Dosimetric evaluation of helical tomotherapy and volumetric-modulated arc therapy for malignant pleural mesothelioma: a planning study for dose escalation

Our plain-English summary of Dosimetric evaluation of helical tomotherapy and volumetric-modulated arc therapy for malignant pleural mesothelioma: a planning study for dose escalation, by F.L. Zhang, N. Lu, H.Y. Jiang, et al (Translational Cancer Research, 2021).

The study

• Authors: F.L. Zhang, N. Lu, H.Y. Jiang, D.D. Chen, Y.D. Wang
• Journal: Translational Cancer Research
• Published: 2021;10(2):914-922
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: To compare the dosimetric differences between helical tomotherapy (HT) and volumetric-modulated arc therapy (VMAT) treatment plans for inoperable malignant pleural mesothelioma (MPM).

Methods: Ten patients with inoperable MPM were retrospectively planned with the HT and VMAT techniques, and the dose-volume histogram (DVH)-based parameters of the planning target volume (PTV) and organs at risk (OARs) were compared.

Results: Compared with the VMAT plans, the target homogeneity index (HI) and conformity index (CI) of the HT plans were significantly better (HI: 1.04±0.01 vs. 1.11±0.03, CI: 0.80±0.07 vs. 0.71±0.12, respectively) (P<0.001, P=0.013, respectively). Regarding the OARs, including the ipsilateral lung, contralateral lung, heart, and spinal cord, the differences among the V30 (Vx: fraction of volume receiving >5, 10, 20, and 30 Gy, respectively) of the ipsilateral lung and V5, V10, and V20 of the contralateral lung were statistically significant (P=0.031, P=0.030, P=0.021, P=0.003, respectively). However, there was no significant differences between HT plans and VMAT plans, regarding the V5, V10 and V20 of the ipsilateral lung, V3 of the contralateral lung, V5 and Dmean of the heart, and Dmax of the cord. The treatment delivery time of the VMAT was significantly shorter than that of the HT (mean delivery time: 3.27±1.65 vs. 11.11±3.75 min, respectively) (P<0.001).

Conclusions: Compared to the VMAT plans, the HT plans not only demonstrated more optimal target coverage and conformity but also considerably reduced the dose-volume parameters of the OARs in both low-dose areas in contralateral lung and high-dose areas in ipsilateral lung and contralateral lung, which is correlated to radiation injury. However, the treatment delivery time of the HT plans was longer.

2021 Translational Cancer Research. All rights reserved.

In plain English

This was a radiotherapy planning study, not a study of asbestos exposure. The authors took the scans of 10 patients with malignant pleural mesothelioma who could not have surgery. The patients were diagnosed between September 2006 and May 2013 and had been treated with static IMRT. Looking back, the authors designed two computer treatment plans for each patient, one with helical tomotherapy (HT) and one with volumetric-modulated arc therapy (VMAT). Both plans prescribed 60 Gy in 2-Gy daily doses. In the HT plans, the dose to the target was more even and fitted the target more closely. The HT plans also exposed smaller fractions of the opposite lung to 3, 10 and 20 Gy, and of the same-side lung to 30 Gy. Several other measures, including heart and spinal cord doses, did not differ significantly. VMAT plans took less time to deliver (mean 3.27 versus 11.11 minutes). The authors concluded that precise radiation of one side of the chest was possible with either technique. They noted that this raised 60 Gy prescription for inoperable mesothelioma had not yet been applied in clinical work. Some of the plans exceeded routine lung dose limits and could not be used clinically.

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 dosimetric (treatment-planning) comparison study: two computer radiotherapy plans (HT and VMAT) made for each patient and compared with the Wilcoxon signed rank test
• Who was studied: 10 patients with inoperable malignant pleural mesothelioma (MPM), diagnosed September 2006 to May 2013 and previously treated with static IMRT; median age 48.5 years; 2 stage II, 6 stage III, 2 stage IV. The study was approved by the ethics board of The Seventh Medical Center of Chinese PLA General Hospital, Beijing, the authors' institution
• Exposure: No asbestos exposure was studied. The comparison was between two radiotherapy planning techniques, helical tomotherapy and volumetric-modulated arc therapy, each with a prescribed dose of 60 Gy in 2-Gy daily fractions to the planning target volume
• Main results:
  • Target dose evenness (homogeneity index) was better in the HT plans than in the VMAT plans: mean 1.04 vs 1.11 (P=0.002 in Table 2)
  • Target conformity index was better in the HT plans than in the VMAT plans: mean 0.80 vs 0.71 (P=0.004 in Table 2)
  • Overall, the HT plans gave significantly better uniformity and conformity than the VMAT plans
  • There were significant differences between HT and VMAT plans in V30 of the ipsilateral lung and in V3, V10 and V20 of the contralateral lung (P=0.037, 0.043, 0.039, 0.004). In Table 3 these values were lower in the HT plans; for example, contralateral lung V20 was 4.45 vs 12.94
  • There was no significant difference between HT and VMAT plans in V5, V10 and V20 of the ipsilateral lung, V5 of the contralateral lung, V5 and mean dose of the heart, or maximum dose to the spinal cord
  • Treatment delivery time was shorter for VMAT than for HT (mean 3.27 vs 11.11 minutes, P=0.002). HT used far more monitor units, and its delivery time was 239.8% longer
• The authors' conclusion: The authors concluded that the study showed precise irradiation of one side of the chest was possible with either HT or VMAT in medically or technically inoperable MPM patients
• Limitations the authors state:
  • The raised 60 Gy prescription used in these plans for inoperable MPM had not yet been applied in clinical work. At that dose, lung dose-volume values for some patients exceeded the tolerated limits of current clinical routine, so some plans could not be used clinically

Topics

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

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