Prospective study evaluating the use of IV contrast on IMRT treatment planning for lung cancer Hua Li, Beth Bottani, Todd DeWees, Daniel A. Low, Jeff M. Michalski, Sasa Mutic, Jeffrey D. Bradley, and Clifford G. Robinson Citation: Medical Physics 41, 031708 (2014); doi: 10.1118/1.4865766 View online: http://dx.doi.org/10.1118/1.4865766 View Table of Contents: http://scitation.aip.org/content/aapm/journal/medphys/41/3?ver=pdfcov Published by the American Association of Physicists in Medicine Articles you may be interested in Evaluation of tumor localization in respiration motion-corrected cone-beam CT: Prospective study in lung Med. Phys. 41, 101918 (2014); 10.1118/1.4896101 Experimental evaluations of the accuracy of 3D and 4D planning in robotic tracking stereotactic body radiotherapy for lung cancers Med. Phys. 40, 041712 (2013); 10.1118/1.4794505 A method for deriving a 4D-interpolated balanced planning target for mobile tumor radiotherapy Med. Phys. 39, 195 (2012); 10.1118/1.3666774 Reconstruction of 3D lung models from 2D planning data sets for Hodgkin’s lymphoma patients using combined deformable image registration and navigator channels Med. Phys. 37, 1017 (2010); 10.1118/1.3284368 Four-dimensional radiotherapy planning for DMLC-based respiratory motion tracking Med. Phys. 32, 942 (2005); 10.1118/1.1879152
Prospective study evaluating the use of IV contrast on IMRT treatment planning for lung cancer Hua Li,a) Beth Bottani, and Todd DeWees Department of Radiation Oncology, Washington University School of Medicine, Saint Louis, Missouri 63110
Daniel A. Low Department of Radiation Oncology, University of California Los Angeles, Los Angeles, California 90095
Jeff M. Michalski, Sasa Mutic, Jeffrey D. Bradley, and Clifford G. Robinson Department of Radiation Oncology, Washington University School of Medicine, Saint Louis, Missouri 63110
(Received 20 August 2013; revised 27 November 2013; accepted for publication 29 January 2014; published 19 February 2014) Purpose: To investigate the impact of exclusively using intravenous (IV) contrast x-ray computed tomography (CT) scans on lung cancer intensity-modulated radiation therapy (IMRT) treatment planning. Methods: Eight patients with lung cancer (one small cell, seven nonsmall cell) scheduled to receive IMRT consented to acquisition of simulation CT scans with and without IV contrast. Clinical treatment plans optimized on the noncontrast scans were recomputed on contrast scans and dose coverage was compared, along with the γ passing rates. Results: IV contrast enhanced scans provided better target and critical structure conspicuity than the noncontrast scans. Using noncontrast scan as a reference, the median absolute/relative differences in mean, maximum, and minimum doses to the planning target volume (PTV) were −4.5 cGy/−0.09%, 41.1 cGy/0.62%, and −19.7 cGy/−0.50%, respectively. Regarding organs-at-risk (OARs), the median absolute/relative differences of maximum dose to heart was −13.3 cGy/−0.32%, to esophagus was −63.4 cGy/−0.89%, and to spinal cord was −16.3 cGy/−0.46%. The median heart region of interest CT Hounsfield Unit (HU) number difference between noncontrast and contrast scans was 136.4 HU (range, 94.2–161.8 HU). Subjectively, the regions with absolute dose differences greater than 3% of the prescription dose were small and typically located at the patient periphery and/or at the beam edges. The median γ passing rate was 0.9981 (range, 0.9654–0.9999) using 3% absolute dose difference/3 mm distance-to-agreement criteria. Overall, all evaluated cases were found to be clinically equivalent. Conclusions: PTV and OARs dose differences between noncontrast and contrast scans appear to be minimal for lung cancer patients undergoing IMRT. Using IV contrast scans as the primary simulation dataset could increase treatment planning efficiency and accuracy by avoiding unnecessary scans, manually region overriding, and planning errors caused by nonperfect image registrations. © 2014 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.4865766] Key words: IV contrast, CT simulations, lung cancer, IMRT treatment planning 1. INTRODUCTION Intravenous (IV) iodine contrast-enhanced computed tomography (CT) simulations are commonly used in thoracic radiation therapy, greatly facilitating both tumor and normal tissue segmentation, particularly in the mediastinum.1–3 However, IV contrast agents increase the CT-imaging linear attenuation coefficients and the subsequent electron densities in the contrast-enhanced regions are erroneously assigned. This raises the concern that the erroneous assigned electron density variations may cause the dose distribution calculation to have clinically relevant errors. As such, it is common to either acquire both noncontrast and IV contrast-enhanced CT scans for treatment planning, or manually override the IV contrast-enhanced regions on the simulation images at the time of treatment planning.4–6 In the first circumstance, IV contrast-enhanced scans are fused to the noncontrast
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Med. Phys. 41 (3), March 2014
scans and used only for tumor target and critical structure delineation, while noncontrast scans are used as the primary data for dose distribution calculations. This process introduces several concerns. First, the radiation exposure from CT simulations will be doubled. Second and more important, patient motion (mainly respiratory motion) may lead to an inaccurate fusion between the noncontrast and IV contrast-enhanced scans, degrading the treatment plan accuracy. In the second circumstance, manually overriding the IV contrast-enhanced regions is a straightforward way to eliminate the concerns over dose calculation accuracy, but this process is quite time consuming and user dependent. In this study, we investigated the severity of CT HU variations on the contrast-affected regions (such as heart), and evaluated the effects of using IV contrast-enhanced CT simulation scans on radiation dosimetry through complete planning target volume (PTV) and organ at risk (OAR) dose difference
0094-2405/2014/41(3)/031708/7/$30.00
© 2014 Am. Assoc. Phys. Med.
