Early FDG-PET imaging after radical radiotherapy for non-small-cell lung cancer: inflammatory changes in normal tissues correlate with tumor response and do not confound therapeutic response evaluation

Association between radiation pneumonitis and tumor response in patients with NSCLC treated with chemoradiation

Dang and colleagues recently reported in the journal that tumor response to definitive chemoradiation, as assessed using the RECIST criteria, and the risk of radiation pneumonitis were positively correlated in patients with non-small cell lung cancer (NSCLC). We had previously reported similar findings in a study that used positron tomography both to measure tumor response and to assess normal tissue toxicity in patients treated with chemoradiation for NSCLC. Taken together these reports suggest that radiosensitivity of normal tissues and tumors may be strongly linked in a proportion of patients with lung cancer.

The role of texture analysis in imaging as an outcome predictor and potential tool in radiotherapy treatment planning

Predicting a tumour's response to radiotherapy prior to the start of treatment could enhance clinical care management by enabling the personalization of treatment plans based on predicted outcome. In recent years, there has been accumulating evidence relating tumour texture to patient survival and response to treatment. Tumour texture could be measured from medical images that provide a non-invasive method of capturing intratumoural heterogeneity and hence could potentially enable a prior assessment of a patient's predicted response to treatment. In this article, work presented in the literature regarding texture analysis in radiotherapy in relation to survival and outcome is discussed. Challenges facing integrating texture analysis in radiotherapy planning are highlighted and recommendations for future directions in research are suggested.

Fluorodeoxyglucose positron-emission tomography ratio in non-small cell lung cancer patients treated with definitive radiotherapy

Purpose

To determine whether the maximum standardized uptake value (SUV) of [¹⁸F] fluorodeoxyglucose uptake by positron emission tomography (FDG PET) ratio of lymph node to primary tumor (mSUVR) could be a prognostic factor for node positive non-small cell lung cancer (NSCLC) patients treated with definitive radiotherapy (RT).

Materials and Methods

A total of 68 NSCLC T1-4, N1-3, M0 patients underwent FDG PET before RT. Optimal cutoff values of mSUVR were chosen based on overall survival (OS). Independent prognosticators were identified by Cox regression analysis.

Results

The most significant cutoff value for mSUVR was 0.9 with respect to OS. Two-year OS was 17% for patients with mSUVR > 0.9 and 49% for those with mSUVR ≤ 0.9 (p = 0.01). In a multivariate analysis, including age, performance status, stage, use of chemotherapy, and mSUVR, only performance status (p = 0.05) and mSUVR > 0.9 (p = 0.05) were significant predictors of OS. Two-year OS for patients with both good performance (Eastern Cooperative Oncology Group [ECOG] ≤ 1) and mSUVR ≤ 0.9 was significantly better than that for patients with either poor performance (ECOG > 1) or mSUVR > 0.9, 23% (71% vs. 23%, p = 0.04).

Conclusion

Our results suggested that the mSUVR was a strong prognostic factor among patients with lymph node positive NSCLC following RT. Addition of mSUVR to performance status identifies a subgroup at highest risk for death after RT.

Quantitative assessment of global lung inflammation following radiation therapy using FDG PET/CT: a pilot study

PURPOSE

Radiation pneumonitis is the most severe dose-limiting complication in patients receiving thoracic radiation therapy. The aim of this study was to quantify global lung inflammation following radiation therapy using FDG PET/CT.

METHODS

We studied 20 subjects with stage III non-small-cell lung carcinoma who had undergone FDG PET/CT imaging before and after radiation therapy. On all PET/CT studies, the sectional lung volume (sLV) of each lung was calculated from each slice by multiplying the lung area by slice thickness. The sectional lung glycolysis (sLG) was calculated by multiplying the sLV and the lung sectional mean standardized uptake value (sSUVmean) on each slice passing through the lung. The lung volume (LV) was calculated by adding all sLVs from the lung, and the global lung glycolysis (GLG) was calculated by adding all sLGs from the lung. Finally, the lung SUVmean was calculated by dividing the GLG by the LV. The amount of inflammation in the lung parenchyma directly receiving radiation therapy was calculated by subtracting tumor measurements from GLG.

RESULTS

In the lung directly receiving radiation therapy, the lung parenchyma SUVmean and global lung parenchymal glycolysis were significantly increased following therapy. In the contralateral lung (internal control), no significant changes were observed in lung SUVmean or GLG following radiation therapy.

CONCLUSION

Global lung parenchymal glycolysis and lung parenchymal SUVmean may serve as potentially useful biomarkers to quantify lung inflammation on FDG PET/CT following thoracic radiation therapy.

Temporal analysis of intratumoral metabolic heterogeneity characterized by textural features in cervical cancer

PURPOSE

The aim of this pilot study was to explore heterogeneity in the temporal behavior of intratumoral [(18)F]fluorodeoxyglucose (FDG) accumulation at a regional scale in patients with cervical cancer undergoing chemoradiotherapy.

METHODS

Included in the study were 20 patients with FIGO stages IB1 to IVA cervical cancer treated with combined chemoradiotherapy. Patients underwent FDG PET/CT before treatment, during weeks 2 and 4 of treatment, and 12 weeks after completion of therapy. Patients were classified based on response to therapy as showing a complete metabolic response (CMR), a partial metabolic response (PMR), or residual disease and the development of new disease (NEW). Based on the presence of residual primary tumor following therapy, patients were divided into two groups, CMR and PMR/NEW. Temporal profiles of intratumoral FDG heterogeneity as characterized by textural features at a regional scale were assessed and compared with those of the standardized uptake value (SUV) indices (SUVmax and SUVmean) within the context of differentiating response groups.

