Customization of a Model For Knowledge-Based Planning to Achieve Ideal Dose Distributions in Volume Modulated arc Therapy for Pancreatic Cancers.

PURPOSE: To evaluate customizing a knowledge-based planning (KBP) model using dosimetric analysis for volumetric modulated arc therapy for pancreatic cancer. MATERIALS AND METHODS: The first model (M1) using 56 plans and the second model (M2) using 31 plans were created in the first 7 months of the study. The ratios of volume of both kidneys overlapping the expanded planning target volume to the total volume of both kidneys (Voverlap/Vwhole) were calculated in all cases to customize M1. Regression lines were derived from Voverlap/Vwhole and mean dose to both kidneys. The third model (M3) was created using 30 plans which data put them below the regression line. For validation, KBP was performed with the three models on 21 patients. RESULTS: V18 of the left kidney for M1 plans was 7.3% greater than for clinical plans. Dmean of the left kidney for M2 plans was 2.2% greater than for clinical plans. There was no significant difference between all kidney doses in M3 and clinical plans. Dmean of the left kidney for M2 plans was 2.2% greater than for clinical plans. Dmean to both kidneys did not differ significantly between the three models in validation plans with Voverlap/Vwhole lower than average. In plans with larger than average volumes, the Dmean of validation plans created by M3 was significantly lower for both kidneys by 1.7 and 0.9 Gy than with M1 and M2, respectively. CONCLUSIONS: Selecting plans to register in a model by analyzing dosimetry and geometry is an effective means of improving the KBP model.

Improvement of image quality and assessment of respiratory motion for hepatocellular carcinoma with portal vein tumor thrombosis using contrast-enhanced four-dimensional dual-energy computed tomography.

To assess the objective and subjective image quality, and respiratory motion of hepatocellular carcinoma with portal vein tumor thrombosis (PVTT) using the contrast-enhanced four-dimensional dual-energy computed tomography (CE-4D-DECT). For twelve patients, the virtual monochromatic image (VMI) derived from the CE-4D-DECT with the highest contrast to noise ratio (CNR) was determined as the optimal VMI (O-VMI). To assess the objective and subjective image quality, the CNR and five-point score of the O-VMI were compared to those of the standard VMI at 77 keV (S-VMI). The respiratory motion of the PVTT and diaphragm was measured based on the exhale and inhale phase images. The VMI at 60 keV yielded the highest CNR (4.8 ± 1.4) which was significantly higher (p = 0.02) than that in the S-VMI (3.8 ± 1.2). The overall image quality (4.0 ± 0.6 vs 3.1 ± 0.5) and tumor conspicuity (3.8 ± 0.8 vs 2.8 ± 0.6) of the O-VMI determined by three radiation oncologists was significantly higher (p < 0.01) than that of the S-VMI. The diaphragm motion in the L-R (3.3 ± 2.5 vs 1.2 ± 1.1 mm), A-P (6.7 ± 4.0 vs 1.6 ± 1.3mm) and 3D (8.8 ± 3.5 vs 13.1 ± 4.9 mm) directions were significantly larger (p < 0.05) compared to the tumor motion. The improvement of objective and subjective image quality was achieved in the O-VMI. Because the respiratory motion of the diaphragm was larger than that of the PVTT, we need to be pay attention for localizing target in radiotherapy.

A Third-Generation Adaptive Statistical Iterative Reconstruction for Contrast-Enhanced 4-Dimensional Dual-Energy Computed Tomography for Pancreatic Cancer.

OBJECTIVES: The objective of this study was to assess the objective and subjective qualities of the contrast-enhanced 4-dimensional dual-energy computed tomography using adaptive statistical iterative reconstruction (ASiR) and ASiR-V. METHODS: The virtual monochromatic images at 60 keV were reconstructed using filtered back projection, ASiR, and ASiR-V (10%-100%) for 14 patients with pancreatic cancer. The contrast-to-noise ratio (CNR) was calculated, and the subjective measurements were compared based on a 5-point score scale. RESULTS: The ASiR-V yielded a significantly higher CNR than ASiR (P < 0.05). The subjective image quality (peak) was significantly improved (P < 0.01) with ASiR (50%) (3.8, 3.5, and 4.0; overall image quality, tumor delineation, and noise, respectively) and with ASiR-V (50%) (3.9, 3.5, and 4.2, respectively) compared with the filtered back projection (3.2, 3.2, and 3.0, respectively). CONCLUSIONS: The ASiR-V yielded higher CNR than ASiR and provided the highest subjective scores regarding the overall image quality.

