Respiratory gated [18F]FDG PET/CT for target volume delineation in stereotactic radiation treatment of liver metastases

Evaluation of Multisource Adaptive MRI Fusion for Gross Tumor Volume Delineation of Hepatocellular Carcinoma

Purpose

Tumor delineation plays a critical role in radiotherapy for hepatocellular carcinoma (HCC) patients. The incorporation of MRI might improve the ability to correctly identify tumor boundaries and delineation consistency. In this study, we evaluated a novel Multisource Adaptive MRI Fusion (MAMF) method in HCC patients for tumor delineation.

Methods

Ten patients with HCC were included in this study retrospectively. Contrast-enhanced T1-weighted MRI at portal-venous phase (T1W_PP), contrast-enhanced T1-weighted MRI at 19-min delayed phase (T1W_DP), T2-weighted (T2W), and diffusion-weighted MRI (DWI) were acquired on a 3T MRI scanner and imported to in-house-developed MAMF software to generate synthetic MR fusion images. The original multi-contrast MR image sets were registered to planning CT by deformable image registration (DIR) using MIM. Four observers independently delineated gross tumor volumes (GTVs) on the planning CT, four original MR image sets, and the fused MRI for all patients. Tumor contrast-to-noise ratio (CNR) and Dice similarity coefficient (DSC) of the GTVs between each observer and a reference observer were measured on the six image sets. Inter-observer and inter-patient mean, SD, and coefficient of variation (CV) of the DSC were evaluated.

Results

Fused MRI showed the highest tumor CNR compared to planning CT and original MR sets in the ten patients. The mean ± SD tumor CNR was 0.72 ± 0.73, 3.66 ± 2.96, 4.13 ± 3.98, 4.10 ± 3.17, 5.25 ± 2.44, and 9.82 ± 4.19 for CT, T1W_PP, T2W, DWI, T1W_DP, and fused MRI, respectively. Fused MRI has the minimum inter-observer and inter-patient variations as compared to original MR sets and planning CT sets. GTV delineation inter-observer mean DSC across the ten patients was 0.81 ± 0.09, 0.85 ± 0.08, 0.88 ± 0.04, 0.89 ± 0.08, 0.90 ± 0.04, and 0.95 ± 0.02 for planning CT, T1W_PP, T2W, DWI, T1W_DP, and fused MRI, respectively. The patient mean inter-observer CV of DSC was 3.3%, 3.2%, 1.7%, 2.6%, 1.5%, and 0.9% for planning CT, T1W_PP, T2W, DWI, T1W_DP, and fused MRI, respectively.

Conclusion

The results demonstrated that the fused MRI generated using the MAMF method can enhance tumor CNR and improve inter-observer consistency of GTV delineation in HCC as compared to planning CT and four commonly used MR image sets (T1W_PP, T1W_DP, T2W, and DWI). The MAMF method holds great promise in MRI applications in HCC radiotherapy treatment planning.

Respiratory 4D-Gating F-18 FDG PET/CT Scan for Liver Malignancies: Feasibility in Liver Cancer Patient and Tumor Quantitative Analysis

Purpose

To evaluate the potential clinical role and effectiveness of respiratory 4D-gating F-18 FDG PET/CT scan for liver malignancies, relative to routine (3D) F-18 FDG PET/CT scan.

Materials and Methods

This study presented a prospective clinical study of 16 patients who received F-18 FDG PET/CT scan for known or suspected malignant liver lesions. Ethics approvals were obtained from the ethics committees of the Hong Kong Baptist Hospital and The Hong Kong Polytechnic University. Liver lesions were compared between the gated and ungated image sets, in terms of 1) volume measurement of PET image, 2) accuracy of maximum standardized uptake value (SUV_max), mean standardized uptake value (SUV_mean), and 3) accuracy of total lesion glycoses (TLG). Statistical analysis was performed by using a two-tailed paired Student t-test and Pearson correlation test.

Results

The study population consisted of 16 patients (9 males and 7 females; mean age of 65) with a total number of 89 lesions. The SUV_max and SUV_mean measurement of the gated PET images was more accurate than that of the ungated PET images, compared to the static reference images. An average of 21.48% (p < 0.001) reduction of the tumor volume was also observed. The SUV_max and SUV_mean of the gated PET images were improved by 19.81% (p < 0.001) and 25.53% (p < 0.001), compared to the ungated PET images.

Conclusions

We have demonstrated the feasibility of implementing 4D PET/CT scan for liver malignancies in a prospective clinical study. The 4D PET/CT scan for liver malignancies could improve the quality of PET image by improving the SUV accuracy of the lesions and reducing image blurring. The improved accuracy in the classification and identification of liver tumors with 4D PET image would potentially lead to its increased utilization in target delineation of GTV, ITV, and PTV for liver radiotherapy treatment planning in the future.

