Internal Gross Target Volumes Research Articles

Intensity-modulated proton and carbon-ion radiotherapy using a fixed-beam system for locally advanced lung cancer: dosimetric comparison with x-ray radiotherapy and normal tissue complication probability (NTCP) evaluation

Objective. To assess the dosimetric consequences and the normal tissue complication probability (NTCP) for the organs at risk (OARs) in intensity-modulated particle radiotherapy of proton (IMPT) and carbon-ion (IMCT) using a fixed-beam delivery system when compared with intensity-modulated photon radiotherapy (IMRT) for locally advanced small-cell lung cancer. Approach. The plans were all designed under the same total relative biological effectiveness (RBE)-weighted prescription dose, in which the planning target volume (PTV) of the internal gross target volume(IGTV) and the PTV of the clinical target volume was irradiated with 69.3 Gy (RBE) and 63 Gy (RBE), respectively, using a simultaneously integrated boosting (SIB) technique. NTCPs were estimated for heart, lung, esophagus and spinal cord by Lyman–Kutcher–Burman (LKB) and logistic models. Dose escalation was simulated under the desired NTCP values (0.05, 0.10 and 0.50) of the three radiation techniques. Main results. Under the similar target coverage, almost all OARs were significantly better spared (p < 0.05) when using the particle radiotherapy except for D1cc (the dose to 1 cm3 of the volume) of the proximal bronchial tree (p > 0.05). At least 57.6% of mean heart dose, 28.8% of mean lung dose and 19.1% of mean esophageal dose were reduced compared with IMRT. The mean NTCP of radiation-induced pneumonitis (RP) in the ipsilateral lung was 0.39 ± 0.33 (0.39 ± 0.31) in IMPT plans and 0.36 ± 0.32 (0.35 ± 0.30) in IMCT plans compared with 0.66 ± 0.30 (0.64 ± 0.28) in IMRT plans by LKB (logistic) models. The target dose could be escalated to 78.3/76.9 Gy (RBE) in IMPT/IMCT plans compared with 61.7 Gy (RBE) in IMRT plans when 0.50 of NTCP in terms of RP in the ipsilateral lung was applied. Significance. This study presents the potential of better control of the side effects and improvement of local control originating from the dosimetric advantage with the application of IMPT and IMCT with the SIB technique for locally advanced lung cancer, even with limited beam directions.

Evaluation of Lung Tumor Target Volume in a Large Sample: Target and Clinical Factors Influencing the Volume Derived From Four-Dimensional CT and Cone Beam CT.

Background and PurposeThis study aimed to systematically evaluate the influence of target-related and clinical factors on volume differences and the similarity of targets derived from four-dimensional computed tomography (4DCT) and cone beam computed tomography (CBCT) images in lung stereotactic body radiation therapy (SBRT).Materials and Methods4DCT and CBCT image data of 210 tumors from 195 patients were analyzed. The internal gross target volume (IGTV) derived from the maximum intensity projection (MIP) of 4DCT (IGTV-MIP) and the IGTV from CBCT (IGTV-CBCT) were compared with the reference IGTV from 10 phases of 4DCT (IGTV-10). The target size, tumor motion, and the similarity between IGTVs were measured. The influence of target-related and clinical factors on the adequacy of IGTVs derived from 4DCT MIP and CBCT images was evaluated.ResultsThe mean tumor motion amplitude in the 3D direction was 6.5 ± 5 mm. The mean size ratio of IGTV-CBCT and IGTV-MIP compared to IGTV-10 in all patients was 0.71 ± 0.21 and 0.8 ± 0.14, respectively. Female sex, greater BSA, and larger target size were protective factors, while the Karnofsky Performance Status, body mass index, and motion were risk factors for the similarity between IGTV-MIP and IGTV-10. Older age and larger target size were protective factors, while adhesion to the heart, coexistence with cardiopathy, and tumor motion were risk factors for the similarity between IGTV-CBCT and IGTV-10.ConclusionClinical factors should be considered when using MIP images for defining ITV, and when using CBCT images for verifying treatment targets.

