Using FDG-PET activity as a surrogate for tumor cell density and its effect on equivalent uniform dose calculation

Novel Diagnostic Approaches for Assessment of the Clinically Negative Neck in Head and Neck Cancer Patients

In head and neck cancer, the presence of nodal disease is a strong determinant of prognosis and treatment. Despite the use of modern multimodality diagnostic imaging, the prevalence of occult nodal metastases is relatively high. This is why in clinically node negative head and neck cancer the lymphatics are treated “electively” to eradicate subclinical tumor deposits. As a consequence, many true node negative patients undergo surgery or irradiation of the neck and suffer from the associated and unnecessary early and long-term morbidity. Safely tailoring head and neck cancer treatment to individual patients requires a more accurate pre-treatment assessment of nodal status. In this review, we discuss the potential of several innovative diagnostic approaches to guide customized management of the clinically negative neck in head and neck cancer patients.

18F-FDG-PET/CT-based treatment planning for definitive (chemo)radiotherapy in patients with head and neck squamous cell carcinoma improves regional control and survival

BACKGROUND AND PURPOSE

Multimodality imaging including ¹⁸F-FDG-PET has improved the detection threshold of nodal metastases in head and neck squamous cell carcinoma (HNSCC). The aim of this retrospective analysis is to investigate the impact of FDG-PET/CT-based nodal target volume definition (FDG-PET/CT-based NTV) on radiotherapy outcomes, compared to conventional CT-based nodal target volume definition (CT-based NTV).

MATERIALS AND METHODS

Six-hundred-thirty-three patients treated for HNSCC with definitive (chemo)radiotherapy using IMRT/VMAT techniques between 2008 and 2017 were analyzed. FDG-PET/CT-based NTV was performed in 46% of the patients. The median follow-up was 31 months. Diagnostic imaging depicting the regional recurrence was co-registered with the initial CT-scan to reconstruct the exact site of the recurrence. Multivariate Cox regression analysis was performed to identify variables associated with radiotherapy outcome.

RESULTS

FDG-PET/CT-based NTV improved control of disease in the CTV_{elective-nodal} (HR: 0.33, p = 0.026), overall regional control (HR: 0.62, p = 0.027) and overall survival (HR: 0.71, p = 0.033) compared to CT-based NTV. The risk for recurrence in the CTV_{elective-nodal} was increased in case of synchronous local recurrence of the primary tumor (HR: 12.4, p < 0.001).

CONCLUSION

FDG-PET/CT-based NTV significantly improved control of disease in the CTV_{elective-nodal}, overall regional control and overall survival compared to CT-based NTV. A significant proportion of CTV_{elective-nodal} recurrences are potentially new nodal manifestations from a synchronous local recurrent primary tumor. These results support the concept of target volume transformation and give an indication of the potential of FDG-PET to guide gradual radiotherapy dose de-escalation in elective neck treatment in HNSCC.

Uniform FDG-PET guided GRAdient Dose prEscription to reduce late Radiation Toxicity (UPGRADE-RT): study protocol for a randomized clinical trial with dose reduction to the elective neck in head and neck squamous cell carcinoma

BACKGROUND

In definitive radiation therapy for head and neck cancer, clinically uninvolved cervical lymph nodes are irradiated with a so-called 'elective dose' in order to achieve control of clinically occult metastases. As a consequence of high-resolution diagnostic imaging, occult tumor volume has significantly decreased in the last decades. Since the elective dose is dependent on occult tumor volume, the currently used elective dose may be higher than necessary. Because bilateral irradiation of the neck contributes to dysphagia, xerostomia and hypothyroidism in a dose dependent way, dose de-escalation to these regions can open a window of opportunity to reduce toxicity and improve quality of life after treatment.