Respiratory Gating and the Performance of PET/CT in Pulmonary Lesions

Background

Motion artifacts related to the patient’s breathing can be the cause of underestimation of the lesion uptake and can lead to missing of small lung lesions. The respiratory gating (RG) technology has demonstrated a significant increase in image quality.

Objective

The aim of this paper was to evaluate the advantages of RG technique on PET/CT performance in lung lesions. The impact of 4D-PET/CT on diagnosis (metabolic characterization), staging and re-staging lung cancer was also assessed, including its application for radiotherapy planning. Finally, new technologies for respiratory motion management were also discussed.

Methods

A comprehensive electronic search of the literature was performed by using Medline database (PubMed) searching “PET/CT”, “gated” and “lung”. Original articles, review articles, and editorials published in the last 10 years were selected, included and critically reviewed in order to select relevant articles.

Results

Many papers compared Standardized Uptake Value (SUV) in gated and ungated PET studies showing an increase in SUV of gated images, particularly for the small lesions located in medium and lower lung. In addition, other features as Metabolic Tumor Volume (MTV), Total Lesion Glycolysis (TLG) and textural-features presented differences when obtained from gated and ungated PET acquisitions. Besides the increase in quantification, gating techniques can determine an increase in the diagnostic accuracy of PET/CT. Gated PET/CT was evaluated for lung cancer staging, therapy response assessment and for radiation therapy planning.

Conclusion

New technologies able to track the motion of organs lesion directly from raw PET data, can reduce or definitively solve problems (i.e.: extended acquisition time, radiation exposure) currently limiting the use of gated PET/CT in clinical routine.

Evaluation of Hybrid PET/MRI for Gross Tumor Volume (GTV) Delineation in Colorectal Cancer Liver Metastases Radiotherapy

Purpose

Hybrid PET/MRI has been increasingly incorporated into the practice of radiation oncologists since it contains both anatomical and biological data and may bring about personalized radiation plans for each patient. The objective of this study was to evaluate the feasibility of GTV delineation from hybrid PET/MRI compared with that from current-practice MRI during radiotherapy planning in patients with colorectal liver metastases.

Patients and Methods

Twenty-four patients (thirty lesions) with colorectal liver metastases were prospectively enrolled in this study. Three physicians delineated the target volume with the most popular delineating methods-the visual method. First of all, differences among the three observers were assessed. The difference and correlation of GTV values obtained by MRI, PET, and hybrid PET/MRI were subjected to statistical analysis afterwards. Finally, the dice similarity coefficient (DSC) was calculated to assess the spatial overlap. Based on the value of DSC, we also evaluate the correlation between DSC and tumor size. GTV-MRI was set as a reference.

Results

There was no significant difference among observers in GTV-MRI (F=0.118, p=0.889), GTV-PET (F=0.070, p=0.933) and GTV-PET/MRI (F=0.40, p=0.961). 83.33% of GTV-PET/MRI and 63.33% of GTV-PET were larger than the reference GTV-MRI. Statistical analysis revealed that GTV-PET/MRI (p<0.001) and GTV-PET (p<0.05) diverged statistically significantly from GTV-MRI. GTV-PET (r=0.992, p<0.001) and GTV-PET/MRI (r=0.997, p<0.001) were significantly related to GTV-MRI. The average DSC value between GTV-MRI and GTV-PET was 0.51 (range 0-0.90) and that between GTV-MRI and GTV-PET/MRI was 0.72 (range 0.42-0.90). There was a positive correlation between the DSC and GTV-MRI (r=0.851, p<0.05).

Conclusion

With the database used, there is good agreement among observers. Hybrid PET/MRI in colorectal liver metastases radiotherapy may affect the GTV delineation. Moreover, the overlap degree between GTV-MRI and GTV-PET/MRI is higher and increases with volume.

Impact of positron emission tomography with computed tomography for image-guided radiotherapy

Therapeutic effectiveness in radiotherapy is partly related to correct staging of the disease and then precise therapeutic targeting. Positron emission tomography (PET) allows the stage of many cancers to be determined and therefore is essential before deciding on radiation treatment. The definition of the therapeutic target is essential to obtain correct tumour control and limit side effects. The part of adaptive radiotherapy remains to be defined, but PET by its functional nature makes it possible to define the prognosis of many cancers and to consider radiotherapy adapted to the initial response allowing an increase over the entire metabolic volume, or targeted at a subvolume at risk per dose painting, or with a decrease in the dose in case of good response at interim assessment.

4D-CT-based motion correction of PET images using 3D iterative deconvolution

Objectives

Positron emission tomography acquisition takes several minutes representing an image averaged over multiple breathing cycles. Therefore, in areas influenced by respiratory movement, PET-positive lesions occur larger, but less intensive than they actually are, resulting in false quantitative assessment. We developed a motion-correction algorithm based on 4D-CT without the need to adapt PET-acquisition.

