Maximum Intensity Projection Volume Research Articles

Improving the Feasibility of Mitigating Phase Errors in 4DCT caused by a Random Reference Breathing Pattern in the Quasar Phantom and the Role of Slice Thickness.

The study aimed to validate a method for minimizing phase errors by combining full-length lung 4DCT (f4DCT) scans with shorter tumor-restricted 4DCT (s4DCT) scans. It assessed the feasibility of integrating two scans one covering the entire phantom length and the other focused on the tumor area. The study also evaluated the impact of Maximum Intensity Projection (MIP) volume and imaging dose for different slice thicknesses (2.5mm and 1.25mm) in both full-length and short target-restricted 4DCT scans. The study utilized the Quasar Programmable Respiratory Motion Phantom, simulating tumor motion with a variable lung insert. The setup included a tumor replica and a six-dot IR reflector marker on the breathing platform. The objective was to analyze volume differences in fMIP_2.5mm compared to sMIP_1.25mm within their respective 4D_MIP CT series. This involved varying breathing periods (2.5s, 3.0s, 4.0s, and 5.0s) and longitudinal tumor sizes (6mm, 8mm, and 10mm). The study also assessed exposure time and expected CTDIvol of s4D_2.5mm and s4D_1.25mm for different breathing periods (5.0s to 2.0s) in the sinusoidal wave motion of the six-dot marker on the breathing platform. Conducting two consecutive 4DCT scans is viable for patients with challenging breathing patterns or when the initial lung tumor scan is in close proximity to the tumor location, eliminating the need for an additional full-length 4DCT. The analysis involves assessing MIP volume, imaging dose (CTDIvol), and exposure time. Longitudinal tumor shifts for 6mm are [16.6-17.2] in fMIP_2.5mm and [16.8-17.5] in sMIP_1.25mm, for 8mm [17.2-18.3] in fMIP_2.5mm and [17.8-18.4] in sMIP_1.25mm, and for 10mm [19-19.9] in fMIP_2.5mm and [19.4-20] in sMIP_1.25mm (p≥ 0.005), respectively. The Quasar Programmable Respiratory Motion Phantom accurately replicated varied breathing patterns and tumor motions. Comprehensive analysis was facilitated through detailed manual segmentation of Internal Target Volumes and Internal Gross Target Volumes.

Account for the Full Extent of Esophagus Motion in Radiation Therapy Planning: A Preliminary Study of the IRV of the Esophagus.

ObjectiveAccounting for esophagus motion in radiotherapy planning is an important basis for accurate assessment of toxicity. In this study, we calculated how much the delineations of the esophagus should be expanded based on three-dimensional (3D) computed tomography (CT), four-dimensional (4D) average projection (AVG), and maximum intensity projection (MIP) scans to account for the full extent of esophagus motion during 4D imaging acquisition.Methods and MaterialsThe 3D and 4D CT scans of 20 lung cancer patients treated with conventional radiotherapy and 20 patients treated with stereotactic ablative radiation therapy (SBRT) were used. Radiation oncologists contoured the esophagus on the 3DCT, AVG, MIP and 25% exhale scans, and the combination of the esophagus in every phase of 4DCT. The union of all 4D phase delineations (U4D) represented the full extent of esophagus motion during imaging acquisition. Surface distances from U4D to 3D, AVG, and MIP volumes were calculated. Distances in the most extreme surface points (1.5 cm most superoinferior, 10% most right/left/anteroposterior) were used to derive margins accounting only for systematic (delineation) errors.ResultsEsophagus delineations on the MIP were the closest to the full extent of motion, requiring only 6.9 mm margins. Delineations on the AVG and 3D scans required margins up to 7.97 and 7.90 mm, respectively. The largest margins were for the inferior, right, and anterior aspects for the delineations on the 3D, AVG, and MIP scans, respectively.ConclusionDelineations on 3D, AVG, or MIP scans required extensions for representing the esophagus’s full extent of motion, with the MIP requiring the smallest margins. Research including daily imaging to determine the random components for the margins and dosimetric measurements to determine the relevance of creating a planning organ at risk volume (PRV) of the esophagus is required.

