Impact of FDG PET/CT on Delineation of the Gross Tumor Volume for Radiation Planning in Non–Small-Cell Lung Cancer

Benefits of Using a Spatially-Variant Penalty Strength With Anatomical Priors in PET Reconstruction

In this study, we explore the use of a spatially-variant penalty strength in penalized image reconstruction using anatomical priors to reduce the dependence of lesion contrast on surrounding activity and lesion location. This work builds on a previous method to make the local perturbation response (LPR) approximately spatially invariant. While the dependence of lesion contrast on the local properties introduced by the anatomical penalty is intentional, the method aims to reduce the influence from surroundings lying along the lines of response (LORs) but not in the penalty neighborhood structure. The method is evaluated using simulated data, assuming that the anatomical information is absent or well-aligned with the corresponding activity images. Since the parallel level sets (PLS) penalty is convex and has shown promising results in the literature, it is chosen as the representative anatomical penalty and incorporated into the previously proposed preconditioned algorithm (L-BFGS-B-PC) for achieving good image quality and fast convergence rate. A 2D disc phantom with a feature at the center and a 3D XCAT thorax phantom with lesions inserted in different slices are used to study how surrounding activity and lesion location affect the visual appearance and quantitative consistency. A bias and noise analysis is also performed with the 2D disc phantom. The consistency of the algorithm convergence rate with respect to different data noise and background levels is also investigated using the XCAT phantom. Finally, an example of reconstruction for a patient dataset with inserted pseudo lesions is used as a demonstration in a clinical context. We show that applying the spatially-variant penalization with PLS can reduce the dependence of the lesion contrast on the surrounding activity and lesion location. It does not affect the bias and noise trade-off curves for matched local resolution. Moreover, when using the proposed penalization, significant improvement in algorithm convergence rate and convergence consistency is observed.

An investigative expansion of a competing risk model for first failure site in locally advanced non-small cell lung cancer

Introduction: We hypothesized that gross tumor volume (GTV) of primary tumor (GTV_T) and nodal volumes (GTV_N) were predictors of first failure site in non-small cell lung cancer (NSCLC). We aimed at also comparing the prognostic model's complexity to its ability to generate absolute risk predictions with emphasis on variables available at the time of diagnosis. Materials and methods: Three hundred and forty-two patients treated with definitive chemoradiotherapy (CRT) for adenocarcinoma (AC) or squamous cell carcinoma (SCC) in 2009-2017 were analyzed. Clinical data, standardized uptake values on FDG-PET/CT, GTV_T and GTV_N were analyzed using multivariate competing risk models. Results: One hundred and thirty-seven patients had SCC. As first site of failure 49 had locoregional failure (LRF), 40 had distant metastasis (DM) and 24 died with no evidence of disease (NED). In 205 patients with AC, 34 had LRF, 118 had DM as first failure site and 17 died with NED. Performance status predicted LRF (p = .02) and UICC stage risk of DM (p = .05 for stage 3, p < .001 for stage 4). Adding histopathology changed predictions with much reduced risk of LRF in AC compared to SCC (HR = 0.5, 95% CI: (0.3-0.75), p = .001). Conversely, AC had a higher rate of DM than SCC (HR = 2.1, 95% CI: (1.5-3.0], p < .001). Addition of FDG metrics and tumor/nodal volume data predicted DM risk (p = .001), but with smaller impact on absolute risk compared to histopathology. Separation of GTV in nodal and tumor lesions did not improve risk predictions. Conclusions: We quantified the effect of adding volumetric and quantitative imaging to competing risk models of first failure site, but did not find tumor volume components to be important. Histopathology remains the simplest and most important factor in prognosticating failure patterns in NSCLC.

Current Methods to Define Metabolic Tumor Volume in Positron Emission Tomography: Which One is Better?

Numerous methods to segment tumors using ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG PET) have been introduced. Metabolic tumor volume (MTV) refers to the metabolically active volume of the tumor segmented using FDG PET, and has been shown to be useful in predicting patient outcome and in assessing treatment response. Also, tumor segmentation using FDG PET has useful applications in radiotherapy treatment planning. Despite extensive research on MTV showing promising results, MTV is not used in standard clinical practice yet, mainly because there is no consensus on the optimal method to segment tumors in FDG PET images. In this review, we discuss currently available methods to measure MTV using FDG PET, and assess the advantages and disadvantages of the methods.

