Function Of Respiratory Phase Research Articles

Dosimetric impact of 4DCT artifact in carbon-ion scanning beam treatment: Worst case analysis in lung and liver treatments

IntroductionWe evaluated the impact of 4DCT artifacts on carbon-ion pencil beam scanning dose distributions in lung and liver treatment. Methods & materials4DCT was performed in 20 liver and lung patients using area-detector CT (original 4DCT). 4DCT acquisition by multi-detector row CT was simulated using original 4DCT by selecting other phases randomly (plus/minus 20% phases). Since tumor position can move over the respiratory range in original 4DCT, mid-exhalation was set as reference phase. Total prescribed dose of 60Gy (RBE) was delivered to the clinical target volume (CTV). Reference dose distribution was calculated with the original CT, and actual dose distributions were calculated with treatment planning parameters optimized using the simulated CT (simulated dose). Dose distribution was calculated by substituting these parameters into the original CT. ResultsFor liver cases, CTV-D95 and CTV-Dmin values for the reference dose were 97.6±0.5% and 89.8±0.6% of prescribed dose, respectively. Values for the simulated dose were significantly degraded, to 88.6±14.0% and 46.3±26.7%, respectively. Dose assessment results for lung cases were 84.8±12.8% and 58.0±24.5% for the simulated dose, showing significant degradation over the reference dose of 95.1±1.5% and 87.0±2.2%, respectively. Conclusions4DCT image quality should be closely checked to minimize degradation of dose conformation due to 4DCT artifacts. Medical staff should pay particular attention to checking the quality of 4DCT images as a function of respiratory phase, because it is difficult to recognize 4DCT artifact on a single phase in some cases

MO-A(SAM)-BRC-01: 4DCT: Methods and Artifacts

4DCT is routinely used in the treatment planning of moving targets. 4D scanning provides information essential for planning, specifically the size, shape and location of the target and organs at risk as a function of respiratory phase. 4D scanning also provides quantitative data on radiological pathlength needed for radiation dose calculations. The amount of scan data has increased by a factor of ∼10 over helical scans. Given the role of 4DCT in aperture design and dose calculation, it is important to analyze how accurately this scanning technique provides quantitative data and what the sources of uncertainty are. The learning objectives of this talk include: 1. Understand methods of 4DCT reconstruction commonly used today 2. Describe the residual artifacts in 4DCT due to irregularities in respiration 3. Describe advances in visualization that

Four-Dimensional Lung Treatment Planning in Layer-Stacking Carbon Ion Beam Treatment: Comparison of Layer-Stacking and Conventional Ungated/Gated Irradiation

We compared four-dimensional (4D) layer-stacking and conventional carbon ion beam distribution in the treatment of lung cancer between ungated and gated respiratory strategies using 4DCT data sets. Twenty lung patients underwent 4DCT imaging under free-breathing conditions. Using planning target volumes (PTVs) at respective respiratory phases, two types of compensating bolus were designed, a full single respiratory cycle for the ungated strategy and an approximately 30% duty cycle for the exhalation-gated strategy. Beams were delivered to the PTVs for the ungated and gated strategies, PTV(ungated) and PTV(gated), respectively, which were calculated by combining the respective PTV(Tn)s by layer-stacking and conventional irradiation. Carbon ion beam dose distribution was calculated as a function of respiratory phase by applying a compensating bolus to 4DCT. Accumulated dose distributions were calculated by applying deformable registration. With the ungated strategy, accumulated dose distributions were satisfactorily provided to the PTV, with D95 values for layer-stacking and conventional irradiation of 94.0% and 96.2%, respectively. V20 for the lung and Dmax for the spinal cord were lower with layer-stacking than with conventional irradiation, whereas Dmax for the skin (14.1 GyE) was significantly lower (21.9 GyE). In addition, dose conformation to the GTV/PTV with layer-stacking irradiation was better with the gated than with the ungated strategy. Gated layer-stacking irradiation allows the delivery of a carbon ion beam to a moving target without significant degradation of dose conformity or the development of hot spots.

