Average Intensity Projection Images Research Articles

A generalized model of cardiac surface motion for evaluating left anterior descending coronary artery dose in left breast cancer radiotherapy.

Retrospective studies indicate that radiation damage to left anterior descending coronary artery (LAD) may be critical for late-stage radiation-induced cardiac morbidity. Developing a method that accurately depicts LAD motion and perform dose assessment is crucial. To construct a generalized cardiac surface motion model for LAD dose assessment in left breast cancer radiotherapy. Cine MRI of 25 cases were divided into training and testing sets for model construction, and five external cases were gathered for generalization validation. Motion prediction from average intensity projection images (AIP) surface point cloud to that of each phase was realized by mapping the relationship between datum points and corresponding points with statistical shape modeling (SSM). Root mean square error (RMSE) for predicted corresponding points and Euclidean distance (ED) for predicted surface point cloud were used to assess model's accuracy. LAD dose assessment for 10 left breast cancer radiotherapy cases was perform by model application. The RMSE in testing cases and external cases were 0.209±0.020mm to 0.841±0.074mm and 0.895±0.093mm to 1.912±0.138mm, respectively; while the ED were 1.399±0.029mm to 1.658±0.100mm, 1.571±0.080mm to 1.779±0.104mm, respectively, proving the generalized model's high accuracy. The volume of LAD characterizing motion range (WPLAD) (2.392±0.639 cm3) was approximately twice that of LAD from superimposed images (SPLAD) (0.927±0.326 cm3) with p<0.05, and the former's Dmax (3582.06±575.92 cGy) was significantly larger than latter's (3222.71±665.37 cGy) (p<0.05). While WPLAD's Dmean (1408.06±413.06 cGy) was slightly smaller than that of SPLAD (1504.15±448.03 cGy), the difference did not reach statistical significance (p>0.05). WPLAD's V20 (23.42%±16.62%) was less than SPLAD's (29.18%±21.07%) with p<0.05, but their comparison in V30 and V40 did not yield statistically significant results. It implies the conventional LAD dose assessment ignores motion impact and may not be justified. The generalized cardiac surface motion model informs LAD dose accurate assessment in left breast cancer radiotherapy.

Treatment planning and delivery practice of lung SBRT: Results of the 2022 ESTRO physics survey

Background and purposeThe use of Stereotactic Body Radiation Therapy (SBRT) in lung cancer is increasing. However, there is no consensus on the most appropriate treatment planning and delivery practice for lung SBRT. To gauge the range of practice, quantify its variability and identify where consensus might be achieved, ESTRO surveyed the medical physics community. Materials and methodsAn online survey was distributed to ESTRO’s physicist membership in 2022, covering experience, dose and fractionation, target delineation, dose calculation and planning practice, imaging protocols, and quality assurance. ResultsTwo-hundred and forty-four unique answers were collected after data cleaning. Most respondents were from Europe the majority of which had more than 5 years’ experience in SBRT. The large majority of respondents deliver lung SBRT with the VMAT technique on C-arm Linear Accelerators (Linacs) employing daily pre-treatment CBCT imaging. A broad spectrum of fractionation schemes were reported, alongside an equally wide range of dose prescription protocols. A clear preference was noted for prescribing to 95% or greater of the PTV. Several issues emerged regarding the dose calculation algorithm: 22% did not state it while 24% neglected to specify the conditions under which the dose was calculated. Contouring was usually performed on Maximum or Average Intensity Projection images while dose was mainly computed on the latter. No clear indications emerged for plan homogeneity, complexity, and conformity assessment. Approximately 40% of the responders participated in inter-centre credentialing of SBRT in the last five years. Substantial differences emerged between high and low experience centres, with the latter employing less accurate algorithms and older equipment. ConclusionThe survey revealed an evident heterogeneity in numerous aspects of the clinical implementation of lung SBRT treatments. International guidelines and codes of practice might promote harmonisation.

Motion-Inclusive Treatment Planning to Assess Normal Tissue Dose for Central Lung Stereotactic Body Radiation Therapy

PurposeFor lung SBRT, 4DCT is often used to delineate target volumes, whereas organs at risk (OARs) are typically outlined on either average intensity projection (AIP) or mid-ventilation (MidV = 30% phase) images. AIP has been widely adopted as it represents a true average, but image blurring often precludes accurate contouring of critical structures such as central airways. Here we compare AIP vs MidV planning for centrally located tumors via respiratory motion-inclusive (RMI) plans to better evaluate dose delivered throughout the breathing cycle. MethodsIndependently contoured and optimized AIP and MidV plans were created for 16 treatments and rigidly copied to each of the 10 breathing phase-specific CT image sets. Resulting dose distributions were deformably registered back to the MidV image set (used as reference due to clearer depiction of anatomy compared to motion-blurred AIP) and averaged to create RMI plans. Doses to central OARs were compared between plans. ResultsMean absolute dose differences were low for all comparisons (range 0.01 – 2.87 Gy), however, individual plans exhibited differences > 20 Gy. Dose differences >5 Gy were observed most often for plan comparisons involving AIP-based plans (MidV vs AIP 23, AIP RMI vs AIP 12, MidV RMI vs AIP RMI 7, and MidV RMI vs MidV 8 times). Inclusion of respiratory motion reduced large dose differences. Standard OAR thresholds were exceeded up to five times for each plan comparison scenario and always involved PBT D4cc tolerance dose. AIP-based contours were larger by on average 3-15%. ConclusionLarge dose differences were observed when plans with AIP-based contours were compared with MidV-based contours indicating that observed dose differences were likely due to contoured volume differences rather than the effect of motion. Because of blurring with AIP images, MidV RMI-based planning may offer a more accurate method to determine dose to critical OARs in the presence of respiratory motion.