METHODS

UPGRADE-RT is a multicenter, phase III, single-blinded, randomized controlled trial. Patients to be treated with definitive radiation therapy for a newly diagnosed stage T2-4 N0-2 M0 squamous cell carcinoma of the oropharynx, hypopharynx or larynx are eligible. Exclusion criteria are recurrent disease, oncologic surgery to the head and neck area, concomitant chemotherapy or epidermal growth factor receptor inhibitors. In total, 300 patients will be randomized in a 2:1 ratio to a treatment arm with or without de-escalation of the elective radiation dose and introduction of an intermediate dose-level for selected lymph nodes. Radiation therapy planning FDG-PET/CT-scans will be acquired to guide risk assessment of borderline-sized cervical nodes that can be treated with the intermediate dose level. Treatment will be given with intensity-modulated radiation therapy or volumetric arc therapy with simultaneous-integrated boost using an accelerated fractionation schedule, 33 fractions in 5 weeks. The primary endpoint is 'normalcy of diet' at 1 year after treatment (toxicity). The secondary endpoint is the actuarial rate of recurrence in electively irradiated lymph nodes at 2 years after treatment (safety).

DISCUSSION

The objective of the UPGRADE-RT trial is to investigate whether de-escalation of elective radiation dose and the introduction of an intermediate dose-level for borderline sized lymph nodes in the treatment of head and neck cancer will result in less radiation sequelae and improved quality of life after treatment without compromising the recurrence rate in the electively treated neck.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02442375 .

Positron emission tomography/computerized tomography for tumor response assessment-a review of clinical practices and radiomics studies

Even with recent advances in cancer diagnosis and therapy, treatment outcomes for many cancers remain dismal. Patients often show different response to the same therapy regimen, supporting the development of personalized medicine. 18F-FDG PET/CT has been used routinely in the assessment of tumor response, in prediction of outcomes, and in guiding personalized treatment. These assessments are mainly based on physician's subjective or semi-quantitative evaluation. Recent development in Radiomics provides a promising objective way for tumor response assessment, which uses computerized tools to extract a large number of image features that capture additional information not currently used in clinic that has prognostic value. In this review, we summarized the clinical use of PET/CT and the PET/CT Radiomics studies for tumor response assessment. Finally, we discussed some challenges and future perspectives.

Patterns of Recurrence in Electively Irradiated Lymph Node Regions After Definitive Accelerated Intensity Modulated Radiation Therapy for Head and Neck Squamous Cell Carcinoma

PURPOSE

To provide a comprehensive risk assessment on the patterns of recurrence in electively irradiated lymph node regions after definitive radiation therapy for head and neck cancer.

METHODS AND MATERIALS

Two hundred sixty-four patients with stage cT2-4N0-2M0 squamous cell carcinoma of the oropharynx, larynx, or hypopharynx treated with accelerated intensity modulated radiation therapy between 2008 and 2012 were included. On the radiation therapy planning computed tomography (CT) scans from all patients, 1166 lymph nodes (short-axis diameter ≥5 mm) localized in the elective volume were identified and delineated. The exact sites of regional recurrences were reconstructed and projected on the initial radiation therapy planning CT scan by performing coregistration with diagnostic imaging of the recurrence.

RESULTS

The actuarial rate of recurrence in electively irradiated lymph node regions at 2 years was 5.1% (95% confidence interval 2.4%-7.8%). Volumetric analysis showed an increased risk of recurrence with increasing nodal volume. Receiver operating characteristic analysis demonstrated that the summed long- and short-axis diameter is a good alternative for laborious volume calculations, using ≥17 mm as cut-off (hazard ratio 17.8; 95% confidence interval 5.7-55.1; P<.001).

CONCLUSIONS

An important risk factor was identified that can help clinicians in the pretreatment risk assessment of borderline-sized lymph nodes. Not overtly pathologic nodes with a summed diameter ≥17 mm may require a higher than elective radiation therapy dose. For low-risk elective regions (all nodes <17 mm), the safety of dose de-escalation below the traditional 45 to 50 Gy should be investigated.