Metal artifact reduction using iterative CBCT reconstruction algorithm for head and neck radiation therapy: A phantom and clinical study.

PURPOSE: To investigate whether a novel iterative cone-beam computed tomography (CBCT) reconstruction algorithm reduces metal artifacts in head and neck patient images. METHOD: An anthropomorphic phantom and 35 patients with dental metal prostheses or implants were analyzed. All CBCT images were acquired using a TrueBeam linear accelerator and reconstructed with a Feldkamp-Davis-Kress algorithm-based CBCT (FDK-CBCT) and an iterative CBCT algorithm. The mean Hounsfield unit (HU) and standard deviation values were measured on the tongue near the metal materials and the unaffected region as reference values. The artifact index (AI) was calculated. For objective image analysis, the HU value and AI were compared between FDK-CBCT and iterative CBCT images in phantom and clinical studies. Subjective image analyses of metal artifact scores and soft tissue visualizations were conducted using a five-point scale by two reviewers in the clinical study. RESULTS: The HU value and AI showed significant artifact reduction for the iterative CBCT than for the FDK-CBCT images (phantom study: 389.8 vs.-10.3 for HU value, 322.9 vs. 96.2 for AI, FDK-CBCT vs. iterative CBCT, respectively; clinical study: 210.3 vs. 69.0 for HU value, 149.6 vs. 70.7 for AI). The subjective scores in the clinical patient study were improved in the iterative CBCT images (metal artifact score: 1.1 vs. 2.9, FDK-CBCT vs. iterative CBCT, respectively; soft tissue visualization: 1.8 vs. 3.6). CONCLUSIONS: The iterative CBCT reconstruction algorithm substantially reduced metal artifacts caused by dental metal prostheses and improved soft tissue visualization compared to FDK-CBCT in phantom and clinical studies.

Stereotactic body radiation therapy planning for liver tumors using functional images from dual-energy computed tomography.

PURPOSE: This study aimed to generate a functional image of the liver using dual-energy computed tomography (DECT) and a functional-image-based stereotactic body radiation therapy plan to minimize the dose to the volume of the functional liver (Vfl). MATERIAL AND METHODS: A normalized iodine density (NID) map was generated for fifteen patients with liver tumors. The volume of liver with an NID < 0.46 was defined as Vfl, and the ratio between Vfl and the total volume of the liver (FLR) was calculated. The relationship between the FLR and Fibrosis-4 (FIB-4) was assessed. For patients with 15% < FLR < 85%, functional volumetric modulated-arc therapy plans (F-VMAT) were retrospectively generated to preserve Vfl, and compared to the clinical plans (C-VMAT). RESULTS: FLR showed a significantly strong correlation with FIB-4 (r = -0.71, p < 0.01). For ten generated F-VMAT plans, the dosimetric parameters of D99%, D50%, D1% and the conformity index were comparable to those of the C-VMAT (p > 0.05). For Vfl, F-VMAT plans achieved lower V5Gy (122.4 ± 31.7 vs 181.1 ± 57.3 cc), V10Gy (44.4 ± 22.2 vs 98.2 ± 33.3 cc), V15Gy (22.6 ± 20.3 vs 49.8 ± 33.7 cc), V20Gy (11.6 ± 14.1 vs 24.9 ± 25.1 cc), and Dmean (3.9 ± 2.3 vs 5.8 ± 3.0 Gy) values than the C-VMAT plans (p < 0.01). CONCLUSIONS: The functional image derived from DECT was successfully used, allowing for a reduction in the dose to the Vfl without compromising target coverage.

Determination of optimal virtual monochromatic energy level for target delineation of brain metastases in radiosurgery using dual-energy CT.

