N Dogan

IMRT commissioning: Multiple institution planning and dosimetry comparisons,a report from AAPM Task Group 119

AAPM Task Group 119 has produced quantitative confidence limits as baseline expectation values for IMRT commissioning. A set of test cases was developed to assess the overall accuracy of planning and delivery of IMRT treatments. Each test uses contours of targets and avoidance structures drawn within rectangular phantoms. These tests were planned, delivered, measured, and analyzed by nine facilities using a variety of IMRT planning and delivery systems. Each facility had passed the Radiological Physics Center credentialing tests for IMRT. The agreement between the planned and measured doses was determined using ion chamber dosimetry in high and low dose regions, film dosimetry on coronal planes in the phantom with all fields delivered, and planar dosimetry for each field measured perpendicular to the central axis. The planar dose distributions were assessed using gamma criteria of 3%/3 mm. The mean values and standard deviations were used to develop confidence limits for the test results using the concept confidence limit = /mean/ + 1.96sigma. Other facilities can use the test protocol and results as a basis for comparison to this group. Locally derived confidence limits that substantially exceed these baseline values may indicate the need for improved IMRT commissioning.

Dose escalation for locally advanced lung cancer using adaptive radiation therapy with simultaneous integrated volume-adapted boost.

PURPOSE To test the feasibility of a planned phase 1 study of image-guided adaptive radiation therapy in locally advanced lung cancer. METHODS AND MATERIALS Weekly 4-dimensional fan beam computed tomographs (4D FBCT) of 10 lung cancer patients undergoing concurrent chemoradiation therapy were used to simulate adaptive radiation therapy: After an initial intensity modulated radiation therapy plan (0-30 Gy/2 Gy), adaptive replanning was performed on week 2 (30-50 Gy/2 Gy) and week 4 scans (50-66 Gy/2 Gy) to adjust for volume and shape changes of primary tumors and lymph nodes. Week 2 and 4 clinical target volumes (CTV) were deformably warped from the initial planning scan to adjust for anatomical changes. On the week 4 scan, a simultaneous integrated volume-adapted boost was created to the shrunken primary tumor with dose increases in 5 0.4-Gy steps from 66 Gy to 82 Gy in 2 scenarios: plan A, lung isotoxicity; plan B, normal tissue tolerance. Cumulative dose was assessed by deformably mapping and accumulating biologically equivalent dose normalized to 2 Gy-fractions (EQD2). RESULTS The 82-Gy level was achieved in 1 in 10 patients in scenario A, resulting in a 13.4-Gy EQD2 increase and a 22.1% increase in tumor control probability (TCP) compared to the 66-Gy plan. In scenario B, 2 patients reached the 82-Gy level with a 13.9 Gy EQD2 and 23.4% TCP increase. CONCLUSIONS The tested image-guided adaptive radiation therapy strategy enabled relevant increases in EQD2 and TCP. Normal tissue was often dose limiting, indicating a need to modify the present study design before clinical implementation.

A protocol to extend the longitudinal coverage of on-board cone-beam CT

The longitudinal coverage of a LINAC‐mounted CBCT scan is limited to the corresponding dimensional limits of its flat panel detector, which is often shorter than the length of the treatment field. These limits become apparent when fields are designed to encompass wide regions, as when providing nodal coverage. Therefore, we developed a novel protocol to acquire double orbit CBCT images using a commercial system, and combine the images to extend the longitudinal coverage for image‐guided adaptive radiotherapy (IGART). The protocol acquires two CBCT scans with a couch shift similar to the “step‐and‐shoot” cine CT acquisition, allowing a small longitudinal overlap of the two reconstructed volumes. An in‐house DICOM reading/writing software was developed to combine the two image sets into one. Three different approaches were explored to handle the possible misalignment between the two image subsets: simple stacking, averaging the overlapped volumes, and a 3D‐3D image registration with the three translational degrees of freedom. Using thermoluminescent dosimeters and custom‐designed holders for a CTDI phantom set, dose measurements were carried out to assess the resultant imaging dose of the technique and its geometric distribution. Deformable registration was tested on patient images generated with the double‐orbit protocol, using both the planning FBCT and the artificially deformed CBCT as source images. The protocol was validated on phantoms and has been employed clinically for IRB‐approved IGART studies for head and neck and prostate cancer patients. PACS number: 87.57.nj

Comparisons of multiple automated anatomy-based image-guidance methods for patient setup before head/neck external beam radiotherapy.