Computerized PET/CT image analysis in the evaluation of tumour response to therapy

Current cancer therapy strategy is mostly population based, however, there are large differences in tumour response among patients. It is therefore important for treating physicians to know individual tumour response. In recent years, many studies proposed the use of computerized positron emission tomography/CT image analysis in the evaluation of tumour response. Results showed that computerized analysis overcame some major limitations of current qualitative and semiquantitative analysis and led to improved accuracy. In this review, we summarize these studies in four steps of the analysis: image registration, tumour segmentation, image feature extraction and response evaluation. Future works are proposed and challenges described.

Radiobiological Modeling Based on 18F-Fluorodeoxyglucose Positron Emission Tomography Data for Esophageal Cancer

Background

We investigated the relationship of standardized uptake values (SUVs) to radiobiological parameters, such a 25 s tumor control probability (TCP), to allow for quantitative prediction of tumor response based on SUVs from ¹⁸F fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) before and after treatment for esophageal cancer.

Methods

We analyzed data from 20 esophageal cancer patients treated with chemoradiotherapy (CRT) followed by surgery. Tumor pathologic response to CRT was assessed in surgical specimens. Patients underwent ¹⁸F-FDG PET imaging before and after CRT. Rigid image registration was performed between both images. Because TCP in a heterogeneous tumor is a function of average cell survival, we modeled TCP as a function of <SUV_R>, a possible surrogate for average cell survival (<SUV_R>=<SUV_after/SUV_before>). TCP was represented by a sigmoid function with two parameters: SUV_R50, the <SUV_R> at which TCP=0.5, and γ₅₀, the slope of the curve at SUV_R50. The two parameters and their confidence intervals (CIs) were estimated using the maximum-likelihood method. The correlation between SUV before CRT and SUV change <SUV_before – SUV_after> was also studied.

Results

A TCP model as a function of SUV before and after treatment was developed for esophageal cancer patients. The maximum-likelihood estimate of SUV_R50 was 0.47 (90% CI, 0.30-0.61) and for γ₅₀ was 1.62 (90% CI, 0-4.2). High initial SUV and larger metabolic response (larger <SUV_before –SUV_after>) were correlated, and this correlation was stronger among responders.

Conclusions

Our TCP model indicates that <SUV_after/SUV_before> is a possible surrogate for cell survival in esophageal cancer patients. Although CIs are large as a result of the small patient sample, parameters for a TCP curve can be derived and an individualized TCP can be calculated for future patients. Initial SUV does not predict response, whereas a correlation is found between surrogates for initial tumor burden and cell kill during therapy.

Predicting pathologic tumor response to chemoradiotherapy with histogram distances characterizing longitudinal changes in 18F-FDG uptake patterns

PURPOSE

A family of fluorine-18 ((18)F)-fluorodeoxyglucose ((18)F-FDG) positron-emission tomography (PET) features based on histogram distances is proposed for predicting pathologic tumor response to neoadjuvant chemoradiotherapy (CRT). These features describe the longitudinal change of FDG uptake distribution within a tumor.

METHODS

Twenty patients with esophageal cancer treated with CRT plus surgery were included in this study. All patients underwent PET/CT scans before (pre-) and after (post-) CRT. The two scans were first rigidly registered, and the original tumor sites were then manually delineated on the pre-PET/CT by an experienced nuclear medicine physician. Two histograms representing the FDG uptake distribution were extracted from the pre- and the registered post-PET images, respectively, both within the delineated tumor. Distances between the two histograms quantify longitudinal changes in FDG uptake distribution resulting from CRT, and thus are potential predictors of tumor response. A total of 19 histogram distances were examined and compared to both traditional PET response measures and Haralick texture features. Receiver operating characteristic analyses and Mann-Whitney U test were performed to assess their predictive ability.