OBJECTIVE: Determination of the optimal energy level of virtual monochromatic image (VMI) for brain metastases in contrast-enhanced dual-energy CT (DECT) for radiosurgery and assessment of the subjective and objective image quality of VMI at the optimal energy level. METHODS: 20 patients (total of 42 metastases) underwent contrast-enhanced DECT. Spectral image analysis of VMIs at energy levels ranging from 40 to 140 keV in 1 keV increments was performed to determine the optimal VMI (VMIopt) as the one corresponding to the highest contrast-to-noise ratio (CNR) between brain parenchyma and the metastases. The objective and subjective values of VMIopt were compared to those of the VMI with 120 kVp equivalent, defined as reference VMI (VMIref, 77 keV). The objective measurement parameters included mean HU value and SD of tumor and brain parenchyma, absolute lesion contrast (LC), and CNR. The subjective measurements included five-point scale assessment of "overall image quality" and "tumor delineation" by three radiation oncologists. RESULTS: The VMI at 63 keV was defined as VMIopt. The LC and CNR of VMIopt were significantly (p < 0.01) higher than those of VMIref (LC: 37.4 HU vs 24.7 HU; CNR: 1.1 vs 0.8, respectively). Subjective analysis rated VMIopt significantly (p < 0.01) superior to VMIref with respect to the overall image quality (3.2 vs 2.9, respectively) and tumor delineation (3.5 vs 2.9, respectively). CONCLUSION: The VMI at 63 keV derived from contrast-enhanced DECT yielded the highest CNR and improved the objective and subjective image quality for radiosurgery, compared to VMIref. ADVANCES IN KNOWLEDGE: This paper investigated for the first time the optimal energy level of VMI in DECT for brain metastases. The findings will lead to improvement in tumor visibility with optimal VMI and consequently supplement accuracy delineation of brain metastases.

Volumetric modulated arc therapy treatment planning based on virtual monochromatic images for head and neck cancer: effect of the contrast-enhanced agent on dose distribution.

Virtual monochromatic images (VMIs) at a lower energy level can improve image quality but the computed tomography (CT) number of iodine contained in the contrast-enhanced agent is dramatically increased. We assessed the effect of the use of contrast-enhanced agent on the dose distributions in volumetric modulated arc therapy (VMAT) planning for head and neck cancer (HNC). Based on the VMIs at 40 keV (VMI40keV ), 60 keV(VMI60keV ), and 77 keV (VMI77keV ) of a tissue characterization phantom, lookup tables (LUTs) were created. VMAT plans were generated for 15 HNC patients based on contrast-enhanced- (CE-) VMIs at 40-, 60-, and 77 keV using the corresponding LUTs, and the doses were recalculated based on the noncontrast-enhanced- (nCE-) VMIs. For all structures, the difference in CT numbers owing to the contrast-enhanced agent was prominent as the energy level of the VMI decreased, and the mean differences in CT number between CE- and nCE-VMI was the largest for the clinical target volume (CTV) (125.3, 55.9, and 33.1 HU for VMI40keV , VMI60keV , and VMI77keV, respectively). The mean difference of the dosimetric parameters (D99% , D50% , D1% , Dmean , and D0.1cc ) for CTV and OARs was <1% in the treatment plans based on all VMIs. The maximum difference was observed for CTV in VMI40keV (2.4%), VMI60keV (1.9%), and VMI77keV (1.5%) plans. The effect of the contrast-enhanced agent was larger in the VMAT plans based on the VMI at a lower energy level for HNC patients. This effect is not desirable in a treatment planning procedure.

Volumetric modulated arc therapy planning based on virtual monochromatic images: Effect of inaccurate CT numbers on dose distributions.

