Osteolytic and Osteoblastic Bone Metastasis Models

¹⁸F-Fluciclovine (trans-1-amino-3-¹⁸F-fluorocyclobutanecarboxylic acid; anti-¹⁸F-FACBC) is a positron emission tomography (PET) tracer for diagnosing cancers (e.g., prostate and breast cancer). The most frequent metastatic organ of these cancers is bone. Fluciclovine-PET can visualize bony lesions in clinical practice; however, such lesions have not been described histologically. Methods: We investigated the potential of ¹⁴C-fluciclovine in aiding the visualization of osteolytic and osteoblastic bone metastases (with histological analyses), compared with ³H-2-deoxy-2-fluoro-D-glucose (³H-FDG), ³H-choline chloride (³H-choline), and ^99mTc-hydroxymethylene diphosphonate (^99mTc-HMDP) by using triple-tracer autoradiography in rat breast cancer osteolytic (on day 12 ± 1 postinjection of MRMT-1) and prostate cancer osteoblastic (on day 20 ± 3 postinjection of AT6.1) metastatic models. Results: The distribution patterns of ¹⁴C-fluciclovine, ³H-FDG, and ³H-choline, but not ^99mTc-HMDP, were similar in both models, and the lesions where these tracers accumulated were, histologically, typical osteolytic and osteoblastic lesions. ^99mTc-HMDP accumulated mostly in osteoblastic lesions. ¹⁴C-fluciclovine could visualize the osteolytic lesions as early as day 6 postinjection of MRMT-1. However, differential distributions in ¹⁴C-fluciclovine and ³H-FDG existed, based on histological differences: low ¹⁴C-fluciclovine and high ³H-FDG accumulation in osteolytic lesions with inflammation. In the osteoblastic metastatic model, visualization of osteoblastic lesions with ¹⁴C-fluciclovine was not clear, yet clearer than with ³H-FDG. Although half of the osteoblastic lesions with ¹⁴C-fluciclovine accumulation showed negligible ³H-choline accumulation in comparison, they were histologically similar to lesions with marked ¹⁴C-fluciclovine and ³H-choline accumulation. Conclusion: These results suggest that fluciclovine-PET can visualize true osteolytic and osteoblastic bone metastatic lesions.

Evaluation of intensity modulated radiation therapy dose painting for localized prostate cancer using 68Ga-HBED-CC PSMA-PET/CT: A planning study based on histopathology reference

PURPOSE

To demonstrate the feasibility and to evaluate the tumour control probability (TCP) and normal tissue complication probability (NTCP) of IMRT dose painting using ⁶⁸Ga-HBED-CC PSMA PET/CT for target delineation in prostate cancer (PCa).

METHODS AND MATERIALS

10 patients had PSMA PET/CT scans prior to prostatectomy. GTV-PET was generated on the basis of an intraprostatic SUVmax of 30%. Two IMRT plans were generated for each patient: Plan⁷⁷ which consisted of whole-prostate IMRT to 77Gy, and Plan⁹⁵ which consisted of whole-prostate IMRT to 77Gy and a simultaneous integrated boost to the GTV-PET up to 95Gy (35 fractions). The feasibility of these plans was judged by their ability to adhere to the FLAME trial protocol. TCP-histo/-PET were calculated on co-registered histology (GTV-histo) and GTV-PET, respectively. NTCPs for rectum and bladder were calculated.

RESULTS

All plans reached prescription doses whilst adhering to dose constraints. In Plan⁷⁷ and Plan⁹⁵ mean doses in GTV-histo were 75.8±0.3Gy and 96.9±1Gy, respectively. Average TCP-histo values for Plan⁷⁷ and Plan⁹⁵ were 70% (range: 15-97%), and 96% (range: 78-100%, p<0.0001). Average TCP-PET values for Plan⁷⁷ and Plan⁹⁵ were 55% (range: 27-82%), and 100% (range: 99-100%, p<0.0001). There was no significant difference between TCP-PET and TCP-histo in Plan⁹⁵ (p=0.25). There were no significant differences in rectal (p=0.563) and bladder (p=0.3) NTCPs.