Effect of abdominal compression on target movement and extension of the external boundary of peripheral lung tumours treated with stereotactic radiotherapy based on four-dimensional computed tomography

BackgroundThis study aimed to investigate the effect of abdominal compression on tumour motion and target volume and to determine suitable planning target volume (PTV) margins for patients treated with lung stereotactic body radiotherapy (SBRT) based on four-dimensional computed tomography (4DCT).MethodsTwenty-three patients diagnosed to have a peripheral pulmonary tumour were selected and divided into an all lesions group (group A), an upper middle lobe lesions group (group B), and a lower lobe lesions group (group C). Two 4DCT scans were performed in each patient, one with and one without abdominal compression. Cone beam computed tomography (CBCT) was performed before starting treatment. The gross target volumes (GTVs) were delineated and internal gross target volumes (IGTVs) were defined. IGTVs were generated using two methods: (1) the maximum intensity projections (MIPs) based on the 4DCT were reconstructed to form a single volume and defined as the IGTVMIP and (2) GTVs from all 10 phases were combined to form a single volume and defined as the IGTV10. A 5-mm, 4-mm, and 3-mm margin was added in all directions on the IGTVMIP and the volume was constructed as PTVMIP5mm, PTVMIP4mm, and PTVMIP3mm.ResultsThere was no significant difference in the amplitude of tumour motion in the left–right, anterior–posterior, or superior-inferior direction according to whether or not abdominal compression was applied (group A, p = 0.43, 0.27, and 0.29, respectively; group B, p = 0.46, 0.15, and 0.45; group C, p = 0.79, 0.86, and 0.37; Wilcoxon test). However, the median IGTVMIP without abdominal compression was 33.67% higher than that with compression (p = 0.00), and the median IGTV10 without compression was 16.08% higher than that with compression (p = 0.00). The median proportion of the degree of inclusion of the IGTVCBCT in PTVMIP5mm, PTVMIP4mm, and PTVMIP3mm ≥ 95% was 100%, 100%, and 83.33%, respectively.ConclusionsAbdominal compression was useful for reducing the size of the IGTVMIP and IGTV10 and for decreasing the PTV margins based on 4DCT. In IGTVMIP with abdominal compression, adding a 4-mm margin to account for respiration is feasible in SBRT based on 4DCT.

A Novel Deep Learning Framework for Internal Gross Target Volume Definition From 4D Computed Tomography of Lung Cancer Patients

In this paper, we study the reliability of a novel deep learning framework for internal gross target volume (IGTV) delineation from 4-D computed tomography (4DCT), which is applied to patients with lung cancer treated by stereotactic body radiation therapy (SBRT). Seventy seven patients who underwent SBRT followed by 4DCT scans were incorporated in this retrospective study. The IGTV_DL was delineated using a novel deep machine learning algorithm with a linear exhaustive optimal combination framework. For the purpose of comparison, three other IGTVs based on common methods was also delineated. We compared the relative volume difference (RVI), matching index (MI), and encompassment index (EI) for the above IGTVs. Then, multiple parameter regression analysis was performed to assess the tumor volume and motion range as clinical influencing factors in the MI variation. The results demonstrated that the deep learning algorithm with linear exhaustive optimal combination framework has a higher probability of achieving optimal MI compared with other currently widely used methods. For patients after simple breathing training by keeping the respiratory frequency in 10 breath per minute (BPM), the four phase combinations of 0%, 30%, 50% and 90% can be considered as a potential solution for an optimal combination to synthesize IGTV in all respiration amplitudes.

Target volume and artifact evaluation of a new data-driven 4D CT

PurposeFour-dimensional computed tomography (4D CT) is often used to define the internal gross target volume (IGTV) for radiation therapy of lung cancer. Traditionally, this technique requires the use of an external motion surrogate; however, a new image, data-driven 4D CT, has become available. This study aims to describe this data-driven 4D CT and compare target contours created with it to those created using standard 4D CT. Methods and materialsCine CT data of 35 patients undergoing stereotactic body radiation therapy were collected and sorted into phases using standard and data-driven 4D CT. IGTV contours were drawn using a semiautomated method on maximum intensity projection images of both 4D CT methods. Errors resulting from reproducibility of the method were characterized. A comparison of phase image artifacts was made using a normalized cross-correlation method that assigned a score from +1 (data-driven “better”) to –1 (standard “better”). ResultsThe volume difference between the data-driven and standard IGTVs was not significant (data driven was 2.1 ± 1.0% smaller, P = .08). The Dice similarity coefficient showed good similarity between the contours (0.949 ± 0.006). The mean surface separation was 0.4 ± 0.1 mm and the Hausdorff distance was 3.1 ± 0.4 mm. An average artifact score of +0.37 indicated that the data-driven method had significantly fewer and/or less severe artifacts than the standard method (P = 1.5 × 10-5 for difference from 0). ConclusionsOn average, the difference between IGTVs derived from data-driven and standard 4D CT was not clinically relevant or statistically significant, suggesting data-driven 4D CT can be used in place of standard 4D CT without adjustments to IGTVs. The relatively large differences in some patients were usually attributed to limitations in automatic contouring or differences in artifacts. Artifact reduction and setup simplicity suggest a clinical advantage to data-driven 4D CT.