Influence of Respiratory Motion on Dose Distribution in Gastric Mucosa-associated Lymphoid Tissue Lymphoma Radiotherapy.

The present study investigated the effect of respiratory motion on planned radiotherapy (RT) dose for gastric mucosa-associated lymphoid tissue (MALT) lymphoma using four-dimensional dose (4D-dose) accumulation. 4D-computed tomography (4D-CT) images of 10 patients with gastric MALT lymphomas were divided into 10 respiratory phases. Further, the 3D-dose was calculated using 3D conformal RT (3D-CRT) and volumetric modulated arc therapy (VMAT) plans based on the average intensity projection (AIP) images. Then, both plans were recalculated according to each phase image. Moreover, the dose distributions in each phase were transferred to the AIP images using deformable image registration. The 4D-dose distribution was calculated by summing the doses of each phase, and it was compared with the dosimetric parameters of the 3D-dose distribution. For 3D-CRT, the D95 and D99 of the 4D-dose in the planning target volume (PTV) were significantly lower than those of the 3D-dose, with mean differences of 0.2 (p=0.009) and 0.1 Gy (p=0.021), respectively. There were no significant differences in the other PTV and organ-at-risk dosimetric parameters of 3D-CRT or in any dosimetric parameters of VMAT between the 3D- and 4D-dose distributions. The effect of respiratory motion on the planned 3D-CRT and VMAT dose distributions for gastric MALT lymphoma is minimal and clinically negligible.

New Data-Driven Gated (DDG) PET/CT for Radiation Treatment Planning of NSCLC

PET/CT for RT simulation of NSCLC is typically conducted in two separate imaging sessions of gated 4D-CT in radiation oncology and fusion with non-gated PET/CT in diagnostic imaging, making treatment response assessment (TRA) with PET/CT and radiation treatment planning (RTP) challenging. To remedy this short-coming, we designed a new data-driven gated (DDG) PET/CT, based on the self-gated PET and self-gated CT data to derive the gated PET/CT data free of tumor blurring and misregistration artifacts without any respiratory monitoring device (ease of use and cost reduction). The new DDG PET/CT also provides the important 4D-CT information of end-inspiratory (EI), end-expiratory (EE), maximum-intensity-projection (MIP) and average-intensity-projection (AIP) CT's. The total imaging time is < 15 min, which makes DDG PET/CT simulation in a single session without any respiratory monitoring device possible. Acquisition is standard PET/CT imaging protocol followed by a cine CT imaging of the tumor area. We utilized the commercial DDG PET from GE Discovery PET/CT and designed a new DDG CT for attenuation correction of the DDG PET for reduction of tumor motion and mis-registration. The AIP and MIP images were from the average and maximum pixel values of the cine CT images, respectively. The cine CT images with the largest and smallest average CT number in the lung region were identified as the EE and EI CT images, respectively. For the image slices without any lung region present, the largest and smallest expansions of the body outline contour were selected to be the EE and EI CT phases, respectively. The AIP and EE CT images were used for attenuation correction of the PET and DDG PET data, respectively. Both DDG PET/CT and 4D-CT of (EI, EE, AIP and MIP) are for RT simulation of NSCLC. 38 4D-CT patient data sets were compared at the EE and EI phases between our DDG CT and 4D-CT to demonstrate the applicability of the newly designed DDG CT. A prototype software on a Dell PC of i5-6500 CPU has been successfully developed to enable DDG PET/CT and 4D-CT on seven GE Discovery PET/CT scanners. The operating system was Ubuntu and the computer language was Python. In the EE phase, the images selected by DDG CT and 4D CT were identical 62.5±21.6% of the time. In the EI phase, the images selected by DDG CT and 4D CT were identical 68.2±18.9% of the time. Inspection of the EE and EI phases of DDG CT and 50% and 0% of 4D-CT demonstrated both data sets of DDG CT and 4D CT were almost identical. A new DDG PET/CT and 4D-CT in a single imaging session without any hardware gating has been developed for TRA and RTP of NSCLC. The utility is available on the network and it enables all PET/CT scanners on the network for TRA and RTP. The new DDG CT provides the benefits of 4D-CT without any requirement of external hardware gating and make possible DDG PET/CT free of tumor motion and misregistration artifacts.

Evaluation of target volume and dose accuracy in intrafractional cases of lung cancer based on 4D-CT and 4D-CBCT images using an in-house dynamic thorax phantom.