CONCLUSIONS

IMRT dose painting using PSMA PET/CT was technically feasible and resulted in significantly higher TCPs without higher NTCPs.

Imaging of Prostate Cancer Using 18F-Choline PET/Computed Tomography

¹⁸F-fluorocholine (FCH) PET/computed tomography (CT) is a valuable imaging modality in prostate cancer disease. Probably, its main role is restaging of patients with biochemical recurrence after radical prostatectomy or external beam radiotherapy. ¹⁸F-FCH PET/CT is strengthening its position in the initial staging, biopsy target definition, radiotherapy planning, and therapy monitoring. Gleason score and prostate-specific antigen value, doubling time, and velocity can influence positivity of ¹⁸F-FCH PET/CT. The influence of androgen deprivation therapy on choline uptake is not precisely clarified. Collaboration between nuclear medicine physicians, radiologists, urologists, oncologists, and radiotherapists is crucial to help patients with prostate cancer disease.

Imaging of Prostate Cancer Using 11C-Choline PET/Computed Tomography

This article reviews the role of ¹¹C-choline-PET/computed tomography (CT) in patients with prostate cancer for diagnosis, staging, and restaging the disease in case of biochemical recurrence after primary treatment. The main application of this imaging procedure is restaging of the disease in case of biochemical recurrence. ¹¹C-Choline-PET/CT proved its value for metastases-directed salvage therapies and for monitoring therapy response in castration-resistant patients. Prostate-specific antigen and prostate-specific antigen kinetics values confirmed their correlation with ¹¹C-choline PET/CT sensitivity.¹¹C-CholinePET/CT, despite low sensitivity to stage disease or in case of biochemical failure with low PSA levels, has an important impact on the management of patients with prostate cancer.

(68)Ga-HBED-CC-PSMA PET/CT Versus Histopathology in Primary Localized Prostate Cancer: A Voxel-Wise Comparison

Purpose: We performed a voxel-wise comparison of ⁶⁸Ga-HBED-CC-PSMA PET/CT with prostate histopathology to evaluate the performance of ⁶⁸Ga-HBED-CC-PSMA for the detection and delineation of primary prostate cancer (PCa).

Methodology: Nine patients with histopathological proven primary PCa underwent ⁶⁸Ga-HBED-CC-PSMA PET/CT followed by radical prostatectomy. Resected prostates were scanned by ex-vivo CT in a special localizer and histopathologically prepared. Histopathological information was matched to ex-vivo CT. PCa volume (PCa-histo) and non-PCa tissue in the prostate (NPCa-histo) were processed to obtain a PCa-model, which was adjusted to PET-resolution (histo-PET). Each histo-PET was coregistered to in-vivo PSMA-PET/CT data.

Results: Analysis of spatial overlap between histo-PET and PSMA PET revealed highly significant correlations (p < 10^-5) in nine patients and moderate to high coefficients of determination (R²) from 42 to 82 % with an average of 60 ± 14 % in eight patients (in one patient R² = 7 %). Mean SUVmean in PCa-histo and NPCa-histo was 5.6 ± 6.1 and 3.3 ± 2.5 (p = 0.012). Voxel-wise receiver-operating characteristic (ROC) analyses comparing the prediction by PSMA-PET with the non-smoothed tumor distribution from histopathology yielded an average area under the curve of 0.83 ± 0.12. Absolute and relative SUV (normalized to SUVmax) thresholds for achieving at least 90 % sensitivity were 3.19 ± 3.35 and 0.28 ± 0.09, respectively.

Conclusions: Voxel-wise analyses revealed good correlations of ⁶⁸Ga-HBED-CC-PSMA PET/CT and histopathology in eight out of nine patients. Thus, PSMA-PET allows a reliable detection and delineation of PCa as basis for PET-guided focal therapies.