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Li et al.: Lung cancer IV contrast IMRT study
analysis and γ passing rate comparisons. The magnitude of potential dose errors and their clinical significance for lung cancer radiation therapy treatments were determined as well. 2. METHODS AND MATERIALS Eight patients with lung cancer (one small cell, seven nonsmall cell) scheduled to receive intensity-modulated radiation therapy (IMRT) consented to acquisition of simulation CT scans with and without IV contrast on a prospective, IRB approved study. Each patient was scanned using either a Philips Brilliance 16-slice Big Bore scanner or a Philips Brilliance 64 slice CT scanner with our routine clinical protocols. The noncontrast CT scans were acquired with the following parameters: 120 kVp, 16 × 1.5 mm collimation setting for the Brilliance 16-slice scanner and 64 × 0.625 mm collimation setting for the Brilliance 64-slice scanner, 500 mm field of view (FOV), 3 mm slice thickness, standard resolution, and standard filter B with mAs/slice (effective mAs) ranging from 400 to 800 according to the patient lateral size. The IV contrast-enhanced CT scans were acquired with same scan protocol but with 50 s delay after the injection of 125 ml iodine contrast (320 mg/ml organically bound iodine) injected at a rate of 2 ml/s. The eight patients received a range of dose and fractionation schemes. Two patients received a dose of 4500 cGy in 150 cGy/fraction twice daily, two received a dose of 4005 cGy at 267 cGy/fraction daily, one received a dose of 5600 cGy at 200 cGy/fraction daily, and the remainder received 6600 cGy at 200 cGy/fraction daily. The median PTV prescription dose was 200 cGy (range, 150–267 cGy) over 30 fractions (range, 15–33 fractions). While the prescription dose and fractionation differed, the patients were similarly planned according to the following routinely used policy in our clinic. During the simulation, a 4DCT scan is acquired following the acquisition of a noncontrast scan and a contrast-enhanced scan. All three scans are acquired with the patients under free breathing. The gross tumor volume (GTV) was defined as the volume visible on CT and a co-registered PET/CT. An internal target volume (ITV) was generated as a modification to the GTV, taking into account tumor motion as captured by the 4DCT scan. The clinical target volume (CTV) was defined as the ITV plus a 7 mm expansion, modified at regions of natural barriers to tumor growth, and the planning target volume was the CTV plus an additional 5 mm isotropic expansion. Planning goals were as follows: >95% of the PTV was to receive >95% of the prescription dose, and hot spots within the PTV were to be limited to
Prospective study evaluating the use of IV contrast on IMRT treatment planning for lung cancer Hua Li,a) Beth Bottani, and Todd DeWees Department of Radiation Oncology, Washington University School of Medicine, Saint Louis, Missouri 63110
Daniel A. Low Department of Radiation Oncology, University of California Los Angeles, Los Angeles, California 90095
Jeff M. Michalski, Sasa Mutic, Jeffrey D. Bradley, and Clifford G. Robinson Department of Radiation Oncology, Washington University School of Medicine, Saint Louis, Missouri 63110
(Received 20 August 2013; revised 27 November 2013; accepted for publication 29 January 2014; published 19 February 2014) Purpose: To investigate the impact of exclusively using intravenous (IV) contrast x-ray computed tomography (CT) scans on lung cancer intensity-modulated radiation therapy (IMRT) treatment planning. Methods: Eight patients with lung cancer (one small cell, seven nonsmall cell) scheduled to receive IMRT consented to acquisition of simulation CT scans with and without IV contrast. Clinical treatment plans optimized on the noncontrast scans were recomputed on contrast scans and dose coverage was compared, along with the γ passing rates. Results: IV contrast enhanced scans provided better target and critical structure conspicuity than the noncontrast scans. Using noncontrast scan as a reference, the median absolute/relative differences in mean, maximum, and minimum doses to the planning target volume (PTV) were −4.5 cGy/−0.09%, 41.1 cGy/0.62%, and −19.7 cGy/−0.50%, respectively. Regarding organs-at-risk (OARs), the median absolute/relative differences of maximum dose to heart was −13.3 cGy/−0.32%, to esophagus was −63.4 cGy/−0.89%, and to spinal cord was −16.3 cGy/−0.46%. The median heart region of interest CT Hounsfield Unit (HU) number difference between noncontrast and contrast scans was 136.4 HU (range, 94.2–161.8 HU). Subjectively, the regions with absolute dose differences greater than 3% of the prescription dose were small and typically located at the patient periphery and/or at the beam edges. The median γ passing rate was 0.9981 (range, 0.9654–0.9999) using 3% absolute dose difference/3 mm distance-to-agreement criteria. Overall, all evaluated cases were found to be clinically equivalent. Conclusions: PTV and OARs dose differences between noncontrast and contrast scans appear to be minimal for