RESULTS

Textural features at a regional scale with emphasis on characterizing contiguous regions of high uptake in tumors decreased significantly with time (P < 0.001) in the CMR group, while features describing contiguous regions of low uptake along with those measuring the nonuniformity of contiguous isointense regions in tumors exhibited significant temporal changes in the PMR/NEW group (P < 0.03) but showed no persistent trends with time. Both SUV indices showed significant changes during the course of the disease in both patient groups (P < 0.001 for SUVmax and SUVmean in the CMR group; P = 0.0109 and 0.0136, respectively, for SUVmax and SUVmean in the PMR/NEW group), and also decreased at a constant rate in the CMR group and decreased up to the 4th week of treatment and then increased in the PMR/NEW group.

CONCLUSION

The temporal changes in the heterogeneity of intratumoral FDG distribution characterized at a regional scale using image-based textural features may provide an adjunctive or alternative option for understanding tumor response to chemoradiotherapy and interpreting FDG accumulation dynamics in patients with malignant cervical tumors during the course of the disease.

Application of FDG-PET/CT in Radiation Oncology

Positron emission tomography (PET)/computed tomography (CT), which combines the advantages of high sensitivity and specificity of PET and high resolution of CT, is a unique tool for cancer management. PET/CT has been widely used in cancer diagnosis and treatment. The article reviews the recent applications of PET/CT in radiation oncology, with a focus on ¹⁸F-fluorodeoxyglucose (FDG)-PET/CT, addressing the applications in treatment planning and treatment response assessment of radiation therapy.

FDG uptake correlates with recurrence and survival after treatment of unresectable stage III non-small cell lung cancer with high-dose proton therapy and chemotherapy

Background

We studied whether maximum standardized uptake values (SUV) from [¹⁸ F] PET/CT predict clinical outcome after concurrent proton/chemotherapy for stage III non-small cell lung cancer (NSCLC).

Methods

Eighty-four patients were treated prospectively with 74 Gy(RBE) proton therapy and concurrent chemotherapy. PET/CT scans were available before (SUV1) and within 6 months after (SUV2) treatment. The predictive value of clinical and PET/CT factors were analyzed with univariate and multivariate Cox regression models.

Results

Median survival time was 29.9 months. At 3 years, the local recurrence-free survival (LRFS) rate was 34.8%; distant metastasis-free survival (DMFS), 35.4%; progression-free survival (PFS), 31.2%; and overall survival (OS), 37.2%. Patients with SUV2 ≥3.6 (the median) had high rates of LR (p = 0.021). Of 12 clinicopathologic features evaluated in univariate analysis, only KPS, SUV1, and SUV2 predicted LRFS, DMFS, PFS, and OS (p <0.05). Multivariate analysis showed that KPS (p = 0.025) and SUV2 (p = 0.017) were independently prognostic for LRFS and that SUV1, SUV2, and KPS were independently prognostic for DMFS, PFS, and OS (p <0.05).

Conclusions

SUV2 predicted LRFS, and SUV1 and SUV2 predicted DMFS, PFS, and OS, in patients with stage III NSCLC treated with concurrent chemotherapy and high-dose proton therapy.

Current concepts in F18 FDG PET/CT-based radiation therapy planning for lung cancer

Radiation therapy is an important component of cancer therapy for early stage as well as locally advanced lung cancer. The use of F18 FDG PET/CT has come to the forefront of lung cancer staging and overall treatment decision-making. FDG PET/CT parameters such as standard uptake value and metabolic tumor volume provide important prognostic and predictive information in lung cancer. Importantly, FDG PET/CT for radiation planning has added biological information in defining the gross tumor volume as well as involved nodal disease. For example, accurate target delineation between tumor and atelectasis is facilitated by utilizing PET and CT imaging. Furthermore, there has been meaningful progress in incorporating metabolic information from FDG PET/CT imaging in radiation treatment planning strategies such as radiation dose escalation based on standard uptake value thresholds as well as using respiratory-gated PET and CT planning for improved target delineation of moving targets. In addition, PET/CT-based follow-up after radiation therapy has provided the possibility of early detection of local as well as distant recurrences after treatment. More research is needed to incorporate other biomarkers such as proliferative and hypoxia biomarkers in PET as well as integrating metabolic information in adaptive, patient-centered, tailored radiation therapy.

[18F]-FDG uptake dose-response correlates with radiation pneumonitis in lung cancer patients

PURPOSE

To quantify the post-radiotherapy 2-[(18)F]-fluoro-2-deoxyglucose (FDG) pulmonary uptake dose-response in lung cancer patients and determine its relationship with radiation pneumonitis symptoms.

METHODS AND MATERIALS

The data from 24 patients treated for lung cancer with thoracic radiotherapy who received restaging PET/CT imaging between 4 and 12 weeks after radiotherapy completion were evaluated. Their radiation dose distribution was registered with the post-treatment restaging PET/CT. Using histogram analysis, the voxel average FDG-PET uptake vs. radiation dose was obtained for each case and linear regression was performed. The resulting slope, the pulmonary metabolic radiation response (PMRR), was used to characterize the dose-response. The Common Toxicity Criteria version 3 was used to score clinical pulmonary toxicity symptoms. Receiver operating characteristic (ROC) curves were used to determine the level of FDG uptake vs. dose, MLD, V(5), V(10), V(20), and V(30) that can best predict symptomatic and asymptomatic patients.