Comparison of Respiratory-Gated and Respiratory-Ungated Planning in Scattered Carbon Ion Beam Treatment of the Pancreas Using Four-Dimensional Computed Tomography

We compared respiratory-gated and respiratory-ungated treatment strategies using four-dimensional (4D) scattered carbon ion beam distribution in pancreatic 4D computed tomography (CT) datasets. Seven inpatients with pancreatic tumors underwent 4DCT scanning under free-breathing conditions using a rapidly rotating cone-beam CT, which was integrated with a 256-slice detector, in cine mode. Two types of bolus for gated and ungated treatment were designed to cover the planning target volume (PTV) using 4DCT datasets in a 30% duty cycle around exhalation and a single respiratory cycle, respectively. Carbon ion beam distribution for each strategy was calculated as a function of respiratory phase by applying the compensating bolus to 4DCT at the respective phases. Smearing was not applied to the bolus, but consideration was given to drill diameter. The accumulated dose distributions were calculated by applying deformable registration and calculating the dose-volume histogram. Doses to normal tissues in gated treatment were minimized mainly on the inferior aspect, which thereby minimized excessive doses to normal tissues. Over 95% of the dose, however, was delivered to the clinical target volume at all phases for both treatment strategies. Maximum doses to the duodenum and pancreas averaged across all patients were 43.1/43.1 GyE (ungated/gated) and 43.2/43.2 GyE (ungated/gated), respectively. Although gated treatment minimized excessive dosing to normal tissue, the difference between treatment strategies was small. Respiratory gating may not always be required in pancreatic treatment as long as dose distribution is assessed. Any application of our results to clinical use should be undertaken only after discussion with oncologists, particularly with regard to radiotherapy combined with chemotherapy.

SU-FF-J-99: 4D Multi-Organ Motion Analysis in Pancreatic Cancer Patients

Purpose: Center of mass (COM) motion, bounding box motion and volume fluctuation analysis of the clinical target volume (CTV), liver,kidneys, stomach and duodenum in pancreatic cancer patients were measured using 4DCT and deformable registration. Methods and Materials: Eight patients with pancreatic cancer underwent 4DCT for treatment planning. The scans were binned into 10 phases (T00 to T90) and a physician contoured the GTV, CTV, and other abdominal volumes of interest (VOIs) on the T30 phase scan. Deformable registration was applied to propagate the contours to other respiratory phases. Subtraction images were used to validate the registration. We calculated the superior‐inferior (SI), anterior‐posterior (AP), and left‐right (LR) coordinates of the VOIs' center of mass, bounding box margin, as well as volume as a function of respiratory phase. Results: The greatest motion was in the SI axis, with lesser motion in the AP direction. Motion in the LR axis was negligible. Bounding box analysis showed anisotropic movement of the SI and AP edges of organs. The superior margin of the liver showed the greatest movement. In multi‐organ motion analysis, several trends were observed: 1) SI motion of the right kidney and liver were nearly identical; 2) right kidney range of motion was greater than the left kidney motion in 6 of 8 patients 3) Volume fluctuation as a function of respiratory phase of all abdominal organs studied was < 8% of the average organ volume. Conclusion: We have validated and implemented 4D routine motion analysis of abdominal organs. Quantification of organ motion is a necessary step in designing the radiation treatment plan of a moving target. Coupled with dosimetric analysis, it provides metrics for evaluating the need for gated treatment.