A comparative study of target volumes based on 18F-FDG PET-CT and ten phases of 4DCT for primary thoracic squamous esophageal cancer.

PurposeTo investigate the correlations in target volumes based on 18F-FDG PET/CT and four-dimensional CT (4DCT) to detect the feasibility of implementing PET in determining gross target volumes (GTV) for tumor motion for primary thoracic esophageal cancer (EC).MethodsThirty-three patients with EC sequentially underwent contrast-enhanced 3DCT, 4DCT, and 18F-FDG PET-CT thoracic simulation. The internal gross target volume (IGTV)10 was obtained by combining the GTV from ten phases of 4DCT. The GTVs based on PET/CT images were defined by setting of different standardized uptake value thresholds and visual contouring. The difference in volume ratio, conformity index (CI), and degree of inclusion (DI) between IGTV10 and GTVPET was compared.ResultsThe images from 20 patients were suitable for further analysis. The optimal volume ratio of 0.95±0.32, 1.06±0.50, 1.07±0.49 was at standardized uptake value (SUV)2.5, SUV20%, or manual contouring. The mean CIs were from 0.33 to 0.54. The best CIs were at SUV2.0 (0.51±0.11), SUV2.5 (0.53±0.13), SUV20% (0.53±0.12), and manual contouring (0.54±0.14). The mean DIs of GTVPET in IGTV10 were from 0.60 to 0.90, and the mean DIs of IGTV10 in GTVPET ranged from 0.35 to 0.78. A negative correlation was found between the mean CI and different SUV (P=0.000).ConclusionNone of the PET-based contours had both close spatial and volumetric approximation to the 4DCT IGTV10. Further evaluation and optimization of PET as a tool for target identification are required.

Image registration of a three-dimensional dynamic phantom in four-dimensional cone-beam computed tomography and four-dimensional computed tomography

Objective To evaluate the image quality and registration accuracy of a three-dimensional (3D) dynamic phantom in four-dimensional computed tomography (4DCT) and four-dimensional cone-beam computed tomography (4DCBCT). Methods The Computerized Imaging Reference Systems Dynamic Thorax Phantom Model 008A was scanned to get 4DCT and 4DCBCT images. Two balls with different diameters (O= 1 cm and O= 2 cm) were used to simulate tumors with different sizes. The motion mode of the balls was 3D sinusoidal motion at 0.25 Hz (the amplitudes along the x, y, and z axes were ±1.0 cm, ±0.4 cm, and ±0.2 cm, respectively). Gross target volumes (GTVs) from 10-phase bins, internal gross target volumes (IGTV), and target volumes on maximum intensity projection (MIP) and mean intensity projection (MeanIP) images were contoured and calculated. Target volumes on 4DCT or 4DCBCT images were compared with the static and dynamic volumes of the balls (VS and VD). The matching index (MI) of target volumes between the 4DCT and 4DCBCT images was analyzed after rigid image registration. Results The GTV in each phase of the image was larger than VS. The difference between the average GTV derived from 10 phases of 4DCT or 4DCBCT images and Vs of the small ball was larger than that of the large ball (35.03% vs. 22.66%; 32.62% vs. 17.00%). All the IGTVs and target volumes on MIP images were slightly larger than VD, but target volumes on MeanIP images were smaller than VD. The average MI of 10-phase bins of the small ball was smaller than that of the large ball (66.76% vs. 82.21%). Moreover, MIs of IGTV, MIP, and MeanIP of the small ball were also smaller than those of the large ball (77.39% vs. 90.29%; 75.90% vs. 89.28%; 74.47% vs. 82.74%). Conclusions In the case of a relatively small tumor volume and a relatively large motion amplitude, 4DCT and 4DCBCT should be used with caution for comparison of image registration. Key words: Tomography, X-ray computed; Tomography, X-ray computed, cone-beam; Imaging registration; Phantom

Detection of the correlations in target volumes for primary tumor of non­small cell lung cancer based on FDG PET/CT and the end­expiration phase of 4D­CT