Fiducial markers coupled with 3D PET/CT offer more accurate radiation treatment delivery for locally advanced esophageal cancer

BACKGROUND AND AIMS

 The role of three-dimensional positron emission tomography/computed tomography (3 D PET/CT) in esophageal tumors that move with respiration and have potential for significant mucosal inflammation is unclear. The aim of this study was to determine the correlation between gross tumor volumes derived from 3 D PET/CT and endoscopically placed fiducial markers.

METHODS

 This was a retrospective, IRB approved analysis of 40 patients with esophageal cancer with fiducials implanted and PET/CT. The centroid of each fiducial was identified on PET/CT images. Distance between tumor volume and fiducials was measured using axial slices. Image features were extracted and tested for pathologic response predictability.

RESULTS

 The median adaptively calculated threshold value of the standardized uptake value (SUV) to define the metabolic tumor volume (MTV) border was 2.50, which corresponded to a median 23 % of the maximum SUV. The median distance between the inferior fiducial centroid and MTV was - 0.60 cm (- 3.9 to 2.7 cm). The median distance between the superior fiducial centroid and MTV was 1.25 cm (- 4.2 to 6.9 cm). There was no correlation between MTV-to-fiducial distances greater than 2 cm and the gastroenterologist who performed the fiducial implantation. Eccentricity demonstrated statistically significant correlations with pathologic response.

CONCLUSIONS

 There was a stronger correlation between inferior fiducial location and MTV border compared to the superior extent. The etiology of the discordance superiorly is unclear, potentially representing benign secondary esophagitis, presence of malignant nodes, inflammation caused by technical aspects of the fiducial placement itself, or potential submucosal disease. Given the concordance inferiorly and the ability to more precisely set up the patient with daily image guidance matching to fiducials, it may be possible to minimize the planning tumor volume (PTV) margin in select patients, thereby, limiting dose to normal structures.

Late-Course Adaptive Adjustment Based on Metabolic Tumor Volume Changes during Radiotherapy May Reduce Radiation Toxicity in Patients with Non-Small Cell Lung Cancer

To reduce the high risk of radiation toxicity and enhance the quality of life of patients with non-small cell lung cancer (NSCLC), we quantified the metabolic tumor volumes (MTVs) from baseline to the late-course of radiotherapy (RT) by fluorodeoxyglucose positron emission tomography computerized tomography (FDG PET-CT) and discussed the potential benefit of late-course adaptive plans rather than original plans by dose volume histogram (DVH) comparisons. Seventeen patients with stage II-III NSCLC who were treated with definitive conventionally fractionated RT were eligible for this prospective study. FDG PET-CT scans were acquired within 1 week before RT (pre-RT) and at approximately two-thirds of the total dose during-RT (approximately 40 Gy). MTVs were taken as gross tumor volumes (GTVs) that included the primary tumor and any involved hilar or mediastinal lymph nodes. An original plan based on the baseline MTVs and adaptive plans based on observations during-RT MTVs were generated for each patient. The DVHs for lung, heart, esophagus and spinal cord were compared between the original plans and composite plans at 66 Gy. At the time of approximately 40 Gy during-RT, MTVs were significantly reduced in patients with NSCLC (pre-RT 136.2±82.3 ml vs. during-RT 64.7±68.0 ml, p = 0.001). The composite plan of the original plan at 40 Gy plus the adaptive plan at 26 Gy resulted in better DVHs for all the organs at risk that were evaluated compared to the original plan at 66 Gy (p<0.05), including V₅, V₁₀, V₁₅, V₂₀, V₂₅, V₃₀ and the mean dose of total lung, V₁₀, V₂₀, V₃₀, V₄₀, V₅₀, V₆₀ and the mean dose of heart, V₃₅, V₄₀, V₅₀, V_55, V₆₀, the maximum dose and mean dose of the esophagus, and the maximum dose of the spinal-cord. PET-MTVs were reduced significantly at the time of approximately 40 Gy during-RT. Late course adaptive radiotherapy may be an effective way to reduce the dose volume to the organs at risk, thus reducing radiation toxicity in patients with NSCLC.

[Role of functional imaging in the definition of target volumes for lung cancer radiotherapy]

Functional imaging with positron emission tomography (PET) is interesting to optimize lung radiotherapy planning, and probably to deliver a heterogeneous dose or adapt the radiation dose during treatment. Only fluorodeoxyglucose (FDG) PET-computed tomography (CT) is validated for staging lung cancer and planning radiotherapy. The optimal segmentation methods remain to be defined as well as the interest of "dose painting" from pre-treatment PET (metabolism: FDG) or hypoxia (fluoromisonidazole: FMISO) and the interest of replanning based on pertherapeutic PET.