PURPOSE: Though virtual monochromatic images (VMIs) at low energy levels can improve image quality, the measured Hounsfield unit (HU) values can be inaccurate. We assessed the dosimetric error due to inaccurate HU estimation in volumetric modulated arc therapy (VMAT) planning. METHODS: Based on the VMIs at 50 keV (VMI50keV), 77 keV (VMI77keV) and single-energy CT (SECT) image for a phantom with different sizes, lookup tables (LUTL and LUTS) were created. Using an anthropomorphic phantom (head and spine regions), VMAT plans were generated based on VMI50keV, VMI77keV and SECT using the corresponding LUTL, and then, the doses were re-calculated using LUTS. For clinical cases, 30 VMAT plans (prostate, brain, and spine cases) were generated based on VMI50keV and VMI77keV. RESULTS: In the anthropomorphic phantom study, the difference in the dosimetric parameters for planning target volume (PTV) in the VMAT plan based on the VMI77keV was smallest (within 0.1 Gy) among three types of treatment planning approach. In clinical cases, in general, the differences of the 3-dimensional gamma passing rate and dosimetric parameters in the treatment plans based on the VMI50keV were larger than those in the VMI77keV. Especially for brain cases, the difference for PTV was more prominent when AXB was used (the maximum difference was 0.5 Gy) than AAA. CONCLUSIONS: The dosimetric error due to the inaccurate HU estimation was larger in the VMIs at low energy levels. This may be clinically insignificant, but should be avoided in the VMAT treatment planning.

Estimation of electron density, effective atomic number and stopping power ratio using dual-layer computed tomography for radiotherapy treatment planning.

PURPOSE: Assess the accuracy for quantitative measurements of electron density relative to water (ρe/ρe,w), effective atomic number (Zeff) and stopping power ratio relative to water (SPRw) using a dual-layer computed tomography (DLCT) system. METHODS AND MATERIALS: A tissue characterization phantom was scanned using DLCT with varying scanning parameters (i.e., tube voltage, rotation time, CTDIvol, and scanning mode) and different reference materials. Then, electron density ρe/ρe,w and atomic number Zeff images were reconstructed, and their values were determined for each reference materials. Based on these two values, SPRw was calculated. Finally, the percent error (PE) against the theoretical values was calculated for reference materials. RESULTS: Significant linear relationships (p < 0.001) were observed between the measured and theoretical ρe/ρe,w (r = 1.000), Zeff (r = 0.989) and SPRw (r = 1.000) values. The PE for each reference material varied from -2.0 to 1.2% (mean, <0.1%) for electron density ρe/ρe,w, from -6.4 to 8.0% (mean, -2.0%) for atomic number Zeff, and from -2.0 to 1.9% (mean, 0.3%) for stopping power ratio SPRw. The mean PE of ρe/ρe,w (<0.1%), Zeff (<-2.5%) and SPRw (<0.4%) was verified across the variation of scanning parameters (p > 0.85). CONCLUSIONS: DLCT provides a reasonable accuracy in the measurements of ρe/ρe,w, Zeff and SPRw, and could enhance radiotherapy treatment planning and the subsequent outcomes.

[Proposal of Requirements Definition Method on Radiation Therapy Information System].

The troubles arising in the introduction of the medical information system are mostly related to the requirement definition. The present study proposed the requirements definition method on radiation therapy information system (RTIS) by using business modeling. The interview was conducted with six medical professionals regarding the entire business in the radiotherapy department. These businesses were modeled using Diamond Mandala Matrix (DMM) and data flow diagram (DFD) methods. Subsequently, functional requirements on RTIS were defined based on these modeling. As a result, 21 DMMs and 129 DFDs were created and 120 functional requirements were defined. By defining the functional requirements of the users, mutual understanding with vendors will deepen, and avoid an expected trouble in introducing RTIS. DMM was effective as an initial modeling such as the interviews and the organization of businesses. DFD was also effective for the business improvement and the definition of system functional requirements.

Accuracy of Quantification of Iodine and Hounsfield Unit Values on Virtual Monochromatic Imaging Using Dual-Energy Computed Tomography: Comparison of Dual-Layer Computed Tomography With Fast Kilovolt-Switching Computed Tomography.

OBJECTIVE: The aim of the study was to compare the accuracy of quantification of iodine and Hounsfield unit (HU) values on virtual monochromatic imaging (VMI) using dual-layer computed tomography (DLCT) and fast kilovolt-switching computed tomography (FKSCT). MATERIALS AND METHODS: This study was performed in 2 phantoms (large and small) using 16 rods representing different materials (iodine, calcium, blood, and adipose tissue) with different dimensions and concentrations. The absolute percentage errors (absolute ratio of measurement error to true iodine concentration) for iodine concentration and HU value on VMI at 50, 70, and 100 keV were compared between DLCT and FKSCT. The Mann-Whitney U test was used to assess statistical significance. RESULTS: Overall, the absolute percentage errors for iodine concentration and HU value on VMI were smaller for DLCT than for FKSCT. CONCLUSIONS: Overall, the accuracy of iodine and HU values was higher for DLCT than for FKSCT.

