Dose in radiation therapy has been reported as the water-equivalent dose using conventional dose calculation algorithms. The Monte Carlo (MC) algorithm employs characterization of human tissues by elemental compositio...Dose in radiation therapy has been reported as the water-equivalent dose using conventional dose calculation algorithms. The Monte Carlo (MC) algorithm employs characterization of human tissues by elemental composition and mass density. It enables more accurate dose calculation for radiation therapy treatment planning and typically reports absorbed dose to medium. Whether one should use dose to medium or tissue (Dm) in place of dose to water (Dw) for MC treatment planning remains the subject of debate. The aim of the current study is to evaluate the differences between dose-volume indices for Dm and Dw MC-calculated IMRT plans. Thirty-seven spine patients were selected for this study. The IMRT optimization and MC calculations were performed using the iPlan RT DoseTM ver 4.1.2 (Brainlab, Munich, Germany) treatment planning system (TPS) with an X-ray Voxel Monte Carlo (XVMC) dose calculation engine. Dw and Dm results for target and critical structures were evaluated using the dose-volume-based indices. Systematic differences between dose-volume indices computed with Dw and Dm were up to 5.2%, 4.2%, and 4.5% for D2, D50 and D98 indices of the clinical target volume (CTV), respectively and up to 1% for the critical structure dose indices. Our study demonstrates that employing Dm in place of Dw in MC-calculated IMRT treatment plans introduces a significant systematic difference in target DVHs. We recommend that for diffused target structures (such as spine tumors), dose to water is a better quantity for dose prescription in photon beam treatment planning using existing MC TPS. While for critical structures, it would be reasonable to report Dm always. However in future with the availability of finer spatial resolution, Dm will be the most suitable variable for both target and critical structures’ dose prescription and reporting in MC treatment planning.展开更多
AIM:To evaluate the feasibility of low contrast medium and radiation dose for hepatic computed tomography(CT) perfusion of rabbit VX2 tumor.METHODS:Eleven rabbits with hepatic VX2 tumor underwent perfusion CT scanning...AIM:To evaluate the feasibility of low contrast medium and radiation dose for hepatic computed tomography(CT) perfusion of rabbit VX2 tumor.METHODS:Eleven rabbits with hepatic VX2 tumor underwent perfusion CT scanning with a 24-h interval between a conventional tube potential(120 k Vp) protocol with 350 mg I/m L contrast medium and filtered back projection,and a low tube potential(80 k Vp) protocol with 270 mg I/m L contrast medium with iterative reconstruction.Correlation and agreement among perfusion parameters acquired by the conventional and low dose protocols were assessed for the viable tumor component as well as whole tumor.Image noise and tumor-to-liver contrast to noise ratio during arterial and portal venous phases were evaluated.RESULTS:A 38% reduction in contrast medium dose(360.1 ± 13.3 mg I/kg vs 583.5 ± 21.5 mg I/kg,P < 0.001) and a 73% decrease in radiation dose(1898.5 m Gy·cm vs 6951.8 m Gy·cm) were observed.Interestingly,there was a strong positive correlation in hepatic arterial perfusion(r = 0.907,P < 0.001;r = 0.879,P < 0.001),hepatic portal perfusion(r = 0.819,P = 0.002;r = 0.831,P = 0.002),and hepatic blood flow(r = 0.945,P < 0.001;r = 0.930,P < 0.001) as well as a moderate correlation in hepatic perfusion index(r = 0.736,P = 0.01;r = 0.636,P = 0.035) between the low dose protocol with iterative reconstruction and the conventional protocol for the viable tumor component and the whole tumor.These two imaging protocols provided a moderate but acceptable agreement for perfusion parameters and similar tumorto-liver CNR during arterial and portal venous phases(5.63 ± 2.38 vs 6.16 ± 2.60,P = 0.814;4.60 ± 1.27 vs 5.11 ± 1.74,P = 0.587).CONCLUSION:Compared with the conventional protocol,low contrast medium and radiation dose with iterative reconstruction has no significant influence on hepatic perfusion parameters for rabbits VX2 tumor.展开更多
Introduction: To compare the measured dose distributions to calculated ones in dose-to-water (Dw) and dose-to-medium (Dm) reporting modes for simple plans and patient-specific intensity modulated radiation therapy (IM...Introduction: To compare the measured dose distributions to calculated ones in dose-to-water (Dw) and dose-to-medium (Dm) reporting modes for simple plans and patient-specific intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans using ArcCHECK with a fixed phantom density. Methods: The recommended density value of 1.18 g/cm3 for Acuros XB and X-ray voxel Monte Carlo was assigned to ArcCHECK on CT images. A total of 45 simple plans, including a 1-field plan, a 3-field plan, a 4-field plan, a half-arc plan from 270° to 90°, and a full-arc plan, were assessed. Subsequently, the patient-specific 96 IMRT and VMAT plans were evaluated. Gamma analysis with a 3% normalized global dose error and a 3 mm distance-to-agreement criteria (γ3%G/3mm) was performed in the Dw and Dm. The change in γ3%G/3mm between Dw and Dm were statistically analyzed using JMPPro11 software. Results: The median values of γ3%G/3mm for all simple plans for Dw and Dm were 98.1% (range, 75.2% - 100%) and 95.5% (range, 23.7% - 100%), respectively (p 0.01). In the patient-specific IMRT and VMAT plans, the median values of γ3%G/3mm for Dw and Dm were 98.6% (range, 90.1% - 100%) and 90.5% (range, 38.5% - 97.2%), respectively (p 0.01). Conclusion: Our results showed that the calculated and measured dose distributions were in good agreement for Dw, but were not for Dm. From the viewpoint of the rationale of dosimetry, Dw shows better agreement with measured dose distribution when using the fixedphantom density recommended by the vendor.展开更多