Magnetic resonance imaging in lung: a review of its potential for radiotherapy

MRI has superior soft-tissue definition compared with existing imaging modalities in radiation oncology; this has the added benefit of functional as well as anatomical imaging. This review aimed to evaluate the current use of MRI for lung cancer and identify the potential of a MRI protocol for lung radiotherapy (RT). 30 relevant studies were identified. Improvements in MRI technology have overcome some of the initial limitations of utilizing MRI for lung imaging. A number of commercially available and novel sequences have shown image quality to be adequate for the detection of pulmonary nodules with the potential for tumour delineation. Quantifying tumour motion is also feasible and may be more representative than that seen on four-dimensional CT. Functional MRI sequences have shown correlation with flu-deoxy-glucose positron emission tomography (FDG-PET) in identifying malignant involvement and treatment response. MRI can also be used as a measure of pulmonary function. While there are some limitations for the adoption of MRI in RT-planning process for lung cancer, MRI has shown the potential to compete with both CT and PET for tumour delineation and motion definition, with the added benefit of functional information. MRI is well placed to become a significant imaging modality in RT for lung cancer.

Dynamic contrast enhanced CT aiding gross tumor volume delineation of liver tumors: an interobserver variability study

PURPOSE

To evaluate the application of perfusion CT for gross tumor volume (GTV) delineation for radiotherapy of intrahepatic tumors.

MATERIALS AND METHODS

15 radiotherapy patients with confirmed liver tumors underwent contrast enhanced 4D-CT (Philips Brilliance Big-bore) as well as dynamic contrast enhanced (DCE) CT (GE 750HD). Perfusion maps were generated with CT perfusion v5 from GE. Five observers delineated GTVs of all intrahepatic foci on the 4D-CT, time-averaged DCE-CT and perfusion CT for every patient. STAPLE consensus contours were generated. Dice's coefficients were compared between GTVs generated by observers on each image set and the corresponding consensus GTVs. Comparisons were also performed with patients stratified by hepatocellular carcinoma (HCC) metastatic tumors, and by tumor volume.

RESULTS

Overall, mean Dice's coefficients were 0.81±0.14, 0.84±0.10, and 0.81±0.14 for 4D-CT, DCECT and perfusion. DCE-CT performed significantly better than 4D-CT and perfusion (p=0.005 and p=0.01 respectively). For patients with HCC, DCE-CT reduced interobserver variability significantly compared to 4D-CT (Dice's coefficients 0.87 vs. 0.84, p<0.05). For patients with metastatic disease time-averaged DCE-CT images decreased variability compared to 4D-CT (Dice's coefficient 0.81 vs. 0.76, p<0.05), especially true for tumors<100cc. The smaller tumors results are important to be included here.

CONCLUSIONS

DCE-CT imaging of liver perfusion reduced interobserver variability in GTV delineation for both HCC and metastatic liver tumors.

Posttransplant Lymphoproliferative Disorder after Cardiac Transplantation in Children: Life Threatening Complications Associated with Chemotherapy Combined with Rituximab

Despite the excellent long-term survival currently achieved in pediatric heart transplant recipients, posttransplant lymphoproliferative disorders (PTLDs) are one of the most important causes of morbidity and mortality after heart transplantation (HTx), especially in children. Timely and accurate diagnosis based on histological examination of biopsy tissue is essential for early intervention for PTLD. Chemotherapy is indicated for patients with poor response to reduction of immunosuppressive medication and for highly aggressive monomorphic PTLD. The use of rituximab in combination with chemotherapy is effective to suppress B cell type PTLD (B-PTLD). However, PTLD relapses frequently and the outcome is still poor. Although everolimus (EVL) has been reported to inhibit growth of human Epstein-Barr-virus- (EBV-) transformed B lymphocytes in vitro and in vivo, EVL has several side effects, such as delayed wound healing and an increase in bacterial infection. During combined treatment of chemotherapy and rituximab, B-PTLDs are sometimes associated with life-threatening complications, such as intestinal perforation and cardiogenic shock due to cytokine release syndrome. In HTx children especially treated with EVL, stoma should be made to avoid reoperation or sepsis in case of intestinal perforation. In cases with cardiac graft dysfunction possibly due to cytokine release syndrome by chemotherapy with rituximab for PTLD, plasma exchange is effective to restore cardiac function and to rescue the patients.