BackgroundThis study aimed to evaluate the target volume and dose accuracy in intrafraction cases using 4-dimensional imaging modalities and an in-house dynamic thorax phantom. Intrafraction motion can create errors in the definition of target volumes, which can significantly affect the accuracy of radiation delivery. Motion management using 4-dimensional modalities is required to reduce the risk.Materials and methodsTwo variations in both breathing amplitude and target size were applied in this study. From these variations, internal target volume (ITVs) contoured in 10 phases of 4D-CT (ITV10), average intensity projection (AIP), and mid-ventilation (Mid-V) images were reconstructed from all 4D-CT datasets as reference images. Free-breathing (FB), augmentation free-breathing (Aug-FB), and static images were also acquired using the 3D-CT protocol for comparisons. In dose evaluations, the 4D-CBCT modality was applied before irradiation to obtain position correction. Then, the dose was evaluated with Gafchromic film EBT3.ResultsThe ITV10, AIP, and Mid-V provide GTVs that match the static GTV. The AIP and Mid-V reference images allowed reductions in ITVs and PTVs without reducing the range of target movement areas compared to FB and Aug-FB images with varying percentages in the range of 29.17% to 48.70%. In the dose evaluation, the largest discrepancies between the measured and planned doses were 10.39% for the FB images and 9.21% for the Aug-FB images.ConclusionThe 4D-CT modality can enable accurate definition of the target volume and reduce the PTV. Furthermore, 4D-CBCT provides localization images during registration to facilitate position correction and accurate dose delivery.

Vulnerabilities of radiomic features to respiratory motion on four-dimensional computed tomography-based average intensity projection images: A phantom study.

PurposeTo evaluate the influence of respiratory motion on the robustness of radiomic features on four‐dimensional computed tomography (4DCT)‐based average intensity projection (AIP) images by employing an anthropomorphic chest phantom.MethodsThree spherical objects (φ30 mm), namely, acrylic (100 Hounsfield unit [HU], homogeneous), rubber (−140 HU, homogeneous), and cork (−630 HU, heterogeneous), were moved with motion amplitudes of 0, 1, 2.5, 4, 6, 8, and 10 mm in the phantom, and 4DCT scans were repeated at four different locations. Thereafter, the AIP images were generated considering the average of the 10 respiratory phases of the 4DCT images. Further, the targets were manually delineated on the AIP images in the lung window setting. A total of 851 radiomic features, including 107 unfiltered features and 744 wavelet filter‐based features, were extracted from the region of interest for each material. The feature robustness among the different target motion amplitude (ε) was evaluated by normalizing the feature variability of the target motion relative to the variability of data from 573 patients with early‐stage non‐small cell lung cancer. The features with absolute ε values ≤0.5 were considered highly robust to target motions.ResultsThe percentage of robust unfiltered and wavelet filter‐based features with a motion amplitude of 1 mm was greater than 83.2% and 93.4%, respectively; however, the percentage decreased by more than 24.3% and 17.6%, respectively, for motion amplitudes greater than 2.5 mm. The movement of cork had a small effect on the feature robustness compared to that of acrylic and rubber, regardless of the target motion amplitudes.ConclusionsOur phantom study demonstrated that target motion amplitudes ≤1 mm led to the robustness of radiomic features on the 4DCT‐based AIP images of thoracic regions. The frequency components and directions of the wavelet filters may be essential factors in 4DCT‐based radiomic analysis.

Determining Radiation Doses of Critical Normal Tissues for Stereotactic Body Radiotherapy (SBRT) of Central Lung Tumors

While respiratory motion is included in the definition of target volumes for lung SBRT, delineation of organs at risk (OARs) and dose calculation are typically performed on average intensity projection images (AIP). This approach often misses structural detail during contouring due to motion blurring on AIP. Including respiratory motion in the dose calculation for OARs will result in more accurate dose assessment, which is necessary to establish reliable dose-effect relationships, particularly for SBRT of central lung tumors with a high risk of critical side effects.For 17 centrally-located lung tumors, clinical 4DCT-based SBRT treatment plans (BED≥100 Gy in 76%) were created for both AIP and mid ventilation image (MidV, 30% breathing phase) and contour sets. Internal GTVs were produced via GTV propagation over all breathing phases. OARs were outlined on both AIP and MidV images according to RTOG 0813. Both plans were also recalculated on all 10 breathing phases and registered back deformably to the MidV to assess differences in the accumulated OAR doses over the full breathing cycle. MidV was selected over the AIP as the reference image for comparison as it does not suffer from motion blurring.Volumes were, on average, larger on AIP than MidV image sets for all OARs by 3-15% (P < 0.05 for heart, lungs, great vessels (GV)), except the esophagus. Mean differences ± SDs in the max doses (Gy) between respiration-averaged MidV and AIP plans were for proximal bronchial tree (PBT) 2.26 ± 2.11, heart 2.24 ± 2.89, GV 1.71 ± 1.12, esophagus 1.38 ± 1.1, spinal cord 1.11 ± 0.67, and trachea 0.71 ± 1.16. Doses were significantly different for heart Dmean/10cc/15cc (P = 0.03/0.03/0.04). Relative to MidV plans, AIP plans resulted in higher max doses for PBT in 11/17 (65%) plans, 9/17 (53%) for esophagus, GV and spinal cord, and 5/17 (29%) for heart and trachea. Max dose differences > 5 Gy were observed for GV and PBT in 2/17 (12%) and for heart in 3/17 (18%) of individual plans. Superior-inferior carina motion ranged from 0.32 to 0.73 cm. No significant correlations between dose differences and carina motion were identified.Though limited by a small sample size, this study represents a comprehensive assessment of OAR doses for SBRT planning of centrally located lung tumors including the effects of respiratory motion. We often observed only small differences in dose delivered to central OARs. However, clinically relevant differences ≥ 5 Gy were observed in individual patients for PBT, GV and heart, resulting in over- or underestimation of the actual OAR dose over the full breathing cycle when using AIP-based planning. We therefore recommend MidV image-based OAR dose assessment to develop reliable dose-effect relationships for central lung OARs.D.A. Cooper: None. L. Padilla: None. A. Watson: None. K. Neiderer: None. B. Smith: None. E. Weiss: Research Grant; NIH. royalties; UpToDate.