RESULTS

The median time between radiotherapy completion and FDG-PET imaging was 59 days (range, 26-70 days). The median of the mean SUV from lung that received 0-5 Gy was 1.00 (range, 0.37-1.48), 5-10 Gy was 1.01 (range, 0.37-1.77), 10-20 Gy was 1.04 (0.42-1.53), and >20 Gy was 1.29 (range, 0.41-8.01). Using the dose range of 0 Gy to the maximum dose minus 10 Gy, hierarchical linear regression model of the radiation dose and normalized FDG uptake per case found an adequate fit with the linear model. Pneumonitis scores were: Grade 0 for 13, Grade 1 for 5, Grade 2 for 6, and Grade 3, 4 or 5 for none. Using a PMRR threshold of 0.017 yields an associated true positive rate of 0.67 and false positive rate of 0.15 with average error of 30%. A V(5) threshold of 57.6 gives an associated true positive rate of 0.67 and false positive rate of 0.05 with a 20% average error.

CONCLUSION

The metabolic radiation pneumonitis dose-response was evaluated from post-treatment FDG-PET/CT imaging. Statistical modeling found a linear relationship. The FDG uptake dose-response and V(5) correlated with symptomatic radiation pneumonitis.

Radiation-induced myositis mimicking chest wall tumor invasion in two patients with lung cancer: a PET/CT study

Two patients with lung cancer who had undergone stereotactic body radiation therapy (SBRT) exhibited increased F-18 FDG uptake in the chest wall after 6 months and 18 months, respectively, after SBRT. The prescribed dose of 50 Gy to the planning target volume was delivered on 4 consecutive days in each patient. It is important for nuclear medicine physicians to be familiar with F-18 FDG PET/CT findings ascribed to radiation-induced myositis in lung cancer patients treated with SBRT so that an appropriate differential diagnosis can be established.

Imaging radiation-induced normal tissue injury

Technological developments in radiation therapy and other cancer therapies have led to a progressive increase in five-year survival rates over the last few decades. Although acute effects have been largely minimized by both technical advances and medical interventions, late effects remain a concern. Indeed, the need to identify those individuals who will develop radiation-induced late effects, and to develop interventions to prevent or ameliorate these late effects is a critical area of radiobiology research. In the last two decades, preclinical studies have clearly established that late radiation injury can be prevented/ameliorated by pharmacological therapies aimed at modulating the cascade of events leading to the clinical expression of radiation-induced late effects. These insights have been accompanied by significant technological advances in imaging that are moving radiation oncology and normal tissue radiobiology from disciplines driven by anatomy and macrostructure to ones in which important quantitative functional, microstructural, and metabolic data can be noninvasively and serially determined. In the current article, we review use of positron emission tomography (PET), single photon emission tomography (SPECT), magnetic resonance (MR) imaging and MR spectroscopy to generate pathophysiological and functional data in the central nervous system, lung, and heart that offer the promise of, (1) identifying individuals who are at risk of developing radiation-induced late effects, and (2) monitoring the efficacy of interventions to prevent/ameliorate them.

Application of metabolic PET imaging in radiation oncology

Positron emission tomography (PET) is a noninvasive imaging technique that provides functional or metabolic assessment of normal tissue or disease conditions and is playing an increasing role in cancer radiotherapy planning. (18)F-Fluorodeoxyglucose PET imaging (FDG-PET) is widely used in the clinic for tumor imaging due to increased glucose metabolism in most types of tumors; its role in radiotherapy management of various cancers is reviewed. In addition, other metabolic PET imaging agents at various stages of preclinical and clinical development are reviewed. These agents include radiolabeled amino acids such as methionine for detecting increased protein synthesis, radiolabeled choline for detecting increased membrane lipid synthesis, and radiolabeled acetate for detecting increased cytoplasmic lipid synthesis. The amino acid analogs choline and acetate are often more specific to tumor cells than FDG, so they may play an important role in differentiating cancers from benign conditions and in the diagnosis of cancers with either low FDG uptake or high background FDG uptake. PET imaging with FDG and other metabolic PET imaging agents is playing an increasing role in complementary radiotherapy planning.

Elevation in exhaled nitric oxide predicts for radiation pneumonitis

PURPOSE

Radiation pneumonitis is a major toxicity after thoracic radiotherapy (RT), with no method available to accurately predict the individual risk. This was a prospective study to evaluate exhaled nitric oxide as a predictive biomarker for radiation pneumonitis in esophageal cancer patients.

PATIENTS AND METHODS

A total of 34 patients prescribed neoadjuvant chemoradiotherapy for esophageal cancer were enrolled in the present trial. Each patient underwent respiratory surveys and exhaled nitric oxide (NO) measurements before, at the end of, and 1 to 2 months after completing RT. Pneumonitis toxicity was scored using the Common Terminology Criteria for Adverse Events, version 4.0. The demographics, dosimetric factors, and exhaled NO levels were evaluated for correlation with symptomatic patients (scores ≥ 2).

RESULTS

Of the 34 patients, 28 were evaluable. All had received 50.4 Gy RT with concurrent chemotherapy. The pneumonitis toxicity score was Grade 3 for 1, Grade 2 for 3, Grade 1 for 7, and Grade 0 for 17. The dosimetric factors were not predictive of symptoms. The mean exhaled NO level measured before, at completion, and at restaging was 17.3 ± 8.5 (range, 5.5-36.7), 16.0 ± 14.2 (range, 5.8-67.7), and 14.7 ± 6.2 (range, 5.5-28.0) parts per billion, respectively. The ratio of exhaled NO at the end of RT vs. before treatment was 3.4 (range, 1.7-6.7) for the symptomatic and 0.8 (range, 0.3-1.3) for the asymptomatic (p = .0017) patients. The elevation in exhaled NO preceded the peak symptoms by 33 days (range, 21-50). The interval to peak symptoms was inversely related to the exhaled NO elevation.