Methods

The algorithm is based on a full 3D iterative Richardson-Lucy-Deconvolution using a point-spread-function constructed using the motion information obtained from the 4D-CT. In a motion phantom study (3 different hot spheres in background activity), optimal parameters for the algorithm in terms of number of iterations and start image were estimated. Finally, the correction method was applied to 3 patient data sets. In phantom and patient data sets lesions were delineated and compared between motion corrected and uncorrected images for activity uptake and volume.

Results

Phantom studies showed best results for motion correction after 6 deconvolution steps or higher. In phantom studies, lesion volume improved up to 23% for the largest, 43% for the medium and 49% for the smallest sphere due to the correction algorithm. In patient data the correction resulted in a significant reduction of the tumor volume up to 33.3 % and an increase of the maximum and mean uptake of the lesion up to 62.1 and 19.8 % respectively.

Conclusion

In conclusion, the proposed motion correction method showed good results in phantom data and a promising reduction of detected lesion volume and a consequently increasing activity uptake in three patients with lung lesions.

Role of textural heterogeneity parameters in patient selection for 177Lu-PSMA therapy via response prediction

Purpose

Prostate cancer is most common tumor in men causing significant patient mortality and morbidity. In newer diagnostic/therapeutic agents PSMA linked ones are specifically important. Analysis of textural heterogeneity parameters is associated with determination of innately aggressive and therapy resistant cell lines thus emphasizing their importance in therapy planning. The objective of current study was to assess predictive ability of tumor textural heterogeneity parameters from baseline ⁶⁸Ga-PSMA PET prior to ¹⁷⁷Lu-PSMA therapy.

Results

Entropy showed a negative correlation (r_s = −0.327, p = 0.006, AUC = 0.695) and homogeneity showed a positive correlation (r_s = 0.315, p = 0.008, AUC = 0.683) with change in pre and post therapy PSA levels.

Conclusions

Study showed potential for response prediction through baseline PET scan using textural features. It suggested that increase in heterogeneity of PSMA expression seems to be associated with an increased response to PSMA radionuclide therapy.

Materials and Methods

Retrospective analysis of 70 patients was performed. All patients had metastatic prostate cancer and were planned to undergo ¹⁷⁷Lu-PSMA therapy. Pre-therapeutic ⁶⁸Ga- PSMA PET scans were used for analysis. 3D volumes (VOIs) of 3 lesions each in bones and lymph nodes were manually delineated in static PET images. Five PET based textural heterogeneity parameters (COV, entropy, homogeneity, contrast, size variation) were determined. Results obtained were then compared with clinical parameters including pre and post therapy PSA, alkaline phosphate, bone specific alkaline phosphate levels and ECOG criteria. Spearman correlation was used to determine statistical dependence among variables. ROC analysis was performed to estimate the optimal cutoff value and AUC.

PET imaging in adaptive radiotherapy of gastrointestinal tumors

INTRODUCTION

Radiotherapy is a cornerstone in the multimodality treatment of several gastrointestinal (GI) tumors. Positron-emission tomography (PET) has an established role in the diagnosis, response assessment and (re-)staging of these tumors. Nevertheless, the value of PET in adaptive radiotherapy remains unclear. This review focuses on the role of PET in adaptive radiotherapy, i.e. during the treatment course and in the delineation process.

EVIDENCE ACQUISITION

The MEDLINE database was searched for the terms ("Radiotherapy"[Mesh] AND "Positron-Emission Tomography"[Mesh] AND one of the site-specific keywords, yielding a total of 1710 articles. After abstract selection, 27 papers were identified for esophageal neoplasms, 1 for gastric neoplasms, 9 for pancreatic neoplasms, 6 for liver neoplasms, 1 for biliary tract neoplasms, none for colonic neoplasms, 15 for rectal neoplasms and 12 for anus neoplasms.

EVIDENCE SYNTHESIS

The use of PET for truly adaptive radiotherapy during treatment for GI tumors has barely been investigated, in contrast to the potential of the PET-defined metabolic tumor volume for optimization of the target volume. The optimized target definition seems useful for treatment individualization such as focal boosting strategies in esophageal, pancreatic and anorectal cancer. Nevertheless, for all GI tumors, further investigation is needed.

CONCLUSIONS

In general, too little data are available to conclude on the role of PET imaging during radiotherapy for ART strategies in GI cancer. On the other hand, based on the available evidence, the use of biological imaging for target volume adaptation seems promising and could pave the road towards individualized treatment strategies.