Technical Note: A 3D-printed phantom for radiochromic film evaluation of moving lung tumor SBRT without dose convolution.

A common dosimetric quality assurance (QA) method in stereotactic body radiation therapy (SBRT) of lung tumors is to use lung phantoms with radiochromic film. However, in most phantoms, the film moves with the tumor, leading to the blurring effect. This technical note presents the QA performance of a novel phantom in which the film is fixed; this phantom can be used for both patient-specific QA and end-to-end testing. Lung tumor motion was simulated with the CIRS Model 008A phantom. A lung-equivalent insert that consisted of a fixed radiochromic film around which a 2-cm tumor moved in the inferior/superior direction (i.e., mimicking respiration-induced tumor motion) was generated by 3D printing. Two common SBRT plans [dynamic conformal arc (DCA) and volumetric-modulated arc therapy (VMAT)] were calculated on the average intensity projection (AIP) image set in Varian Eclipse using the dose calculation algorithm Acuros XB. The plans were delivered by a Varian TrueBeam STx accelerator using 6-MV flattening filter-free energy. EBT3 films were used for treatment-dose verification. The measured and planned dose distributions were compared by using the local gamma index at 3% and 2 mm. Mean gamma pass rates of film and planned dose distributions were all ≥95%. DCA and VMAT plans did not differ in gamma pass rates. Planned and measured dose distributions agreed well, as did planned and measured gamma maps. With this new insert, measured and planned dose distributions were very similar, which supports the current view in the field that dose calculations on AIP image sets account sufficiently for tumor motion during treatment. The phantom also performed well despite challenging breathing parameters (large tumor amplitude and slow breathing rate) and the application of a complex treatment technique (VMAT). This phantom could facilitate clinical and end-to-end film-based dosimetric QA for lung SBRT. Twenty-seven TH- Radiation dose measurement devices. Eleven Phantoms for dosimetric measurement.

The impact of respiratory motion and CT pitch on the robustness of radiomics feature extraction in 4DCT lung imaging

Purpose/Objective(s)The precise radiomics analysis on thoracic 4DCT data is easily compromised by the respiratory motion and CT scan parameter setting, thus leading to the risk of overfitting and/or misinterpretation of data in AI-enabled therapeutic model building. In this study, we investigated the impact of respiratory amplitudes, frequencies and CT scan pitch settings within the thoracic 4DCT scan on robust radiomics feature selection. Materials/MethodsA Three-dimensional QUSARTM lung tumor phantom was used to simulate different respiratory amplitudes and frequencies along with different CT scan pitch settings. A total of 43 tumor respiratory patterns extracted from 43 patients with non-small cell lung cancer were used to drive the QUSARTM lung tumor phantom to mimic the human tumor motion. The 4DCT images of the QUSARTM lung tumor phantom with different respiratory patterns and different CT scan pitch setups were acquired for radiomics feature extraction. A static high-quality CT images of the phantom acquired were also used as a reference for radiomics feature extraction. The range of respiratory amplitudes was mimicked at 3mm at left and right (LR) and anterior and posterior (AP) directions and 3mm - 15 mm at the superior and inferior (SI) direction with an interval of 2 mm. The respiratory frequencies were set at 10, 11, 12, 13, 14, 15 and 20 beats per minute (BPMs), respectively. The CT scan pitches were set at 0.025, 0.048, 0.071, 0.93, 0.108, 0.14, 0.16, 0.18, 0.21, 0.23, and 0.25, respectively, which was based on a procedure described in Med. Phys. 30(1):88-97. The pairwise Concordance Correlation Coefficient (CCC) was used to determine the robustness of radiomics feature extraction via comparing the agreement in feature values between 1766 radiomics features extracted from each image acquired under different combinations of respiratory amplitudes and frequencies and CT scan pitches of 4DCT and those extracted from the static CT images. Results(1) When the respiratory amplitudes were at 3, 5, 7, 9, 12 and 15mm in the SI direction, the maximum CCC index could be achieved at the reconstructed 4DCT phase images of 60%, 70%, 30%, 20%, 60%~70% and 10%, respectively. Under these six amplitudes, the maximum intensity projection (MIP) and average intensity projection (AIP) images reconstructed show mean CCC values of 0.778 and 0.609, respectively, in pairwise radiomics feature extraction comparison between 4DCT and static CT. (2) When the respiratory amplitude was set at 12 mm in the SI direction, the maximum CCC index could be consistently achieved at the reconstructed 4DCT phase of 90% for the seven respiratory frequencies of 10, 11, 12, 13, 14, 15 and 20 BPMs, respectively. Under these respiratory states, the MIP and AIP images reconstructed show mean CCC values of 0.702 and 0.562, respectively. (3) When the respiratory amplitude was set at 12 mm and the respiratory frequency was set at 13 BPM, the maximum CCC index could be obtained at the reconstructed 4DCT phase of 90% for all scan pitches used except the 0% phase which was obtained at the pitch setting of 0.048. Under these CT scan pitch settings, the MIP and AIP images reconstructed show mean CCC values of 0.558 and 0.782, respectively. (4) The total number of robust features were 50, 34 and 35 with different respiratory amplitudes and phases and CT scanning pitch used (CCC values ≥ 0.99). ConclusionIn 4DCT, the respiratory amplitude, frequency and CT scan pitch are three limiting factors that greatly affect the robustness of radiomics feature extraction. The reconstructed 4DCT phases with better robustness along with suitable respiratory amplitude, frequency and CT scan pitch determined could be used to guide the breathing training for patients with lung cancer for radiation therapy to improve the robust radiomics feature extraction process.

