1562P - Optimal definition of target volumes in lung-sparing pleural radiotherapy for malignant pleural mesothelioma (MPM)

Date 29 September 2014
Event ESMO 2014
Session Poster Display session
Topics Mesothelioma
Surgery and/or Radiotherapy of Cancer
Presenter Angela Botticella
Citation Annals of Oncology (2014) 25 (suppl_4): iv542-iv545. 10.1093/annonc/mdu357
Authors A. Botticella1, G. Defraene1, K. Nackaerts2, C. Deroose3, J. Coolen4, P. Nafteux5, S. Peeters1, D. De Ruysscher1
  • 1Radiation Oncology, University Hospitals Leuven - Campus Gasthuisberg, 3000 - Leuven/BE
  • 2Respiratory Oncology Unit, University Hospital Leuven, 3000 - Leuven/BE
  • 3Nuclear Medicine, University Hospitals Leuven - Campus Gasthuisberg, 3000 - Leuven/BE
  • 4Department Of Radiology, University Hospitals Leuven - Campus Gasthuisberg, Leuven/BE
  • 5Thoracic Surgery, University Hospitals Leuven - Campus Gasthuisberg, 3000 - Leuven/BE

Abstract

Aim

High dose lung-sparing pleural radiotherapy for malignant mesothelioma is difficult. Accurate target delineation is critical. The optimal imaging modality to define radiotherapy target volumes has not been studied in depth. This is the aim of the present study.

Methods

Twelve consecutive patients with a histopathological diagnosis of stage I-III MPM (6 left-sided and 6 right-sided) were included. CT scans with iv contrast, 18FDG-CT/PET scans and MRI scans were obtained. CT scans were rigidly co-registered with 18FDG-CT-PET and with MRI scans. Four sets of pleural GTVs were defined: based on CT, on CT/PET, on CT/MRI and on CT/PET/MRI. The pleural tumour was contoured; mediastinal nodes were excluded. “Quantitative” evaluation of the volumesincluded the coefficient of variation [COV, defined as the ratio between the standard deviation and the mean]) and pairwise comparison of the overlap index with the Jaccard index (JI, defined as the ratio of the intersection between two volumes and their union). “Qualitative” (visual) assessment of the different volumes was also performed, in order to evaluate the “geographical miss”.

Results

Pairwise comparison with the Jaccard Index
PAIRWISE COMPARISON JI
CT vs. CT+CT-PET 0.97
CT vs. CT+MRI 0.91
CT vs. CT+PET+MRI 0.91
CT+CT-PET vs. CT+MRI 0.91
CT+CT-PET vs. CT+PET+MRI 0.91
CT+MRI vs. CT+PET+MRI 0.99

Mean GTV CT was the smallest volume (655.9+322.1 cc): when compared with CT/PET-based, CT/MRI-based and CT/PET/MRI-based volumes, they were respectively 1.26%, 5.33% and 5.9% larger. COV was lower in MRI-based contours (0.43 vs 0.48-0.49), indicating a lower dispersion of the values. Mean JI ranges from 0.91 and 0.99: a lower concordance was registered between CT/MRI-based contours versus all the others. “Geographical miss” was identified in 11/12 patients in CT/MRI-based contours and in 4/12 patients in CT/PET-based volumes.

Conclusions

To the best of our knowledge, this is the first study showing that the integration of MRI into the target volume definition in hemithoracic radiotherapy in MPM may allow to improve the accuracy of target delineation and reduce the likelihood of geographical misses.

Disclosure

All authors have declared no conflicts of interest.