Iterative Sorting for 4DCT Images Based ON Internal Anatomy Motion

Geometric uncertainties caused by respiratory motion complicate radiotherapy treatment planning. Therefore 4D CT imaging is important in characterizing anatomy motion during breathing. Current 4D CT imaging techniques using multislice CT scanners involve multiple scans at several axial positions and retrospective sorting processes. Most sorting methods are based on externally monitored signals recorded by external monitoring instruments, which may not always accurately catch the actual breathing status and may lead to severe discontinuity artifacts in the sorted CT volumes. We propose a method to reconstruct time-resolved CT volumes based on internal motion to avoid the inaccuracies caused by external breathing signals. In our method, we iteratively sort the 4D CT slices using internal motion based breathing indices. In each iteration, respiratory motion is estimated by updating a motion model to best match a deformed reference volume to each moving multi-slice sub-volumes. The breathing indices as well as the reference volumes are refined for each iteration based on the currently estimated respiratory motion. An example is presented to illustrate the feasibility of our 4D CT sorting method without using any external motion monitoring systems.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85803/1/Fessler229.pd

Relational database of treatment planning system information

The purpose of the present work was to develop a relational database and associated applications to facilitate retrospective review of data present in radiation treatment plans. The data source was a commercial radiation treatment planning system (Pinnacle3, Philips Medical Systems, Milpitas CA), which is specifically characterized by an open data storage format and internal scripting capability. The database is an open-source, relational database (PostgreSQL, PostgreSQL Global Development Group, http://www.postgresql.org). The data is presented through a web interface in addition to being fully query-accessible using standard tools. A database schema was created to organize the large collection of parameters used to generate treatment plans as well as the parameters that characterized these plans. The system was implemented through a combination of the treatment planning systems internal scripting language and externally executed code. Data is exported in a way that is transparent to the user, through integration into an existing and routinely-used process. The system has been transparently incorporated into our radiation treatment planning workflow. The website-based database interface has allowed users with minimal training to extract information from the database

How extensive of a 4D dataset is needed to estimate cumulative dose distribution plan evaluation metrics in conformal lung therapy?a)

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134757/1/mp0624.pd

Dose perturbations from implanted helical gold markers in proton therapy of prostate cancer

Implanted gold fiducial markers are widely used in radiation therapy to improve targeting accuracy. Recent investigations have revealed that metallic fiducial markers can cause severe perturbations in dose distributions for proton therapy, suggesting smaller markers should be considered. The objective of this study was to estimate the dosimetric impact of small gold markers in patients receiving proton therapy for prostate cancer. Small, medium, and large helical wire markers with lengths of 10 mm and helix diameters of 0.35 mm, 0.75 mm, and 1.15 mm, respectively, were implanted in an anthropomorphic phantom. Radiographic visibility was confirmed using a kilovoltage x-ray imaging system, and dose perturbations were predicted from Monte Carlo simulations and confirmed by measurements. Monte Carlo simulations indicated that size of dose perturbation depended on marker size, orientation, and distance from the beam\u27s end of range. Specifically, the perturbation of proton dose for the lateral-opposed-pair treatment technique was 31% for large markers and 23% for medium markers in a typical oblique orientation. Results for perpendicular and parallel orientations were respectively lower and higher. Consequently, these markers are not well suited for use in patients receiving proton therapy for prostate cancer. Dose perturbation was not observed for the small markers, but these markers were deemed too fragile for transrectal implantation in the prostate