CONCLUSIONS

Elevations in exhaled NO at the end of RT was found to predict for radiation pneumonitis symptoms.

Combined PET/CT image characteristics for radiotherapy tumor response in lung cancer

BACKGROUND AND PURPOSE

Prediction of local failure in radiotherapy patients with non-small cell lung cancer (NSCLC) remains a challenging task. Recent evidence suggests that FDG-PET images can be used to predict outcomes. We investigate an alternative multimodality image-feature approach for predicting post-radiotherapy tumor progression in NSCLC.

MATERIAL AND METHODS

We analyzed pre-treatment FDG-PET/CT studies of twenty-seven NSCLC patients for local and loco-regional failures. Thirty-two tumor region features based on SUV or HU, intensity-volume-histogram (IVH) and texture characteristics were extracted. Statistical analysis was performed using Spearman's correlation (rs) and multivariable logistic regression.

RESULTS

For loco-regional recurrence, IVH variables had the highest univariate association. In PET, IVH-slope reached rs=0.3426 (p=0.0403). Motion correction slightly improved correlation of texture features. In CT, coefficient of variation had the highest association rs=-0.2665 (p=0.0871). Similarly for local failure, a CT-IVH parameter reached rs=0.4530 (p=0.0105). For loco-regional and local failures, a 2-parameter model of PET-V(80) and CT-V(70) yielded rs=0.4854 (p=0.0067) and rs=0.5908 (p=0.0013), respectively. Addition of dosimetric variables provided improvement in cases of loco-regional but not local failures.

CONCLUSIONS

We proposed a feature-based approach to evaluate radiation tumor response. Our study demonstrates that multimodality image-feature modeling provides better performance compared to existing metrics and holds promise for individualizing radiotherapy planning.

PET/CT imaging in different types of lung cancer: an overview

Lung cancer (LC) still represents one of the most common tumours in both women and men. PET/CT is a whole-body non-invasive imaging procedure that has been increasingly used for the assessment of LC patients. In particular, PET/CT added value to CT is mainly related to a more accurate staging of nodal and metastatic sites and to the evaluation of the response to therapy. Although the most common PET tracer for LC evaluation is 18F-FDG, new tracers have been proposed for the evaluation of lung neuroendocrine tumours (68Ga-DOTA-peptides, 18F-DOPA) and for the assessment of central nervous system metastasis (11C-methionine). This review focuses on the main clinical applications and accuracy of PET/CT for the detection of non-small cells lung cancer (NSCLC), broncho-alveolar carcinoma (BAC), small cells lung cancer (SCLC), lung neuroendocrine tumours (NET) and solitary pulmonary nodules (SPN).

Positron emission tomography imaging approaches for external beam radiation therapies: current status and future developments

In an era in which it is possible to deliver radiation with high precision, there is a heightened need for enhanced imaging capabilities to improve tumour localisation for diagnostic, planning and delivery purposes. This is necessary to increase the accuracy and overall efficacy of all types of external beam radiotherapy (RT), including particle therapies. Positron emission tomography (PET) has the potential to fulfil this need by imaging fundamental aspects of tumour biology. The key areas in which PET may support the RT process include improving disease diagnosis and staging; assisting tumour volume delineation; defining tumour phenotype or biological tumour volume; assessment of treatment response; and in-beam monitoring of radiation dosimetry. The role of PET and its current developmental status in these key areas are overviewed in this review, highlighting the advantages and drawbacks.

Fluorodeoxyglucose positron emission tomography for evaluating early response during neoadjuvant chemoradiotherapy in patients with potentially curable esophageal cancer

BACKGROUND

Neoadjuvant chemoradiotherapy before surgery can improve survival in patients with potentially curable esophageal cancer, but not all patients respond. Fluorodeoxyglucose positron emission tomography (FDG-PET) has been proposed to identify nonresponders early during neoadjuvant chemoradiotherapy. The aim of the present study was to determine whether FDG-PET could differentiate between responding and nonresponding esophageal tumors early in the course of neoadjuvant chemoradiotherapy.

METHODS

This clinical trial comprised serial FDG-PET before and 14 days after start of chemoradiotherapy in patients with potentially curable esophageal carcinoma. Histopathologic responders were defined as patients with no or less than 10% viable tumor cells (Mandard score on resection specimen). PET response was measured using the standardized uptake value (SUV). Receiver operating characteristic analysis was used to evaluate the ability of SUV in distinguishing between histopathologic responders and nonresponders.

RESULTS

In 100 included patients, 64 were histopathologic responders. The median SUV decrease 14 days after the start of therapy was 30.9% for histopathologic responders and 1.7% for nonresponders (P = 0.001). In receiver operating characteristic analysis, the area under the curve was 0.71 (95% CI = 0.60-0.82). Using a 0% SUV decrease cutoff value, PET correctly identified 58 of 64 responders (sensitivity 91%) and 18 of 36 nonresponders (specificity 50%). The corresponding positive and negative predictive values were 76% and 75%, respectively.

