Does selective pleural irradiation of malignant pleural mesothelioma allow radiation dose escalation? : A planning study

Our plain-English summary of Does selective pleural irradiation of malignant pleural mesothelioma allow radiation dose escalation? : A planning study, by A. Botticella, G. Defraene, K. Nackaerts, et al (Strahlentherapie und Onkologie, 2017).

The study

• Authors: A. Botticella, G. Defraene, K. Nackaerts, C. Deroose, J. Coolen, P. Nafteux, B. Vanstraelen, S. Joosten, L.A.W. Michiels, S. Peeters, D. De Ruysscher
• Journal: Strahlentherapie und Onkologie
• Published: 2017;193(4):285-294
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

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

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

In plain English

This was a retrospective radiotherapy planning study. The authors made computer treatment plans; the article does not report these plans being given to patients. They used scans of 12 patients with stage I–IV malignant pleural mesothelioma (6 left-sided, 6 right-sided; 10 men and 2 women) diagnosed between 2010 and 2013 at their institution, none of whom had received chemotherapy. For each patient they made two plans. One targeted only the visible tumor on the pleura (selective). The other targeted the whole pleura on that side (elective). The question was whether the selective plans allowed a higher tumor dose within set limits for nearby organs. In the selective plans, the median tumor dose ranged from 40.99 to 63.62 Gy. Four of 12 patients could receive 58 Gy or more with selective plans, versus 1 of 12 with elective plans. The heart prevented further dose increases in 11 of 12 selective plans. The authors concluded that selective irradiation allowed higher doses in some patients. They noted the small sample size and that it was a planning study. The article does not study asbestos exposure.

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 radiotherapy treatment-planning (contouring) study comparing two computer-generated plan types for each patient
• Who was studied: 12 consecutive patients with biopsy-proven, previously untreated stage I–IV malignant pleural mesothelioma, diagnosed January 2010 to December 2013 at the authors' institution (affiliations in Leuven, Belgium). There were 6 left-sided and 6 right-sided cases, 10 men and 2 women, and none had received chemotherapy. Patients with prior pleurodesis were excluded.
• Exposure: Not an asbestos exposure study. What was compared was two volumetric modulated arc therapy (VMAT) radiation plans per patient. The selective plan (SPI) targeted only the involved pleura (gross tumor). The elective plan (EPI) targeted the whole ipsilateral pleura. Doses were in 2 Gy fractions, and the selective plans tried escalating in 4 Gy steps.
• Main results:
  • A dose of 58 Gy or more was achievable in 4 of 12 patients with selective plans, compared with 1 of 12 patients with elective plans.
  • The proportion of patients who could receive 58 Gy or more significantly favored the selective plans (p = 0.003).
  • In the selective plans, the median dose to the selective target volume ranged from 40.99 to 63.62 Gy (mean 53.57 Gy, SD 5.47).
  • In the selective plans, 10 of 12 patients reached a median dose of at least 50 Gy to the selective target volume.
  • The median dose to the selective target volume was 53.6 Gy in the selective plans and 49.1 Gy in the elective plans (p = 0.003).
  • The authors described the difference in median doses between plan types as rather small in absolute terms (3.5 Gy).
  • The heart was the organ that most often limited further dose escalation: 11 of 12 patients in the selective plans.
• The authors' conclusion: The authors concluded that leaving out irradiation of the whole ipsilateral pleural space allowed dose escalation from 49 Gy to more than 58 Gy in 4 of 12 chemotherapy-naive patients. They said this strategy may form the basis for nonsurgical radical combined-modality treatment of malignant pleural mesothelioma.
• Limitations the authors state:
  • Small sample size, and it is a planning study rather than a treatment study
  • Rigid (rather than deformable) coregistration of CT and MRI images when outlining the tumor, described as suboptimal fusion
  • Planning CT scans were taken during free breathing, which may have affected the lung dose limits in planning

Topics

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

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

Related studies

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• Tomotherapy PET-guided dose escalation: A dosimetric feasibility study for patients with malignant pleural mesothelioma — A. Maggio, C. Cutaia, et al. (2016)
• Intensity-Modulated Radiation Therapy Improves the Target Coverage Over 3-D Planning While Meeting Lung Tolerance Doses for All Patients With Malignant Pleural Mesothelioma — S. Ulger, E. Cetin, et al. (2017)
• Geometric dose prediction model for hemithoracic intensity-modulated radiation therapy in mesothelioma patients with two intact lungs — L. Kuo, E.D. Yorke, et al. (2016)
• Tomotherapy after pleurectomy/decortication or biopsy for malignant pleural mesothelioma allows the delivery of high dose of radiation in patients with intact lung — E. Minatel, M. Trovo, et al. (2012)
• Intensity-modulated radiation therapy with simultaneous integrated boost in unresected left-sided pleural mesothelioma: a case report — S. Cilla, C. Digesú, et al. (2010)

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