RESULTS

Among all tested histogram distances, seven bin-to-bin and seven crossbin distances outperformed traditional PET response measures using maximum standardized uptake value (AUC = 0.70) or total lesion glycolysis (AUC = 0.80). The seven bin-to-bin distances were: L(2) distance (AUC = 0.84), χ(2) distance (AUC = 0.83), intersection distance (AUC = 0.82), cosine distance (AUC = 0.83), squared Euclidean distance (AUC = 0.83), L(1) distance (AUC = 0.82), and Jeffrey distance (AUC = 0.82). The seven crossbin distances were: quadratic-chi distance (AUC = 0.89), earth mover distance (AUC = 0.86), fast earth mover distance (AUC = 0.86), diffusion distance (AUC = 0.88), Kolmogorov-Smirnov distance (AUC = 0.88), quadratic form distance (AUC = 0.87), and match distance (AUC = 0.84). These crossbin histogram distance features showed slightly higher prediction accuracy than texture features on post-PET images.

CONCLUSIONS

The results suggest that longitudinal patterns in (18)F-FDG uptake characterized using histogram distances provide useful information for predicting the pathologic response of esophageal cancer to CRT.

New PET/CT Features for the Evaluation of Tumor Response

With the emerging multi-modality imaging performed at multiple time points for each patient, it becomes more important to analyze the serial images quantitatively, select and combine both complementary and contradictory information from various sources, for accurate and personalized evaluation of tumor response to therapy.

Complementarity between (18)F-FDG PET/CT and Ultrasonography or Angiography in Carotid Plaque Characterization

Background and Purpose

To estimate clinical roles of 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) versus angiography and ultrasonography in carotid plaque characterization.

Methods

We characterized two groups of patients with recently (<1 month) symptomatic (n=14; age=71.8±8.6 years, mean±SD) or chronic (n=13, age=68.9±9.0 years) carotid stenosis using a battery of imaging tests: diffusion magnetic resonance (MR) imaging, MR or transfemoral angiography, duplex ultrasonography (DUS), and carotid FDG-PET/computed tomography.

Results

The degree of angiographic stenosis was greater in patients with recently symptomatic carotid plaques (67.5±21.5%) than in patients with chronic carotid plaques (32.4±26.8%, p=0.001). Despite the significant difference in the degree of stenosis, lesional maximum standardized uptake values (maxSUVs) on the carotid FDG-PET did not differ between the recently symptomatic (1.56±0.53) and chronic (1.56±0.34, p=0.65) stenosis groups. However, lesional-to-contralesional maxSUV ratios were higher in the recently symptomatic stenosis group (113±17%) than in the chronic stenosis group (98±10%, p=0.017). The grayscale median value of the lesional DUS echodensities was lower in the recently symptomatic stenosis group (28.2±10.0, n=9) than in the chronic stenosis group (53.9±14.0, n=8; p=0.001). Overall, there were no significant correlations between angiographic stenosis, DUS echodensity, and FDG-PET maxSUV. Case/subgroup analyses suggested complementarity between imaging modalities.

Conclusions

There were both correspondences and discrepancies between the carotid FDG-PET images and DUS or angiography data. Further studies are required to determine whether FDG-PET could improve the clinical management of carotid stenosis.

A theoretical framework for prescribing radiotherapy dose distributions using patient-specific biological information

We present a formalism for using functional imaging both to derive patient-specific radiobiological properties and consequently to prescribe optimal nonuniform radiotherapy dose distributions. The ability to quantitatively assess the response to an initial course of radiotherapy would allow the derivation of radiobiological parameters for individual patients. Both an iterative optimization and an analytical approach to this problem were investigated and illustrated by application to the linear-quadratic model of cell killing using simulated parametric data for a modeled tumor. Potential gains in local control were assessed by comparing uniform dose distributions with optimized dose distributions of equal integral dose. The effect on local prescribed dose of variations in effective radiosensitivity, tumor burden, and proliferation rate was investigated, with results suggesting that dose variations would be significant but clinically achievable. The sensitivity of derived parameters to image noise and the effect of varying the initial fractionation and imaging schedule were assessed. The analytical approach proved remarkably robust, with 10% image noise resulting in dose errors of approximately 1% for a clinically relevant set of parameters. Potential benefits were demonstrated by using this formalism to prescribe nonuniform dose distributions for model tumors using a range of literature-derived parameters. The redistribution of dose improved tumor control probability by factors between 1.03 and 4.27 for a range of model tumors.