Treatment planning based on water density image generated using dual-energy computed tomography for pancreatic cancer with contrast-enhancing agent: Phantom and clinical study.

PURPOSE: A contrast-enhancing agent is imperative for the accurate target delineation of pancreatic tumors. This study demonstrates the potential use of treatment planning for patients with pancreatic tumors based on the water density image (WDI) generated by dual-energy computed tomography (DECT). METHODS: Tissue characterization and multi-energy phantom scanning were performed through DECT and the physical characteristics of the WDI and a virtual monochromatic image (VMI) were assessed. The measured and the corresponding theoretical electron density relative to water (RED) and mass density (MD) were compared. Treatment plans based on the WDI (TPWDI ) and VMI (TPVMI ) were compared for 22 pancreatic cancer patients who underwent contrast-enhanced DECT scan. RESULTS: The total absolute difference in the HU value between the conventional 120 kVp images and the VMI was the smallest at the energy level of 77 keV (3.3 HU), and the VMI at 77 keV was used for subsequent analysis. The difference between the measured and theoretical values of RED and MD for iodine using the VMI (>15%) was larger than that using WDI (<4%). In clinical cases, the maximum difference in the dosimetric parameters between TPWDI and TPWDI for the planning target volume was 3.0% when the doses were calculated using AXB, and for the duodenum, it was 1.7%. CONCLUSIONS: The WDI estimated the RED and MD accurately and could form the basis for a new treatment planning approach for pancreatic cancer using contrast-enhancing agent.

How Well Does Dual-Energy Computed Tomography With Metal Artifact Reduction Software Improve Image Quality and Quantify Computed Tomography Number and Iodine Concentration?

OBJECTIVE: The objective of this study was to assess the accuracy of the quantitative measurements obtained using dual-energy computed tomography with metal artifact reduction software (MARS). METHODS: Dual-energy computed tomography scans (fast kV-switching) are performed on a phantom, by varying the number of metal rods (Ti and Pb) and reference iodine materials. Objective and subjective image analyses are performed on retroreconstructed virtual monochromatic images (VMIs) (VMI at 70 keV). RESULTS: The maximum artifact indices for VMI-Ti and VMI-Pb (5 metal rods) with MARS (without MARS) were 17.4 (166.7) and 34.6 (810.6), respectively; MARS significantly improved the mean subjective 5-point score (P < 0.05). The maximum differences between the measured Hounsfield unit and theoretical values for 5 mg/mL iodine and 2-mm core rods were -42.2% and -68.5%, for VMI-Ti and VMI-Pb (5 metal rods), respectively, and the corresponding differences in the iodine concentration were -64.7% and -73.0%, respectively. CONCLUSIONS: Metal artifact reduction software improved the objective and subjective image quality; however, the quantitative values were underestimated.

Clinical implementation of contrast-enhanced four-dimensional dual-energy computed tomography for target delineation of pancreatic cancer.

BACKGROUND AND PURPOSE: The accurate delineation of pancreatic tumor with respiratory motion is challenging. This study demonstrates the application of contrast-enhanced four-dimensional dual-energy computed tomography (CE-4D-DECT) for tumor delineation and assesses the objective and subjective image quality. MATERIAL AND METHODS: Twelve patients underwent CE-4D-DECT, and quantitative spectral analysis was performed on the resulting virtual monochromatic images (VMI) to determine the optimal VMI (O-VMI) with the highest contrast-to-noise ratio (CNR). The objective value of the CNR between pancreatic parenchyma and tumor, and the subjective measurement with five-point scale were compared between O-VMI, standard VMI (S-VMI, 77 keV) and single energy CT (SECT, 120 kVp). RESULTS: The CNR was the highest in the VMI at 60 keV, and the corresponding CNR in the O-VMI (3.4) was significantly higher (p < 0.05) than that in the S-VMI (2.4) and the SECT (2.7). The overall mean subjective measurements among 4 radiation oncologists were higher for the O-VMI over the S-VMI and SECT with respect to overall image quality (4.0, 3.3 and 3.7, respectively), tumor enhancement (3.4, 2.6 and 3.2, respectively), and vessel delineation (4.2, 3.6 and 4.2, respectively). CONCLUSIONS: The O-VMI derived from the CE-4D-DECT demonstrated its superiority over the S-VMI and SECT in depicting pancreatic tumor.