Integration of (68)Ga-PSMA-PET imaging in planning of primary definitive radiotherapy in prostate cancer: a retrospective study

Background

Prostate cancer (PC) is one of the most commonly treated cancer entities with radiation therapy (RT). Risk group-adapted treatment and avoidance of unnecessary toxicities relies primarily on accurate tumor staging. Thus, the introduction of prostate-specific membrane antigen (PSMA) in diagnosis and treatment of PC is a highly interesting development in radiation oncology of urologic tumors. The present work is to evaluate the integration of ⁶⁸Ga-PSMA-PET imaging into standard radiation planning of primary definitive treatment of PC and to determine the impact of PSMA imaging on tumor staging.

Methods

The data of 15 patients treated for PC between August 2013 and April 2015 were evaluated. Treatment planning included ⁶⁸Ga-PSMA-PET imaging. We analyzed whether the use of PSMA-imaging led to a change of the TNM stage and if it influenced the RT treatment approach or the target volume, due to changes in the gross tumor volume (GTV) or clinical target volume (CTV), in the final treatment plan.

Results

In 53.3 % of the analyzed patients a change occurred in the TNM stage based on ⁶⁸Ga-PSMA-PET examination. The RT concept changed in 33.3 % of all patients, leading to relevant changes in the planning target volume. Among these, an additional irradiation of the pelvic lymph drainage due to tracer uptake in lymph nodes was performed in 25 %. Furthermore, boost volumes of PET-positive lymph nodes were added in 80 % of these cases. A down staging due to the ⁶⁸Ga-PSMA-PET examination occurred in 13.3 % of all cases.

Conclusions

The integration of ⁶⁸Ga-PSMA-PET-imaging into the RT treatment planning process can be useful for detailed target volume planning. The performance of a ⁶⁸Ga-PSMA-PET frequently leads to changes in the TNM stage, altering the RT treatment regimen and the target volume. A prospective trial is underway to evaluate the impact of ⁶⁸Ga-PSMA-PET based treatment planning on outcome.

[Positron-emission tomography in urooncology]

The use of positron emission tomography (PET) is an established method for the diagnosis of urological malignancies. Several tracers are currently available to obtain metabolic information or directly detect molecular targets. While (18)F-FDG-PET is recognized in current guidelines for the staging of seminoma, PET is not used in clinical routine in renal malignancies due to the lack of specific tracers. Despite initial promising results in bladder cancer, no relevant additional diagnostic value with PET using (18)F-FDG or choline-based tracers could be obtained in most patients and therefore should be used with caution or only within clinical trials. In prostate cancer, however, after development of new tracers that, for example, target prostate-specific membrane antigen (PSMA), a paradigm shift in imaging can be recognized. Here, (68)Ga-PSMA-PET might be included in the future as part of standard imaging work-up.

Tumour delineation in oesophageal cancer - A prospective study of delineation in PET and CT with and without endoscopically placed clip markers

PURPOSE

The objective was to analyse the value of F-18-fluorodesoxyglucose (FDG)-positron emission tomography/computed tomography (PET/CT) for delineation of the Gross Tumour Volumes (GTVs) in primary radiotherapy of oesophageal cancer.

METHOD

20 consecutive and prospective patients (13 men, 7 women) underwent FDG-PET/CT for initial staging and radiation treatment planning. After endoscopy-guided clipping of the tumour another CT study was acquired. The CT and the FDG-PET/CT were registered with a rigid and a non-rigid registration algorithm to compare the overlap between GTV contours defined with the following methods: manual GTV definition in (1) the CT image of the FDG-PET/CT, (2) the PET image of the FDG-PET/CT, (3) the CT study based on endoscopic clips (CT clip), and (4) in the PET-data using different semi-automatic PET segmentation algorithms including a gradient-based algorithm. The absolute tumour volumes, tumour length in cranio-caudal direction, as well as the overlap with the reference volume (CT-clip) were compared for all lesions and separately for proximal/distal tumours.