A heterogeneous dose distribution in simultaneous integrated boost: the role of the clonogenic cell density on the tumor control probability

IMRT with inverse planning allows simultaneous integrated boost strategies that exploit the heterogeneous dose distribution within the planning target volumes (PTVs). In this scenario, the location of cold spots within the target becomes a crucial issue and has to be related to the distribution of the clonogenic cell density (CCD). The main aim of this work is to provide the means to calculate the optimal prescription dose in a relative inhomogeneous dose distribution. To achieve this, the prescription dose has to be assigned to obtain the same tumor control probability (TCP) as the ideal homogeneous distribution, taking into account different CCDs in different PTVs (i.e. visible and subclinical regions). An adapted formulation of the linear-quadratic model, within the F-factor formalism, has been derived to preserve a chosen TCP value for the whole target volume. The F-factor has been investigated to show its potential applications in clinical practice.

Computational modeling of cancer cachexia

PURPOSE OF REVIEW

Measurements of whole-body energy expenditure, body composition, and in-vivo metabolic fluxes are required to quantitatively understand involuntary weight loss in cancer cachexia. Such studies are rare because cancer cachexia occurs near the end of life when invasive metabolic tests may be precluded. Thus, models of cancer-associated weight loss are an important tool for helping to understand this debilitating condition.

RECENT FINDINGS

A computational model of human macronutrient metabolism was recently developed that simulates the normal metabolic adaptations to semi-starvation and re-feeding. Here, this model was used to integrate data on the metabolic changes in patients with cancer cachexia. The resulting computer simulations show how the known metabolic disturbances synergize with reduced energy intake to result in a progressive loss of body weight, fat mass, and fat-free mass. The model was also used to simulate the effects of nutritional support and investigate inhibition of lipolysis versus proteolysis as potential therapeutic approaches for cancer cachexia.

SUMMARY

Computational modeling is a new tool that can integrate clinical data on the metabolic changes in cancer cachexia and provide a conceptual framework to help understand involuntary weight loss and predict the effects of potential therapies.

PET/CT image registration: Preliminary tests for its application to clinical dosimetry in radiotherapy

The quality of dosimetry in radiotherapy treatment requires the accurate delimitation of the gross tumor volume. This can be achieved by complementing the anatomical detail provided by CT images through fusion with other imaging modalities that provide additional metabolic and physiological information. Therefore, use of multiple imaging modalities for radiotherapy treatment planning requires an accurate image registration method. This work describes tests carried out on a Discovery LS positron emission/computed tomography (PET/CT) system by General Electric Medical Systems (GEMS), for its later use to obtain images to delimit the target in radiotherapy treatment. Several phantoms have been used to verify image correlation, in combination with fiducial markers, which were used as a system of external landmarks. We analyzed the geometrical accuracy of two different fusion methods with the images obtained with these phantoms. We first studied the fusion method used by the PET/CT system by GEMS (hardware fusion) on the basis that there is satisfactory coincidence between the reconstruction centers in CT and PET systems; and secondly the fiducial fusion, a registration method, by means of least-squares fitting algorithm of a landmark points system. The study concluded with the verification of the centroid position of some phantom components in both imaging modalities. Centroids were estimated through a calculation similar to center-of-mass, weighted by the value of the CT number and the uptake intensity in PET. The mean deviations found for the hardware fusion method were: deltax/ +/-sigma = 3.3 mm +/- 1.0 mm and /deltax/ +/-sigma = 3.6 mm +/- 1.0 mm. These values were substantially improved upon applying fiducial fusion based on external landmark points: /deltax/ +/-sigma = 0.7 mm +/- 0.8 mm and /deltax/ +/-sigma = 0.3 mm 1.7 mm. We also noted that differences found for each of the fusion methods were similar for both the axial and helical CT image acquisition protocols.