Study on the Effect of 4D-CT Special Reconstruction Images for Evaluation of the Cardiac Structure Dose in Radiotherapy for Breast Cancer.

Objective: To study the dosimetric effect on special reconstruction images obtained from an electrocardiograph-gated four-dimensional computed tomography (ECG 4D-CT) series and compare it with the accumulation dose assessment of ECG 4D-CT.Methods: Fifteen patients underwent ECG 4D-CT scans to obtain a 4D-CT series. The 20 phase images of 0–95% were reconstructed at intervals of 5% of the cardiac cycle by the 4D-CT series. The 4D-CT series was specially reconstructed, and the maximum intensity projection (MIP), minimum intensity projection (MinIP), average intensity projection (AIP), and sum intensity projection (SIP) were obtained. The left ventricular muscle (LV) and the anterior descending branch of the left coronary artery (LAD) were delineated on all series. The intensity-modulated radiation therapy (IMRT) plan for left breast cancer was designed on the basis of the 0% phase, and the accumulative dose (Dose−acc) of 20 phases was obtained by deformation registration. The dose-volume indexes of the LV and LAD were compared based on different CT series.Results: The dose-volume indices of V5, V30, V40, Dmax, and Dmean of the LV on MIP images were 3.8, 2.0, 0.9, 3.8, and 1.7%, respectively (relative to the Dose−acc). There was no significant difference in V5 or Dmax between the MIP and Dose−acc (P > 0.05). The change rates of Dmax on the MinIP, SIP, and AIP images were 2.5, 3.1, and 1.5%, respectively (relative to the Dose−acc) (P < 0.05).Conclusion: In the dose-volume evaluation of the LV, V30, V40, and Dmean obtained by MIP were essentially the same as those obtained by the Dose−acc and can be used instead of the 4D-CT series to evaluate dose-volume indexes.

Comparison of the dose on specific 3DCT images and the accumulated dose for cardiac structures in esophageal tumors radiotherapy: whether specific 3DCT images can be used for dose assessment?

BackgroundCardiac activity could impact the accuracy of dose assessment for the heart, pericardium and left ventricular myocardium (LVM). The purpose of this study was to explore whether it is possible to perform dose assessment by contouring the cardiac structures on specific three-dimensional computed tomography (3DCT) images to reduce the impact of cardiac activity.MethodsElectrocardiograph-gated 4DCT (ECG-gated 4DCT) images of 22 patients in breath-hold were collected. MIM Maestro 6.8.2 (MIM) was used to reconstruct specific 3DCT images to obtain the Maximal intensity projection (MIP) image, Average intensity projection (AIP) image and Minimum intensity projection (Min-IP) image. The heart, pericardium and LVM were contoured in 20 phases of 4DCT images (0, 5%... 95%) and the MIP, AIP and Min-IP images. Then, a radiotherapy plan was designed at the 0% phase of the 4DCT images, and the dose was transplanted to all phases of 4DCT to acquire the dose on all phases, the accumulated dose of all phases was calculated using MIM. The dose on MIP, AIP and Min-IP images were also obtained by deformable registration of the dose. The mean dose (Dmean), V5, V10, V20, V30 and V40 for the heart, pericardium and LVM in MIP, AIP and Min-IP images were compared with the corresponding parameters after dose accumulation.ResultsThe mean values of the difference between the Dmean in the MIP image and the Dmean after accumulation for the heart, pericardium and LVM were all less than 1.50 Gy, and the dose difference for the pericardium and LVM was not statistically significant (p > 0.05). For dose-volume parameters, there was no statistically significant difference between V5, V10, and V20 of the heart and pericardium in MIP, AIP, and Min-IP images and those after accumulation (p > 0.05). For the LVM, only in the MIP image, the differences of V5, V10, V20, V30 and V40 were not significant compared to those after dose accumulation (p > 0.05).ConclusionsThere was a smallest difference for the dosimetry parameters of cardiac structures on MIP image compared to corresponding parameters after dose accumulation. Therefore, it is recommended to use the MIP image for the delineation and dose assessment of cardiac structures in clinical practice.

