S Yaddanapudi

WE‐C‐214‐04: ADQ — A Software Tool That Automatically, Autonomously, Intelligently and Instantly Verify Patient Radiation Therapy Beam Deliveries

Purpose: To effectively mitigate errors in IMRTradiation therapydelivery, all beams, all fractions, for all patients should be checked in vivo, immediately, automatically, autonomously and intelligently for integrity, quality and safety. For this purpose, ADQ or Automatic Dynalog QA, is implemented for instant and automatic patient delivery beam verification. Methods: ADQ contains multiple functional modules. DICOM receiver program is developed in C++ to receive DICOM‐RT Plans from treatment planning systems, process data and save to database. The verification tool is implemented in MATLAB that automatically validates beam parameters (gantry angle, collimator angle and positions, MLC positions, fluence maps, etc.) between the treatment plans and recorded dynamic MLC log files, generate reports for each treatment session, and send out alert emails for detected urgent problems. Report reviewer is implemented in C++ that enables physicists to review, comment and confirm reports. ADQ programs use own database and Mosaiq R&V database. Simple, automatic and no human intervention is needed unless an error is detected. Results: ADQ is running to generate near real‐time QA reports for every treatment date. DICOM receiver is running 24 hours to collect plans. Report reviewer deployed through network facilitates easy access to reports. All IMRT beams delivered to the patients are checked for a period of four months to study the reliability, MLC performance, false positive rate and importantly identify true positive. More than 80000 thousand beams from 4 different Linacs were analyzed up‐to‐date. Conclusions: We developed new software tools to improve the RT treatment QA by automatic checking patient treatment beam delivery records for each patient and each treatment session. Report data achieved in database can be easily used for further studies, for example, analysis of MLC leaf failures.

SU-C-304-04: A Compact Modular Computational Platform for Automated On-Board Imager Quality Assurance

Purpose: Traditionally, the assessment of X-ray tube output and detector positioning accuracy of on-board imagers (OBI) has been performed manually and subjectively with rulers and dosimeters, and typically takes hours to complete. In this study, we have designed a compact modular computational platform to automatically analyze OBI images acquired with in-house designed phantoms as an efficient and robust surrogate. Methods: The platform was developed as an integrated and automated image analysis-based platform using MATLAB for easy modification and maintenance. Given a set of images acquired with the in-house designed phantoms, the X-ray output accuracy was examined via cross-validation of the uniqueness and integration minimization of important image quality assessment metrics, while machine geometric and positioning accuracy were validated by utilizing pattern-recognition based image analysis techniques. Results: The platform input was a set of images of an in-house designed phantom. The total processing time is about 1–2 minutes. Based on the data acquired from three Varian Truebeam machines over the course of 3 months, the designed test validation strategy achieved higher accuracy than traditional methods. The kVp output accuracy can be verified within +/−2 kVp, the exposure accuracy within 2%, and exposure linearity with a coefficient of variation (CV) of 0.1.morexa0» Sub-millimeter position accuracy was achieved for the lateral and longitudinal positioning tests, while vertical positioning accuracy within +/−2 mm was achieved. Conclusion: This new platform delivers to the radiotherapy field an automated, efficient, and stable image analysis-based procedure, for the first time, acting as a surrogate for traditional tests for LINAC OBI systems. It has great potential to facilitate OBI quality assurance (QA) with the assistance of advanced image processing techniques. In addition, it provides flexible integration of additional tests for expediting other OBI quality assurance tests, such as 2D/3D image quality, making completely automated QA possible. Research Funding from Varian Medical Systems Inc. . Dr. Sasa Mutic receives compensation for providing patient safety training services from Varian Medical Systems, the sponsor of this study.«xa0less

SU-E-T-269: Differential Hazard Analysis For Conventional And New Linac Acceptance Testing Procedures

Purpose: New techniques and materials have recently been developed to expedite the conventional Linac Acceptance Testing Procedure (ATP). The new ATP method uses the Electronic Portal Imaging Device (EPID) for data collection and is presented separately. This new procedure is meant to be more efficient then conventional methods. While not clinically implemented yet, a prospective risk assessment is warranted for any new techniques. The purpose of this work is to investigate the risks and establish the pros and cons between the conventional approach and the new ATP method. Methods: ATP tests that were modified and performed with the EPID were analyzed. Five domain experts (Medical Physicists) comprised the core analysis team. Ranking scales were adopted from previous publications related to TG 100. The number of failure pathways for each ATP test procedure were compared as well as the number of risk priority numbers (RPN’s) greater than 100 were compared. Results: There were fewer failure pathways with the new ATP compared to the conventional, 262 and 556, respectively. There were fewer RPN’s > 100 in the new ATP compared to the conventional, 41 and 115. Failure pathways and RPN’s > 100 for individual ATP tests on average were 2 and 3.5 times higher in the conventional ATP compared to the new, respectively. The pixel sensitivity map of the EPID was identified as a key hazard to the new ATP procedure with an RPN of 288 for verifying beam parameters. Conclusion: The significant decrease in failure pathways and RPN’s >100 for the new ATP mitigates the possibilities of a catastrophic error occurring. The Pixel Sensitivity Map determining the response and inherent characteristics of the EPID is crucial as all data and hence results are dependent on that process. Grant from Varian Medical Systems Inc.