[Stereotactic body radiotherapy for liver tumors: State of the art]

Thanks to the improvement in radiotherapy physics, biology, computing and imaging, patients presenting with liver tumors can be efficiently treated by radiation. Radiotherapy has been included in liver tumors treatment guidelines at all disease stages. Liver stereotactic radiotherapy has to be preferred to standard fractionated radiotherapy whenever possible, as potentially more efficient because of higher biological equivalent dose. Liver stereotactic radiotherapy planning and delivery require extensive experience and optimal treatment quality at every step, thus limiting its availability to specialized centres. Multicentre studies are difficult to develop due to a large technical heterogeneity. Respiratory management, image guidance and immobilization are considerations as important as machine type. The use of multimodal planning imaging is compulsory to achieve expected contouring quality. Treatment efficacy is difficult to assess following liver stereotactic radiotherapy, but local control is high and toxicity unusual. As a consequence, liver stereotactic radiotherapy is part of multimodal and multidisciplinary management of liver tumors.

The utility of positron emission tomography/computed tomography in target delineation for stereotactic body radiotherapy for liver metastasis from primary gastric cancer: an illustrative case report and literature review

The liver is a common site for metastatic disease for many cancers. Radiation therapy is one means of treatment for liver metastases, especially for patients unable to undergo surgery or ineligible for systemic chemotherapy. In particular, stereotactic body radiotherapy (SBRT) has become an important option in the treatment of metastatic disease in the liver. SBRT delivers ablative doses of radiation in relatively few fractions. As such, precise and clear imaging plays an important role in maximizing disease control while minimizing normal tissue toxicity. We present a case that highlights the importance of using multiple imaging modalities for target volume delineation in stereotactic radiation treatment of liver metastases.

SBRT planning for liver metastases: A focus on immobilization, motion management and planning imaging techniques

AIM

To evaluate the different techniques used for liver metastases Stereotactic Body Radiation Therapy (SBRT) planning. We especially focused on immobilization devices, motion management and imaging used for contouring.

BACKGROUND

Although some guidelines exist, there is no consensus regarding the minimal requirements for liver SBRT treatments.

MATERIALS AND METHODS

We reviewed the main liver metastases SBRT publications and guidelines; and compared the techniques used for immobilization, motion management, margins and imaging.

RESULTS

There is a wide variety of techniques used for immobilization, motion management and planning imaging.

CONCLUSIONS

We provide a subjective critical analysis of minimal requirements and ideal technique for liver SBRT planning.

Assessment of tumor heterogeneity in treatment-naïve adrenocortical cancer patients using (18)F-FDG positron emission tomography

As an orphan malignancy, only limited treatment options are available in adrenocortical carcinoma (ACC). Non-invasive risk assessment has not been described but may be of value to stratify patients for treatment. We aimed to evaluate the potential value of intra-individual tumor heterogeneity as assessed by (18)F-fluorodeoxyglucose ((18)F-FDG) positron emission tomography/computed tomography (PET/CT) for outcome prediction in treatment-naïve ACC patients. Ten patients with primary diagnosis of ACC were included in this study. Prior to any treatment initiation, baseline (18)F-FDG PET scans were performed. Tumor staging was performed using the European Network for the Study of Adrenal Tumors (ENS@T). Intratumoral heterogeneity of the primary tumor was assessed by manual segmentation using conventional PET parameters (standardized uptake values and tumor-to-liver ratios) and textural features. The impact of tumoral heterogeneity based on pre-therapeutic (18)F-FDG PET to predict progression-free (PFS) and overall survival (OS) was evaluated by receiver operating characteristic analysis. On average, tumor recurrence or progression was detected after median of 561 days (range 71-1434 days) after the pre-therapeutic baseline PET scan. 50 % of the patients died of ACC within the follow-up period (mean 983 ± 404 days). Pre-therapeutic tumor volume was associated with PFS (r = -0.67, p = 0.05) and Ki67 index with OS (r = -0.66, p = 0.04). ENS@T tumor stage was the only parameter to correlate with both PFS and OS (r = -0.82, p = 0.001, and r = -0.72, p = 0.01, respectively). In the subgroup of patients without distant metastases (ENS@T stages II and III), age and pre-therapeutic tumor volume correlated significantly with PFS (r = 0.96, p = 0.01 and r = -0.93, p = 0.02, respectively) and OS (r = 0.95, p = 0.02 and r = -0.90, p = 0.04, respectively). None of the investigated classic or textural PET parameters predicted PFS or OS. In this pilot study in treatment-naïve ACC patients, conventional (18)F-FDG PET-derived parameters and textural tumor heterogeneity features were not suitable to identify high-risk patients.

Application of stereotactic body radiation therapy to cancer liver metastasis

As an accurate external beam irradiation method, stereotactic body radiotherapy (SBRT) has been increasingly used to deliver high dose in less fractions. The liver is one of the most common organs for cancer metastasis. Recently, there have been several trials applying SBRT to cancer liver metastasis and have proved to be effective and safe with local control (LC) rates ranging from 70% to 100% within one or two years and 2-year overall survival (OS) rates ranging from 30% to 38%. Many published studies indicate that SBRT for cancer liver metastasis results in good outcomes without severe toxicities. However, the validated contribution of SBRT to an improved progression-free survival is still missing and more randomized trials should be conducted.