Objective To investigate the correlations in target volumes based on positron emission tomography CT (PET/CT) and the end-expiration phase of four-dimensional CT (4D-CT) images for non-small cell lung cancer (NSCLC). Methods Seventeen patients with NSCLC sequentially underwent three-dimensional CT (3DCT), 4D-CT and 18F-FDG PET/CT thoracic simulation scans. The gross target volume (GTV) was contoured on the end-expiration phase (50%) of 4D-CT and defined as GTV50%. The internal gross target volumes (IGTV) based on PET/CT images (IGTVPET) were determined by the standardized uptake value (SUV) 2.0 (IGTVPET2.0) and 20% percentage of the maximal standardized uptake value (SUVmax) (IGTVPET20%). The following parameters were calculated to analyze the correlation between IGTVPET and GTV50% in volume ratio (VR) and conformity index (CI): maximum transverse diameter of GTV50%, volume of GTV50%, the displacement of GTV in the cranial-caudal direction and 3D Vector calculated from 4D-CT dataset as well as the SUVmax. Results There was no significant correlation between the VR of IGTVPET2.0 to GTV50% and the maximum transverse diameter of GTV50%, volume of GTV50%, the displacement of GTV in the cranial-caudal direction, 3D Vector and the SUVmax (P>0.05). The VR between IGTVPET20% and GTV50% inversely related to maximum transverse diameter of GTV50%, volume of GTV50% and SUVmax (r=-0.663, -0.669, -0.752, P<0.05). The CI between IGTVPET2.0 and GTV50% positively related to volume of GTV50% and maximum transverse diameter of GTV50% (r=0.613, 0.483, P<0.05). Conclusions 3D PET images provide a time-averaged image of the tumor during the numerous breathing cycle. They fail to include the full information of moving tumor. The target volumes based on 3D PET might not reflect the real IGTV of NSCLC. Key words: Non-small cell lung cancer; Fluorodeoxyglucose positron emission tomography; Four-dimensional computed tomography; Standardized uptake value; Internal gross target volume

A proposed framework for consensus-based lung tumour volume auto-segmentation in 4D computed tomography imaging

This work aims to propose and validate a framework for tumour volume auto-segmentation based on ground-truth estimates derived from multi-physician input contours to expedite 4D-CT based lung tumour volume delineation. 4D-CT datasets of ten non-small cell lung cancer (NSCLC) patients were manually segmented by 6 physicians. Multi-expert ground truth (GT) estimates were constructed using the STAPLE algorithm for the gross tumour volume (GTV) on all respiratory phases. Next, using a deformable model-based method, multi-expert GT on each individual phase of the 4D-CT dataset was propagated to all other phases providing auto-segmented GTVs and motion encompassing internal gross target volumes (IGTVs) based on GT estimates (STAPLE) from each respiratory phase of the 4D-CT dataset. Accuracy assessment of auto-segmentation employed graph cuts for 3D-shape reconstruction and point-set registration-based analysis yielding volumetric and distance-based measures. STAPLE-based auto-segmented GTV accuracy ranged from (81.51 ± 1.92) to (97.27 ± 0.28)% volumetric overlap of the estimated ground truth. IGTV auto-segmentation showed significantly improved accuracies with reduced variance for all patients ranging from 90.87 to 98.57% volumetric overlap of the ground truth volume. Additional metrics supported these observations with statistical significance. Accuracy of auto-segmentation was shown to be largely independent of selection of the initial propagation phase. IGTV construction based on auto-segmented GTVs within the 4D-CT dataset provided accurate and reliable target volumes compared to manual segmentation-based GT estimates. While inter-/intra-observer effects were largely mitigated, the proposed segmentation workflow is more complex than that of current clinical practice and requires further development.

