156PD - Optimization of gross tumour volume definition and treatment planning in lung-sparing volumetric modulated arc therapy for pleural mesothelioma

Date 16 April 2015
Event ELCC 2015
Session Medical and radiation oncology
Topics Mesothelioma
Surgery and/or Radiotherapy of Cancer
Presenter Angela Botticella
Citation Annals of Oncology (2015) 26 (suppl_1): 48-50. 10.1093/annonc/mdv052
Authors A. Botticella1, G. Defraene1, K. Nackaerts2, C. Deroose3, J. Coolen4, P. Nafteux5, S. Peeters6, D. De Ruysscher6
  • 1Department Of Oncology, Experimental Radiation Oncology, KU Leuven, 3000 - Leuven/BE
  • 2Respiratory Diseases/respiratory Oncology Unit, University Hospitals Leuven - Campus Gasthuisberg, 3000 - Leuven/BE
  • 3Department Of Imaging And Pathology, KU Leuven-University of Leuven, University Hospitals Leuven, 3000 - Leuven/BE
  • 4Radiology Department, University Hospitals Leuven - Campus Gasthuisberg, 3000 - Leuven/BE
  • 5Department Of Thoracic Surgery, University Hospitals Leuven - Campus Gasthuisberg, 3000 - Leuven/BE
  • 6Department Of Radiation Oncology, KU Leuven-University of Leuven, University Hospitals Leuven, 3000 - Leuven/BE

Abstract

Aim/Background

Our purpose is to optimize target definition and treatment planning in lung-sparing volumetric modulated arc therapy (VMAT) for malignant pleural mesothelioma.

Methods

Sixteen consecutive stage I-IV MPM patients were retrospectively identified from an institutional database and included. For the contouring phase, a CT with IV contrast, 18FDG-PET/CT and MRI 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. For the planning phase, the GTV with the highest rate of newly-identified tumor sites was chosen to generate the PTV. The first 6 consecutive left-sided and right-sided patients were selected, for a total of 12 patients. For all patients, VMAT plans were generated. Prescription dose was 50 Gy in 2-Gy fractions delivered to the PTV, and progressive dose-escalation steps (with 4 Gy increment) were attempted. The correlation between the contralateral/ipsilateral lung volume ratio and the PTV/total lung volume ratio with the achieved PTV dose was investigated.

Results

Compared to CT, PET/CT identified geographical miss in 12/16 patients, while MRI avoided frank GTV underestimation in 15/16 patients. Differences in mean volumes were not significantly different, and ranged from 5 to 6%. For 10/12 patients was possible to generate a 50 Gy VMAT plan. The maximum achievable dose was 54 Gy, 58 Gy and 62 Gy in 7, 4 and 1 patients, respectively. A significant correlation between the contralateral/ipsilateral lung volume ratio and the PTV/total lung volume ratio with the achieved PTV dose was found (p = 0.05).

Conclusions

This is the first report showing that MRI-based target definition may improve the accuracy of GTV delineation and thus reduce the probability of geographical misses. Patients with a higher ratio of contralateral/ipsilateral lung volume and lower ratio of PTV/total lung volume are less likely to achieve a therapeutic RT dose.

Disclosure

All authors have declared no conflicts of interest.