CONCLUSIONS

SUV decrease 14 days after the start of chemoradiotherapy was significantly associated with histopathologic tumor response, but its accuracy in detecting nonresponders was too low to justify the clinical use of FDG-PET for early discontinuation of neoadjuvant chemoradiotherapy in patients with potentially curable esophageal cancer.

18F-FDG PET/CT for the prediction and detection of local recurrence after radiofrequency ablation of malignant lung lesions

The utility of (18)F-FDG PET/CT for response assessment in malignant lung tumors treated with radiofrequency ablation (RFA) and for the detection and prediction of local recurrence was investigated.

METHODS

Between December 17, 2003, and April 9, 2008, 68 consecutive patients (mean age, 68 y) with 94 pulmonary lesions, including metastases (n = 38) and primary lung cancers (n = 44), underwent RFA. Because of inadequate imaging follow-up in 12 patients, only 82 lesions were analyzed (CT scans, n = 82; (18)F-FDG PET/CT scans, n = 62). The median follow-up was 25 mo (range, 12-66 mo). A baseline study was defined as (18)F-FDG PET/CT performed no more than 3 mo before RFA. The first postablation scan was defined as PET/CT performed between 1 and 4 mo after RFA; additional follow-up studies were obtained in some cases between 6 and 12 mo after RFA. The unidimensional maximum diameter of the lesion was recorded on a pretherapy diagnostic CT scan or on the CT component of a pretherapy (18)F-FDG PET/CT scan, whichever was obtained most recently, using lung windows. Maximum standardized uptake values (SUVs) were recorded for all lesions imaged by (18)F-FDG PET/CT. (18)F-FDG uptake patterns on post-RFA scans were classified as favorable or unfavorable. Survival and recurrence probabilities were estimated using the Kaplan-Meier method. Uni- and multivariate analyses were also performed.

RESULTS

Before RFA, factors predicting greater local recurrence-free survival included initial lesion size less than 3 cm (P = 0.01) and SUV less than 8 (P = 0.02), although the latter was not an independent predictor in multivariate analysis. Treated metastases recurred less often than treated primary lung cancers (P = 0.03). Important post-RFA factors that related to reduced recurrence-free survival included an unfavorable uptake pattern (P < 0.01), post-RFA SUV (P < 0.01), and an increase in SUV over time after ablation (P = 0.05).

CONCLUSION

(18)F-FDG PET/CT parameters on both preablation and postablation scans may predict local recurrence in patients treated with RFA for lung metastases and primary lung cancers.

A pilot trial of serial 18F-fluorodeoxyglucose positron emission tomography in patients with medically inoperable stage I non-small-cell lung cancer treated with hypofractionated stereotactic body radiotherapy

PURPOSE

Routine assessment was made of tumor metabolic activity as measured by 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) in Stage I non-small-cell lung cancer (NSCLC). This report describes PET correlates prospectively collected after stereotactic body radiotherapy (SBRT) for patients with medically inoperable NSCLC.

METHODS AND MATERIALS

14 consecutive patients with medically inoperable Stage I NSCLC were enrolled. All patients received SBRT to 60-66 Gy in three fractions. Patients underwent serial planned FDG-PET/computed tomography fusion imaging before SBRT and at 2, 26, and 52 weeks after SBRT.

RESULTS

With median follow-up of 30.2 months, no patients experienced local failure. One patient developed regional failure, 1 developed distant failure, and 1 developed a second primary. The median tumor maximum standardized uptake value (SUV(max)) before SBRT was 8.70. The median SUV(max) values at 2, 26, and 52 weeks after SBRT were 6.04, 2.80, and 3.58, respectively. Patients with low pre-SBRT SUV were more likely to experience initial 2-week rises in SUV, whereas patients with high pre-SBRT SUV commonly had SUV declines 2 weeks after treatment (p = 0.036). Six of 13 patients had primary tumor SUV(max) >3.5 at 12 months after SBRT but remained without evidence of local disease failure on further follow-up.

CONCLUSIONS

A substantial proportion of patients may have moderately elevated FDG-PET SUV(max) at 12 months without evidence of local failure on further follow-up. Thus, slightly elevated PET SUV(max) should not be considered a surrogate for local treatment failure. Our data do not support routine serial FDG-PET/computed tomography for follow-up of patients receiving SBRT for Stage I NSCLC.

From RECIST to PERCIST: Evolving Considerations for PET response criteria in solid tumors

The purpose of this article is to review the status and limitations of anatomic tumor response metrics including the World Health Organization (WHO) criteria, the Response Evaluation Criteria in Solid Tumors (RECIST), and RECIST 1.1. This article also reviews qualitative and quantitative approaches to metabolic tumor response assessment with (18)F-FDG PET and proposes a draft framework for PET Response Criteria in Solid Tumors (PERCIST), version 1.0.

METHODS

PubMed searches, including searches for the terms RECIST, positron, WHO, FDG, cancer (including specific types), treatment response, region of interest, and derivative references, were performed. Abstracts and articles judged most relevant to the goals of this report were reviewed with emphasis on limitations and strengths of the anatomic and PET approaches to treatment response assessment. On the basis of these data and the authors' experience, draft criteria were formulated for PET tumor response to treatment.

