Optimal gross tumor volume definition in lung-sparing intensity modulated radiotherapy for pleural mesothelioma: an in silico study

Our plain-English summary of Optimal gross tumor volume definition in lung-sparing intensity modulated radiotherapy for pleural mesothelioma: an in silico study, by A. Botticella, G. Defraene, K. Nackaerts, et al (Acta Oncologica, 2016).

The study

• Authors: A. Botticella, G. Defraene, K. Nackaerts, C.M. Deroose, J. Coolen, P. Nafteux, S. Peeters, U. Ricardi, D. De Ruysscher
• Journal: Acta Oncologica
• Published: 2016;55(12):1450-1455
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: The gross tumor volume (GTV) definition for malignant pleural mesothelioma (MPM) is ill-defined. We therefore investigated which imaging modality is optimal: computed tomography (CT) with intravenous contrast (IVC), positron emission tomography-CT (PET/CT) or magnetic resonance imaging (MRI).

Material And Methods: Sixteen consecutive patients with untreated stage I-IV MPM were included. Patients with prior pleurodesis were excluded. CT with IVC, 18FDG-PET/CT and MRI (T2 and contrast-enhanced T1) were obtained. CT was rigidly co-registered with PET/CT and with MRI. Three sets of pleural GTVs were defined: GTVCT, GTVCT+PET/CT and GTVCT+MRI. Quantitative and qualitative evaluations of the contoured GTVs were performed.

Results: Compared to CT-based GTV definition, PET/CT identified additional tumor sites (defined as either separate nodules or greater extent of a known tumor) in 12/16 patients. Compared to either CT or PET/CT, MRI identified additional tumor sites in 15/16 patients (p = .7). The mean GTVCT, GTVCT+PET/CT and GTVCT+MRI [±standard deviation (SD)] were 630.1 cm3 (±302.81), 640.23 cm3 (±302.83) and 660.8 cm3 (±290.8), respectively. Differences in mean volumes were not significant. The mean Jaccard Index was significantly lower in MRI-based contours versus all the others.

Conclusion: As MRI identified additional pleural disease sites in the majority of patients, it may play a role in optimal target volume definition.

In plain English

This retrospective study from the authors' institution in Leuven, Belgium, compared three scan types for outlining malignant pleural mesothelioma when planning lung-sparing radiotherapy. It did not study asbestos exposure. Sixteen of 66 patients in an institutional database, diagnosed between January 2010 and December 2013, had all three scans: CT with intravenous contrast, FDG-PET/CT and MRI. For each patient, radiation oncologists outlined the tumor three ways: on CT alone, on CT combined with PET/CT, and on CT combined with MRI. Compared with CT, PET/CT showed additional tumor sites in 12 of 16 patients. MRI showed additional sites in 15 of 16 patients compared with either CT or PET/CT, particularly in the diaphragm, parietal pleura and chest wall. Mean tumor volumes (630.1, 640.23 and 660.8 cm3) did not differ significantly. MRI-based outlines overlapped significantly less with the other outlines. The authors concluded that the study supports adding thoracic MRI to tumor outlining. They noted the small sample, the retrospective design, imperfect image alignment, and that extra sites seen on scans were not confirmed by pathology.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Retrospective contouring (in silico) study comparing tumor outlines drawn with different imaging methods
• Who was studied: 16 patients with biopsy-proven, previously untreated stage I to IV malignant pleural mesothelioma (12 men, 4 women), diagnosed between January 2010 and December 2013 at the authors' institution in Leuven. They were selected from 66 patients in an institutional database. Patients with prior pleurodesis were excluded.
• Exposure: No asbestos exposure was studied. The comparison was between imaging methods used to define the gross tumor volume: CT with intravenous contrast, 18F-FDG-PET/CT, and MRI (T2 and contrast-enhanced T1).
• Main results:
  • Compared with CT, PET/CT identified additional tumor sites in 12 of 16 patients.
  • Among the 12 patients with additional sites on PET/CT, the new site was the diaphragm in 7.
  • MRI identified additional tumor sites in 15 of 16 patients compared with either CT or PET/CT.
  • Compared with CT, MRI found additional sites in the diaphragm in 13 of 15 patients (p = .001), in the parietal pleura in 11 of 15 (p = .001) and in the chest wall in 5 of 15 (p = .07).
  • Compared with PET/CT, MRI found new sites in the parietal pleura in 9 of 15 patients, the diaphragm in 7 of 15 and the chest wall in 5 of 15.
  • Mean tumor volumes were 630.1 cm3 (SD 302.81) for CT, 640.23 cm3 (SD 302.83) for CT plus PET/CT and 660.8 cm3 (SD 290.8) for CT plus MRI. The differences were not statistically significant.
  • Overlap between outlines (Jaccard Index) ranged from 0.91 to 0.97. Overlap was significantly lower when MRI-based outlines were compared with non-MRI-based outlines.
• The authors' conclusion: The authors concluded that, by their assessment, adding MRI would have potentially avoided missing tumor areas in 15 of 16 patients, and that the study supports integrating thoracic MRI into pleural tumor volume definition for lung-sparing radiotherapy.
• Limitations the authors state:
  • Relatively small sample size, retrospective design, no gated images, and rigid (sub-optimal) co-registration between imaging methods.
  • The study assumed that additional possible tumor sites seen on imaging were truly disease; there was no pathologic confirmation.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma, Pleurodesis.

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