lung cancer patients undergoing IMRT. Using IV contrast scans as the primary simulation dataset could increase treatment planning efficiency and accuracy by avoiding unnecessary scans, manually region overriding, and planning errors caused by nonperfect image registrations. © 2014 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.4865766] Key words: IV contrast, CT simulations, lung cancer, IMRT treatment planning 1. INTRODUCTION Intravenous (IV) iodine contrast-enhanced computed tomography (CT) simulations are commonly used in thoracic radiation therapy, greatly facilitating both tumor and normal tissue segmentation, particularly in the mediastinum.1–3 However, IV contrast agents increase the CT-imaging linear attenuation coefficients and the subsequent electron densities in the contrast-enhanced regions are erroneously assigned. This raises the concern that the erroneous assigned electron density variations may cause the dose distribution calculation to have clinically relevant errors. As such, it is common to either acquire both noncontrast and IV contrast-enhanced CT scans for treatment planning, or manually override the IV contrast-enhanced regions on the simulation images at the time of treatment planning.4–6 In the first circumstance, IV contrast-enhanced scans are fused to the noncontrast
031708-1
Med. Phys. 41 (3), March 2014
scans and used only for tumor target and critical structure delineation, while noncontrast scans are used as the primary data for dose distribution calculations. This process introduces several concerns. First, the radiation exposure from CT simulations will be doubled. Second and more important, patient motion (mainly respiratory motion) may lead to an inaccurate fusion between the noncontrast and IV contrast-enhanced scans, degrading the treatment plan accuracy. In the second circumstance, manually overriding the IV contrast-enhanced regions is a straightforward way to eliminate the concerns over dose calculation accuracy, but this process is quite time consuming and user dependent. In this study, we investigated the severity of CT HU variations on the contrast-affected regions (such as heart), and evaluated the effects of using IV contrast-enhanced CT simulation scans on radiation dosimetry through complete planning target volume (PTV) and organ at risk (OAR) dose difference
0094-2405/2014/41(3)/031708/7/$30.00
© 2014 Am. Assoc. Phys. Med.
031708-1
031708-2
Li et al.: Lung cancer IV contrast IMRT study
analysis and γ passing rate comparisons. The magnitude of potential dose errors and their clinical significance for lung cancer radiation therapy treatments were determined as well. 2. METHODS AND MATERIALS Eight patients with lung cancer (one small cell, seven nonsmall cell) scheduled to receive intensity-modulated radiation therapy (IMRT) consented to acquisition of simulation CT scans with and without IV contrast on a prospective, IRB approved study. Each patient was scanned using either a Philips Brilliance 16-slice Big Bore scanner or a Philips Brilliance 64 slice CT scanner with our routine clinical protocols. The noncontrast CT scans were acquired with the following parameters: 120 kVp, 16 × 1.5 mm collimation setting for the Brilliance 16-slice scanner and 64 × 0.625 mm collimation setting for the Brilliance 64-slice scanner, 500 mm field of view (FOV), 3 mm slice thickness, standard resolution, and standard filter B with mAs/slice (effective mAs) ranging from 400 to 800 according to the patient lateral size. The IV contrast-enhanced CT scans were acquired with same scan protocol but with 50 s delay after the injection of 125 ml iodine contrast (320 mg/ml organically bound iodine) injected at a rate of 2 ml/s. The eight patients received a range of dose and fractionation schemes. Two patients received a dose of 4500 cGy in 150 cGy/fraction twice daily, two received a dose of 4005 cGy at 267 cGy/fraction daily, one received a dose of 5600 cGy at 200 cGy/fraction daily, and the remainder received 6600 cGy at 200 cGy/fraction daily. The median PTV prescription dose was 200 cGy (range, 150–267 cGy) over 30 fractions (range, 15–33 fractions). While the prescription dose and fractionation differed, the patients were similarly planned according to the following routinely used policy in our clinic. During the simulation, a 4DCT scan is acquired following the acquisition of a noncontrast scan and a contrast-enhanced scan. All three scans are acquired with the patients under free breathing. The gross tumor volume (GTV) was defined as the volume visible on CT and a co-registered PET/CT. An internal target volume (ITV) was generated as a modification to the GTV, taking into account tumor motion as captured by the 4DCT scan. The clinical target volume (CTV) was defined as the ITV plus a 7 mm expansion, modified at regions of natural barriers to tumor growth, and the planning target volume was the CTV plus an additional 5 mm isotropic expansion. Planning goals were as follows: >95% of the PTV was to receive >95% of the prescription dose, and hot spots within the PTV were to be limited to
