Distribution of lymph node metastases on FDG-PET/CT in inoperable or unresectable oesophageal cancer patients and the impact on target volume definition in radiation therapy

Inter-observer variation in gross tumour volume delineation of oesophageal cancer on MR, CT and PET/CT

BACKGROUND

The aim of our study was to assess the inter-observer variability in delineation of the gross tumour volume (GTV) of oesophageal cancer on magnetic resonance (MR) in comparison to computed tomography (CT) and positron emission tomography and CT (PET/CT).

PATIENTS AND METHODS

Twenty-three consecutive patients with oesophageal cancer treated with chemo-radiotherapy were enrolled. All patients had PET/CT and MR imaging in treatment position. Five observers independently delineated the GTV on CT alone, MR alone, CT with co-registered MR, PET/CT alone and MR with co-registered PET/CT. Volumes of GTV were measured per patient and imaging modality. Inter-observer agreement, expressed in generalized conformity index (CIgen), volumetric conformity index (VCI), planar conformity index (PCI) and inter-delineation distance (IDD) were calculated per patient and imaging modality. Linear mixed models were used for statistical analysis.

RESULTS

GTV volume was significantly lower on MR (33.03 cm3) compared to CT (37.1 cm3; p = 0.002) and on PET/CT MR (35.2 cm3; p = 0.018) compared to PET/CT (39.1 cm3). The CIgen was lowest on CT (0.56) and highest on PET/CT MR (0.67). The difference in CIgen between MR (0.61) and CT was borderline significant (p = 0.048). The VCI was significantly higher on MR (0.71; p = 0.007) and on CT MR (0.71; p = 0.004) compared to CT (0.67). The PCI was significantly higher on CT MR (0.67; p = 0.031) compared to CT (0.64). The largest differences were observed in the cranio-caudal direction.

CONCLUSIONS

The highest inter-observer agreement was found for PET/CT MR and the lowest for CT. MR could reduce the difference in delineation between observers and provide additional information about the local extent of the tumour.

The Role of MRI and PET/CT in Radiotherapy Target Volume Determination in Gastrointestinal Cancers-Review of the Literature

Positron emission tomography with computed tomography (PET/CT) and magnetic resonance imaging (MRI) could improve accuracy in target volume determination for gastrointestinal cancers. A systematic search of the PubMed database was performed, focusing on studies published within the last 20 years. Articles were considered eligible for the review if they included patients with anal canal, esophageal, rectal or pancreatic cancer, as well as PET/CT or MRI for radiotherapy treatment planning, and if they reported interobserver variability or changes in treatment planning volume due to different imaging modalities or correlation between the imaging modality and histopathologic specimen. The search of the literature retrieved 1396 articles. We retrieved six articles from an additional search of the reference lists of related articles. Forty-one studies were included in the final review. PET/CT seems indispensable for target volume determination of pathological lymph nodes in esophageal and anal canal cancer. MRI seems appropriate for the delineation of primary tumors in the pelvis as rectal and anal canal cancer. Delineation of the target volumes for radiotherapy of pancreatic cancer remains challenging, and additional studies are needed.

[F18] FDG-PET/CT for manual or semiautomated GTV delineation of the primary tumor for radiation therapy planning in patients with esophageal cancer: is it useful?

Background

Target volume definition of the primary tumor in esophageal cancer is usually based on computed tomography (CT) supported by endoscopy and/or endoscopic ultrasound and can be difficult given the low soft-tissue contrast of CT resulting in large interobserver variability. We evaluated the value of a dedicated planning [F18] FDG-Positron emission tomography/computer tomography (PET/CT) for harmonization of gross tumor volume (GTV) delineation and the feasibility of semiautomated structures for planning purposes in a large cohort.

Methods

Patients receiving a dedicated planning [F18] FDG-PET/CT (06/2011–03/2016) were included. GTV was delineated on CT and on PET/CT (GTV_CT and GTV_PET/CT, respectively) by three independent radiation oncologists. Interobserver variability was evaluated by comparison of mean GTV and mean tumor lengths, and via Sørensen–Dice coefficients (DSC) for spatial overlap. Semiautomated volumes were constructed based on PET/CT using fixed standardized uptake values (SUV) thresholds (SUV30, 35, and 40) or background- and metabolically corrected PERCIST-TLG and Schaefer algorithms, and compared to manually delineated volumes.

Results

45 cases were evaluated. Mean GTV_CT and GTV_PET/CT were 59.2/58.0 ml, 65.4/64.1 ml, and 60.4/59.2 ml for observers A–C. No significant difference between CT- and PET/CT-based delineation was found comparing the mean volumes or lengths. Mean Dice coefficients on CT and PET/CT were 0.79/0.77, 0.81/0.78, and 0.8/0.78 for observer pairs AB, AC, and BC, respectively, with no significant differences. Mean GTV volumes delineated semiautomatically with SUV30/SUV35/SUV40/Schaefer’s and PERCIST-TLG threshold were 69.1/23.9/18.8/18.6 and 70.9 ml. The best concordance of a semiautomatically delineated structure with the manually delineated GTV_CT/GTV_PET/CT was observed for PERCIST-TLG.

