Influence of Intravenous Contrast Agent on Thoracic CT Simulation Investigated with the 5-bulk...
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lung doses were reduced by 3 Gy. The mean reductions in the percentage of irradiated volume of 5 Gy (V5) and 10 Gy (V10) were substantially reduced from that of IMRT plans with constraints. The dose-function histogram shows that the method improves the functional lung sparing significantly. Conclusions: The functional distribution derived from 4D-CT was used to guide IMRT planning and it was shown to be effective in preserving normal lung function. Incorporation of functional information from different functional imaging techniques is impor- tant to better preserve the organ function and provides improved patient care. Author Disclosure: M. Chao, None; L. Lee, None; L. Xing, None. 3006 Influence of Intravenous Contrast Agent on Thoracic CT Simulation Investigated with the 5-bulk Density Heterogeneous Dose Calculation A. I. Saito 1 , J. G. Li 2 , C. Liu 2 , K. R. Olivier 2 , K. Karasawa 1 , J. F. Dempsey 3 1 Juntendo University School of Medicine, Tokyo, Japan, 2 University of Florida, Gainesville, FL, 3 ViewRay Inc., Cleveland, OH Purpose/Objective(s): Contrast-enhanced (CE+) computed tomography (CT) is used in some treatment planning to improve the delineation of the target and/or normal tissue. In the CE+ CT images the overall densities of the tissue may increase. The contrast agent (CA) is only injected for treatment planning and artificially changes the apparent density of the patient’s tissues. Using the 5- bulk density heterogeneous dose calculation, we investigated whether this change in density affects the dose calculation accuracy in the thoracic area. Materials/Methods: CT images of 17 consecutive cancer patients (lung, 15; esophagus, 2) who underwent thoracic CE+ CTs for treatment planning at the University of Florida were analyzed. Full-resolution CT (Org.) plans and 5-bulk density plans were gen- erated for all patients using a commercial treatment planning system with an adaptive convolution dose calculation algorithm. As bulk densities, air, lung, fat, soft tissue, and bone were applied to regions identified by an iso-density segmentation tool for each case. The population-averaged electron density of each region was calculated and compared with the population-averaged electron density of the same region calculated in our previous study in which 66 non-contrast-enhanced (CE-) thoracic CT data were used. To model dose distribution during radiotherapy, where no CA is injected, by applying the population-averaged electron densities of the 66 CE- CTs to each region of the 17 CE+ CTs, a new plan (CE- plan) was created. The dose volume histograms (DVH) were compared between the Org. plan and CE- plan. Results: The average electron densities for the segmented air, lung, fat, soft tissue, and bone for CE+ were 0.14, 0.29, 0.90, 1.03, and 1.13 g/cc, respectively, and for CE- they were 0.14, 0.26, 0.89, 1.02, and 1.12 g/cc, respectively. In all cases, the normal tissue DVH agreed to better than 1%. In 15 of the 17 cases, the target DVH agreed to better than 3%. In 1 case, the average target dose showed 4.6% difference and in 2 cases the dose covering 95% or more of the target volume showed 3.1% and 6.7% differences, respectively. The CT plan for the patient with the largest discrepancy had a strong injection artifact within the target, and the other patient with more than 3% difference in the average target dose had a beam going through the injection artifact. Conclusions: In 88% of the patients, the difference between the CE- plan and the Org. plan was minimal. Two patients with a strong injection artifact in the target or beam showed larger than 3% discrepancy in the target dose. If taking CE+ CT for treatment plan- ning, to reduce the effect caused by the CA, a technique to suppress the injection artifact has to be used or an effort has to be made to exclude strong injection artifacts from the target and beams. Author Disclosure: A.I. Saito, ViewRay Inc., A. Employment; J.G. Li, None; C. Liu, None; K.R. Olivier, None; K. Karasawa, None; J.F. Dempsey, ViewRay Inc., A. Employment. 