文摘Dose in radiation therapy has been reported as the water-equivalent dose using conventional dose calculation algorithms. The Monte Carlo (MC) algorithm employs characterization of human tissues by elemental composition and mass density. It enables more accurate dose calculation for radiation therapy treatment planning and typically reports absorbed dose to medium. Whether one should use dose to medium or tissue (Dm) in place of dose to water (Dw) for MC treatment planning remains the subject of debate. The aim of the current study is to evaluate the differences between dose-volume indices for Dm and Dw MC-calculated IMRT plans. Thirty-seven spine patients were selected for this study. The IMRT optimization and MC calculations were performed using the iPlan RT DoseTM ver 4.1.2 (Brainlab, Munich, Germany) treatment planning system (TPS) with an X-ray Voxel Monte Carlo (XVMC) dose calculation engine. Dw and Dm results for target and critical structures were evaluated using the dose-volume-based indices. Systematic differences between dose-volume indices computed with Dw and Dm were up to 5.2%, 4.2%, and 4.5% for D2, D50 and D98 indices of the clinical target volume (CTV), respectively and up to 1% for the critical structure dose indices. Our study demonstrates that employing Dm in place of Dw in MC-calculated IMRT treatment plans introduces a significant systematic difference in target DVHs. We recommend that for diffused target structures (such as spine tumors), dose to water is a better quantity for dose prescription in photon beam treatment planning using existing MC TPS. While for critical structures, it would be reasonable to report Dm always. However in future with the availability of finer spatial resolution, Dm will be the most suitable variable for both target and critical structures’ dose prescription and reporting in MC treatment planning.
基金National Natural Science Foundation of China,No.NSFC 81171389Key Program of Basic Research from Shanghai Municipal Science and Technology Commission,No.12JC1406500the Program of Shanghai Municipal Health Outstanding Discipline Leader,No.XBR 2013110
文摘AIM:To evaluate the feasibility of low contrast medium and radiation dose for hepatic computed tomography(CT) perfusion of rabbit VX2 tumor.METHODS:Eleven rabbits with hepatic VX2 tumor underwent perfusion CT scanning with a 24-h interval between a conventional tube potential(120 k Vp) protocol with 350 mg I/m L contrast medium and filtered back projection,and a low tube potential(80 k Vp) protocol with 270 mg I/m L contrast medium with iterative reconstruction.Correlation and agreement among perfusion parameters acquired by the conventional and low dose protocols were assessed for the viable tumor component as well as whole tumor.Image noise and tumor-to-liver contrast to noise ratio during arterial and portal venous phases were evaluated.RESULTS:A 38% reduction in contrast medium dose(360.1 ± 13.3 mg I/kg vs 583.5 ± 21.5 mg I/kg,P < 0.001) and a 73% decrease in radiation dose(1898.5 m Gy·cm vs 6951.8 m Gy·cm) were observed.Interestingly,there was a strong positive correlation in hepatic arterial perfusion(r = 0.907,P < 0.001;r = 0.879,P < 0.001),hepatic portal perfusion(r = 0.819,P = 0.002;r = 0.831,P = 0.002),and hepatic blood flow(r = 0.945,P < 0.001;r = 0.930,P < 0.001) as well as a moderate correlation in hepatic perfusion index(r = 0.736,P = 0.01;r = 0.636,P = 0.035) between the low dose protocol with iterative reconstruction and the conventional protocol for the viable tumor component and the whole tumor.These two imaging protocols provided a moderate but acceptable agreement for perfusion parameters and similar tumorto-liver CNR during arterial and portal venous phases(5.63 ± 2.38 vs 6.16 ± 2.60,P = 0.814;4.60 ± 1.27 vs 5.11 ± 1.74,P = 0.587).CONCLUSION:Compared with the conventional protocol,low contrast medium and radiation dose with iterative reconstruction has no significant influence on hepatic perfusion parameters for rabbits VX2 tumor.
文摘Introduction: To compare the measured dose distributions to calculated ones in dose-to-water (Dw) and dose-to-medium (Dm) reporting modes for simple plans and patient-specific intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans using ArcCHECK with a fixed phantom density. Methods: The recommended density value of 1.18 g/cm3 for Acuros XB and X-ray voxel Monte Carlo was assigned to ArcCHECK on CT images. A total of 45 simple plans, including a 1-field plan, a 3-field plan, a 4-field plan, a half-arc plan from 270° to 90°, and a full-arc plan, were assessed. Subsequently, the patient-specific 96 IMRT and VMAT plans were evaluated. Gamma analysis with a 3% normalized global dose error and a 3 mm distance-to-agreement criteria (γ3%G/3mm) was performed in the Dw and Dm. The change in γ3%G/3mm between Dw and Dm were statistically analyzed using JMPPro11 software. Results: The median values of γ3%G/3mm for all simple plans for Dw and Dm were 98.1% (range, 75.2% - 100%) and 95.5% (range, 23.7% - 100%), respectively (p 0.01). In the patient-specific IMRT and VMAT plans, the median values of γ3%G/3mm for Dw and Dm were 98.6% (range, 90.1% - 100%) and 90.5% (range, 38.5% - 97.2%), respectively (p 0.01). Conclusion: Our results showed that the calculated and measured dose distributions were in good agreement for Dw, but were not for Dm. From the viewpoint of the rationale of dosimetry, Dw shows better agreement with measured dose distribution when using the fixedphantom density recommended by the vendor.