COMPREHENSIVE CALCULATION-BASED IMRT QA USING R&V DATA, TREATMENT RECORDS, AND A SECOND TREATMENT PLANNING SYSTEM

Purpose: Traditional patient-specific IMRT QA measurements are labor intensive and consume machine time. Calculation-based IMRT QA methods typically are not comprehensive. We have developed a comprehensive calculation-based IMRT QA method to detect uncertainties introduced by the initial dose calculation, the data transfer through the Record-and-Verify (R&V) system, and various aspects of the physical delivery. Methods: We recomputed the treatment plans in the patient geometry for 48 cases using data from the R&V, and from the delivery unit to calculate the “as-transferred” and “as-delivered” doses respectively. These data were sent to the original TPS to verify transfer and delivery or to a second TPS to verify the original calculation. For each dataset we examined the dose computed from the R&V record (RV) and from the delivery records (Tx), and the dose computed with a second verification TPS (vTPS). Each verification dose was compared to the clinical dose distribution using 3D gamma analysis and by comparison of mean dose and ROI-specific dose levels to target volumes. Plans were also compared to IMRT QA absolute and relative dose measurements. Results: The average 3D gamma passing percentages using 3%-3mm, 2%-2mm, and 1%-1mm criteria for the RV plan were 100.0 (σ=0.0), 100.0 (σ=0.0), and 100.0 (σ=0.1); for the Tx plan they were 100.0 (σ=0.0), 100.0 (σ=0.0), and 99.0 (σ=1.4); and for the vTPS plan they were 99.3 (σ=0.6), 97.2 (σ=1.5), and 79.0 (σ=8.6). When comparing target volume doses in the RV, Tx, and vTPS plans to the clinical plans, the average ratios of ROI mean doses were 0.999 (σ=0.001), 1.001 (σ=0.002), and 0.990 (σ=0.009) and ROI-specific dose levels were 0.999 (σ=0.001), 1.001 (σ=0.002), and 0.980 (σ=0.043), respectively. Comparing the clinical, RV, TR, and vTPS calculated doses to the IMRT QA measurements for all 48 patients, the average ratios for absolute doses were 0.999 (σ=0.013), 0.998 (σ=0.013), 0.999 σ=0.015), and 0.990 (σ=0.012), respectively, and the average 2D gamma(5%-3mm) passing percentages for relative doses for 9 patients was were 99.36 (σ=0.68), 99.50 (σ=0.49), 99.13 (σ=0.84), and 98.76 (σ=1.66), respectively. Conclusions: Together with mechanical and dosimetric QA, our calculation-based IMRT QA method promises to minimize the need for patient-specific QA measurements by identifying outliers in need of further review

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

<p>Abstract</p> <p>Background</p> <p>To 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.</p> <p>Methods</p> <p>We 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: (<it>1</it>) combining the gross tumor volume (GTV) contours from ten respiratory phases (IGTV_AllPhases); (<it>2</it>) combining the GTV contours from two extreme respiratory phases (0% and 50%) (IGTV_2Phases); (<it>3</it>) defining the GTV contour using the maximum intensity projection (MIP) (IGTV_MIP); and (<it>4</it>) defining the GTV contour using the MIP with modification based on visual verification of contours in individual respiratory phase (IGTV_MIP-Modified). Using the IGTV_AllPhasesas the optimum IGTV, we compared volumes, matching indices, and extent of target missing using the IGTVs based on the other three approaches.</p> <p>Results</p> <p>The IGTV_MIPand IGTV_2Phaseswere significantly smaller than the IGTV_AllPhases(<it>p </it>< 0.006 for stage I and <it>p </it>< 0.002 for stage III). However, the values of the IGTV_MIP-Modifiedwere close to those determined from IGTV_AllPhases(<it>p </it>= 0.08). IGTV_MIP-Modifiedalso matched the best with IGTV_AllPhases.</p> <p>Conclusion</p> <p>IGTV_MIPand IGTV_2Phasesunderestimate IGTVs. IGTV_MIP-Modifiedis recommended to improve IGTV delineation in lung cancer.</p

A step towards true delivered dose with dose accumulation in radiotherapy

https://openworks.mdanderson.org/sumexp21/1188/thumbnail.jp

Upright CBCT: A novel imaging technique

Purpose: We present a method for acquiring and correcting upright images using the on board CBCT imager. An upright imaging technique would allow for the introduction of upright radiation therapy treatments, which would benefit a variety of patients including those with thoracic cancers whose lung volumes are increased in an upright position and those who experience substantial discomfort during supine treatment positions.Methods: To acquire upright CBCT images, the linac head was positioned at 0 degrees, the KV imager and detector arms extended to their lateral positions, and the couch placed at 270 degrees. The KV imager was programmed to begin taking continuous fluoroscopic projections as the couch rotated from 270 to 90 degrees. The FOV was extended by performing this procedure twice, once with the detector shifted 14.5 cm towards the gantry and once with it shifted 14.5 cm away from the gantry. The two resulting sets of images were stitched together prior to reconstruction. The imaging parameters were chosen to deliver the some dose as that delivered during a simulation CT. A simulation CT was deformably registered to an upright CBCT reconstruction in order to evaluate the possibility of correcting the HU values via mapping.Results: Both spatial linearity and high contrast resolution were maintained in upright CBCT when compared to a simulation CT. Low contrast resolution and HU linearity decreased. Streaking artifacts were caused by the limited 180 degree arc angle and a sharp point artifact in the center of the axial slices resulted at the site of the stitching. A method for correcting the HUs was shown to be robust against these artifacts.Conclusion: Upright CBCT could be of great benefit to many patients. This study demonstrates its feasibility and presents solutions to some of its first hurdles before clinical implementation.--------------------------Cite this article as:Fave X, Yang J, Balter P, Court L. Upright CBCT: A novel imaging technique. Int J Cancer Ther Oncol 2014; 2(2):020221. DOI: 10.14319/ijcto.0202.2