RESULTS

Approximately 3,000 potentially relevant references were screened. Anatomic imaging alone using standard WHO, RECIST, and RECIST 1.1 criteria is widely applied but still has limitations in response assessments. For example, despite effective treatment, changes in tumor size can be minimal in tumors such as lymphomas, sarcoma, hepatomas, mesothelioma, and gastrointestinal stromal tumor. CT tumor density, contrast enhancement, or MRI characteristics appear more informative than size but are not yet routinely applied. RECIST criteria may show progression of tumor more slowly than WHO criteria. RECIST 1.1 criteria (assessing a maximum of 5 tumor foci, vs. 10 in RECIST) result in a higher complete response rate than the original RECIST criteria, at least in lymph nodes. Variability appears greater in assessing progression than in assessing response. Qualitative and quantitative approaches to (18)F-FDG PET response assessment have been applied and require a consistent PET methodology to allow quantitative assessments. Statistically significant changes in tumor standardized uptake value (SUV) occur in careful test-retest studies of high-SUV tumors, with a change of 20% in SUV of a region 1 cm or larger in diameter; however, medically relevant beneficial changes are often associated with a 30% or greater decline. The more extensive the therapy, the greater the decline in SUV with most effective treatments. Important components of the proposed PERCIST criteria include assessing normal reference tissue values in a 3-cm-diameter region of interest in the liver, using a consistent PET protocol, using a fixed small region of interest about 1 cm(3) in volume (1.2-cm diameter) in the most active region of metabolically active tumors to minimize statistical variability, assessing tumor size, treating SUV lean measurements in the 1 (up to 5 optional) most metabolically active tumor focus as a continuous variable, requiring a 30% decline in SUV for "response," and deferring to RECIST 1.1 in cases that do not have (18)F-FDG avidity or are technically unsuitable. Criteria to define progression of tumor-absent new lesions are uncertain but are proposed.

CONCLUSION

Anatomic imaging alone using standard WHO, RECIST, and RECIST 1.1 criteria have limitations, particularly in assessing the activity of newer cancer therapies that stabilize disease, whereas (18)F-FDG PET appears particularly valuable in such cases. The proposed PERCIST 1.0 criteria should serve as a starting point for use in clinical trials and in structured quantitative clinical reporting. Undoubtedly, subsequent revisions and enhancements will be required as validation studies are undertaken in varying diseases and treatments.

PET/CT in radiation oncology

PET/CT is an effective tool for the diagnosis, staging and restaging of cancer patients. It combines the complementary information of functional PET images and anatomical CT images in one imaging session. Conventional stand-alone PET has been replaced by PET/CT for improved patient comfort, patient throughput, and most importantly the proven clinical outcome of PET/CT over that of PET and that of separate PET and CT. There are over two thousand PET/CT scanners installed worldwide since 2001. Oncology is the main application for PET/CT. Fluorine-18 deoxyglucose is the choice of radiopharmaceutical in PET for imaging the glucose uptake in tissues, correlated with an increased rate of glycolysis in many tumor cells. New molecular targeted agents are being developed to improve the accuracy of targeting different disease states and assessing therapeutic response. Over 50% of cancer patients receive radiation therapy (RT) in the course of their disease treatment. Clinical data have demonstrated that the information provided by PET/CT often changes patient management of the patient and/or modifies the RT plan from conventional CT simulation. The application of PET/CT in RT is growing and will become increasingly important. Continuing improvement of PET/CT instrumentation will also make it easier for radiation oncologists to integrate PET/CT in RT. The purpose of this article is to provide a review of the current PET/CT technology, to project the future development of PET and CT for PET/CT, and to discuss some issues in adopting PET/CT in RT and potential improvements in PET/CT simulation of the thorax in radiation therapy.

PET for Therapeutic Response Monitoring in Oncology

After diagnosis and staging of cancer, the most important process in modern oncology is assessment of therapeutic response. Timely identification of patients with poor response may allow introduction of alternative therapies, sparing patients the toxicity of ineffective treatments, reducing health care cost, and potentially delivering better outcomes. Metabolic imaging using PET is increasingly recognized as providing earlier and more robust assessment than conventional imaging. There are now ample clinical data indicating that PET metabolic response should be strongly considered for inclusion in evaluation of clinical response in individual high-risk malignancies to both direct the care of individual patients and to guide application of new therapies in particular cancer populations.

Combined imaging modalities: PET/CT and SPECT/CT

The recent development of new radiopharmaceuticals now permits molecular imaging of biologic processes at the cellular level to improve both the diagnosis and treatment of disease. Fused PET/CT and SPECT/CT imaging systems now provide metabolic and functional information from PET or SPECT combined with the high spatial resolution and anatomic information of CT. Because the two sets of images are fused, areas of normal and abnormal metabolic activity can be mapped to recognizable anatomic structures. This fusion of function and anatomy has quickly demonstrated its clinical value, especially in the field of oncology. There are also growing clinical indications in the areas of cardiology, neurology, and imaging of infection. F-18 fluorodeoxyglucose (FDG) is the PET imaging agent currently in most common use. While FDG uptake is nonspecific, it has demonstrated important applications, especially for patients with cancer. Continued progress in fused anatomic and molecular imaging can be anticipated, both in the development of more advanced instrumentation (integrated CT or MRI with PET and SPECT camera technology) and with new radiopharmaceuticals that image more specific physiologic aspects of organ and cell biology.