SU‐GG‐J‐198: Phantom Evaluation of Implanted Coil Localization Accuracy of the BrainLab ExacTrac Gating System and 4DCT

Purpose: The purpose of this study was to evaluate the accuracy of measured target motion using 4DCT scanning and BrainLab ExacTrac (ET) Gating system for gated therapy. Motions of an implantable coil as a function of respiratory phase were compared from the two systems to the known motion for a commercial gating phantom. Method and Materials: A Quasar respiratory motion phantom containing an implantable coil as a surrogate target was used. Phantom motion was sinusoidal with a 4‐second period and amplitudes of 5–25 mm. 4DCT datasets were sorted in 10 distinct respiratory phases, reconstructed, and imported into the Pinnacle TPS. Coil endpoints were identified on each phase‐sorted CT datasets to measure coil distortion. To compare coil localization accuracy, both systems imaged the implanted coil at the same respiratory phases and measured overall relative coil displacement as a function of respiratory phase. Results: Coil length errors measured on the 4DCT were &lt;0.8 mm at end inhale/exhale phases, but 8.1 mm at mid‐inhalation. Maximum localization error from the expected position for all motion profiles was 5.5 mm for both coil tips in 4DCT. but only 0.8 mm for the ET Gating system. Even at the greatest coil velocity, ExacTrac coil localization agrees with calculated coil motion within 1 mm. 4DCT showed problems resolving a coil during large respiratory‐induced velocities, but accurately resolved the coil length within 1 mm of actual coil length at end expiration/inhalation. Conclusion: 4DCT can provide accurate representation of the phantom at end‐respiration for treatment planning. ExacTrac can accurately localize the coil to determine target motion over all phases. Good agreement of the techniques will allow minimization of internal motion margins in gated radiotherapy. Conflict of Interest: This work was supported in part by a research agreement with BrainLab, Inc.

Evaluation of patient dose using a virtual CT scanner: Applications to 4DCT simulation and Kilovoltage cone-beam imaging

This work evaluates the effects of patient size on radiation dose from simulation imaging studies such as four-dimensional computed tomography (4DCT) and kilovoltage cone-beam computed tomography (kV-CBCT). 4DCT studies are scans that include temporal information, frequently incorporating highly over-sampled imaging series necessary for retrospective sorting as a function of respiratory phase. This type of imaging study can result in a significant dose increase to the patient due to the slower table speed as compared with a conventional axial or helical scan protocol. Kilovoltage cone-beam imaging is a relatively new imaging technique that requires an on-board kilovoltage x-ray tube and a flat-panel detector. Instead of porting individual reference fields, the kV tube and flat-panel detector are rotated about the patient producing a cone-beam CT data set (kV-CBCT). To perform these investigations, we used Monte Carlo simulation methods with detailed models of adult patients and virtual source models of multidetector computed tomography (MDCT) scanners. The GSF family of three-dimensional, voxelized patient models, were implemented as input files using the Monte Carlo code MCNPX. The adult patient models represent a range of patient sizes and have all radiosensitive organs previously identified and segmented. Simulated 4DCT scans of each voxelized patient model were performed using a multi-detector CT source model that includes scanner specific spectra, bow-tie filtration, and helical source path. Standard MCNPX tally functions were applied to each model to estimate absolute organ dose based upon an air-kerma normalization measurement for nominal scanner operating parameters.

Cardiorespiratory‐resolved magnetic resonance imaging: Measuring respiratory modulation of cardiac function

A technique for cardiac- and respiratory-resolved MRI is described. A retrospectively gated-segmented acquisition scheme similar to that used in conventional cine cardiac imaging was used to collect image data that spanned both the cardiac and respiratory cycles. Raw k-space data were regridded in a cardiorespiratory phase space to allow image reconstruction at target cardiac and respiratory phases. The approach can be applied with various k-space trajectories and pulse sequences, and was implemented in this study with both a Cartesian steady-state free precession (SSFP) sequence and a radial phase-contrast (PC) pulse sequence. Free-breathing short-axis SSFP images of the heart were reconstructed at multiple respiratory and cardiac phases to illustrate separation of cardiac and respiratory motion without artifacts. A respiratory-resolved radial PC experiment was used to quantify the volumetric flow rates in the inferior vena cava (IVC), pulmonary artery (PA), and aorta (Ao) in five free-breathing normal volunteers and a positive-pressure ventilated dog. Total flow (ml/min) in each vessel was quantified as a function of respiratory phase (peak/minimum output = 1.85 +/- 0.29 (IVC), 1.36 +/- 0.15 (PA), 1.24 +/- 0.09 (Ao)). Peak flow occurred during inspiration for the IVC and PA, and during expiration for the Ao, and there was a complete pattern reversal for the positive-pressure ventilated dog.