Comparative evaluation of respiratory-gated and ungated FDG-PET for target volume definition in radiotherapy treatment planning for pancreatic cancer

OBJECTIVE

The purpose of this study was to evaluate the usefulness of respiratory-gated positron emission tomography (4D-PET) in pancreatic cancer radiotherapy treatment planning (RTTP).

MATERIALS AND METHODS

Fourteen patients with 18F-fluorodeoxyglucose (FDG)-avid pancreatic tumours were evaluated between December 2013 and March 2015. Two sets of volumes were contoured for the pancreatic tumour of each patient. The biological target volume in three-dimensional RTTP (BTV3D) was contoured using conventional respiratory un-gated PET. The BTV3D was then expanded using population-based margins to generate a series of internal target volume 3D (ITV3D) values. The ITV 4D (ITV4D) was contoured using 4D-PET. Each of the five phases of 4D-PET was used for 4D contouring, and the ITV4D was constructed by summing the volumes defined on the five individual 4D-PET images. The relative volumes and normalized volumetric overlap were computed between ITV3D and ITV4D.

RESULTS

On average, the FDG-avid tumour volumes were 1.6 (range: 0.8-2.3) fold greater in the ITV4D than in the BTV3D. On average, the ITV3D values were 2.0 (range: 1.1-3.4) fold larger than the corresponding ITV4D values.

CONCLUSION

The ITV generated from 4D-PET can be used to improve the accuracy or reduce normal tissue irradiation compared with conventional un-gated PET-based ITV.

4D-Listmode-PET-CT and 4D-CT for optimizing PTV margins in gastric lymphoma : Determination of intra- and interfractional gastric motion

PURPOSE

New imaging protocols for radiotherapy in localized gastric lymphoma were evaluated to optimize planning target volume (PTV) margin and determine intra-/interfractional variation of the stomach.

METHODS

Imaging of 6 patients was explored prospectively. Intensity-modulated radiotherapy (IMRT) planning was based on 4D/3D imaging of computed tomography (CT) and positron-emission tomography (PET)-CT. Static and motion gross tumor volume (sGTV and mGTV, respectively) were distinguished by defining GTV (empty stomach), clinical target volume (CTV = GTV + 5 mm margin), PTV (GTV + 10/15/20/25 mm margins)  plus paraaortic lymph nodes and proximal duodenum. Overlap of 4D-Listmode-PET-based mCTV with 3D-CT-based PTV (increasing margins) and V95/D95 of mCTV were evaluated. Gastric shifts were determined using online cone-beam CT. Dose contribution to organs at risk was assessed.

RESULTS

The 4D data demonstrate considerable intra-/interfractional variation of the stomach, especially along the vertical axis. Conventional 3D-CT planning utilizing advancing PTV margins of 10/15/20/25 mm resulted in rising dose coverage of mCTV (4D-Listmode-PET-Summation-CT) and rising D95 and V95 of mCTV. A PTV margin of 15 mm was adequate in 3 of 6 patients, a PTV margin of 20 mm was adequate in 4 of 6 patients, and a PTV margin of 25 mm was adequate in 5 of 6 patients.

CONCLUSION

IMRT planning based on 4D-PET-CT/4D-CT together with online cone-beam CT is advisable to individualize the PTV margin and optimize target coverage in gastric lymphoma.

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.

The importance of surrounding tissues and window settings for contouring of moving targets

AIM

The aim of the study was to assess the importance of surrounding tissues for the delineation of moving targets in tissue-specific phantoms and to find optimal settings for lung, soft tissue, and liver tumors.

MATERIALS AND METHODS

Tumor movement was simulated by a water-filled table tennis ball (target volume, TV). Three phantoms were created: corkboards to simulate lung tissue (lung phantom, LunPh), animal fat as fatty soft tissue (fatty tissue phantom, FatPh), and water enhanced with contrast medium as the liver tissue (liver phantom, LivPh). Slow planning three-dimensional compute tomography images (3D-CTs) were acquired with and without phantom movements. One-dimensional tumor movement (1D), three-dimensional tumor movement (3D), as well as a real patient's tumor trajectories were simulated. The TV was contoured using two lung window settings, two soft-tissue window settings, and one liver window setting. The volumes were compared to mathematical calculated values.

