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Title: Accuracy of dose measurements and calculations within and beyond heterogeneous tissues for 6 MV photon fields smaller than 4 cm produced by Cyberknife

Abstract

For the small radiation field sizes used in stereotactic radiosurgery, lateral electronic disequilibrium and steep dose gradients exist in a large portion of these fields, requiring the use of high-resolution measurement techniques. These relatively large areas of electronic disequilibrium make accurate dosimetry as well as dose calculation more difficult, and this is exacerbated in regions of tissue heterogeneity. Tissue heterogeneity was considered insignificant in the brain where stereotactic radiosurgery was first used. However, as this technique is expanded to the head and neck and other body sites, dose calculations need to account for dose perturbations in and beyond air cavities, lung, and bone. In a previous study we have evaluated EBT Gafchromic film (International Specialty Products, Wayne, NJ) for dosimetry and characterization of the Cyberknife radiation beams and found that it was comparable to other common detectors used for small photon beams in solid water equivalent phantoms. In the present work EBT film is used to measure dose in heterogeneous slab phantoms containing lung and bone equivalent materials for the 6 MV radiation beams of diameter 7.5 to 40 mm produced by the Cyberknife (Accuray, Sunnyvale, CA). These measurements are compared to calculations done with both the clinically utilized Raytracemore » algorithm as well as the newly developed Monte Carlo based algorithm available on the Cyberknife treatment planning system. Within the low density material both the measurements and Monte Carlo calculations correctly model the decrease in dose produced by a loss of electronic equilibrium, whereas the Raytrace algorithm incorrectly predicts an enhancement of dose in this region. Beyond the low density material an enhancement of dose is correctly calculated by both algorithms. Within the high density bone heterogeneity the EBT film measurements represent dose to unit density tissue in bone and agree with the Monte Carlo results when corrected to dose to unit density tissue in bone. We conclude that EBT film is an appropriate dosimeter for measuring dose in heterogeneous materials and these measurements agree with Monte Carlo calculations of dose as implemented in the Cyberknife treatment planning system.« less

Authors:
;  [1]
  1. Radiation Oncology Department, Saint Francis Hospital, 114 Woodland Street, Hartford, Connecticut 06105 (United States)
Publication Date:
OSTI Identifier:
21120744
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 35; Journal Issue: 6; Other Information: DOI: 10.1118/1.2912179; (c) 2008 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-2405
Country of Publication:
United States
Language:
English
Subject:
61 RADIATION PROTECTION AND DOSIMETRY; ACCURACY; ALGORITHMS; BRAIN; DOSEMETERS; FILM DOSIMETRY; LUNGS; MONTE CARLO METHOD; PERTURBATION THEORY; PHANTOMS; PHOTON BEAMS; RADIATION DOSES; RADIOTHERAPY; SKELETON; SURGERY

Citation Formats

Wilcox, Ellen E, and Daskalov, George M. Accuracy of dose measurements and calculations within and beyond heterogeneous tissues for 6 MV photon fields smaller than 4 cm produced by Cyberknife. United States: N. p., 2008. Web. doi:10.1118/1.2912179.
Wilcox, Ellen E, & Daskalov, George M. Accuracy of dose measurements and calculations within and beyond heterogeneous tissues for 6 MV photon fields smaller than 4 cm produced by Cyberknife. United States. https://doi.org/10.1118/1.2912179
Wilcox, Ellen E, and Daskalov, George M. 2008. "Accuracy of dose measurements and calculations within and beyond heterogeneous tissues for 6 MV photon fields smaller than 4 cm produced by Cyberknife". United States. https://doi.org/10.1118/1.2912179.
@article{osti_21120744,
title = {Accuracy of dose measurements and calculations within and beyond heterogeneous tissues for 6 MV photon fields smaller than 4 cm produced by Cyberknife},
author = {Wilcox, Ellen E and Daskalov, George M},
abstractNote = {For the small radiation field sizes used in stereotactic radiosurgery, lateral electronic disequilibrium and steep dose gradients exist in a large portion of these fields, requiring the use of high-resolution measurement techniques. These relatively large areas of electronic disequilibrium make accurate dosimetry as well as dose calculation more difficult, and this is exacerbated in regions of tissue heterogeneity. Tissue heterogeneity was considered insignificant in the brain where stereotactic radiosurgery was first used. However, as this technique is expanded to the head and neck and other body sites, dose calculations need to account for dose perturbations in and beyond air cavities, lung, and bone. In a previous study we have evaluated EBT Gafchromic film (International Specialty Products, Wayne, NJ) for dosimetry and characterization of the Cyberknife radiation beams and found that it was comparable to other common detectors used for small photon beams in solid water equivalent phantoms. In the present work EBT film is used to measure dose in heterogeneous slab phantoms containing lung and bone equivalent materials for the 6 MV radiation beams of diameter 7.5 to 40 mm produced by the Cyberknife (Accuray, Sunnyvale, CA). These measurements are compared to calculations done with both the clinically utilized Raytrace algorithm as well as the newly developed Monte Carlo based algorithm available on the Cyberknife treatment planning system. Within the low density material both the measurements and Monte Carlo calculations correctly model the decrease in dose produced by a loss of electronic equilibrium, whereas the Raytrace algorithm incorrectly predicts an enhancement of dose in this region. Beyond the low density material an enhancement of dose is correctly calculated by both algorithms. Within the high density bone heterogeneity the EBT film measurements represent dose to unit density tissue in bone and agree with the Monte Carlo results when corrected to dose to unit density tissue in bone. We conclude that EBT film is an appropriate dosimeter for measuring dose in heterogeneous materials and these measurements agree with Monte Carlo calculations of dose as implemented in the Cyberknife treatment planning system.},
doi = {10.1118/1.2912179},
url = {https://www.osti.gov/biblio/21120744}, journal = {Medical Physics},
issn = {0094-2405},
number = 6,
volume = 35,
place = {United States},
year = {Sun Jun 15 00:00:00 EDT 2008},
month = {Sun Jun 15 00:00:00 EDT 2008}
}