Does selective pleural irradiation of malignant pleural mesothelioma allow radiation dose escalation?

Background After lung-sparing radiotherapy for malignant pleural mesothelioma (MPM), local failure at sites of previous gross disease represents the dominant form of failure. Our aim is to investigate if selective irradiation of the gross pleural disease only can allow dose escalation.

Materials and methods In all, 12 consecutive stage I-IV MPM patients (6 left-sided and 6 right-sided) were retrospectively identified and included. A magnetic resonance imaging-based pleural gross tumor volume (GTV) was contoured. Two sets of planning target volumes (PTV) were generated for each patient: (1) a "selective" PTV (S-PTV), originating from a 5-mm isotropic expansion from the GTV and (2) an "elective" PTV (E-PTV), originating from a 5-mm isotropic expansion from the whole ipsilateral pleural space. Two sets of volumetric modulated arc therapy (VMAT) treatment plans were generated: a "selective" pleural irradiation plan (SPI plan) and an "elective" pleural irradiation plan (EPI plan, planned with a simultaneous integrated boost technique [SIB]).

Results In the SPI plans, the average median dose to the S-PTV was 53.6Gy (range 41-63.6Gy). In 4 of 12 pa-tients, it was possible to escalate the dose to the S-PTV to > 58Gy. In the EPI plans, the average median doses to the E-PTV and to the S-PTV were 48.6Gy (range 38.5-58.7) and 49Gy (range 38.6-59.5Gy), respectively. No significant dose escalation was achievable.

Conclusion The omission of the elective irradiation of the whole ipsilateral pleural space allowed dose escalation from 49Gy to more than 58Gy in 4 of 12 chemonaive MPM patients. This strategy may form the basis for nonsurgical radical combined modality treatment of MPM.