RESULTS

In 6 of the patients, FDG-PET/CT discovered previously unknown tumour locations, which resulted in either altered target volumes (n=3) or altered intent of treatment from curative to palliative (n=3) by upstaging to stage IV. For tumour segmentation a large variability between all algorithms was found. For the absolute tumour volumes with CT-clip as reference, no single PET-based segmentation algorithm performed better compared to using the manual CT delineation alone. The best correlation was found between the CT-clip and the gradient based segmentation algorithm (PET-edge, R(2)=0.84) as well as the manual CT-delineation (CT-manual R(2)=0.89). Non-rigid registration between CT and image FDG-PET/CT did not decrease variability between segmentation methods compared to rigid registration statistically significant. For the analysis of tumour length no homogeneous correlation was found.

CONCLUSION

Whereas FDG-PET was highly relevant for staging purposes, CT imaging with clipping of the tumour extension remains the gold standard for GTV delineation.

Oesophageal cancer: assessment of tumour response to chemoradiotherapy with tridimensional CT

PURPOSE

To investigate whether changes in tumour volume were predictive of histopathological response to neoadjuvant therapy for oesophageal cancer.

MATERIALS AND METHODS

Thirty-five consecutive patients with locally advanced oesophageal cancer were treated with chemoradiotherapy and surgery in responders from July 2007 to July 2009. Tumour volume (TV) was calculated using innovative tumour volume estimation software which analysed computed tomography (CT) data. Tumour diameter and area were also evaluated. Variations in tumour measurements following neoadjuvant treatment were compared with the histopathological data.

RESULTS

Median baseline tumour diameter, area and volume were 3.51 cm (range 1.67-6.61), 7.51 cm(2) (range 1.79-21.0) and 33.80 cm(3) (range 3.36-101.6), respectively. Differences in TV between the pre- and post-treatment values were significantly correlated with the pathological stage (τ = 0.357, p = 0.004) and the tumour regression grade index (τ = 0.368, p = 0.005). According to the receiver operating characteristic analysis, TV measurements following treatment had moderate predictive values for the pathological T stage (area under the curve, AUC = 0.742, sensitivity = 55.56 %, specificity = 92.86 %, p = 0.005).Comparison of pathological and radiological volume showed a good precision (Pearson rho 0.77).

CONCLUSIONS

Changes in TV calculated on CT scans have a limited role in predicting pathological response to neoadjuvant treatment in oesophageal cancer patients. New imaging techniques based on metabolic imaging may provide better results.

11C-Choline PET/pathology image coregistration in primary localized prostate cancer

PURPOSE

The aim of this study was to develop a methodology for the comparison of pathology specimens after prostatectomy (post-S) with PET images obtained before surgery (pre-S). This method was used to evaluate the merit of (11)C-choline PET/CT for delineation of gross tumour volume (GTV) in prostate cancer (PC).

METHODS

In 28 PC patients, (11)C-choline PET/CT was performed before surgery. PET/CT data were coregistered with the pathology specimens. GTV on PET images (GTV-PET) was outlined automatically and corrected manually. Tumour volume in the prostate (TVP) was delineated manually on the pathology specimens. Based on the coregistered PET/pathology images, the following parameters were assessed: SUVmax and SUVmean in the tumoral and nontumoral prostate (NP), GTV-PET (millilitres) and TVP (millilitres).

RESULTS

PET/pathology image coregistration was satisfactory. Mean SUVmax in the TVP was lower than in the NP: 5.0 and 5.5, respectively (p = 0.093). Considering the entire prostate, SUVmax was located in the TVP in two patients, in the TVP and NP in 12 patients and exclusively in NP in 14 patients. Partial overlap the TVP and GTV-PET was seen in 71% of patients, and complete overlap in 4%.

CONCLUSION

PET/pathology image coregistration can be used for evaluation of different imaging modalities. (11)C-Choline PET failed to distinguish tumour from nontumour tissue.

Potential of hybrid ¹⁸F-fluorocholine PET/MRI for prostate cancer imaging

PURPOSE

To report the first results of hybrid (18)F-fluorocholine PET/MRI imaging for the detection of prostate cancer.

