Functional image guided radiation therapy planning in volumetric modulated arc therapy for patients with malignant pleural mesothelioma

Our plain-English summary of Functional image guided radiation therapy planning in volumetric modulated arc therapy for patients with malignant pleural mesothelioma, by Y. Doi, T. Kimura, T. Nakashima, et al (Advances in Radiation Oncology, 2017).

The study

• Authors: Y. Doi, T. Kimura, T. Nakashima, Y. Takeuchi, I. Takahashi, I. Nishibuchi, Y. Murakami, Y. Nagata
• Journal: Advances in Radiation Oncology
• Published: 2017;2(2):183-191
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Purpose: To investigate the incorporation of functional lung image-derived low-attenuation area (LAA) based on 4-dimensional computed tomography (4D-CT) in volumetric modulated arc therapy (VMAT) planning for patients with malignant pleural mesothelioma (MPM) after extrapleural pneumonectomy.

Methods And Materials: Twelve patients with MPM after extrapleural pneumonectomy were included. The primarily affected side was the right in 6 patients and the left in 6 patients. LAA was generated from 4D-CT data according to CT values with a threshold of less than -860 Hounsfield units (HU). Functional lung image was defined as the area where LAA was excluded from contralateral lung image. Two radiation therapy plans were designed: (1) Plan C, conventional VMAT and (2) Plan F, functional VMAT plan based on the functional lung. Both plans were compared in each patient with respect to the following dosimetric parameters: fV20, V20, fV10, V10, fV5, and V5, the percentages of functional or contralateral lung volumes irradiated with >20 Gy, 10 Gy, or 5 Gy, respectively; functional mean lung dose (fMLD) and mean lung dose (MLD), the mean dose to the functional or contralateral lung, respectively; maximum dose to the cord; mean doses to the liver and heart; and planning target volume homogeneity index.

Results: fV5 and MLD were significantly lower in Plan F (fV5, median 57.5% in Plan C vs 38.5% in Plan F, P < .01; MLD, median 7.0 Gy in Plan C vs 6.4 Gy in Plan F, P = .04). fV10, V5, and fMLD were also significantly lower in Plan F. Compared with Plan C, planning target volume homogeneity index and liver, heart, and cord doses were not significantly elevated in Plan F.

Conclusions: Significant reductions in fV5, fV10, fMLD, V5, and MLD were achieved with the functional image guided VMAT plan without negative effects on other factors. LAA-based functional image guided radiation therapy planning in VMAT is a feasible method to spare the functional lung in patients with MPM.

In plain English

This simulation study of radiation planning for malignant pleural mesothelioma was done at Hiroshima University Hospital, Japan. It used scans of 12 men who had the affected-side lung removed (extrapleural pneumonectomy) and then radiation therapy between 2010 and 2013. All had a history of asbestos exposure. For each man, the authors designed two plans aiming radiation at the operated side of the chest while limiting dose to the remaining lung. One was conventional; the other, a 'functional' plan, also aimed to spare the better-working part of that lung, identified on CT by excluding low-density areas. These areas averaged 46.6% of the remaining lung. With the functional plan, the median share of working lung receiving 5 Gy fell from 57.5% to 38.5%, and the median mean dose to the remaining lung fell from 7.0 Gy to 6.4 Gy. Doses to the target, liver, heart and spinal cord did not differ significantly. The study compared plans only; it reported no patient outcomes. The authors concluded the approach appears effective in preserving functional lung, noted their small patient numbers, and called for prospective trials.

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: Treatment-planning simulation study comparing two radiation therapy plans (conventional and functional-lung-sparing VMAT) for each patient
• Who was studied: 12 male patients with malignant pleural mesothelioma who had definitive radiation therapy after extrapleural pneumonectomy at Hiroshima University Hospital, Japan, from 2010 to 2013 (6 right-sided, 6 left-sided). All had a history of asbestos exposure.
• Exposure: The study compared two volumetric modulated arc therapy (VMAT) plans prescribing 54 Gy in 27 fractions. In both, the target included the entire preoperative ipsilateral hemithorax, scars, drain sites and involved nodal stations. Plan C was conventional and based on the total contralateral lung. Plan F was functional, adding the functional lung, defined as the contralateral lung minus low-attenuation areas on 4-dimensional CT. Patients' asbestos exposure was noted but not described further, and no fiber type was given.
• Main results:
  • Percentage of functional lung receiving 5 Gy (fV5): median 57.5% for Plan C vs 38.5% for Plan F, P less than .01
  • Percentage of functional lung receiving 10 Gy (fV10): median 14.8% for Plan C vs 8.9% for Plan F, P less than .01
  • Mean dose to functional lung (fMLD): median 6.8 Gy for Plan C vs 5.5 Gy for Plan F, P less than .01
  • Percentage of total contralateral lung receiving 5 Gy (V5): median 51.4% for Plan C vs 41.6% for Plan F, P less than .01
  • Mean dose to total contralateral lung (MLD): median 7.0 Gy for Plan C vs 6.4 Gy for Plan F (P = .04)
  • fV20, V10 and V20 were lower for Plan F, but the differences were not statistically significant
  • No significant differences between plans in planning target volume coverage, homogeneity index, or doses to liver, heart and spinal cord
  • On average, the low-attenuation areas covered 46.6% of the total contralateral lung
• The authors' conclusion: The authors concluded that functional, low-attenuation-area-based image guided VMAT planning appears to be effective in preserving functional lung volume in patients with MPM. They stated that further investigations and prospective trials are required.
• Limitations the authors state:
  • The number of patients was not sufficient
  • The CT value thresholds for detecting low-attenuation areas, and their correlation with lung function, have not been validated in patients with MPM after extrapleural pneumonectomy
  • Plan F tended toward higher doses to other organs at risk, although the differences were not statistically significant
  • Prospective trials are needed to determine whether this planning improves outcomes such as survival and complication rates

Topics

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma, Extrapleural Pneumonectomy (EPP).

Related studies

• Dosimetric evaluation of helical tomotherapy and volumetric-modulated arc therapy for malignant pleural mesothelioma: a planning study for dose escalation — F.L. Zhang, N. Lu, et al. (2021)
• Clinical experience of volumetric modulated arc therapy for malignant pleural mesothelioma after extrapleural pneumonectomy — T. Kimura, Y. Doi, et al. (2015)
• 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)
• Extra-pleural pneumonectomy in the era of image-guided intensity-modulated radiotherapy — M. Trovo, D. Franceschini, et al. (2019)
• Intensity-modulated radiotherapy and volumetric-modulated arc therapy for malignant pleural mesothelioma after extrapleural pleuropneumonectomy — J. Krayenbuehl, O. Riesterer, et al. (2013)
• Dosimetric Comparison Between Helical Tomotherapy and Volumetric Modulated Arc Therapy in Patients With Malignant Pleural Mesothelioma — T. Müdder, G.R. Sarria, et al. (2022)

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