4DCT MIP图像与FDG PET-CT不同SUV阈值勾画NSCLC IGTV的比较研究

Objective To compare the positional and volumetric differences between internal gross target volumes (IGTV) based on the maximum intensity projection (MIP) images of four-dimensional computed tomography (4DCT) and different standardized uptake value (SUV) thresholds of fluorodeoxyglucose (FDG) positron emission tomography/CT (PET/CT) for the primary tumor of non-small cell lung cancer (NSCLC).Methods Ten patients with NSCLC sequentially underwent contrast-enhanced 3DCT and 4DCT,as well as FDG PET-CT (with the same body position and positional parameters).IGTVMIP of the primary tumor was delineated on the MIP images of 4DCT.IGTVPET2.0,IGTVPET25,IGTVPET3.0,IGTVPET3.5,IGTVPET20％,IGTVPET25％,IGTVPET30％,IGTVPET35％,IGTVPET40％ and IGTVPETman were automatically and manually delineated based on different SUV thresholds of FDG PET/CT and different percentages of SUVmax.The differences in position,volume,matching index (MI),and degree of inclusion (DI) between IGTVPET and IGTVMIP were evaluated by paired t-test.Results There were significant differences in center coordinate between IGTVPET and IGTVMIP only in z axes (P =0.014-0.044).In terms of volume,IGTVPET2.0 and IGTVPET20％ were most similar to IGTNMIP,with volume ratios of 1.02 and 1.06(P =0.806).The highest MI was seen between IGTVMIP and IGTVPET2.0 and between IGTVMIP and IGTVPET20％ (0.46 and 0.45,P =0.603).The DI of IGTVPET20％ or IGTVPET2.0 in IGTVMIP was the highest (0.61 or 0.61,P =0.963).Conclusions IGTVPET20 and IGTVPET20％ are most similar to IGTVMIP in terms of volume and matching index,but neither of them could replace IGTVMIP in spatial position.When the IGTV of the primary tumor of NSCLC is delineated based on PET-CT,target position correction should be done with reference to 4DCT images while selecting the suitable SUV threshold. Key words: Tomography, positron-emission, fluorodeoxyglucose ; Tomography, X-ray computed,four-dimensional; Maximum intensity projection; Internal gross target volume; Lung neoplasms/radiotherapy

Poster - Thur Eve - 11: A realistic respiratory trace generator and its application to respiratory management techniques.

Respiratory motion complicates radiotherapy treatment of thoracic and abdominal tumours. Simplified respiratory motions such as sinusoidal and single patient traces are often used to determine the impact of motion on respiratory management techniques in radiotherapy. Such simplifications only accurately model a small portion of patients, as most patients exhibit variability and irregularity beyond these models. We have preformed a comprehensive analysis of respiratory motion and developed a software tool that allows for explicit inclusion of variability. We utilize our realistic respiratory generator to customize respiratory traces to test the robustness of the estimate of internal gross target volumes (IGTV) by 4DCT and CBCT. We confirmed that good agreement is found between 4DCT and CBCT for regular breathing motion. When amplitude variability was introduced the accuracy of the estimate slightly, but the absolute differences were still < 3 mm for both modalities. Poor agreement was shown with the addition of baseline drifts. Both modalities were found to underestimate the IGTV by as much as 30% for 4DCT and 25% for CBCT. Both large and small drifts deteriorated the estimate accuracy. The respiratory trace generator was advantageous for examining the difference between 4DCT and CBCT IGTV estimation under variable motions. It provided useful implementation abilities to test specific attributes of respiratory motion and detected issues that were not seen with the regular motion studies. This is just one example of how the respiratory trace generator can be utilized to test applications of respiratory management techniques.

Determination of patient-specific internal gross tumor volumes for lung cancer using four-dimensional computed tomography

BackgroundTo determine the optimal approach to delineating patient-specific internal gross target volumes (IGTV) from four-dimensional (4-D) computed tomography (CT) image data sets used in the planning of radiation treatment for lung cancers.MethodsWe analyzed 4D-CT image data sets of 27 consecutive patients with non-small-cell lung cancer (stage I: 17, stage III: 10). The IGTV, defined to be the envelope of respiratory motion of the gross tumor volume in each 4D-CT data set was delineated manually using four techniques: (1) combining the gross tumor volume (GTV) contours from ten respiratory phases (IGTVAllPhases); (2) combining the GTV contours from two extreme respiratory phases (0% and 50%) (IGTV2Phases); (3) defining the GTV contour using the maximum intensity projection (MIP) (IGTVMIP); and (4) defining the GTV contour using the MIP with modification based on visual verification of contours in individual respiratory phase (IGTVMIP-Modified). Using the IGTVAllPhases as the optimum IGTV, we compared volumes, matching indices, and extent of target missing using the IGTVs based on the other three approaches.ResultsThe IGTVMIP and IGTV2Phases were significantly smaller than the IGTVAllPhases (p < 0.006 for stage I and p < 0.002 for stage III). However, the values of the IGTVMIP-Modified were close to those determined from IGTVAllPhases (p = 0.08). IGTVMIP-Modified also matched the best with IGTVAllPhases.ConclusionIGTVMIP and IGTV2Phases underestimate IGTVs. IGTVMIP-Modified is recommended to improve IGTV delineation in lung cancer.