METHODS

This analysis included 26 consecutive patients scheduled for prostate PET/MRI before radical prostatectomy. The examinations were performed on a hybrid whole-body PET/MRI scanner. The MR acquisitions which included T2-weighted, diffusion-weighted and dynamic contrast-enhanced sequences were followed during the same session by whole-body PET scans. Parametric maps were constructed to measure normalized T2-weighted intensity (nT2), apparent diffusion coefficient (ADC), volume transfer constant (K (trans)), extravascular extracellular volume fraction (v e) and standardized uptake values (SUV). With pathology as the gold standard, ROC curves were calculated using logistic regression for each parameter and for the best combination with and without PET to obtain a MR model versus a PETMR model.

RESULTS

Of the 26 patients initially selected, 3 were excluded due to absence of an endorectal coil (2 patients) or prosthesis artefacts (1 patient). In the whole prostate, the area under the curve (AUC) for SUVmax, ADC, nT2, K (trans) and v e were 0.762, 0.756, 0.685, 0.611 and 0.529 with a best threshold at 3.044 for SUVmax and 1.075 × 10(-3) mm(2)/s for ADC. The anatomical distinction between the transition zone and the peripheral zone showed the potential of the adjunctive use of PET. In the peripheral zone, the AUC of 0.893 for the PETMR model was significantly greater (p = 0.0402) than the AUC of 0.84 for the MR model only. In the whole prostate, no relevant correlation was observed between ADC and SUVmax. The SUVmax was not affected by the Gleason score.

CONCLUSION

The performance of a hybrid whole-body (18)F-fluorocholine PET/MRI scan in the same session combined with a prostatic MR examination did not interfere with the diagnostic accuracy of the MR sequences. The registration of the PET data and the T2 anatomical MR sequence data allowed precise localization of hypermetabolic foci in the prostate. While in the transition zone the adenomatous hyperplasia interfered with cancer detection by PET, the quantitative analysis tool performed well for cancer detection in the peripheral zone.

[Molecular multimodal hybrid imaging in prostate and bladder cancer]

Since the introduction of combined radiologic-nuclear imaging procedures like PET/CT and PET/MRI, new and promising diagnostic tools in bladder and prostate cancer imaging are available to physicians. Although PET-based hybrid imaging in bladder cancer is currently utilized only in selected cases, an increase in PET imaging can be observed in prostate cancer due to the development of cancer-specific PET tracers. Especially novel ligands of prostate-specific membrane antigen (PSMA) exhibit great potential to effectively influence future staging of prostate cancer. However, before recommendations for implication in routine staging can be given, evaluation in the context of prospective multicenter clinical trials are mandatory.

Correlation of metabolic tumor volume and 11C-choline uptake with the pathology of prostate cancer: evaluation by use of simultaneously recorded MR and PET images

PURPOSE

This study was conducted to assess the relationship between (11)C-choline uptake and pathologic findings obtained by combined use of magnetic resonance (MR) and positron emission tomography (PET) imaging of patients with prostate cancer.

MATERIALS AND METHODS

We retrospectively evaluated 69 patients with prostate cancer who underwent (11)C-choline PET-CT and magnetic resonance imaging before radical prostatectomy. Combined MR-PET images were acquired to obtain precise anatomic information. The maximum standardized uptake value (SUVmax) and metabolic tumor volume (MTV) were compared with pathologic findings from resected specimens as the reference standard.

RESULTS

The mean and standard deviation of tumor SUVmax and MTV were 3.9 ± 1.8 and 12.9 ± 16.4, respectively. Tumors with high MTV (≧8.2) were more likely to be admixed with prostatic intraepithelial neoplasia (PIN) (p < 0.0001) or hyperplasia (p < 0.0001) in the background than those without these findings. Multiple regression analysis also revealed that the presence of hyperplasia (OR; 4.25, 95% CI 1.25-14.4, p = 0.02) and PIN (OR; 9.22, 95% CI 2.60-32.7, p = 0.001) were associated with tumors with high MTV.

CONCLUSION

We have demonstrated, by pathologic evaluation of patients with prostate cancer, that (11)C-choline uptake volume is greater for prostate cancer admixed with PIN and hyperplasia than that without.