The purpose was to assess the variability in automated translational head/neck setup corrections computed from several different imaging modalities and rigid registration methods using patient anatomy. Shifts were calculated using three commercial and one in‐house automated rigid registration methods for nine head/neck patients who were imaged with three different image‐guidance systems. The mean difference between the daily isocenter shifts determined by the four methods ranged from 2.8 to 12.5 mm for all of the test cases. These differences are much greater than the variability observed for a rigid imaging phantom. Image‐guided setup procedures have an uncertainty that depends on the imaging modality, the registration algorithm, the image resolution and the image content. In the absence of an absolute ground truth, the variation in the shifts calculated by several different methods provides a useful estimate of that uncertainty. PACS number: 87,55,km, 87.57.nj, 87.59.‐e, 87.59.bd

SU‐GG‐T‐261: An Integrated Software Environment for Image Guided Adaptive Radiation Therapy Research

Purpose: Modern research in Image Guided Adaptive Radiation Therapy (IGART) generates very large quantities of imaging data, as it is no longer uncommon to collect upwards of 200GBytes of imaging data, stored as thousands of files, per research patient. Such proliferation of data requires new software infrastructure which can handle collection, anonymization, indexing and automated processing of data. Software infrastructure, in support of NIH sponsored research program on IGART, had to be developed, ab initio, at our institution. Materials and Methods: Patient data is initially collected by networked Personal Computers provided by vendors of imaging equipment. Disk synchronization software is used to create a UNIX disk mirror of data bearing disks, which is hosted on EMC Clariion networked storage devices supported by the university computing group. Automated Patient Accumulator (APA) application extracts data from the mirror, accumulates data for selected patients, and performs initial tests of data integrity. Automated Database Builder (ADB) application monitors accumulated data, creates anonymized copy of newly acquired data, and organizes anonymized data into the Reference Data Database (RDD). A customized interface to Philips Pinnacle Treatment Planning System (TPS) supports dynamic building of TPS patients from RDD images, as well as saving of image segmentation and treatment planning data back into the RDD. A dedicated C++ library, called Research Computing Framework (RCF), supports programmatic access to RDD data, building of automated data processing pipelines, and storage of derived research data into temporary research databases. Data visualization is based on the AVS Express toolkit, combined with the RCF library as means of converting research data types into AVS data types. Results: A comprehensive software infrastructure to support IGART research has been built, ab initio, at our institution. This infrastructure is currently being used to perform IGART research. Acknowledgments: Supported by NIH Grant P01 CA11602

IMRT for Carcinomas of the Oropharynx and Oral Cavity

The major potential advantages of IMRT have been addressed in a number of preliminary clinical investigations/trials which have generated encouraging results that salivary gland sparing can be achieved with improvements in xerostomia without risking increased failure rates. Dose escalation trials, although documenting the potential of IMRT as a tool for dose escalation, require refinement and intense physician involvement but have produced encouraging loco-regional tumor control rates. Finally, the ability of generating plans with outstanding dose conformality in the radiotherapeutic management of HNSCCs of the OP/(OC) has been clearly established.

Quantitative Assessment of Volumetric Changes Using Fan Beam and Cone Beam Computed Tomography During Head and Neck Image Guided Radiotherapy

Purpose/Objectives: To develop a standardized methodology for cranial nerves IX-XII contouring among patients treated with intensitymodulated radiotherapy (IMRT) for head and neck cancer (HNC). Materials/Methods: Using anatomic texts, radiologic data, and T1/2 magnetic resonance imaging (MRI), a standardized method for delineating the cranial nerves IX-XII on computed tomography (CT) was performed. A neuroradiologist assisted with identification of the cranial nerves IX-XII and adjacent structures (i.e. Midbrain, Pons, and Medulla Oblongata). These organs at risk were then contoured on 5 consecutive patients undergoing IMRT for locally advanced HNC (i.e. base of skull, nasopharyngeal and Paranasal-sinus cancer). Dosevolume histogram (DVH) curves were generated by applying the proposed cranial nerves contour to the initial treatment plan. Due to anatomical nature and proximity of cranial nerves IX, X and XI, they were contoured as one structure while cranial nerve XII was contoured individually. Results: The median total dose to the planning target volume (PTV) was 70 (ranged from 66–70 Gy). The median cranial nerves (IX-XI) and (XII) volumes were 20 cm3 (15–25) and 18 cm3 (15–22) respectively. The median V50, V60, V66, and V70 of the cranial nerves (IX-XI) and (XII) volumes were (85, 77, 71, 65) and (88, 80, 74, 64) respectively. The maximal dose to the cranial nerves (IX-XI) and (XII) were 72 (66–77) and 71 Gy (64–78) respectively. Conclusions: The proposed methodology provides a highly reproducible, defined and standardized way for delineating the cranial nerves IX-XII organ at risk on IMRT based CT planning. Our dosimetric analysis should serve as pilot data for prospective studies for patients undergoing IMRT for HNC to establish a limiting dose for these structures at risk.