Comparing Maximum Dose to Central Airways in Mid-Ventilation Versus Average Intensity Projection-Based 4DCT Planning for Lung Stereotactic Body Radiation Therapy (SBRT)

Four-Dimensional Computed Tomography (4DCT) is typically used in radiation treatment planning for improved targeting of intrathoracic tumors. While tumor definition uses all in- and expiration image sets to account for the full range of respiratory motion, the definition of organs at risk (OARs) is less well defined. We investigated OAR dose differences for two commonly used image sets for SBRT dose calculation: average intensity projection (AIP) and mid-point in ventilation (midV). Determining accurate OAR doses is particularly important for proximal airways, as RTOG 0813 results have shown that increased dose to these structures can result in unacceptable, at times fatal toxicity. Fifteen 4DCT-based lung SBRT plans originally generated on 30% MidV image sets were transferred to associated AIP images. Fractionation schedules were 50 Gy in 5 fractions in 5, 48 Gy in 4 fractions in 9, and 40 Gy in 5 fractions in 1 plan. Internal gross tumor volumes (iGTV) were delineated on maximum intensity projection (MIP) images. OARs were contoured per RTOG 0813 protocol on both MidV and AIP datasets. Maximum doses were reported for each OAR (trachea, proximal bronchial tree (PBT), heart, and great vessels (GV)) on original MidV plans and after plan transfer to AIP image sets with field arrangements and monitor unit (MU) values unchanged. AIP volumes were, on average, greater by 4.26 ± 5.44 cc for trachea and 13.11 ± 12.21 for PBT, and reduced by 21.6 ± 70.42 for heart and 6.06 ± 41.14 cc for GV. Average superior-inferior movement of tumor and carina were 7.1 ± 4.1 and 7.6 ± 4.7 mm, respectively. The average absolute difference between AIP and MidV in maximum doses to trachea, PBT, heart, and GV were 1.01 ± 1.37, 1.68 ± 3.10, 1.45 ± 2.05, and 1.07 ± 1.21 Gy, respectively. Maximum dose to PBT was increased in 3 of 15 (20%) plans after transfer to AIP image sets, with an average increase of 3.03 ± 2.97 Gy (0.09 to 7.10). Of the remaining 12 plans (80%), this was decreased by an average of 1.35 ± 3.04 Gy (0.01 to 11.31). Fourteen (93%) plans exhibited an absolute difference in maximum dose of > 1 Gy to at least one OAR. Absolute difference in maximum dose to heart showed a positive correlation with carina motion (R2 = 0.61), and GV a weak positive correlation with tumor motion (R2 = 0.40). Our results show a difference in maximum dose to OARs between AIP and MidV image sets. These differences are confounded by tumor and carina motion and associated differences in contoured volumes. Although this study does not allow to identify the better image set, AIP images are more likely to account for a true positional average, and AIP-based plans are expected to be more representative of the true maximum OAR dose. To calculate correct OAR doses, both tumor and OARs require contouring and planning on all respiratory phases which might be necessary for critical central structures such as PBT, if they are in the high dose area.

Spatial-temporal variability of radiomic features and its effect on the classification of lung cancer histology

The purpose of this research was to study the sensitivity of Computed Tomography (CT) radiomic features to motion blurring and signal-to-noise ratios (SNR), and investigate its downstream effect regarding the classification of non-small cell lung cancer (NSCLC) histology.Forty-three radiomic features were considered and classified into one of four categories: Morphological, Intensity, Fine Texture, and Coarse Texture. First, a series of simulations were used to study feature-sensitivity to changes in spatial-temporal resolution. A dynamic digital phantom was used to generate images with different breathing amplitudes and SNR, from which features were extracted and characterized relative to initial simulation conditions. Stage I NSCLC patients were then retrospectively identified, from which three different acquisition-specific feature-spaces were generated based on free-breathing (FB), average-intensity-projection (AIP), and end-of-exhalation (EOE) CT images. These feature-spaces were derived to cover a wide range of spatial-temporal tradeoff. Normalized percent differences and concordance correlation coefficients (CCC) were used to assess the variability between the 3D and 4D acquisition techniques. Subsequently, three corresponding acquisition-specific logistic regression models were developed to classify lung tumor histology. Classification performance was compared between the different data-dependent models.Simulation results demonstrated strong linear dependences (p > 0.95) between respiratory motion and morphological features, as well as between SNR and texture features. The feature Short Run Emphasis was found to be particularly stable to both motion blurring and changes in SNR. When comparing FB-to-EOE, 37% of features demonstrated high CCC agreement (CCC > 0.8), compared to only 30% for FB-to-AIP. In classifying tumor histology, EoE images achieved an average AUC, Accuracy, Sensitivity, and Specificity of , respectively. FB images achieved respective values of , and AIP images achieved respective values of .Several radiomic features have been identified as being relatively robust to spatial-temporal variations based on both simulation data and patient data. In general, features that were sensitive to motion blurring were not necessarily the same features that were sensitive to changes in SNR. Our modeling results suggest that the EoE phase of a 4DCT acquisition may provide useful radiomic information, particularly for features that are highly sensitive to respiratory motion.

Effects of irregular respiratory motion on the positioning accuracy of moving target with free breathing cone-beam computerized tomography.