3 Tesla multiparametric MRI for GTV-definition of Dominant Intraprostatic Lesions in patients with Prostate Cancer--an interobserver variability study

PURPOSE

To evaluate the interobserver variability of gross tumor volume (GTV) - delineation of Dominant Intraprostatic Lesions (DIPL) in patients with prostate cancer using published MRI criteria for multiparametric MRI at 3 Tesla by 6 different observers.

MATERIAL AND METHODS

90 GTV-datasets based on 15 multiparametric MRI sequences (T2w, diffusion weighted (DWI) and dynamic contrast enhanced (DCE)) of 5 patients with prostate cancer were generated for GTV-delineation of DIPL by 6 observers. The reference GTV-dataset was contoured by a radiologist with expertise in diagnostic imaging of prostate cancer using MRI. Subsequent GTV-delineation was performed by 5 radiation oncologists who received teaching of MRI-features of primary prostate cancer before starting contouring session. GTV-datasets were contoured using Oncentra Masterplan® and iplan® Net. For purposes of comparison GTV-datasets were imported to the Artiview® platform (Aquilab®), GTV-values and the similarity indices or Kappa indices (KI) were calculated with the postulation that a KI > 0.7 indicates excellent, a KI > 0.6 to < 0.7 substantial and KI > 0.5 to < 0.6 moderate agreement. Additionally all observers rated difficulties of contouring for each MRI-sequence using a 3 point rating scale (1 = easy to delineate, 2 = minor difficulties, 3 = major difficulties).

RESULTS

GTV contouring using T2w (KI-T2w = 0.61) and DCE images (KI-DCE = 0.63) resulted in substantial agreement. GTV contouring using DWI images resulted in moderate agreement (KI-DWI = 0.51). KI-T2w and KI-DCE was significantly higher than KI-DWI (p = 0.01 and p = 0.003). Degree of difficulty in contouring GTV was significantly lower using T2w and DCE compared to DWI-sequences (both p < 0.0001). Analysis of delineation differences revealed inadequate comparison of functional (DWI, DCE) to anatomical sequences (T2w) and lack of awareness of non-specific imaging findings as a source of erroneous delineation.

CONCLUSIONS

Using T2w and DCE sequences at 3 Tesla for GTV-definition of DIPL in prostate cancer patients by radiation oncologists with knowledge of MRI features results in substantial agreement compared to an experienced MRI-radiologist, but for radiotherapy purposes higher KI are desirable, strengthen the need for expert surveillance. DWI sequence for GTV delineation was considered as difficult in application.

Role of choline PET/CT in guiding target volume delineation for irradiation of prostate cancer

Choline PET/CT has shown limitations for the detection of primary prostate cancer and nodal metastatic disease, mainly due to limited sensitivity and specificity. Conversely in the restaging of prostate cancer recurrence, choline PET/CT is a promising imaging modality for the detection of local regional and nodal recurrence with an impact on therapy management. This review highlights current literature on choline PET/CT for radiation treatment planning in primary and recurrent prostate cancer. Due to limited sensitivity and specificity in differentiating between benign and malignant prostatic tissues in primary prostate cancer, there is little enthusiasm for target volume delineation based on choline PET/CT. Irradiation planning for the treatment of single lymph node metastases on the basis of choline PET/CT is controversial due to its limited lesion-based sensitivity in primary nodal staging. In high-risk prostate cancer, choline PET/CT might diagnose lymph node metastases, which potentially can be included in the conventional irradiation field. Prior to radiation treatment of recurrent prostate cancer, choline PET/CT may prove useful for patient stratification by excluding distant disease which would require systemic therapy. In patients with local recurrence, choline PET/CT can be used to delineate local sites of recurrence within the prostatic resection bed allowing a boost to PET-positive sites. In patients with lymph node metastases outside the prostatic fossa and regional metastatic lymph nodes, choline PET/CT might influence radiation treatment planning by enabling extension of the target volume to lymphatic drainage sites with or without a boost to PET-positive lymph nodes. Further clinical randomized trials are required to assess treatment outcomes following choline-based biological radiation treatment planning in comparison with conventional radiation treatment planning.