SU-E-T-775: Use of Electronic Portal Imaging Device (EPID) for Quality Assurance (QA) of Electron Beams On Varian Truebeam System

Purpose: In a previous study we have demonstrated the feasibility of using EPID to QA electron beam parameters on a single Varian TrueBeam LINAC. This study aims to provide further investigation on (1) reproducibility of using EPID to detect electron beam energy changes on multiple machines and (2) evaluation of appropriate calibration methods to compare results from different EPIDs. Methods: Ad-hoc mode electron beam images were acquired in developer mode with XML code. Electron beam data were collected on a total of six machines from four institutions. A custom-designed double-wedge phantom was placed on the EPID detector. Two calibration methods - Pixel Sensitivity Map (PSM) and Large Source-to-Imager Distance Flood Field (LSID-FF) - were used. To test the sensitivity of EPID in detecting energy drifts, Bending Magnet Current (BMC) was detuned to invoke energy changes corresponding to ∼±1.5 mm change in R50% of PDD on two machines from two institutions. Percent depth ionization (PDI) curves were then analyzed and compared with the respective baseline images using LSID-FF calibration. For reproducibility testing, open field EPID images and images with a standard testing phantom were collected on multiple machines. Images with and without PSM correction for same energies on different machines were overlaid and compared. Results: Two pixel shifts were observed in PDI curve when energy changes exceeded the TG142 tolerance. PSM showed the potential to correct the differences in pixel response of different imagers. With PSM correction, the histogram of images differences obtained from different machines showed narrower distributions than those images without PSM correction. Conclusion: EPID is sensitive for electron energy changes and the results are reproducible on different machines. When overlaying images from different machines, PSM showed the ability to partially eliminate the intrinsic variation of various imagers. Research Funding from Varian Medical Systems Inc.Dr. Sasa Mutic receives compensation for providing patient safety training services from Varian Medical Systems, the sponsor of this study.

A self-sufficient method for calibration of Varian electronic portal imaging device

Electronic portal imaging device (EPID) is currently used for dosimetric verification of IMRT fields and linac quality assurance (QA). It is critical to understand the dosimetric response and perform an accurate and robust calibration of EPID. We present the implementation of an efficient method for the calibration and the validation of a Varian EPID, which relies only on data collected with that specific device. The calibration method is based on images obtained with five shifts of EPID panel. With this method, the relative gain (sensitivity) of each element of a detector matrix is calculated and applied on top of the calibration determined with the flood-field procedure. The calibration procedure was verified using a physical wedge inserted in the beam line and the corrected profile shows consistent results with the measurements using a calibrated 2D array. This method does not rely on the beam profile used in the flood-field calibration process, which allows EPID calibration in 10 minutes with no additional equipment compared to at least 2 hours to obtain beam profile and scanning beam equipment requirement with the conventional method.

FMEA of manual and automated methods for commissioning a radiotherapy treatment planning system

Purpose To evaluate the level of risk involved in treatment planning system (TPS) commissioning using a manual test procedure, and to compare the associated process‐based risk to that of an automated commissioning process (ACP) by performing an in‐depth failure modes and effects analysis (FMEA). Methods The authors collaborated to determine the potential failure modes of the TPS commissioning process using (a) approaches involving manual data measurement, modeling, and validation tests and (b) an automated process utilizing application programming interface (API) scripting, preloaded, and premodeled standard radiation beam data, digital heterogeneous phantom, and an automated commissioning test suite (ACTS). The severity (S), occurrence (O), and detectability (D) were scored for each failure mode and the risk priority numbers (RPN) were derived based on TG‐100 scale. Failure modes were then analyzed and ranked based on RPN. The total number of failure modes, RPN scores and the top 10 failure modes with highest risk were described and cross‐compared between the two approaches. RPN reduction analysis is also presented and used as another quantifiable metric to evaluate the proposed approach. Results The FMEA of a MTP resulted in 47 failure modes with an RPNave of 161 and Save of 6.7. The highest risk process of “Measurement Equipment Selection” resulted in an RPNmax of 640. The FMEA of an ACP resulted in 36 failure modes with an RPNave of 73 and Save of 6.7. The highest risk process of “EPID Calibration” resulted in an RPNmax of 576. Conclusions An FMEA of treatment planning commissioning tests using automation and standardization via API scripting, preloaded, and pre‐modeled standard beam data, and digital phantoms suggests that errors and risks may be reduced through the use of an ACP.