For positioning a moving target, a maximum intensity projection (MIP) or average intensity projection (AIP) image derived from 4DCT is often used as the reference image which is matched to free breathing cone-beam CT (FBCBCT) before treatment. This method can be highly accurate if the respiratory motion of the patient is stable. However, a patient’s breathing pattern is often irregular. The purpose of this study is to investigate the effects of irregular respiration on positioning accuracy for a moving target aligned with FBCBCT. Nine patients’ respiratory motion curves were selected to drive a Quasar motion phantom with one embedded cubic and two spherical targets. A 4DCT of the phantom was acquired on a CT scanner (Philips Brilliance 16) equipped with a Varian RPM system. The phase binned 4DCT images and the corresponding MIP and AIP images were transferred into Eclipse for analysis. FBCBCTs of the phantom driven by the same respiratory curves were also acquired on a Varian TrueBeam and fused such that both CBCT and MIP/AIP images share the same target zero positions. The sphere and cube volumes and centroid differences (alignment error) determined by MIP, AIP and FBCBCT images were calculated, respectively. Compared to the volume determined by MIP, the volumes of the cube, large sphere, and small sphere in AIP and FBCBCT images were smaller. The alignment errors for the cube, large sphere and small sphere with center to center matches between MIP and FBCBCT were 2.5 ± 1.8mm, 2.4±2.1 mm, and 3.8±2.8 mm, and the alignment errors between AIP and FBCBCT were 0.5±1.1mm, 0.3±0.8mm, and 1.8±2.0 mm, respectively. AIP images appear to be superior reference images to MIP images. However, irregular respiratory pattern could compromise the positioning accuracy, especially for smaller targets.

Associations of Radiomic Data Extracted from Static and Respiratory-Gated CT Scans with Disease Recurrence in Lung Cancer Patients Treated with SBRT

Radiomics aims to quantitatively capture the complex tumor phenotype contained in medical images to associate them with clinical outcomes. This study investigates the impact of different types of computed tomography (CT) images on the prognostic performance of radiomic features for disease recurrence in early stage non-small cell lung cancer (NSCLC) patients treated with stereotactic body radiation therapy (SBRT). 112 early stage NSCLC patients treated with SBRT that had static free breathing (FB) and average intensity projection (AIP) images were analyzed. Nineteen radiomic features were selected from each image type (FB or AIP) for analysis based on stability and variance. The selected FB and AIP radiomic feature sets had 6 common radiomic features between both image types and 13 unique features. The prognostic performances of the features for distant metastasis (DM) and locoregional recurrence (LRR) were evaluated using the concordance index (CI) and compared with two conventional features (tumor volume and maximum diameter). P-values were corrected for multiple testing using the false discovery rate procedure. None of the FB radiomic features were associated with DM, however, seven AIP radiomic features, that described tumor shape and heterogeneity, were (CI range: 0.638–0.676). Conventional features from FB images were not associated with DM, however, AIP conventional features were (CI range: 0.643–0.658). Radiomic and conventional multivariate models were compared between FB and AIP images using cross validation. The differences between the models were assessed using a permutation test. AIP radiomic multivariate models (median CI = 0.667) outperformed all other models (median CI range: 0.601–0.630) in predicting DM. None of the imaging features were prognostic of LRR. Therefore, image type impacts the performance of radiomic models in their association with disease recurrence. AIP images contained more information than FB images that were associated with disease recurrence in early stage NSCLC patients treated with SBRT, which suggests that AIP images may potentially be more optimal for the development of an imaging biomarker.

SU‐F‐R‐52: A Comparison of the Performance of Radiomic Features From Free Breathing and 4DCT Scans in Predicting Disease Recurrence in Lung Cancer SBRT Patients

Purpose:There is a clinical need to identify patients who are at highest risk of recurrence after being treated with stereotactic body radiation therapy (SBRT). Radiomics offers a non‐invasive approach by extracting quantitative features from medical images based on tumor phenotype that is predictive of an outcome. Lung cancer patients treated with SBRT routinely undergo free breathing (FB image) and 4DCT (average intensity projection (AIP) image) scans for treatment planning to account for organ motion. The aim of the current study is to evaluate and compare the prognostic performance of radiomic features extracted from FB and AIP images in lung cancer patients treated with SBRT to identify which image type would generate an optimal predictive model for recurrence.Methods:FB and AIP images of 113 Stage I‐II NSCLC patients treated with SBRT were analysed. The prognostic performance of radiomic features for distant metastasis (DM) was evaluated by their concordance index (CI). Radiomic features were compared with conventional imaging metrics (e.g. diameter). All p‐values were corrected for multiple testing using the false discovery rate.Results:All patients received SBRT and 20.4% of patients developed DM. From each image type (FB or AIP), nineteen radiomic features were selected based on stability and variance. Both image types had five common and fourteen different radiomic features. One FB (CI=0.70) and five AIP (CI range=0.65–0.68) radiomic features were significantly prognostic for DM (p&lt;0.05). None of the conventional features derived from FB images (range CI=0.60–0.61) were significant but all AIP conventional features were (range CI=0.64–0.66).Conclusion:Features extracted from different types of CT scans have varying prognostic performances. AIP images contain more prognostic radiomic features for DM than FB images. These methods can provide personalized medicine approaches at low cost, as FB and AIP data are readily available within a large number of radiation oncology departments.R.M. had consulting interest with Amgen (ended in 2015).