RESULTS

TVs were underestimated in all phantoms due to movement. The use of soft-tissue windows in the LivPh led to a significant underestimation of the TV (70.8% of calculated TV). When common window settings [LunPh + 200 HU/-1,000 HU (upper window/lower window threshold); FatPh: + 240 HU/-120 HU; LivPh: + 175 HU/+ 50 HU] were used, the contoured TVs were: LivPh, 84.0%; LunPh, 93.2%, and FatPh, 92.8%. The lower window threshold had a significant impact on the size of the delineated TV, whereas changes of the upper threshold led only to small differences.

CONCLUSION

The decisive factor for window settings is the lower window threshold (for adequate TV delineation in the lung and fatty-soft tissue it should be lower than density values of surrounding tissue). The use of a liver window should be considered.

The association of tumor-to-background ratios and SUVmax deviations related to point spread function and time-of-flight F18-FDG-PET/CT reconstruction in colorectal liver metastases

Background

The maximum standardized uptake value (SUVmax) is a common clinical parameter for quantification in F18-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT), but it is influenced by image reconstruction. The aim of this study was to analyze the association of SUVmax deviations related to point spread function (PSF) and time-of-flight (TOF) reconstruction with tumor-to-background ratios (TBR) in colorectal liver metastases (CRLM).

Methods

Fifteen patients (f, 6; m, 9; median age, 59 years; range, 32 to 72 years) with 28 liver metastases were included retrospectively. FDG-PET/CT imaging (median activity, 237 MBq; range, 231 to 252 MBq; median uptake, 61 min; range, 55 to 67 min) was performed on a Siemens Biograph mCT 64 followed by image reconstruction using 3D-ordered subset expectation maximization (3D-OSEM) or 3D-OSEM with PSF modeling - both with and without TOF information. Differences in SUVmax were analyzed using the Friedman test and Wilcoxon test for paired non-parametric data. The correlation of inter-method differences with the lesions’ TBR was studied using Spearman’s rank correlation coefficient (rho). Differences between lesions with low (<4.8) and high (>4.8) TBR were analyzed using the Mann-Whitney U test (TBR measured with 3D-OSEM; binarized by its median).

Results

There was a significant correlation of the lesions’ TBR with relative SUVmax differences related to PSF (PSF + TOF vs. 3D-OSEM + TOF, rho = 0.61; PSF vs. 3D-OSEM, rho = 0.52) or TOF (PSF + TOF vs. PSF, rho = −0.58; 3D-OSEM + TOF vs. 3D-OSEM, rho = −0.61). Accordingly, PSF algorithms only showed higher SUVmax than non-PSF algorithms in lesions with a high TBR (median differences at low/high TBR, +2.6%/+9.1% [PSF + TOF vs. 3D-OSEM + TOF]; +0.7%/+6.4% [PSF vs. 3D-OSEM]). TOF integration also led to higher SUVmax but mainly at low TBR (low/high TBR, +10.4%/+1.8% [PSF + TOF vs. PSF]; +8.6%/−0.1% [3D-OSEM + TOF vs. 3D-OSEM]).

Conclusions

Both PSF and TOF reconstruction resulted in a substantial alteration of SUVmax in CRLM. TOF provided the highest SUVmax increase in low-contrast lesions while - vice versa - PSF showed the most relevant increase in high-contrast lesions. Thus, one should be aware that quantitative analyses of lesions with varying TBR, e.g., in radiotherapy or follow-up studies, may be mainly affected by either PSF or TOF reconstruction, respectively.

Prognostic value of positron emission tomography-assessed tumor heterogeneity in patients with thyroid cancer undergoing treatment with radiopeptide therapy

INTRODUCTION

Peptide receptor radionuclide therapy (PRRT) is a treatment option for both iodine-refractory differentiated and advanced medullary thyroid cancer (TC). It requires over-expression of somatostatin receptor subtype II (SSTR) that can be non-invasively assessed by positron emission tomography (PET). Assessment of tumor heterogeneity is increasingly used as a tool for prognostication prediction. We investigated the potential of SSTR-PET to assess intraindividual tumor heterogeneity and thereby treatment response prior to PRRT.

METHODS

12 patients with progressive radioiodine-refractory differentiated (1 papillary, 1 oxyphilic, 2 oncocytic, 4 follicular) or medullary (n=4) TC were enrolled. SSTR-PET was performed at baseline. Conventional PET parameters and heterogeneity parameters were analyzed regarding their potential to predict progression-free (PFS, mean, 221 days) and overall survival (OS, mean, 450 days). Parameters of a subgroup of lesions (n=23) were also correlated with morphological response according to modified RECIST criteria.

RESULTS

In patient-based analysis, all conventional parameters failed to predict PFS. Several textural parameters showed a significant capability to assess PFS. Thereby, "Grey level non uniformity" had the highest area under the curve (AUC, 0.93) in Receiver operating characteristics analysis followed by "Contrast" (AUC, 0.89). In lesion-based analysis, only "Entropy" revealed potential to evaluate disease progression. OS could not be assessed by any parameter investigated.