3007 Impact of Multi-leaf Collimator Leaf Width on Quantitative Dosimetry of Stereotactic Body Radiation Therapy Plans L. Ku, M. Fuss Oregon Health & Science University, Portland, OR Purpose/Objective(s): Safe and effective delivery of SBRT requires highly conformal dose distributions and steep dose gradients. It is assumed that multi-leaf collimators (MLC) with narrower leaf width are better suited to accomplish this goal. A high-definition MLC (HD-MLC, Varian) with 2.5 mm leaf width projection at isocenter has recently been installed in our institution. We evaluated the dosimetric impact of narrower leaf size on SBRT plan dosimetry. Materials/Methods: Twenty-six SBRT patient plans (10 liver, 6 spine, 10 lung) were the basis for this study. The original plans utilized 8 to 14 intensity-modulated static beams collimated by a 120-leaf MLC with 0.5 mm leaf width at isocenter (Millennium, Varian). All clinical plans were copied, and re-calculated with identical planning parameters, replacing the clinically utilized Mil- lennium MLC with the new HD-MLC. All plans were normalized to achieve the same target volume coverage as the Millennium MLC plans (typically 95% of PTV coverage with the prescribed dose). A series of conformality indices (CI 100% , CI 90% , CI 50% , CI 25% ; expressed as the volume of the respective CI divided by the PTV) were assessed as well as doses to organs at risk (spinal cord, esophagus, major airways, lung). Results: In general only very minor differences between Millennium 120 leaf and the HD-MLC plans were observed. In 12/26 SBRT plans, isodose coverage at any dose level and organ-at-risk dose exposure was virtually identical. In 8 and 6 cases, use of the HD-MLC bettered the original plans or produced slightly inferior plans, respectively. Differences were in general lower than 3% (delta CI 100%, mean 2.7%), with a single instance of a 7% volume difference included in the prescription 100% isodose in favor of the Millennium 120 plan. At lower isodose levels, plans appeared slightly more favorable when using the HD-MLC collimator, with 12 plans having lower volumes exposed to the 50% and 25% dose level. However, absolute volume differences were again small ( \3%). Proceedings of the 50th Annual ASTRO Meeting S621
Transcript of Influence of Intravenous Contrast Agent on Thoracic CT Simulation Investigated with the 5-bulk...
Proceedings of the 50th Annual ASTRO Meeting S621
lung doses were reduced by�3 Gy. The mean reductions in the percentage of irradiated volume of 5 Gy (V5) and 10 Gy (V10) weresubstantially reduced from that of IMRT plans with constraints. The dose-function histogram shows that the method improves thefunctional lung sparing significantly.
Conclusions: The functional distribution derived from 4D-CT was used to guide IMRT planning and it was shown to be effectivein preserving normal lung function. Incorporation of functional information from different functional imaging techniques is impor-tant to better preserve the organ function and provides improved patient care.
Author Disclosure: M. Chao, None; L. Lee, None; L. Xing, None.
3006 Influence of Intravenous Contrast Agent on Thoracic CT Simulation Investigated with the 5-bulk Density
Heterogeneous Dose CalculationA. I. Saito1, J. G. Li2, C. Liu2, K. R. Olivier2, K. Karasawa1, J. F. Dempsey3
1Juntendo University School of Medicine, Tokyo, Japan, 2University of Florida, Gainesville, FL, 3ViewRay Inc., Cleveland, OH
Purpose/Objective(s): Contrast-enhanced (CE+) computed tomography (CT) is used in some treatment planning to improve thedelineation of the target and/or normal tissue. In the CE+ CT images the overall densities of the tissue may increase. The contrastagent (CA) is only injected for treatment planning and artificially changes the apparent density of the patient’s tissues. Using the 5-bulk density heterogeneous dose calculation, we investigated whether this change in density affects the dose calculation accuracy inthe thoracic area.
