Dosimetric Comparison of Lung-Sparing Radiation Therapy between Volumetric Arc Therapy and Helical Tomotherapy for Unresectable Malignant Pleural Mesothelioma

Our plain-English summary of Dosimetric Comparison of Lung-Sparing Radiation Therapy between Volumetric Arc Therapy and Helical Tomotherapy for Unresectable Malignant Pleural Mesothelioma, by B. Pehlivan, K. Sengul, A. Yesil, et al (BioMed Research International, 2019).

The study

• Authors: B. Pehlivan, K. Sengul, A. Yesil, N. Nalbant, O. Ozturk, Y. Ozdemir, E. Topkan
• Journal: BioMed Research International
• Published: 2019;2019:4568958
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objective: To compare volumetric arc therapy (VMAT) and helical tomotherapy (HT) plans in terms of dosimetric parameters in positron emission tomography- (PET-) computerized tomography- (CT-) based radiation therapy planning in unresectable malignant pleural mesothelioma (MPM).

Methods: CT and coregistered PET-CT data from seven patients with histologically-proven MPM were utilized for VMAT and HT plans. Target volumes and organs at risk (OARs) were delineated. The prescription doses for planning target volume 1 (PTV1) and PTV2 were 45.0 Gy and 54 Gy in 1.8 Gy/fr, respectively. Each technique was evaluated in terms of target volume coverage and OAR doses.

Findings: Although the maximum (p=0.001) and mean (p < 0.001) doses of PTV1, and PTV2 (p < 0.001 for maximum and p=0.001 for mean doses) favored the HT technique over VMAT, both techniques efficiently covered the target volumes. Additionally, HT also provided more homogeneous dose distribution (p < 0.001) and numerically lower doses received by most OARs, but again both rotational techniques were successful in keeping the OAR doses below the universally accepted limits. The major disadvantage of the HT technique was the requirement for longer treatment times (7.4 versus 2.5 minutes/fr; p < 0.001) to accomplish the intended treatment.

Conclusion: Results of this dosimetric comparison clearly demonstrated the possibility of safe hemithoracic irradiation of medically/technically unresectable MPM patients with either of the two rotational RT techniques, namely the VMAT and HT. Clinically, considering their poor prognosis, these promising findings may open a potential new window for curative treatment of unresectable MPM patients, if further confirmed by future clinical studies.

Copyright © 2019 Berrin Pehlivan et al.

In plain English

This Turkish planning study did not examine asbestos exposure. Using scans from seven patients (four men, three women, aged 40 to 72) with malignant pleural mesothelioma that surgery could not remove, the authors made two plans per patient, one with volumetric arc therapy (VMAT) and one with helical tomotherapy (HT). The plans prescribed 45 Gy and 54 Gy to two target volumes in the affected chest; both covered the targets as intended. HT gave a more even dose and significantly lower lung, heart, esophagus and spinal cord doses. The median mean total lung dose was 16.1 Gy with HT versus 19.8 Gy with VMAT. Kidney and liver doses were similar. The authors wrote that both techniques met accepted organ limits, but their table shows exceptions: a median VMAT mean heart dose of 33.3 Gy against a stated limit below 26 Gy, and lung values above stated limits with both techniques. Planned HT treatment time was longer: 7.4 versus 2.5 minutes per fraction. The authors concluded that either technique made safe irradiation of the affected side of the chest possible, pending clinical confirmation.

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: Dosimetric (treatment-planning) comparison study using existing patient scans; the authors call it a pure dosimetric comparison
• Who was studied: Seven patients with unresectable malignant pleural mesothelioma (4 male, 3 female, aged 40 to 72), selected from the records of the authors' institutions in Turkey; dates are not given
• Exposure: No asbestos exposure is reported. The study compared two radiation therapy planning techniques, VMAT and HT, with prescription doses of 45.0 Gy to PTV1 and 54 Gy to PTV2 in 1.8 Gy fractions
• Main results:
  • For all plans, 95% of the planning target volumes received at least 95% of the prescribed dose. Minimum target doses did not differ significantly between the two techniques
  • Maximum doses in the target volumes were lower with HT. For example, the median PTV54 maximum dose was 64.3 Gy with VMAT versus 57.8 Gy with HT (p less than 0.001)
  • HT gave a significantly more homogeneous dose distribution: the median homogeneity index was 1.1 for VMAT versus 1.036 for HT (p less than 0.001)
  • Across the seven patients, the median of the plans' mean total lung doses was 16.1 Gy with HT versus 19.8 Gy with VMAT. The median total lung V20 was 29.3% versus 36.2%. Ipsilateral and contralateral lung doses were also significantly lower with HT
  • Maximum spinal cord dose and heart and esophageal doses were significantly lower with HT. Kidney and liver doses were similar between the techniques
  • The authors stated that both techniques met the QUANTEC organ dose constraints for every organ
  • Table 2 shows values above the stated limits. The stated heart limit was a mean dose below 26 Gy, but the median mean heart dose was 33.3 Gy (range 12.1 to 54.9) with VMAT, and the HT range reached 45.7 Gy
  • The stated total lung limits were a mean dose of 21 Gy or less and V20 of 40% or less. Reported total lung mean dose ranges reached 33.0 Gy with VMAT and 24.4 Gy with HT. V20 ranges reached 69.0% and 45.5%
  • The HT plans required more monitor units (median 6590 versus 529 per fraction, p less than 0.001) than the VMAT plans. Their calculated treatment times were longer (median 7.4 versus 2.5 minutes per fraction)
• The authors' conclusion: The authors concluded that, although HT gave better dosimetric measures in some respects, either technique made safe hemithoracic irradiation of medically or technically unresectable MPM patients possible. They added that clinical studies must confirm this before routine use
• Limitations the authors state:
  • The results are dosimetric only; the authors state that clinical translation must be confirmed by further clinical studies
  • Dose escalation was not examined in this study
  • The longer HT irradiation times make it more vulnerable to breathing motion problems

Topics

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

Medical terms in this study, explained in our Lexicon: Unresectable, Pleural Mesothelioma, PET-CT, Prognosis.

Related studies

• Dosimetric Comparison Between Helical Tomotherapy and Volumetric Modulated Arc Therapy in Patients With Malignant Pleural Mesothelioma — T. Müdder, G.R. Sarria, et al. (2022)
• 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)
• Dosimetric Correlates of Pulmonary Toxicity in Patients with Malignant Pleural Mesothelioma Receiving Radiation Therapy to the Intact Lungs — M.R. Thompson, V.A. Dumane, et al. (2019)
• Safety and efficacy of helical tomotherapy following lung-sparing surgery in locally advanced malignant pleural mesothelioma — J.P. Layer, P. Fischer, et al. (2024)
• 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)
• Tomotherapy PET-guided dose escalation: A dosimetric feasibility study for patients with malignant pleural mesothelioma — A. Maggio, C. Cutaia, et al. (2016)

Browse more research in BioMed Research International, or return to medical research.