Computed Tomography, Positron Emission Tomography, Positron Emission Tomography/Computed Tomography, and Magnetic Resonance Imaging for Staging of Limited Pleural Mesothelioma: Initial Results

Management of malignant pleural mesothelioma

Malignant pleural mesothelioma is a rare neoplasm arising from the surface serosal cells of the pleural cavity. More than 80% of cases of malignant pleural mesothelioma have been attributed to asbestos exposure. In its natural course median survival is 4 to 12 months. If untreated most of patients die due to local complications of the disease. Surgery improves local control but is not sufficient as a single treatment modality. The recommended treatment strategy for a select group of patients is multimodal therapy that includes surgery, radiotherapy and chemotherapy.

SPECT/CT stabilizes the interpretation of somatostatin receptor scintigraphy findings: a retrospective analysis of inter-rater agreement

OBJECTIVE

Correlating the anatomical information from CT with the functional information from SPECT improves diagnostic accuracy of somatostatin-receptor-scintigraphy (SRS) in patients with neuroendocrine tumors (NET). The aim of the present study was to investigate the impact of dual modality SPECT/CT on the inter-rater agreement in SRS.

METHODS

Twenty-five unselected patients with suspected or histologically proven NET in whom whole body planar imaging and low-dose SPECT/CT had been performed after injection of 200 MBq In-111-octreotide were included retrospectively. Images were interpreted independently by 2 nuclear medicine physicians, an experienced one and an inexperienced one. Both readers first re-evaluated the planar whole-body images alone, then added the SPECT images, and finally the CT-images. Lesions with pathologically increased tracer uptake were categorized according to the following 3-point score: equivocal, probably pathologic, and definitely pathologic. Cohen's linear-weighted kappa coefficient kappa was used to quantify inter-rater agreement.

RESULTS

A total number of 50 lesions were described in 23 of the 25 patients. The two readers showed only moderate agreement in the interpretation of the planar findings (kappa = 0.593). Agreement improved to substantial by adding SPECT (kappa = 0.736) and to very good by adding SPECT/CT (kappa = 0.860). SPECT/CT resulted in up-staging of 18% of the lesions and down-staging of 12% compared to planar + SPECT (experienced reader). In addition, SPECT/CT tended to reduce the frequency of indefinite scores (equivocal, probably pathologic), from 18% in planar + SPECT to 6% (p = 0.065). Change of lesion localization by SPECT/CT tended to contribute to the change of lesion score (p = 0.055).

CONCLUSION

The present results suggest that low-dose SPECT/CT stabilizes report quality in SRS by improving inter-rater agreement.

Comparison of CT and integrated PET-CT based radiation therapy planning in patients with malignant pleural mesothelioma

BACKGROUND

When combined with adequate tumoricidal doses, accurate target volume delineation remains to be the one of the most important predictive factors for radiotherapy (RT) success in locally advanced or medically inoperable malignant pleural mesothelioma (MPM) patients. Recently, 18-fluorodeoxyglucose positron emission tomography (PET) has demonstrated significant improvements in diagnosis and accurate staging of MPM. However, role of additional PET data has not been studied in RT planning (RTP) of patients with inoperable MPM or in those who refuse surgery. Therefore, we planned to compare CT with co-registered PET-CT as the basis for delineating target volumes in these patients group.

METHODS

Retrospectively, the CT and co-registered PET-CT data of 13 patients with histologically proven MPM were utilized to delineate target volumes separately. For each patient, target volumes (gross tumor volume [GTV], clinical target volume [CTV], and planning target volume [PTV]) were defined using the CT and PET-CT fusion data sets. The PTV was measured in two ways: PTV1 was CTV plus a 1-cm margin, and PTV2 was GTV plus a 1-cm margin. We analyzed differences in target volumes.

RESULTS

In 12 of 13 patients, compared to CT-based delineation, PET-CT-based delineation resulted in a statistically significant decrease in the mean GTV, CTV, PTV1, and PTV2. In these 12 patients, mean GTV decreased by 47.1% +/- 28.4%, mean CTV decreased by 38.7% +/- 24.7%, mean PTV1 decreased by 31.1% +/- 23.1%, and mean PTV2 decreased by 40.0% +/- 24.0%. In 4 of 13 patients, hilar lymph nodes were identified by PET-CT that was not identified by CT alone, changing the nodal status of tumor staging in those patients.

CONCLUSION

This study demonstrated the usefulness of PET-CT-based target volume delineation in patients with MPM. Co-registration of PET and CT information reduces the likelihood of geographic misses, and additionally, significant reductions observed in target volumes may potentially allow escalation of RT dose beyond conventional limits potential clinical benefits in tumor control rates, which needs to be tested in future studies.