Conclusion

We were not able to show that the integration of PET/CT for GTV delineation of the primary tumor resulted in reduced interobserver variability. The PERCIST-TLG algorithm seemed most promising compared to other thresholds for further evaluation of semiautomated delineation of esophageal cancer.

Recent advances of PET imaging in clinical radiation oncology

Radiotherapy and radiation oncology play a key role in the clinical management of patients suffering from oncological diseases. In clinical routine, anatomic imaging such as contrast-enhanced CT and MRI are widely available and are usually used to improve the target volume delineation for subsequent radiotherapy. Moreover, these modalities are also used for treatment monitoring after radiotherapy. However, some diagnostic questions cannot be sufficiently addressed by the mere use standard morphological imaging. Therefore, positron emission tomography (PET) imaging gains increasing clinical significance in the management of oncological patients undergoing radiotherapy, as PET allows the visualization and quantification of tumoral features on a molecular level beyond the mere morphological extent shown by conventional imaging, such as tumor metabolism or receptor expression. The tumor metabolism or receptor expression information derived from PET can be used as tool for visualization of tumor extent, for assessing response during and after therapy, for prediction of patterns of failure and for definition of the volume in need of dose-escalation. This review focuses on recent and current advances of PET imaging within the field of clinical radiotherapy / radiation oncology in several oncological entities (neuro-oncology, head & neck cancer, lung cancer, gastrointestinal tumors and prostate cancer) with particular emphasis on radiotherapy planning, response assessment after radiotherapy and prognostication.

Nodal FDG-PET/CT uptake influences outcome and relapse location among esophageal cancer patients submitted to chemotherapy or radiochemotherapy

PURPOSE

Our aim was investigate whether lymph node uptake is associated with survival and regional relapses, and relapse patterns with respect to the radiotherapy fields in esophageal cancer (EC).

MATERIALS AND METHODS

The FDG-PET/CT image datasets of 56 patients were analyzed. All patients underwent definitive or neoadjuvant radio/chemotherapy (RCT). All patients suffering from persistent or recurrent local/regional-only disease after RCT were considered for salvage resection. Patients with adenocarcinoma without metastatic disease were considered for planned resection (usually within 3 months of treatment).

RESULTS

Patients with PET-positive lymph nodes before treatment had a worse overall survival and a shorter disease-free survival than those without PET-positive nodes. They also had worse node and metastatic relapse-free survival. N2 patients had statistically significant poorer outcomes than N1-N0 patients and a better survival if the involved nodes were closer to the esophageal tumor. Involved node location by PET/CT also affected global, nodal and metastatic relapses. In addition, an increment of SUVmax value increased relative risk of death and increased relative risk of node and metastatic relapses. The first site of relapse was metastatic recurrence and, second, local recurrence. The most frequent were "in-field" loco/regional recurrence. We observed a relationship between patients classified-N1 and out-field nodal recurrence (p = 0.024), and between patients-N2 and in-field nodal recurrence. The number of PET-positive nodes was an independent significant prognostic predictor for relapse (p < 0.001).

CONCLUSION

Our study shows that only FDG-PET/CT can provide prognostic information in EC. Nodal PET/CT uptake influences outcome and relapse location among EC patients.

Identification of risk factors and the pattern of lower cervical lymph node metastasis in esophageal cancer: implications for radiotherapy target delineation

Radiotherapy remains the important therapeutic strategy for patients with esophageal cancer (EC). At present, there is no uniform opinion or standard care on the range of radiotherapy in the treatment of EC patients. This study aimed to investigate the risk factors associated with lower cervical lymph node metastasis (LNM) and to explore the distribution pattern of lower cervical metastatic lymph nodes. It could provide useful information regarding accurate target volume delineation for EC. We identified 239 patients who initial diagnosed with esophageal squamous cell carcinoma. The clinicopathological factors related to LNM were analyzed and the locations of the lower cervical metastatic lymph nodes were transferred onto computed tomography images. The lower cervical area was further divided into four subgroups areas. The results showed that the incidence of lower cervical LNM was 37.2 % (89 of 239) and 94.4 % (84 of 89 patients) patients had subgroup II and/or subgroup III region LNM. Of those patients, 151 nodes were considered to be clinical metastatic in the lower cervical region and 96% nodes were located in group II and group III. Based on the present study, prophylactic irradiating to lower cervical areas is recommended for patients with deeper tumor invasion, the mediastinal level 1, 2, and 4 station LNM and the more number of LNM. The atlas showed that, for the lower cervical area, the subgroup II and III region should be precisely covered in the target volume and the subgroup I and IV may be spared for minimizing the toxicity.