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Title: SU-F-J-162: Is Bulky Electron Density Assignment Appropriatefor MRI-Only Based Treatment Planning for Lung Cancer?

Abstract

Purpose: To assess the appropriateness of bulky electron density assisment for MRI-only treatment planning for lung cancer via comparing dosimetric difference between MRI- and CT-based plans. Methods: Planning 4DCTs acquired for six representative lung cancer patients were used to generate CT-based IMRT plans. To avoid the effect of anatomic difference between CT and MRI, MRI-based plans were generated using CTs by forcing the relative electron density (rED) of organ specific values from ICRU report 46 and using the mean rED value of the internal target volume (ITV) of the patient for the ITV. Both CT and “MRI” plans were generated using a research planning system (Monaco, Elekta) employing Monte Carlo dose calculation the following dose-volume-parameters (DVPs): D99 – dose delivered to 99% of the ITV/PTV volume; D95; D5; D1; Vpd –volume receiving the prescription dose; V5 – volume of normal lung irradiated > 5 Gy; and V20. The percent point difference and dose difference was used for comparison for Vpd-V5-V20 and D99-D1, respectively. Four additional plans per patient were calculated with rEDITV = 0.6 and 1.0 and rEDlung = 0.1 and 0.5. Results: Noticeable differences in the ITV and PTV point doses and DVPs were observed. Variations in Vpd rangedmore » from 0.0–6.4% and 0.32–18.3% for the ITV and PTV, respectively. The ITV and PTV variations in D99, D95, D5 and D1 were 0.15–3.2 Gy. The normal lung V5 & V20 variations were no larger than 1.9%. In some instances, varying the rEDITV between rEDmean, 0.6 and 1.0 resulted in D95 increases ranging from 3.9–6.3%. Uniform rED assignment on normal lung affected DVPs of ITV and PTV by 4.0–9.8% and 0.3–19.6%, respectively. Conclusion: The commonly-used uniform rED assignment in MRI-only based planning may not be appropriate for lung-cancer. A voxel based method, e.g. synthetic CT generated from MRI data, is required. This work was partially funded by Elekta, Inc.« less

Authors:
; ; ; ;  [1]
  1. Medical College of Wisconsin, Milwaukee, WI (United States)
Publication Date:
OSTI Identifier:
22634763
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; 61 RADIATION PROTECTION AND DOSIMETRY; COMPUTERIZED TOMOGRAPHY; ELECTRON DENSITY; ICRU; IRRADIATION; LUNGS; MONTE CARLO METHOD; NEOPLASMS; NMR IMAGING; PATIENTS; RADIATION DOSES; RADIOTHERAPY

Citation Formats

Prior, P, Chen, X, Johnstone, C, Gore, E, and Li, X. SU-F-J-162: Is Bulky Electron Density Assignment Appropriatefor MRI-Only Based Treatment Planning for Lung Cancer?. United States: N. p., 2016. Web. doi:10.1118/1.4956070.
Prior, P, Chen, X, Johnstone, C, Gore, E, & Li, X. SU-F-J-162: Is Bulky Electron Density Assignment Appropriatefor MRI-Only Based Treatment Planning for Lung Cancer?. United States. doi:10.1118/1.4956070.
Prior, P, Chen, X, Johnstone, C, Gore, E, and Li, X. Wed . "SU-F-J-162: Is Bulky Electron Density Assignment Appropriatefor MRI-Only Based Treatment Planning for Lung Cancer?". United States. doi:10.1118/1.4956070.
@article{osti_22634763,
title = {SU-F-J-162: Is Bulky Electron Density Assignment Appropriatefor MRI-Only Based Treatment Planning for Lung Cancer?},
author = {Prior, P and Chen, X and Johnstone, C and Gore, E and Li, X},
abstractNote = {Purpose: To assess the appropriateness of bulky electron density assisment for MRI-only treatment planning for lung cancer via comparing dosimetric difference between MRI- and CT-based plans. Methods: Planning 4DCTs acquired for six representative lung cancer patients were used to generate CT-based IMRT plans. To avoid the effect of anatomic difference between CT and MRI, MRI-based plans were generated using CTs by forcing the relative electron density (rED) of organ specific values from ICRU report 46 and using the mean rED value of the internal target volume (ITV) of the patient for the ITV. Both CT and “MRI” plans were generated using a research planning system (Monaco, Elekta) employing Monte Carlo dose calculation the following dose-volume-parameters (DVPs): D99 – dose delivered to 99% of the ITV/PTV volume; D95; D5; D1; Vpd –volume receiving the prescription dose; V5 – volume of normal lung irradiated > 5 Gy; and V20. The percent point difference and dose difference was used for comparison for Vpd-V5-V20 and D99-D1, respectively. Four additional plans per patient were calculated with rEDITV = 0.6 and 1.0 and rEDlung = 0.1 and 0.5. Results: Noticeable differences in the ITV and PTV point doses and DVPs were observed. Variations in Vpd ranged from 0.0–6.4% and 0.32–18.3% for the ITV and PTV, respectively. The ITV and PTV variations in D99, D95, D5 and D1 were 0.15–3.2 Gy. The normal lung V5 & V20 variations were no larger than 1.9%. In some instances, varying the rEDITV between rEDmean, 0.6 and 1.0 resulted in D95 increases ranging from 3.9–6.3%. Uniform rED assignment on normal lung affected DVPs of ITV and PTV by 4.0–9.8% and 0.3–19.6%, respectively. Conclusion: The commonly-used uniform rED assignment in MRI-only based planning may not be appropriate for lung-cancer. A voxel based method, e.g. synthetic CT generated from MRI data, is required. This work was partially funded by Elekta, Inc.},
doi = {10.1118/1.4956070},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = {Wed Jun 15 00:00:00 EDT 2016},
month = {Wed Jun 15 00:00:00 EDT 2016}
}