U.S. Department of EnergyOffice of Scientific and Technical Information
Improved treatment planning for COMS eye plaques
Abstract
Purpose: A recent reanalysis of the Collaborative Ocular Melanoma Study (COMS) medium tumor trial concluded that incorporating factors to account for anisotropy, line source approximation, the gold plaque, and attenuation in the Silastic seed carrier into the dose calculations resulted in a significant and consistent reduction of calculated doses to structures of interest within the eye. The authors concluded that future eye plaque dosimetry should be 'performed using the most up-to-date parameters available.' The reason these factors are important is attributable to the low energy {sup 125}I radiation (approximately 28 keV) that is primarily absorbed by the photoelectric process. Photoelectric absorption is quite dependent on the atomic composition of the absorbing material. Being 40% silicon by weight, the effective atomic number of Silastic is significantly greater than that of water. Although the AAPM TG43 brachytherapy formalism inherently addresses the issues of source anisotropy and geometry, its parameter that accounts for scatter and attenuation, the radial dose function g(r), assumes that the source is immersed in infinite homogeneous water. In this work, factors are proposed for {sup 125}I that correct for attenuation in the Silastic carrier and scatter deficits resulting from the gold plaque and nearby air. The implications of usingmore »
- Authors:
-
- Department of Radiation Oncology, University of Southern California Norris Cancer Hospital, Los Angeles, CA (United States)
- Publication Date:
- OSTI Identifier:
- 20696154
- Resource Type:
- Journal Article
- Journal Name:
- International Journal of Radiation Oncology, Biology and Physics
- Additional Journal Information:
- Journal Volume: 61; Journal Issue: 4; Other Information: DOI: 10.1016/j.ijrobp.2004.09.062; PII: S0360-3016(04)02705-1; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0360-3016
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 62 RADIOLOGY AND NUCLEAR MEDICINE; ANISOTROPY; ATTENUATION; BRACHYTHERAPY; CARRIERS; GOLD; IODINE 125; MELANOMAS; MONTE CARLO METHOD; PALLADIUM 103; PLANNING; RADIATION DOSE DISTRIBUTIONS; RADIATION DOSES; SILASTIC; THERMOLUMINESCENT DOSIMETRY
Citation Formats
Astrahan, Melvin A. Improved treatment planning for COMS eye plaques. United States: N. p., 2005.
Web. doi:10.1016/j.ijrobp.2004.09.062.
Astrahan, Melvin A. Improved treatment planning for COMS eye plaques. United States. https://doi.org/10.1016/j.ijrobp.2004.09.062
Astrahan, Melvin A. 2005.
"Improved treatment planning for COMS eye plaques". United States. https://doi.org/10.1016/j.ijrobp.2004.09.062.
@article{osti_20696154,
title = {Improved treatment planning for COMS eye plaques},
author = {Astrahan, Melvin A},
abstractNote = {Purpose: A recent reanalysis of the Collaborative Ocular Melanoma Study (COMS) medium tumor trial concluded that incorporating factors to account for anisotropy, line source approximation, the gold plaque, and attenuation in the Silastic seed carrier into the dose calculations resulted in a significant and consistent reduction of calculated doses to structures of interest within the eye. The authors concluded that future eye plaque dosimetry should be 'performed using the most up-to-date parameters available.' The reason these factors are important is attributable to the low energy {sup 125}I radiation (approximately 28 keV) that is primarily absorbed by the photoelectric process. Photoelectric absorption is quite dependent on the atomic composition of the absorbing material. Being 40% silicon by weight, the effective atomic number of Silastic is significantly greater than that of water. Although the AAPM TG43 brachytherapy formalism inherently addresses the issues of source anisotropy and geometry, its parameter that accounts for scatter and attenuation, the radial dose function g(r), assumes that the source is immersed in infinite homogeneous water. In this work, factors are proposed for {sup 125}I that correct for attenuation in the Silastic carrier and scatter deficits resulting from the gold plaque and nearby air. The implications of using {sup 103}Pd seeds in COMS plaques are also discussed. Methods and materials: An existing TG43-based ophthalmic plaque planning system was modified to incorporate additional scatter and attenuation correction factors that better account for the path length of primary radiation in the Silastic seed carrier and the distance between the dose calculation point and the eye-air interface. Results: Compared with homogeneous water, the dose-modifying effects of the Silastic and gold are greatest near the plaque surface and immediately adjacent to the plaque, while being least near the center of the eye. The calculated dose distribution surrounding a single {sup 125}I seed centered in a COMS 20 mm plaque was found to be consistent with previously published examples that used thermoluminescent dosimetry measurements and Monte Carlo methods. For fully loaded 12 and 20 mm plaques, calculated dose to critical ocular structures ranged from 16%-50% less than would have been reported using the standard COMS dose calculation protocol. Conclusions: Treatment planning for COMS eye plaques that accurately accounts for the presence of the gold, Silastic and extraocular air is both possible and practical.},
doi = {10.1016/j.ijrobp.2004.09.062},
url = {https://www.osti.gov/biblio/20696154},
journal = {International Journal of Radiation Oncology, Biology and Physics},
issn = {0360-3016},
number = 4,
volume = 61,
place = {United States},
year = {Tue Mar 15 00:00:00 EST 2005},
month = {Tue Mar 15 00:00:00 EST 2005}
}
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