How Well Does Dual-energy CT with Fast Kilovoltage Switching Quantify CT Number and Iodine and Calcium Concentrations?

RATIONALE AND OBJECTIVES: Because it is imperative for understanding the performance of dual-energy computed tomography scanner to determine clinical diagnosis, we aimed to assess the accuracy of quantitative measurements using dual-energy computed tomography with fast kilovoltage switching. MATERIALS AND METHODS: Quantitative measurements were performed for 16 reference materials (physical density, 0.965-1.550 g/cm3; diameter of rod, 2.0-28.5 mm; iodine concentration, 2-15 mg/mL; and calcium concentration, 50-300 mg/mL) with varying scanning settings, and the measured values were compared to their theoretical values. RESULTS: For high-density material, the maximum differences in Hounsfield unit values in the virtual monochromatic images at 50, 70, and 100 keV were -176.2, 61.0, and -35.2 HU, respectively, and the standard deviations over short- and long-term periods were 11.1, 6.1, and 3.5 HU at maximum. The accuracy of the Hounsfield unit measurement at 50 and 70 keV was significantly higher (P < 0.05) with higher radiation output and smaller phantom size. The difference in the iodine and calcium measurements in the large phantom were up to -2.6 and -60.4 mg/mL for iodine (5 mg/mL with 2-mm diameter) and calcium (300 mg/mL) materials, and the difference was improved with a small phantom. Metal artifact reduction software improved subjective image quality; however, the quantitative values were significantly underestimated (P < 0.05) (-49.5, -26.9, and -15.3 HU for 50, 70, and 100 keV, respectively; -1.0 and -17 mg/mL for iodine and calcium concentration, respectively) compared to that acquired without a metal material. CONCLUSIONS: The accuracy of quantitative measurements can be affected by material density and the size of the object, radiation output, phantom size, and the presence of metal materials.

Comparison of Interfractional Setup Reproducibility between Two Types of Patient Immobilization Devices in Image-Guided Radiation Therapy for Prostate Cancer.

PURPOSE: The aim of this study is to compare the interfractional setup reproducibility of two types of patient immobilization devices for prostate cancer receiving image-guided radiation therapy (IGRT). MATERIALS AND METHODS: The MOLDCARE (MC) involves hydraulic fixation, whereas the BlueBAG (BB) and Vac-Lock (VL) involve vacuum fixation. For 72 patients, each immobilization device was individually customized during computed tomography (CT) simulation. Before the treatment, bony registration was performed using orthogonal kV images and digitally reconstructed radiographs. The shift of the treatment couch was recorded as a benchmark in the first session. In subsequent sessions, the shifts from the benchmark were measured and analyzed. Soft-tissue registration was performed weekly by cone-beam CT and CT images, and the shifts were measured and analyzed. RESULTS: In the superior-inferior and left-right directions, there were nearly no changes in the overall mean among the immobilization devices. In the anterior-posterior (AP) direction, the overall mean for the MC, BB, and VL were 0.34 ± 1.33, -0.47 ± 1.27, and -1.82 ± 1.65 mm, respectively. The mean shifts along the AP direction were approximately 1 mm more in patients immobilized on the BB and 2.5 mm more in those on the VL, compared to those on the MC, after the twentieth treatment. No significant changes were observed among the patients immobilized on those devices, respectively, in soft-tissue registration. CONCLUSION: It can be concluded that the settling of the vacuum fixation was caused by air leakage in the latter-half treatment, and the immobilization device type has no effect on the treatment-position reproducibility in IGRT.