SU‐E‐T‐437: Four‐Dimensional Treatment Planning for Lung VMAT‐SBRT

Purpose:To assess optimal treatment planning approach of Volumetric Modulated Arc Therapy for lung Stereotactic Body Radiation Therapy (VMAT‐SBRT).Methods:Subjects were 10 patients with lung cancer who had undergone 4DCT. The internal target volume (ITV) volume ranged from 2.6 to 16.5cm3 and the tumor motion ranged from 0 to 2cm. From 4DCT, which was binned into 10 respiratory phases, 4 image data sets were created; maximum intensity projection (MIP), average intensity projection (AIP), AIP with the ITV replaced by 0HU (RITV‐AIP) and RITV‐AIP with the planning target volume (PTV) minus the internal target volume was set to −200 HU (HR‐AIP). VMAT‐SBRT plans were generated on each image set for a patient. 48Gy was prescribed to 95% of PTV. The plans were recalculated on all phase images of 4DCT and the dose distributions were accumulated using a deformable image registration software MIM Maestro™ as the 4D calculated dose to the gross tumor volume (GTV). The planned dose to the ITV and 4D calculated dose to the GTV were compared.Results:In AIP plan, 10 patients average of all dose parameters (D1%, D_mean, and D99%) discrepancy were 1Gy or smaller. MIP and RITV‐AIP plans resulted in having common tendency and larger discrepancy than AIP plan. The 4D dose was lower than the planned dose, and 10 patients average of all dose parameters discrepancy were in range 1.3 to 2.6Gy. HR‐AIP plan had the largest discrepancy in our trials. 4D calculated D1%, D_mean, and D99% were resulted in 3.0, 4.1, and 6.1Gy lower than the expected in plan, respectively.Conclusion:For all patients, the dose parameters expected in AIP plan approximated to 4D calculated. Using AIP image set seems optimal treatment planning approach of VMAT‐SBRT for a mobile tumor.Funding Support: This work was supported by the Japan Society for the Promotion of Science Core‐to‐Core program (No. 23003).

Treatment of Moving Lesions With Helical Intensity Modulated Radiation Therapy (HIMR): A Phantom Study

Treatments performed with Helical Intensity-Modulated Radiation therapy (HIMR) on moving lung lesions might be inaccurate due to the simultaneous gantry rotation, patient couch translation and lesion movement. Moreover depending on the technique used to acquire/reconstruct the planning CT data (Free-Breathing (FB), Breath-Hold (BH) or Average Intensity Projection (AIP) from 4DCT) different results are obtained during HIMR planning. In this study the outcome of how these factors interplay and their effects on dose distribution are explored using a moving phantom and radiochromic EBT3 films. A phantom made of two pieces of tissue equivalent material embedded in two adjacent polystyrene slabs, slid in a cranio-caudal direction using a motor-driven motion platform (3cm and 16cycle/min movement extension and rate). A CT scanner was used to acquire/reconstruct FB and AIP images of the moving phantom and BH images of the static phantom. The three data sets were sent to the HIMR planning station where three plans for delivering 2Gy to the central tissue equivalent material were prepared. The phantom was put on the patient couch, radiochromic EBT3 films were inserted between the two phantom parts and the three treatments were delivered. In order to compare planning and delivered dose distributions radiochromic films, sandwiched between the two phantom parts, were also fixed to an external support that enable the phantom to slit while films stand still. A significant difference between planned and delivered dose distributions was observed in the moving phantom. Gamma index passing rates (3%, 3mm, 10% threshold, local criterion) changed from 89,48% for the static phantom and BH CT data set to 63,89% and 61.38% for the moving phantom using AIP and FB CT data set respectively. Dose delivered by treatments planned on FB and AIP CT data sets shows under dosages (up to 4%) and over dosages (up to 50%) in the target region and surrounding regions, respectively, compared to that delivered to the static target. The over dosage effect is more pronounced in caudal direction. The most evident effect on dose distribution was dose blurring. This effect also impacted dose gradients which tended to decrease in the peripheral region. Treatments performed with HIMR on moving targets showed a significant difference between planned and delivered dose distributions. The use of Average Intensity Projection (AIP) CT images, adequate for dose calculation in most circumstances, does not seem to provide better results. Contouring strategies that keep into account these effects should be explored.

SU-E-J-150: To Design a Methodology Based on Numerical Phantom for Reconstruction of Dose Delivered to Moving Lung Tumors.

To design a methodology based on numerical phantom for reconstruction of dose delivered to moving lung tumors. MatlabTM 7.6 was used to generate a 4D numerical lung phantom (NLP). Customer parameter files were used as input to this NLP, which consists of multiple ellipsoids representing body, lung, cord and tumor. In this study, we studied the impact of varying breathing pattern on a left lower lobe tumor, where the tumor motion was simulated on the daily breathing pattern of the patient acquired using real time positioning management (RPMTM) system from Varian Medical Systems. Based on the daily breathing pattern, the original RPM signal and the original tumor trajectory, 5 sets of motion trajectories were simulated. This was then used to build 10 different phases of the numerical phantom. Average Intensity Projection (AIP) was then generated from the different phases. The actual delivered dose on the 5 AIP sets were compared to the intended dose on the original planning AIP image set. The mean target coverage (TC) recomputed on the 5 AIP sets was approximately 18% lower than the TC for the planning AIP image set. The mean homogeneity index (HI) recomputed on the 5 sets, was approximately 5 times higher than HI for the planning AIP image set. The lung NTDmean dose was approximately 9.5 Gy3 and did not differ much. The presented numerical simulation framework may assist in monitoring the changes in dose accumulation due to changes in the patient's breathing on a daily basis. This can also be used for validation of new motion tracking algorithms and its impact of dose coverage.