CONCLUSIONS

Tumor heterogeneity seems to be a predictor of response to PRRT in patients with iodine-refractory differentiated/advanced medullary thyroid cancer and outperforms conventional PET parameters like standardized uptake value. In a "theranostic" approach, assessment of textural parameters may help in selecting patients who might benefit from PRRT.

Integrating respiratory-gated PET-based target volume delineation in liver SBRT planning, a pilot study

Background

To assess the feasibility and benefit of integrating four-dimensional (4D) Positron Emission Tomography (PET) – computed tomography (CT) for liver stereotactic body radiation therapy (SBRT) planning.

Methods

8 patients with 14 metastases were accrued in the study. They all underwent a non-gated PET and a 4D PET centered on the liver. The same CT scan was used for attenuation correction, registration, and considered the planning CT for SBRT planning. Six PET phases were reconstructed for each 4D PET. By applying an individualized threshold to the 4D PET, a Biological Internal Target Volume (BITV) was generated for each lesion. A gated Planning Target Volume (PTVg) was created by adding 3 mm to account for set-up margins. This volume was compared to a manual Planning Target Volume (PTV) delineated with the help of a semi-automatic Biological Target Volume (BTV) obtained from the non-gated exam. A 5 mm radial and a 10 mm craniocaudal margins were applied to account for tumor motion and set-up margins to create the PTV.

Results

One undiagnosed liver metastasis was discovered thanks to the 4D PET. The semi-automatic BTV were significantly smaller than the BITV (p = 0.0031). However, after applying adapted margins, 4D PET allowed a statistically significant decrease in the PTVg as compared to the PTV (p = 0.0052).

Conclusions

In comparison to non-gated PET, 4D PET may better define the respiratory movements of liver targets and improve SBRT planning for liver metastases. Furthermore, non respiratory-gated PET exams can both misdiagnose liver metastases and underestimate the real internal target volumes.

Influence of experience and qualification on PET-based target volume delineation. When there is no expert--ask your colleague

BACKGROUND AND PURPOSE

The integration of positron emission tomography (PET) information for target volume delineation in radiation treatment planning is routine in many centers. In contrast to automatic contouring, research on visual-manual delineation is scarce. The present study investigates the dependency of manual delineation on experience and qualification.

PATIENTS AND METHODS

A total of 44 international interdisciplinary observers each defined a [(18)F]fluorodeoxyglucose (FDG)-PET based gross tumor volume (GTV) using the same PET/CT scan from a patient with lung cancer. The observers were "experts" (E; n = 3), "experienced interdisciplinary pairs" (EP; 9 teams of radiation oncologist (RO) + nuclear medicine physician (NP)), "single field specialists" (SFS; n = 13), and "students" (S; n = 10). Five automatic delineation methods (AM) were also included. Volume sizes and concordance indices within the groups (pCI) and relative to the experts (eCI) were calculated.

RESULTS

E (pCI = 0.67) and EP (pCI = 0.53) showed a significantly higher agreement within the groups as compared to SFS (pCI = 0.43, p = 0.03, and p = 0.006). In relation to the experts, EP (eCI = 0.55) showed better concordance compared to SFS (eCI = 0.49) or S (eCI = 0.47). The intermethod variability of the AM (pCI = 0.44) was similar to that of SFS and S, showing poorer agreement with the experts (eCI = 0.35).

CONCLUSION

The results suggest that interdisciplinary cooperation could be beneficial for consistent contouring. Joint delineation by a radiation oncologist and a nuclear medicine physician showed remarkable agreement and better concordance with the experts compared to other specialists. The relevant intermethod variability of the automatic algorithms underlines the need for further standardization and optimization in this field.

Single-dose radiosurgical treatment for hepatic metastases--therapeutic outcome of 138 treated lesions from a single institution

BACKGROUND

Local ablative therapies such as stereotactically guided single-dose radiotherapy or helical intensity-modulated radiotherapy (tomotherapy) with high single-doses are successfully applied in many centers in patients with liver metastasis not suitable for surgical resection. This study presents results from more than 10 years of clinical experience and evaluates long-term outcome and efficacy of this therapeutic approach.

PATIENTS AND METHODS

From 1997 to 2009 a total of 138 intrahepatic tumors of 90 patients were irradiated with single doses of 17 to 30 Gy (median dose 24 Gy). Median age of the patients was 64 years (range 31-89 years). Most frequent underlying tumor histologies were colorectal adenocarcinoma (70 lesions) and breast cancer (27 lesions). In 35 treatment sessions multiple targets were simultaneously irradiated (up to four lesions at once). Local progression-free (PFS) and overall survival (OS) after treatment were investigated using uni- and multiple survival regression models.

