Illumination profile characterization of a light device for the dosimetry of intra-pleural photodynamic therapy for mesothelioma

Our plain-English summary of Illumination profile characterization of a light device for the dosimetry of intra-pleural photodynamic therapy for mesothelioma, by C. Munck, S. Mordon, N. Betrouni (Photodiagnosis and Photodynamic Therapy, 2016).

The study

• Authors: C. Munck, S. Mordon, N. Betrouni
• Journal: Photodiagnosis and Photodynamic Therapy
• Published: 2016;16:23-26
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Complete and homogeneous illumination of the pleural cavity is essential to the success of photodynamic therapy (PDT) for mesothelioma, but remains a challenge. Knowing the repartition and propagation of light around the light applicator could be the first step towards optimizing dosimetry. Here we propose a characterization method of the illumination profile of a specific light device.

Methods: The light wand, made of a cylindrical diffuser located inside an endotracheal tube, was fixed in a tank filled with dilute 0.01% intralipid. Light dosimetry was performed around the tip of the wand using two complementary methods: direct measurements of light power with an isotropic probe and measurements of light distribution characterization.

Results: Dosimetry with the isotropic probe showed an ellipse-shaped illumination. An optimized effective attenuation coefficient was deduced. Combined with the spatial representation, a theoretical illumination profile was established with iso-surfaces of fluence rate, defining a gradient light dose according to the distance from the diffuser.

Conclusion: A theoretical illumination profile of a light device was established and could be part of an intra-operative dosimetry system to improve light delivery during intrapleural PDT.

Copyright © 2016 Elsevier B.V. All rights reserved.

In plain English

This laboratory study from Lille, France, examined a light device used in photodynamic therapy (PDT), in which light is delivered inside the chest during surgery for malignant pleural mesothelioma, after as much of the tumor as possible has been removed. No patients were studied, and asbestos exposure was not examined. The authors built a light wand from an endotracheal tube holding a cylindrical light diffuser. They fixed it in a tank of dilute 0.01% intralipid solution meant to reproduce the pleural cavity and powered it with a 635 nm laser at 0.5 W to 3 W. Light was measured with a probe at 124 points and by photography. The light formed ellipse-shaped surfaces and fell off exponentially with distance from the diffuser. Repeated measurements varied by a mean of 9%, and rotating the wand gave a mean variation of 6%. The authors reported a mean error of 5.32% in estimating delivered power. They noted that the profile does not account for factors such as blood in the fluid. The authors concluded that the method gave an accurate theoretical illumination profile that could be combined with a tracking system to monitor light dose in real time.

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: Laboratory (bench) experiment characterizing the light output of a light device for intrapleural photodynamic therapy; no human or animal subjects
• Who was studied: No people were studied. The subject was a laboratory-built light wand (an endotracheal tube with a 40 mm cylindrical light diffuser). It was fixed in a black plastic tank of about 2300 ml of dilute 0.01% intralipid solution meant to reproduce the pleural cavity. The authors are based in Lille, France.
• Exposure: Not an asbestos exposure study. The exposure was red laser light from a diode laser (635 nm, plus or minus 3 nm), delivered through the wand at output powers of 0.5 W, 1 W, 1.5 W, 2 W, 2.5 W and 3 W.
• Main results:
  • Light power was measured with an isotropic probe every 5 mm around the cuff of the wand, for a total of 124 measurement points.
  • The measured light around the wand formed ellipse-shaped surfaces, and light power decreased exponentially with distance from the center of the diffuser.
  • When the measurements were repeated three times under the same ('standard') conditions, the mean variation was 9%.
  • When the wand was rotated about its long axis (0, 90, 180 and 270 degrees), the mean variation was 6%. The authors took this to mean that the two-dimensional measurements could be extended to a three-dimensional profile.
  • Table 1 gives the effective attenuation coefficient estimated for each laser power: from 0.648 to 0.66 per cm across powers of 0.5 W to 3.0 W. The authors stated that a mean value of 0.70 per cm was used for all values.
  • A calibration factor of 14446 per square cm was derived to convert probe power readings into fluence rate.
  • The authors reported that the approach estimated delivered power at a specific location with a precision of more than 94%, a mean error of 5.32% between measured and analytically estimated values.
• The authors' conclusion: The authors concluded that their light dosimetry method gives an accurate theoretical illumination profile of the light device. They proposed that in the future it could be combined with a spatial tracking system for real-time light dose monitoring.
• Limitations the authors state:
  • The illumination profile does not account for outside factors that may alter light distribution. One example is hemoglobin, from micro-bleeding after tumor resection, appearing in the intralipid solution during light delivery.
  • The photographic method shows light distribution only on the surface of the intralipid solution, not on the surface of the light device.

Topics

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

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

Related studies

• Real-time light dosimetry for intra-cavity photodynamic therapy: Application for pleural mesothelioma treatment — N. Betrouni, C. Munck, et al. (2017)
• Response of Photofrin-sensitised mesothelioma xenografts to photodynamic therapy with 514 nm light — T.H. Foster, S.L. Gibson, et al. (1996)
• Photodynamic therapy for lung cancer and malignant pleural mesothelioma — C.B. Simone, K.A. Cengel (2014)
• Photodynamic therapy as adjuvant therapy in surgically treated pleural malignancies — P. Baas, L. Murrer, et al. (1997)
• Intrapleural Photodynamic Therapy for Mesothelioma: What Place and Which Future? — C. Munck, S.R. Mordon, et al. (2015)
• In vitro killing of human malignant mesothelioma by photodynamic therapy — S.M. Keller, D.D. Taylor, et al. (1990)

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