SU‐E‐J‐46: Evaluation of Inter‐Fraction Deformable Registration of 4DCT Scans: Direct vs. Composed Registration

Purpose: To evaluate the direct versus composed registration in inter‐fraction deformable image registration of 4D CT scans of thoracic cancer patients. Methods: Lungcancer patients treated under an institutional IRB protocol were selected for this study. Each patient had a planning and subsequent weekly 4D CTimages that were acquired at ten discrete respiratory phases during their treatment course. GTV, lungs,heart, cord, and esophagus were manually delineated for all ten phases on each image set. A Small Deformation Inverse Consistent Linear Elastic (SICLE) non‐rigid‐registration algorithm was utilized for the generation of displacement vector fields (DVFs). The end of inhalation phase images from the weekly on‐treatment 4DCTs were deformably‐registered to the end of inhalation phase image from the planning 4DCT using two different registration permutations. In the ‘Composed’ method, each end of inhalation phase image was registered to the subsequent weekly image, and the resulting DVFs were composed or ‘chained’ to create the mapping from any weekly image to the planning image. For evaluation, contours on different image sets were mapped back to the planning 4D CT. Deformation maps generated by “Direct” versus “Composed” registration methods were evaluated using “volume histograms of the vector difference length for each structure”, “Jacobian”, “Dice similarity coefficient (DSC)” and Center of Mass (COM). Results: The average spatial discrepancy for all structures was less then 1mm using “direct” vs. “composed” registration. The differences in the average Jacobian for all structures obtained with “direct” vs. “composed” DVFs were also negligible. Differences between deformably‐mapped GTV, lung and esophagus contours obtained with “direct” and “composed” registration DVFs were <0.5mm. Conclusions: The evaluation of the “direct” versus “composed” registration of weekly 4D CT scans showed that there are very small differences in “Direct” vs. “Composed” registration DVFs although there are numerically noticeable differences. Supported by NIHgrant‐P01CA11602

SU‐E‐T‐32: An Integrated IGART Planning Environment

Purpose: Open Radiological Archiving and Communication System(ORACS) relational research database, which stores images, projections, plans, trials and doses etc, is the backbone for Image Guided Adaptive Radiation Therapy (IGART) Research Project at VCU. Philips Pinnacle3 is being used by this project for IGART adaptive planning of Virtual Clinical Trials (VCT). Therefore, in order to establish a user‐friendly interactive environment and facilitate collaboration between different sub‐projects, seamless integration of these two systems will be a must. Methods: It is well‐known that Pinnacle3 lacks the capacity to interact with a database server. However, we take advantage of Pinnacles configurability and scripting power to enhance Pinnacle with new GUI controls, which invoke a middleware layer to access ORACS database. Users can import images from ORACS database through remote web services or locally, and save contours and plans and doses and other derived Pinnacle data back to ORACS database by simply clicking these new GUI controls. Moreover, a Pinnacle database can be re‐created easily and entirely from ORACS database through these new GUI controls and the middleware layer. The same technique can be used to create connection between Pinnacle3 and other database servers. Also because ORACS database uses web services for data access, if a specific middleware is created, any Treatment Planning System can access ORACS database interactively. Results: We presented a software infrastructure for seamless integration of ORACS research database and Philips Pinnacle3, which created an integrated virtual clinical trial environment for IGART researchers at our institution. Conclusions: Contemporary IGART research imposes new demands on the IT infrastructure of Radiation Oncology departments. We created a data management system which takes first steps towards managing new and complex tasks of automated analysis of large data sets. NIH Grant P01 CA11602

SU‐E‐T‐278: Volume Based Comparison of Deformable Image Registration Algorithms Using Spatial Discrepancy Volume Histograms

Purpose: Accurate Deformable Image Registration (DIR) algorithms are essential to clinical implementation of adaptive planning strategies hence finding validation strategies for DIR algorithms remains a pressing concern. Most validation efforts are based on contour or landmark tracking, thus sampling the Deformable Vector Field (DVF) relatively sparsely. The primary purpose of this work is to assess interchangeability of DIR algorithms in dose accumulation, and assess if contour based methods are sufficient to validate the equivalence of DIR algorithms. Methods: We registered peak inhale and peak exhale phases of thirteen lung patients using three DIR algorithms. The DVF maps were pairwise compared through voxel‐by‐voxel subtraction of vector fields. The vector difference maps were analyzed by building volume histograms on regions of interest. This method of analysis is directly relevant to the Dose Volume Histogram accumulation, as vector difference between the maps will be translated into a distance between dose interpolation points. We further compared Jacobian distributions for the three maps, as local derivatives of DVF maps would be important to any algorithm that attempts local density corrections. We performed contour based comparison of the three algorithms, to connect this validation method to prior work. Results: The volume histogram analysis shows that differences between DVFs in 2% tails of volume histogram are in the 1cm – 4cm range, although the contour‐based analysis using Dices Similarity Coefficient (DSC) would suggest that the three algorithms are nearly equivalent. For most structures, spatial differences between maps are below 0.5cm over approximately 70% of structure volume, and exceed 0.5cm over the remainder. Jacobian distributions differ significantly, implying that local density corrections are strongly algorithm dependent. Conclusions: Differences between algorithms are potentially significant for dose accumulation, and such differences are not revealed by contour based comparisons. Acknowledgments: Supported by NIH Grant P01 CA11602