RESULTS

Median overall survival of all patients was 24.3 months. Local PFS was 87%, 70% and 59% after 6, 12 and 18 months, respectively. Median time to local progression was 25.5 months. Patients with a single lesion and no further metastases at time of RT had a favorable median PFS of 43.1 months according to the Kaplan-Meier estimator. The type of tumor showed a statistical significant influence on local PFS, with a better prognosis for breast cancer histology than for colorectal carcinoma in uni- and multiple regression analysis (p = 0.05). Multiple regression analysis revealed no influence of planning target volume (PTV), patient age and radiation dose on local PFS. Treatment was well tolerated with no severe adverse events.

CONCLUSION

This study confirms safety of SBRT in liver lesions, with 6- and 12 months local control of 87% and 70%. The dataset represents the clinical situation in a large oncology setting, with many competing treatment options and heterogeneous patient characteristics.

Radiotherapy with volumetric modulated arc therapy for hepatocellular carcinoma patients ineligible for surgery or ablative treatments

PURPOSE

The aim of this article is to report the dosimetric and clinical findings in the treatment of primary hepatocellular carcinoma (HCC) with volumetric modulated arc therapy (VMAT, RapidArc).

METHODS AND MATERIALS

A total of 138 patients were investigated. Dose prescription ranged from 45-66 Gy. Most patients (88.4 %) presented AJCC stage III or IV and 83 % were N0-M0. All were classified as Barcelona Clinic Liver Cancer (BCLC) stage A-C. All patients were treated using 10 MV photons with single or multiple, coplanar or non-coplanar arcs, and cone-down technique in case of early response of tumors.

RESULTS

The patients' median age was 66 years (range 27-87 years), 83 % were treated with 60 Gy (12 % at 45 Gy, 6 % at 66 Gy), 62 % with cone-down, 98 % with multiple arcs. The mean initial planning target volume (PTV) was 777 ± 632 cm(3); the mean final PTV (after the cone-down) was 583 ± 548 cm(3). High target coverage was achieved. The final PTV was V98% > 98 %. Kidneys received on average 5 and 8 Gy (left and right), while the maximum dose to the spinal cord was 22 Gy; mean doses to esophagus and stomach were 23 Gy and 15 Gy, respectively. The average volume of healthy liver receiving more than 30 Gy was 294 ± 145 cm(3). Overall survival at 12 months was 45 %; median survival was 10.3 months (95 % confidence interval 7.2-13.3 months). Actuarial local control at 6 months was 95 % and 93.7 % at 12 months. The median follow-up was 9 months and a maximum of 28 months.

CONCLUSION

This study showed from the dosimetric point of view the feasibility and technical appropriateness of RapidArc for the treatment of HCC. Clinical results were positive and might suggest, with appropriate care, to consider RapidArc as an additional therapeutic opportunity for these patients.

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

PURPOSE

PET has been proven to be helpful in the delineation of gross tumour volume (GTV) for external radiation therapy in several tumour entities. The aim of this study was to determine if [(11)C]choline PET could be used to localize the carcinomatous tissue within the prostate in order to specifically target this area for example with high-precision radiation therapy.

METHODS

Included in this prospective study were 20 patients with histological proven prostate carcinoma who underwent [(11)C]choline PET/CT before radical prostatectomy. After surgical resection, specimens were fixed and cut into 5-mm step sections. In each section the area of the carcinoma was delineated manually by an experienced pathologist and digitalized, and the histopathological tumour volume was calculated. Shrinkage due to resection and fixation was corrected using in-vivo and ex-vivo CT data of the prostate. Histopathological tumour location and size were compared with the choline PET data. Different segmentation algorithms were applied to the PET data to segment the intraprostatic lesion volume.

RESULTS

A total of 28 carcinomatous lesions were identified on histopathology. Only 13 (46 %) of these lesions had corresponding focal choline uptake. In the remaining lesions, no PET uptake (2 lesions) or diffuse uptake not corresponding to the area of the carcinoma (13 lesions) was found. In the patients with corresponding PET lesions, no suitable SUV threshold (neither absolute nor relative) was found for GTV segmentation to fit the volume to the histological tumour volume.

CONCLUSION

The choline uptake pattern corresponded to the histological localization of prostate cancer in fewer than 50 % of lesions. Even when corresponding visual choline uptake was found, this uptake was highly variable between patients. Therefore SUV thresholding with standard algorithms did not lead to satisfying results with respect to defining tumour tissue in the prostate.

Motion Artifacts in Oncological and Cardiac PET Imaging

Image quality in PET examinations is influenced by several factors. Patient motion during PET data acquisition is a substantial problem that potentially leads to smearing artifacts, resulting in the loss of diagnostic accuracy both in visual and quantitative image analyses. In hybrid imaging, coregistration of functional (PET) and morphologic (CT or MR imaging) data can be hampered by patient movement between the acquisitions, resulting in additional sources of error. This article describes the artifacts due to patient movement.