The prognostic value of PET and PET/CT in cervical cancer

Cervical cancer ranks among the top three cancer diagnoses in women worldwide. In the United States, the SEER Cancer Statistics Review identified cervical cancer as the third leading cause (following childhood cancers and testicular cancer) of average years of life lost per person dying of cancer for all races and both genders. Approximately one-third of cervical cancer patients develop disease recurrence and the majority of these recurrences occur within the first 2 years after completion of therapy. Predictors of disease recurrence include stage and lymph node status at the time of initial diagnosis. The initial diagnosis and staging of cervical cancer has traditionally been achieved by history and physical examination and by use of selected imaging studies. Accurate staging is important both for selecting appropriate therapy and for prognosis. Computed tomography (CT) has been the most widely used imaging method for assessment of nodal involvement and detection of distant metastatic disease. Positron emission tomography (PET) has become an established imaging tool for cervical cancer. The functional information about regional glucose metabolism provided by fluorodeoxyglucose (FDG)-PET provides for greater sensitivity and specificity in most cancer imaging applications by comparison with CT and other anatomic imaging methods. PET is superior to conventional imaging modalities for evaluating patients with cervical cancer.

(18)F-fluorodeoxyglucose positron emission tomography-based assessment of local failure patterns in non-small-cell lung cancer treated with definitive radiotherapy

PURPOSE

To assess the pattern of local failure using (18)F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) scans after radiotherapy (RT) in non-small-cell lung cancer (NSCLC) patients treated with definitive RT whose gross tumor volumes (GTVs) were defined with the aid of pre-RT PET data.

METHOD AND MATERIALS

The data from 26 patients treated with involved-field RT who had local failure and a post-RT PET scan were analyzed. The patterns of failure were visually scored and defined as follows: (1) within the GTV/planning target volume (PTV); (2) within the GTV, PTV, and outward; (3) within the PTV and outward; and (4) outside the PTV. Local failure was also evaluated as originating from nodal areas vs. the primary tumor.

RESULTS

We analyzed 34 lesions. All 26 patients had recurrence originating from their primary tumor. Of the 34 lesions, 8 (24%) were in nodal areas, 5 of which (63%) were marginal or geographic misses compared with only 1 (4%) of the 26 primary recurrences (p = 0.001). Of the eight primary tumors that had received a dose of <60 Gy, six (75%) had failure within the GTV and two (25%) at the GTV margin. At doses of > or = 60 Gy, 6 (33%) of 18 had failure within the GTV and 11 (61%) at the GTV margin, and 1 (6%) was a marginal miss (p < 0.05).

CONCLUSION

At lower doses, the pattern of recurrences was mostly within the GTV, suggesting that the dose might have been a factor for tumor control. At greater doses, the treatment failures were mostly at the margin of the GTV. This suggests that visual incorporation of PET data for GTV delineation might be inadequate, and more sophisticated approaches of PET registration should be evaluated.

Radiation pneumonitis: correlation of toxicity with pulmonary metabolic radiation response

PURPOSE

To characterize the relationship between radiation pneumonitis (RP) clinical symptoms and pulmonary metabolic activity on post-treatment [(18)F]-fluorodeoxyglucose positron emission tomography (FDG-PET).

PATIENTS AND METHODS

We retrospectively studied 101 esophageal cancer patients who underwent restaging FDG-PET/computed tomography imaging 3-12 weeks after completing thoracic radiotherapy. The National Institutes of Health Common Toxicity Criteria, version 3, was used to score the RP clinical symptoms. Linear regression was applied to the FDG-PET/computed tomography images to determine the normalized FDG uptake vs. radiation dose. The pulmonary metabolic radiation response (PMRR) was quantified as this slope. Modeling was performed to determine the interaction of PMRR, mean lung dose (MLD), and the percentage of lung receiving >20 Gy with RP outcomes.

RESULTS

Of the 101 patients, 25 had Grade 0, 10 had Grade 1, 60 had Grade 2, 5 had Grade 3, and 1 had Grade 5 RP symptoms. Logistic regression analysis demonstrated that increased values of both MLD and PMRR were associated with a greater probability of RP clinical symptoms (p = 0.032 and p = 0.033, respectively). Spearman's rank correlation found no association between the PMRR and the dosimetric parameters (planning target volume, MLD, percentage of lung receiving >5-30 Gy). Twofold cross-validation demonstrated that the combination of MLD and PMRR was superior to either alone for assessing the development of clinical RP symptoms. The combined MLD (or percentage of lung receiving >20 Gy) and PMRR had a greater sensitivity and accuracy (53.3% and 62.5%, respectively) than either alone.

CONCLUSION

The results of this study have demonstrated a significant correlation between RP clinical symptoms and the PMRR measured by FDG-PET/computed tomography after thoracic radiotherapy.

Posttreatment FDG-PET uptake in the supraglottic and glottic larynx correlates with decreased quality of life after chemoradiotherapy

PURPOSE

Inflammation and increased metabolic activity associated with oxidative stress in irradiated normal tissues may contribute to both complications following radiotherapy and increased glucose uptake as detected by posttherapy fluorodeoxyglucose (FDG)-PET imaging. We sought to determine whether increased glucose uptake in normal tissues after chemoradiotherapy is associated with increased toxicity.

METHODS AND MATERIALS

Consecutive patients with locoregionally advanced head and neck cancers treated with intensity-modulated radiation therapy and free of recurrence at 1 year were studied. FDG-PET imaging was obtained at 3 and 12 months posttreatment. Standardized uptake value (SUV) levels were determined at various head and neck regions. Functional outcome was measured using a quality of life questionnaire and weight loss and type of diet tolerated 1 year after therapy. A one-tailed Pearson correlation test was used to examine associations between SUV levels and functional outcome measures.

RESULTS

Standardized uptake value levels in the supraglottic and glottic larynx from FDG-PET imaging obtained 12 months posttreatment were inversely associated with quality of life measures and were correlated with a more restricted diet 1 year after therapy. SUV levels at 3 months after therapy did not correlate with functional outcome. Increases in SUV levels in normal tissues between 3 and 12 months were commonly found in the absence of recurrence.