TU‐C‐ValA‐06: Quantifying the Properties and Accuracy of a Deformable Image Registration Algorithm for 4D Treatment Planning

Purpose: A necessary tool to facilitate automated four‐dimensional and adaptive radiotherapy planning is deformable image registration (DIR). The purpose of the current study was to quantify the accuracy of a DIR algorithm by comparing automatically transferred and manually segmented structures on 4DCT images. Method and Materials: 780 structures were manually segmented on thirteen patient 4DCT image sets each consisting of 10 respiratory phases. A large deformable diffeomorphic DIR algorithm, integrated with a commercial treatment planning system, was used to map each CT set from the inspiration respiratory phase CT image set respiratory phase images. The calculated displacement vector fields were used to deform and transfer structures defined on the inspiration CT to the other respiratory phase CT image sets. The manually and automatically segmented structures were compared using volumetric, displacement, and surface congruence metrics. Results: Deformation with respiration was observed for the lung tumor and normal tissues. This deformation was verified by examining the mapping of high contrast objects, such as the lungs and cord, between image sets. The auto‐ and manual methods showed similar trends, with a smaller difference observed between the GTVs than other structures. The auto‐contoured structures were more consistent both in terms of centroid displacement and volume as a function of respiratory phase than manual contours. 1.6% of the time, deficiencies of manual contouring has been detected using auto contouring. Image artifacts play a crucial role in auto contouring. Conclusion: An automated system is established to auto‐contour structures starting from one 4DCT image phase to other 4DCT image phases. The auto‐contoured structures generally agree with the manually drawn structures. However the auto‐contoured structures are more consistent in trajectory and volume, and also highlighted some large errors in the manually drawn contours. Careful assessment is needed in the presence of 4DCT artifacts.

WE‐C‐ValA‐03: The Use of CT Density Changes at Internal Tissue Interfaces to Monitor Respiratory Induced Lung Tumor Motion

Purpose: To describe a non‐invasive method to monitor the motion of internal organs affected by respiration without using external markers or spirometry, to apply the method to construct 4D‐CT datasets, to test the correlation with external markers, and to calculate any time shift between the datasets.Method and Materials: Ten lung cancer patients were CT scanned with a General Electric Fast 4‐Slice CT scanner operating in ciné mode. An external signal was also acquired simultaneously using the Real‐Time Position Management (RPM) Respiratory Gating System (Varian Medical Systems). We retrospectively reconstructed the raw CT data to obtain consecutive 0.5s reconstructions at 0.1s intervals to increase image sampling. We defined regions of interest containing tissue interfaces that move due to breathing on each axial slice and measured the mean CT number as a function of respiratory phase. We constructed 4D‐CT data sets by retrospectively sorting each image set based on the respiratory phase determined by the mean CT number curve. The external marker and tumor motion were directly correlated using the sample coefficient of determination, r2. Any time shift between the two data sets was calculated by shifting the tumor motion curve until r2 was maximized. Results: Only three of the ten patients showed correlation higher than r2=0.80 between tumor motion and external marker position. However, after taking into account time shifts (ranging between 0s and 0.4s) between the two data sets, all ten patients showed correlation better than r2=0.8. Conclusions: 4D‐CT acquisition using an internal method improves the temporal registration of CT images affected by respiratory motion without the need for external markers or spirometry. A non‐invasive method to directly correlate the motion of external markers and internal organs can be used to help guide decisions regarding the validity of the RPM system for respiratory gated radiotherapy on a patient‐specific basis.