Motion management in positron emission tomography/computed tomography for radiation treatment planning

Hybrid positron emission tomography (PET)/computed tomography (CT) scanners combine, in a unique gantry, 2 of the most important diagnostic imaging systems, a CT and a PET tomograph, enabling anatomical (CT) and functional (PET) studies to be performed in a single study session. Furthermore, as the 2 scanners use the same spatial coordinate system, the reconstructed CT and PET images are spatially co-registered, allowing an accurate localization of the functional signal over the corresponding anatomical structure. This peculiarity of the hybrid PET/CT system results in improved tumor characterization for oncological applications, and more recently, it was found to be also useful for target volume definition (TVD) and treatment planning in radiotherapy (RT) applications. In fact, the use of combined PET/CT information has been shown to improve the RT treatment plan when compared with that obtained by a CT alone. A limiting factor to the accuracy of TVD by PET/CT is organ and tumor motion, which is mainly due to patient respiration. In fact, respiratory motion has a degrading effect on PET/CT image quality, and this is also critical for TVD, as it can lead to possible tumor missing or undertreatment. Thus, the management of respiratory motion is becoming an increasingly essential component in RT treatment planning; indeed, it has been recognized that the use of personalized motion information can improve TVD and, consequently, permit increased tumor dosage while sparing surrounding healthy tissues and organs at risk. This review describes the methods used for motion management in PET/CT for radiation treatment planning. The article covers the following: (1) problems caused by organ and lesion motion owing to respiration, and the artifacts generated on CT, PET, and PET/CT images; (2) data acquisition and processing techniques used to manage respiratory motion in PET/CT studies; and (3) the use of personalized motion information for TVD and radiation treatment planning.

Interobserver delineation variation in lung tumour stereotactic body radiotherapy

OBJECTIVES

In radiotherapy, delineation uncertainties are important as they contribute to systematic errors and can lead to geographical miss of the target. For margin computation, standard deviations (SDs) of all uncertainties must be included as SDs. The aim of this study was to quantify the interobserver delineation variation for stereotactic body radiotherapy (SBRT) of peripheral lung tumours using a cross-sectional study design.

METHODS

22 consecutive patients with 26 tumours were included. Positron emission tomography/CT scans were acquired for planning of SBRT. Three oncologists and three radiologists independently delineated the gross tumour volume. The interobserver variation was calculated as a mean of multiple SDs of distances to a reference contour, and calculated for the transversal plane (SD(trans)) and craniocaudal (CC) direction (SD(cc)) separately. Concordance indexes and volume deviations were also calculated.

RESULTS

Median tumour volume was 13.0 cm(3), ranging from 0.3 to 60.4 cm(3). The mean SD(trans) was 0.15 cm (SD 0.08 cm) and the overall mean SD(cc) was 0.26 cm (SD 0.15 cm). Tumours with pleural contact had a significantly larger SD(trans) than tumours surrounded by lung tissue.

CONCLUSIONS

The interobserver delineation variation was very small in this systematic cross-sectional analysis, although significantly larger in the CC direction than in the transversal plane, stressing that anisotropic margins should be applied. This study is the first to make a systematic cross-sectional analysis of delineation variation for peripheral lung tumours referred for SBRT, establishing the evidence that interobserver variation is very small for these tumours.

Clinical significance of metabolic tumor volume by PET/CT in stages II and III of diffuse large B cell lymphoma without extranodal site involvement

The objective of this study was to investigate whether metabolic tumor volume (MTV) by positron emission tomography (PET) can be a potential prognostic tool when compared with Ann Arbor stage, in stages II and III nodal diffuse large B cell lymphoma (DLBCL). We evaluated 169 patients with nodal stages II and III DLBCL who underwent measurements with PET prior to rituximab combined with cyclophosphamide, adriamycin, vincristine, and prednisone (R-CHOP). Cutoff point of MTV was measured using the receiver operating characteristic (ROC) curve. During a median period of 36 months, stage II was 59.2% and III was 40.8%. Using the ROC curve, the MTV of 220 cm³ was the cutoff value. The low MTV group (<220 cm³) had longer progression-free survival (PFS) and overall survival (OS), compared with the high MTV group (≥220 cm³) (p < 0.001, p < 0.001). Stage II patients had longer survival than those in stage III (PFS, p = 0.011; OS, p = 0.001). The high MTV group had lower PFS and OS patterns, regardless of stage, compared with the low MTV group (p < 0.001, p < 0.001). Multivariate analysis revealed an association of the high MTV group with lower PFS and OS (PFS, hazard ratio (HR) = 5.300, p < 0.001; OS, HR = 7.009, p < 0.001), but not stage III (PFS, p = 0.187; OS, p = 0.054). Assessment of MTV by PET had more potential predictive power than Ann Arbor stage in the patients that received R-CHOP.