Acceleration techniques for cubic interpolation MIP volume rendering

Maximum intensity projection (MIP) is a volume visualization technique that is important in modern medical imaging systems. We propose a method to accelerate high-quality MIP volume rendering using cubic interpolation. First, our method skips more regions of volume data that do not affect the output image. To do this, we propose a method of transforming the B-spline interpolation function into a sub-division of Bezier spline interpolation. We generate the B-spline interpolation control points then the Bezier interpolation control points from three dimensional voxel values. The maximum value of each block is approximated using the Bezier interpolation control points due to the convex hull property of the Bezier spline. By accurately approximating the maximum value of each block, we can skip more unnecessary blocks. Second, we propose an efficient method of parallelization when performing volume visualization using a GPU. In order to reduce the number of memory transfers, our method determines the working shape of a warp, a bundle of 32 GPU threads, depending on the viewing direction. As a result, our method achieves a remarkable rendering speed improvement with no loss of image quality compared to previous studies, and performs high-quality MIP volume rendering using cubic interpolation at interactive speed.

Protecting the Heart: A Practical Approach to Account for the Full Extent of Heart Motion in Radiation Therapy Planning

Emerging evidence suggests that the heart is more radiosensitive than previously assumed; therefore, accounting for heart motion in radiation therapy planning is becoming more critical. In this study, we determined how much heart delineations based on 3-dimensional (3D) computed tomography (CT), 4-dimensional (4D) average projection (AVG), and maximum intensity projection (MIP) images should be extended to represent the full extent of heart motion during 4D imaging acquisition. The 3D and 4D CT scans of 10 lung cancer patients treated with stereotactic ablative radiation therapy were used. Median surfaces were derived from heart delineations of 3 observers on the 3D CT, AVG, MIP, and 25% exhale scans. Per patient, the 25% exhale contour was propagated on every phase of the 4D scan. The union of all 4D phase delineations (U4D) represented the full extent of heart motion during imaging acquisition. Surface distances from U4D to 3D, AVG, and MIP volumes were calculated. Distances in the most extreme surface points (1.5 cm most superoinferior, 10% most right/left/anteroposterior) were used to derive margins accounting only for systematic (delineation) errors. Heart delineations on the MIP were the closest to the full extent of motion, requiring only ≤2.5-mm margins. Delineations on the AVG and 3D scans required margins up to 3.4 and 7.1 mm, respectively. The largest margins were for the inferior, right, and anterior aspects for the delineations on the 3D, AVG, and MIP scans, respectively. Delineations on 3D, AVG, or MIP scans required extensions for representing the heart's full extent of motion, with the MIP requiring the smallest margins. Research including daily imaging to determine the random components for the margins and dosimetric measurements to determine the relevance of creating a planning organ at risk volume of the heart is required.

Improved Reproducibility in Measuring the Laminar Thickness on Enhanced Depth Imaging SD-OCT Images Using Maximum Intensity Projection

To investigate whether the thin-slab maximum intensity projection (MIP) image improves the reproducibility of the measurement of spectral domain optical coherence tomography (SD-OCT) based lamina cribrosa thickness (LCT). Optic discs of 63 open angle glaucoma patients or glaucoma suspects were scanned with enhanced depth imaging spectral domain optical coherence tomography (SD-OCT). The B-scan images were constructed three-dimensionally using maximum intensity projection (MIP). The whole mip volume was then cut into thin slabs of two scan-line distance width (approximately 64 μm) at three 3 locations: mid-horizontal, and superior and inferior mid-peripheral regions of the optic nerve head. The LCT was measured in the thin-slab MIP images (LCT-MIP) and the three B-scans corresponding to each thin-slab MIP image (LCT-Bscan) at the three regions in each eye. The interobserver and intraobserver reproducibility of measuring the LCT-MIP and LCT-Bscan were evaluated by calculating the intraclass correlation coefficient (ICC), coefficient of variation (CV), and coefficient of repeatability (CR). The agreement between the LCT-MIP and the LCT-Bscan was assessed by Bland-Altman analysis. The thin-slab MIP images provided better image contrast with more distinct borders of the lamina cribrosa compared to the B-scan images. Both intraobserver and interobserver ICCs were higher for LCT-MIP than for LCT-Bscan in all areas. The 95% limit of agreement of measurement differences between LCT-Bscan and LCT-MIP ranged from -29.43 to 32.55 μm. The thin-slab MIP images provided a higher reproducibility in measuring the LCT using SD-OCT than the B-scan images. With thin-slab MIP images, the detection of the laminar borders was more straightforward. This technique should facilitate the evaluation of the lamina cribrosa.