Materials/Methods: CT images of 17 consecutive cancer patients (lung, 15; esophagus, 2) who underwent thoracic CE+ CTs fortreatment planning at the University of Florida were analyzed. Full-resolution CT (Org.) plans and 5-bulk density plans were gen-erated for all patients using a commercial treatment planning system with an adaptive convolution dose calculation algorithm. Asbulk densities, air, lung, fat, soft tissue, and bone were applied to regions identified by an iso-density segmentation tool for eachcase. The population-averaged electron density of each region was calculated and compared with the population-averaged electrondensity of the same region calculated in our previous study in which 66 non-contrast-enhanced (CE-) thoracic CT data were used.To model dose distribution during radiotherapy, where no CA is injected, by applying the population-averaged electron densities ofthe 66 CE- CTs to each region of the 17 CE+ CTs, a new plan (CE- plan) was created. The dose volume histograms (DVH) werecompared between the Org. plan and CE- plan.
Results: The average electron densities for the segmented air, lung, fat, soft tissue, and bone for CE+ were 0.14, 0.29, 0.90, 1.03,and 1.13 g/cc, respectively, and for CE- they were 0.14, 0.26, 0.89, 1.02, and 1.12 g/cc, respectively. In all cases, the normaltissue DVH agreed to better than 1%. In 15 of the 17 cases, the target DVH agreed to better than 3%. In 1 case, the averagetarget dose showed 4.6% difference and in 2 cases the dose covering 95% or more of the target volume showed 3.1% and6.7% differences, respectively. The CT plan for the patient with the largest discrepancy had a strong injection artifact withinthe target, and the other patient with more than 3% difference in the average target dose had a beam going through the injectionartifact.
Conclusions: In 88% of the patients, the difference between the CE- plan and the Org. plan was minimal. Two patients with a stronginjection artifact in the target or beam showed larger than 3% discrepancy in the target dose. If taking CE+ CT for treatment plan-ning, to reduce the effect caused by the CA, a technique to suppress the injection artifact has to be used or an effort has to be made toexclude strong injection artifacts from the target and beams.
Author Disclosure: A.I. Saito, ViewRay Inc., A. Employment; J.G. Li, None; C. Liu, None; K.R. Olivier, None; K. Karasawa,None; J.F. Dempsey, ViewRay Inc., A. Employment.
3007 Impact of Multi-leaf Collimator Leaf Width on Quantitative Dosimetry of Stereotactic Body Radiation
Therapy PlansL. Ku, M. Fuss
Oregon Health & Science University, Portland, OR
Purpose/Objective(s): Safe and effective delivery of SBRT requires highly conformal dose distributions and steep dose gradients.It is assumed that multi-leaf collimators (MLC) with narrower leaf width are better suited to accomplish this goal. A high-definitionMLC (HD-MLC, Varian) with 2.5 mm leaf width projection at isocenter has recently been installed in our institution. We evaluatedthe dosimetric impact of narrower leaf size on SBRT plan dosimetry.
Materials/Methods: Twenty-six SBRT patient plans (10 liver, 6 spine, 10 lung) were the basis for this study. The original plansutilized 8 to 14 intensity-modulated static beams collimated by a 120-leaf MLC with 0.5 mm leaf width at isocenter (Millennium,Varian). All clinical plans were copied, and re-calculated with identical planning parameters, replacing the clinically utilized Mil-lennium MLC with the new HD-MLC. All plans were normalized to achieve the same target volume coverage as the MillenniumMLC plans (typically 95% of PTV coverage with the prescribed dose). A series of conformality indices (CI100%, CI90%, CI50%,CI25%; expressed as the volume of the respective CI divided by the PTV) were assessed as well as doses to organs at risk (spinalcord, esophagus, major airways, lung).
Results: In general only very minor differences between Millennium 120 leaf and the HD-MLC plans were observed. In 12/26SBRT plans, isodose coverage at any dose level and organ-at-risk dose exposure was virtually identical. In 8 and 6 cases, useof the HD-MLC bettered the original plans or produced slightly inferior plans, respectively. Differences were in general lowerthan 3% (delta CI100%, mean 2.7%), with a single instance of a 7% volume difference included in the prescription 100% isodosein favor of the Millennium 120 plan. At lower isodose levels, plans appeared slightly more favorable when using the HD-MLCcollimator, with 12 plans having lower volumes exposed to the 50% and 25% dose level. However, absolute volume differenceswere again small (\3%).
