Compensator-based intensity-modulated radiation therapy for malignant pleural mesothelioma post extrapleural pneumonectomy

Our plain-English summary of Compensator-based intensity-modulated radiation therapy for malignant pleural mesothelioma post extrapleural pneumonectomy, by K. Javedan, C.W. Stevens, K.M. Forster (Journal of Applied Clinical Medical Physics, 2008).

The study

• Authors: K. Javedan, C.W. Stevens, K.M. Forster
• Journal: Journal of Applied Clinical Medical Physics
• Published: 2008;9(4):98-109
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The present work investigated the potential of compensator-based intensity-modulated radiation therapy (CB-IMRT) as an alternative to multileaf collimator (MLC)-based intensity-modulated radiation therapy (IMRT) to treat malignant pleural mesothelioma (MPM) post extrapleural pneumonectomy. Treatment plans for 4 right-sided and 1 left-sided MPM post-surgery cases were generated using a commercial treatment planning system, XIO/CMS (Computerized Medical Systems, St. Louis, MO). We used a 7-gantry-angle arrangement with 6 MV beams to generate these plans. The maximum required field size was 30 x 40 cm. We evaluated IMRT plans with brass compensators (.Decimal, Sanford, FL) by examining isodose distributions, dose-volume histograms, metrics to quantify conformal plan quality, and homogeneity. Quality assurance was performed for one of the compensator plans. Conformal dose distributions were achieved with CB-IMRT for all 5 cases, the average planning target volume (PTV) coverage being 95.1% of the PTV volume receiving the full prescription dose. The average lung V20 (volume of lung receiving 20 Gy) was 1.8%, the mean lung dose was 6.7 Gy, and the average contralateral kidney V15 was 0.6%. The average liver dose V30 was 34.0% for the right-sided cases and 10% for the left-sided case. The average monitor units (MUs) per fraction were 980 MUs for the 45-Gy prescriptions (mean: 50 Gy) and 1083 MUs for the 50-Gy prescriptions (mean: 54 Gy). Post surgery, CB-IMRT for MPM is a feasible IMRT technique for treatment with a single isocenter. Compensator plans achieved dose objectives and were safely delivered on a Siemens Oncor machine (Siemens Medical Solutions, Malvern, PA). These plans showed acceptably conformal dose distributions as confirmed by multiple measurement techniques. Not all linear accelerators can deliver large-field MLC-based IMRT, but most can deliver a maximum conformal field of 40 x 40 cm. It is possible and reasonable to deliver IMRT with compensators for fields this size with most conventional linear accelerators.

In plain English

This was a radiation treatment-planning study. It did not study asbestos exposure. The authors tested whether intensity-modulated radiation therapy shaped by custom brass blocks (compensators) could treat malignant pleural mesothelioma after extrapleural pneumonectomy, an operation that removes the lung on the affected side. Using data from 5 patients (4 right-sided, 1 left-sided), they planned treatment with 6 MV beams. All plans gave the prescribed dose to 99.2% of the clinical target volume and 95.5% of the planning target volume. In the remaining lung, the share receiving 20 Gy was under 2%, and the mean lung dose ranged from 5 Gy to 8 Gy. The share of the liver receiving 30 Gy averaged 34.0% in the right-sided cases and was 10% in the left-sided case. In 2 cases the authors also planned the machine's standard leaf-based method for comparison, and it needed about double the machine output units. Measurements on one plan agreed with the calculated dose within 3%. The authors concluded that the approach produced acceptable plans from a single beam centre, though the first beam arrangement produced heavy modulators.

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: Radiation treatment-planning (dosimetric) study using patient data sets, with quality-assurance measurements in phantoms for one plan; not a study of asbestos exposure or disease risk
• Who was studied: Data sets from 5 patients with malignant pleural mesothelioma after extrapleural pneumonectomy: 4 right-sided and 1 left-sided cases. The article does not state when the patients were treated.
• Exposure: No asbestos exposure was studied. What was studied was compensator-based intensity-modulated radiation therapy with 6 MV beams. Results were based on a 45 Gy reference prescription, and one plan was re-optimized for 50 Gy. Two cases were also planned with segmented multileaf collimator IMRT for comparison.
• Main results:
  • Across all compensator plans, 99.2% of the clinical target volume and 95.5% of the planning target volume received the prescription dose
  • Across all plans, the volume of the remaining lung receiving 20 Gy was less than 2%, and the mean lung dose ranged between 5 Gy and 8 Gy
  • The average liver volume receiving 30 Gy (liver V30) was 34.0% for the right-sided cases and 10% for the left-sided case
  • The compensator plans averaged 980 monitor units per daily fraction (range 882 to 1040). The average daily delivery time was 33 minutes, including entering the room to change compensators.
  • In the 2 cases also planned with segmented multileaf collimator IMRT, total monitor units were doubled compared with compensators (for example 1993 versus 976 for plan 1). Total treatment time was slightly shorter with compensators.
  • When plan 1 (right-sided) was re-optimized for 50 Gy, at least 95% of the planning target volume received 50 Gy with a mean dose of 54 Gy. Liver V30 was less than 36%, contralateral lung mean dose was 5.7 Gy and lung V20 was 1%, and total monitor units were 1083.
  • In quality-assurance measurements on one compensator plan, at least 95% of measured and calculated dose distributions agreed within 3% and 3 mm for all individual compensator fields. Measured absolute dose agreed within 3% of calculated dose.
  • Film measurements showed hot spots of 117% where split fields joined, consistent with the predicted value
  • In the final 11-field arrangement, the median compensator weight was 7.5 kg (range 5.2 to 10.0 kg)
• The authors' conclusion: The authors concluded that compensator-based IMRT produced dosimetrically acceptable plans with a single isocenter, but the 7-field version produced heavy modulators. The 11-field version gave acceptable conformal plans with easier-to-manage modulators. Delivering IMRT with compensators for such large fields is possible and reasonable with most conventional linear accelerators.
• Limitations the authors state:
  • The authors note that the technique produced heavy modulators
  • The authors report that the heaviest (15.9-kg) modulators were difficult for most therapists to handle
  • The authors did not have weight-limit information for the wedge tray slot accessory used to hold the modulators

Topics

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

Medical terms in this study, explained in our Lexicon: Intensity-Modulated Radiation Therapy (IMRT), Pleural Mesothelioma, Extrapleural Pneumonectomy (EPP).

Related studies

• Patterns of failure, toxicity, and survival after extrapleural pneumonectomy and hemithoracic intensity-modulated radiation therapy for malignant pleural mesothelioma — D.R. Gomez, D.S. Hong, et al. (2013)
• High-dose-rate surface brachytherapy to boost elongated, curvilinear incisional scars after extrapleural pneumonectomy for malignant pleural mesothelioma treated with adjuvant intensity-modulated radiation therapy — L.A. Doyle, T.N. Showalter, et al. (2010)
• Intensity modulated radiation therapy after extra-pleural pneumonectomy for malignant pleural mesothelioma is feasible without fatal pulmonary toxicity and provides good survival — S. Jhavar, J. Pruszynski, et al. (2018)
• Intensity-modulated radiotherapy and volumetric-modulated arc therapy for malignant pleural mesothelioma after extrapleural pleuropneumonectomy — J. Krayenbuehl, O. Riesterer, et al. (2013)
• Current readings: improvements in intensity-modulated radiation therapy for malignant pleural mesothelioma — K.E. Rosenzweig (2013)
• Evaluation of the dose calculation accuracy in intensity-modulated radiation therapy for mesothelioma, focusing on low doses to the contralateral lung — L.E. Court, D. Ching, et al. (2009)

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