Determination of Internal Target Volume From a Single Positron Emission Tomography/Computed Tomography Scan in Lung Cancer

The use of four-dimensional computed tomography (4D-CT) to determine the tumor internal target volume (ITV) is usually characterized by high patient radiation exposure. The objective of this study was to propose and evaluate an approach that relies on a single static positron emission tomography (PET)/CT scan to determine the ITV, thereby eliminating the need for 4D-CT and thus reduce patient radiation dose. The proposed approach is based on the concept that the observed PET image is the result of a joint convolution of an ideal PET image (free from motion and partial volume effect) with a motion-blurring kernel (MBK) and partial volume effect. In this regard, the MBK and tumor ITV are then estimated from the deconvolution of this joint model. To test this technique, phantom and patient studies were performed using different sphere/tumor sizes and motion trajectories. In all studies, a 4D-CT and a PET/CT image of the sphere/tumor were acquired. The ITV from the proposed technique was then compared to the maximum intensity projection (MIP) volume of the 4D-CT images. A Dice coefficient of the two volumes was calculated to represent the similarity between the two ITVs. The average ITVs of the proposed technique were 97.2% ± 0.3% and 81.0% ± 16.7% similar to the MIP volume in the phantom and patient studies, respectively. The average dice coefficients were 0.87 ± 0.05 and 0.73 ± 0.16, respectively, for the two studies. Using the proposed approach, a single static PET/CT scan has the potential to replace a 4D-CT to determine the tumor ITV. This approach has the added advantage of reducing patient radiation exposure and determining the tumor MBK compared to 4D-CT/MIP-CT.

SU-E-T-568: A Comparison of Apparent Tumor Volume on Treatment Planning Scans and Daily Volumetric Imaging Scans for Lung SBRT

Purpose: The effectiveness of stereotactic body radiation therapy(SBRT) depends on proper alignment of the patient and tumor. The objective of this study is to analyze the apparent tumor volume measured on daily volumetric imaging scans compared to the volume measured on various simulation and planning computed tomography(CT)images. Methods: Gross tumor volumes (GTVs) were contoured retrospectively in MIMVista for 10 lungcancer patients who underwent SBRT. Daily pretreatment megavoltage CT (MVCT) GTVs were compared to the treatment plan internal target volume (ITV), a contour derived solely from four‐dimensional CT (4DCT) cine in MIMVista, the maximum intensity projection (MIP) of the 4DCT data, and the average (phase‐binned) intensity projection (AIP). Results: On average, the ITV was 2.1 +/− 1.08 times larger than the MVCT GTV. Similarly, the MIP volume was 1.85 +/− 0.84 and the AIP volume was 1.07 +/− 0.37 times larger. Minimum and maximum values ranged from 0.95 to 6.93 times larger for the ITV and 0.92 to 5.73 for the MIP. Results for the AIP were more centrally distributed, ranging from 0.54 to 2.97 Conclusions: For lungcancer patients, daily MVCT scans show significantly smaller tumor volumes than treatment planningCT scans. For 9 out of 10 patients, all MVCTs showed smaller tumor volumes than the ITV and MIP. Because lungtumors are not stationary, this could cause uneven target dose and greater dose to healthy tissue. MVCT GTVs were closest in size to the AIP, but the minimum and maximum deviations were still significant. The largest tumor displayed relatively small deviations from the ITV and MIP volume, but there was no clear relationship between tumor volume and the magnitude of the deviations. This effect was less pronounced for the AIP. Further investigation will determine the effect this volume difference has on daily target registration.

SU‐GG‐T‐162: Using Tumor Motion Trajectory as a Constraint for 4D‐IMRT Treatment Planning

Purpose: To develop a 4D‐IMRT treatment planning technique by adding a tumor motion trajectory (TMTJ) as a constraint in a commercially available Treatment Planning System (TPS). The goal is to create an IMRT plan with a set of MLC segments catering for the motion of the patient anatomy extracted from 4D‐CT images. Method and Materials: 4D‐CT images were obtained from three lung cancer patients. The 4D protocol divided the breathing cycle into ten phases followed by a Maximum Intensity Projection (MIP) volume reconstruction. ITVs were contoured based on the MIP volumes. GTVs were contoured on all ten CT phases to generate a TMTJ, defined as the position of the centroid of the GTV on all phases. A tube shaped contour (TBC) with about 1 cm diameter along the TMTJ and inside the GTV was generated. TBC was added to the objective function as a constraint with minimum dose‐volume histogram (DVH) set to prescribed dose. IMRT plans were generated by using Pinnacle DMPO with and without the TMTJ constraint. Results: The IMRT plans generated with TMTJ constraints optimized the MLC segment shapes and weights for each beam with the TBC being forced/encouraged to inside of the segmented fields. The percentage of total MUs delivered to the largest area segments in each beam increased from 16.4% of the total MUs to 21.5%. The MU weight increased up to 20% by using TMTJ constrain. The DVHs for PTV and ORs, dose distributions and total MUs for plans with/without TMTJ constraints were very similar. Conclusion: The 4D tumor motion trajectory information can be used as a constraint in the Pinnacle DMPO to obtain tempospatially optimized IMRT plans. The method shows the potential to significantly reducing the dosimetric inaccuracies introduced by the interplay between organ motion and multileaf collimator (MLC) motion for IMRT.