CONCLUSION

Altered metabolism in irradiated tissues persists 1 year after therapy. FDG-PET scans may be used to assess normal tissue damage following chemoradiotherapy. These data support investigating hypermetabolic conditions associated with either inflammation, oxidative stress, or both, as causal agents for radiation-induced normal tissue damage.

Impact of PET on radiation therapy planning in lung cancer

The superiority of PET imaging to structural imaging in many cancers is rapidly transforming the practice of radiotherapy planning, especially in lung cancer. Although most lung cancers are potentially treatable with radiation therapy, only patients who have truly locoregionally confined disease can be cured by this modality. PET improves selection for high-dose radiation therapy by excluding many patients who have incurable distant metastasis or extensive locoregional spread. In those patients suitable for definitive treatment, PET can help shape the treatment fields to avoid geographic miss and minimize unnecessary irradiation of normal tissues. PET will allow for more accurately targeted dose escalation studies in the future and could potentially lead to better long-term survival.

A Pilot Study of [18F]Fluorodeoxyglucose Positron Emission Tomography Scans During and After Radiation-Based Therapy in Patients With Non–Small-Cell Lung Cancer

Purpose

To study whether changes of [18F]fluorodeoxyglucose positron emission tomography (FDG-PET) during treatment correlate with post-treatment responses in tumor and normal lung in patients with non–small-cell lung cancer (NSCLC).

Patients and Methods

Patients with stage I to III NSCLC requiring a definitive dose of fractionated radiation therapy (RT) were eligible. FDG-PET/computed tomography scans were acquired before, during, and after RT. Tumor and lung metabolic responses were assessed qualitatively by physicians and quantitatively by normalized peak FDG activity (the ratio of the maximum FDG activity divided by the mean of the aortic arch background).

Results

The study reached the goal of recruiting 15 patients between February 2004 and August 2005. Of these, 11 patients had partial metabolic response, two patients had complete metabolic response, and two patients had stable disease at approximately 45 Gy during RT. The mean peak tumor FDG activity was 5.2 (95% CI, 4.0 to 6.4), 2.5 (95% CI, 2.0 to 3.0), and 1.7 (95% CI, 1.3 to 2.0) on pre-, during, and post-RT scans, respectively. None of the patients had appreciable changes in the lung during RT. The peak FDG activity of the lung was 0.47 (95% CI, 0.36 to 0.59), 0.52 (95% CI, 0.40 to 0.64), and 1.29 (95% CI, 0.82 to 1.76), on pre-, during-, and post-RT scans, respectively. The qualitative response during RT correlated with the overall response post-RT (P = .03); the peak tumor FDG activity during RT correlated with those 3 months post-RT (R2 = 0.7; P < .001).

Conclusion

This pilot study suggests a significant correlation in tumor metabolic response and no association in lung FDG activity between during RT scans and 3 months post-RT scans in patients with NSCLC. Additional study with a large number of patients is needed to validate these findings.

Correlating metabolic and anatomic responses of primary lung cancers to radiotherapy by combined F-18 FDG PET-CT imaging

Background

To correlate the metabolic changes with size changes for tumor response by concomitant PET-CT evaluation of lung cancers after radiotherapy.

Methods

36 patients were studied pre- and post-radiotherapy with¹⁸FDG PET-CT scans at a median interval of 71 days. All of the patients were followed clinically and radiographically after a mean period of 342 days for assessment of local control or failure rates. Change in size (sum of maximum orthogonal diameters) was correlated with that of maximum standard uptake value (SUV) of the primary lung cancer before and after conventional radiotherapy.

Results

There was a significant reduction in both SUV and size of the primary cancer after radiotherapy (p < 0.00005). Among the 20 surviving patients, the sensitivity, specificity, and accuracy using PET (SUV) were 94%, 50%, 90% respectively and the corresponding values using and CT (size criteria) were 67%, 50%, and 65% respectively. The metabolic change (SUV) was highly correlated with the change in size by a quadratic function. In addition, the mean percentage metabolic change was significantly larger than that of size change (62.3 ± 32.7% vs 47.1 ± 26.1% respectively, p = 0.03)

Conclusion

Correlating and incorporating metabolic change by PET into size change by concomitant CT is more sensitive in assessing therapeutic response than CT alone.

Positron emission tomography in the management of lung cancer

(18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) is a useful technique to characterize the solitary pulmonary nodule, diagnose primary lung cancer, carry out mediastinal and extrathoracic staging, plan radiotherapy, therapeutic response assessment and detect recurrence. PET may help to determine the ideal site for tissue diagnosis as well as predict prognosis. Combined PET and computed tomography (PET/CT) has the best of both worlds of metabolic and anatomic imaging and may provide optimal disease assessment.

Positron emission tomography imaging in nonsmall-cell lung cancer

Positron emission tomography (PET) using 18F-2-deoxy-D-glucose, a D-glucose analog labeled with fluorine-18, complements conventional radiologic assessment in the evaluation of patients with nonsmall-cell lung cancer (NSCLC). PET is being routinely used to improve the detection of nodal and extrathoracic metastases. PET is also currently being evaluated in the assessment of prognosis and therapeutic response and by potentially allowing an earlier assessment of response may prove invaluable in the oncologic management of patients. The article discusses the diagnosis, staging, and assessment of treatment response and prognosis with an emphasis on the appropriate clinical use of PET in management.