SU‐GG‐J‐04: Determination of Tumor Volume Using a Joint Motion‐PVE Correction Technique in PET/CT Imaging

Objective: 4D‐CT has been used to determine the tumor volume (TV) for lung/thoracic radiation therapy treatment planning primarily due to its ability to detect the tumor motion extent and trajectory. However, 4‐D CT is usually characterized by high patient radiation exposure. The objective of this abstract is to propose and evaluate an approach that relies on a single static PET/CT scan than can determine the TV by simultaneously correcting for respiratory motion artifact and partial volume effect (PVE) thereby eliminating the need for 4D‐CT and reducing patient exposure.Materials and Methods: The proposed joint correction approach incorporates a model of motion blurring, PVE and object size/shape. A motion blurring kernel (MBK) is then estimated from the deconvolution of the joint model while the TV is derived from convolving the MBK by the object size/shape obtained from the CT image. To test this technique, two studies were performed using 2 spheres of different sizes moving in a 2cm 1D‐sinusoidal and 2D‐circular waveforms respectively. In both cases, a 4D‐CT and a PET/CT of the 2 spheres were acquired. For both studies, the TV from the proposed technique was compared to the maximum‐intensity projection (MIP) volume of the 4D‐CT. Also a Dice coefficient of the two volumes was calculated. Results: The TV of the proposed technique was on average 3% different from the MIP volume. The average Dice coefficient was 0.87. The motion trajectory derived from the proposed technique is continuous while that of the 4D‐CT is discrete. Conclusion: Using this approach, a single static PET/CT can replace a 4D‐CT to determine the TV. This approach also has the ability to determine the tumor motion extent and trajectory and has the added advantage of reducing patient radiation exposure and determining the tumor locale probability (or MBK) compared to 4D‐CT.

SU-FF-T-614: A Clinical Study of the Accuracy of Maximum Intensity Projection for Lung Tumor Volume

Purpose: To evaluate tumor motion and accuracy of the Maximum Intensity Projection (MIP) reconstruction volume as it pertains to Internal Target Volume (ITV) targeting for treatment planning in radiation oncology.Method and Materials: Eight respiratory gating 4DCT lung cases were examined in this study. Gated scans were acquired on a Phillips Brilliance Big Bore 16 slice CT scanner with Varian RPM gating equipment using helical 3mm contiguous slices with a maximum pitch based on the minimum breath rate of the patient. The 4D protocol divided the breathing cycle into ten reconstructed phases followed by a MIP volume reconstruction. Tumor Loc was used to select a treatment isocenter and contour an ITV based on the MIP volume. The difference between the MIP reconstruction and maximum phase in each direction was measured to validate reconstruction. Additionally, the difference was measured between the MIP volume and a “non‐gated” volume. Breath statistics were evaluated for average full inhalation and exhalation phase, amplitude range, and amplitude standard deviation. Maximum tumor movement was measured in the anterior/posterior, superior/inferior, and right/left directions between the average full inhalation and average full exhalation phases at the isocenter. Finally, a water filled ping‐pong ball was scanned with motion provided by a Varian RPM phantom to evaluate motion artifacts and to evaluate discrepancy between the actual volume and gating reconstructed volumes. Results: Measurements between the MIP and the maximum phase reconstructions revealed discrepancy within expected measurement error. Conclusion: This study showed that the MIP reconstruction is quite accurate and reliable for ITV targeting. Additionally the 4DCT protocol is appropriate for central disease and particularly valuable for peripheral disease. Breath statistics is a useful tool for selecting gated treatment to ensure the patient's breathing pattern is predictable and reproducible so as to benefit from gating.