SU-E-T-781: Using An Electronic Portal Imaging Device (EPID) for Correlating Linac Photon Beam Energies

Purpose: Electronic portal imaging devices (EPIDs) have proven to be useful for measuring several parameters of interest in linear accelerator (linac) quality assurance (QA). The purpose of this project was to evaluate the feasibility of using EPIDs for determining linac photon beam energies. Methods: Two non-clinical Varian TrueBeam linacs (Varian Medical Systems, Palo Alto, CA) with 6MV and 10MV photon beams were used to perform the measurements. The linacs were equipped with an amorphous silicon based EPIDs (aSi1000) that were used for the measurements. We compared the use of flatness versus percent depth dose (PDD) for predicting changes in linac photon beam energy. PDD was measured in 1D water tank (Sun Nuclear Corporation, Melbourne FL) and the profiles were measured using 2D ion-chamber array (IC-Profiler, Sun Nuclear) and the EPID. Energy changes were accomplished by varying the bending magnet current (BMC). The evaluated energies conformed with the AAPM TG142 tolerance of ±1% change in PDD. Results: BMC changes correlating with a ±1% change in PDD corresponded with a change in flatness of ∼1% to 2% from baseline values on the EPID. IC Profiler flatness values had the same correlation. We observed a similar trend for the 10MV beam energy changes. Our measurements indicated a strong correlation between changes in linac photon beam energy and changes in flatness. For all machines and energies, beam energy changes produced change in the uniformity (AAPM TG-142), varying from ∼1% to 2.5%. Conclusions: EPID image analysis of beam profiles can be used to determine linac photon beam energy changes. Flatness-based metrics or uniformity as defined by AAPM TG-142 were found to be more sensitive to linac photon beam energy changes than PDD. Research funding provided by Varian Medical Systems. Dr. Sasa Mutic receives compensation for providing patient safety training services from Varian Medical Systems, the sponsor of this study.

Transmission detectors are safe and the future for patient-specific QA in radiation therapy

Real-time radiation dose monitoring during treatment delivery is highly desired for quality assurance purposes but has been hampered in its clinical implementation due to various technical challenges. Recent advances in transmission detector technology offer a potential solution for real-time dosimetric measurements of treatment delivery. While some are optimistic about the clinical adoption of transmission detector technology for enhancing the safety of radiation therapy, others have some significant concerns about using transmission detectors for dosimetric measurements. This is the premise debated in this months Point/Counterpoint. This article is protected by copyright. All rights reserved.

SU‐E‐J‐45: Verification of Beam‐Line Geometry of Truebeam Using MV‐EPID

PURPOSEnGeometrical accuracy of beam-line components of a linear-accelerator (LINAC) is indispensible for quality of patient treatments. Positional reproducibility of the flattening filters (FF) may directly affect the beam flatness and symmetry while uncertainties in the imager position may directly impact target localization. In this study we have investigated the positional uncertainties of both of these components.nnnMETHODSnImages of both flattened and flatness-filter-free (FFF) beams of 6 and10 MV were acquired using the megavoltage electronic portal imaging Device (MV-EPID) over a period of time to investigate the positional uncertainties in the beam-line geometry. Due to forward peaked nature of the MV beams FFF beams show a cone-shaped dose distributions that was used determine the center of the X-ray beams and used as reference points. Central portion of the flattened beams show the image of the FF. These circular objects were used to determine the center of the flatness-filter with respect to the reference point. Imager reproducibility was also tested against the reference point which is the center of the source. Positional reproducibility of the FF and the imager were tracked over a period of two months.nnnRESULTSnCenters of both 6X and 10X FFs were systematically shifted by 2.2mm in X-and - 0.7 in Y-directions. However, the shifts were magnified due to the fact that the FF being close to the MV-source while the imager is far away (at 108cm) from the source. When corrected for this magnification, the real uncertainty in the FF position is approximately 0.2mm and - 0.06 mm in X-and Y-directions. The imager positional reproducibility was found to be within ±1 pixel (<0.5mm).nnnCONCLUSIONnIn this study we have shown a new method to detect positional uncertainty of the flatness-filter and MV-EPID. This methodology may be useful for QA of the LINACs. This project is supported by Varian Medical Systems.

SU‐E‐T‐36: Comprehensive End to End Data Transfer Integrity Check of Delivery Parameters Using TrueBeam Trajectory Log Files Analysis

Purpose: Traditional manual quality assurance checks of a patient treatment plan beam parameters transfer involve visually checking the information printed from the treatment planning system against the record‐and verify system for one‐to‐one correspondence. To provide the efficiency and accuracy of data transfer check, we have utilized the Varian TrueBeam log files which contain the complete delivery parameters. Methods: The approved plans are transferred to the Record and Verify (R&V) system, and the beams are delivered in the Truebeam Linac. The expected and actual status of TrueBeam delivery parameters are recorded during the delivery. Compared to traditional dynalog files from Varian, TrueBeam log files offer complete delivery parameters, which enable complete data transfer QA. An automatic program was designed to read the planned parameters from TPS and delivered parameters from Linac workstation. The program can verify the delivered parameters for all the external deliveries, including 3D conformal, EDW delivery, IMRT, VMAT, and electrons treatments. Results: The patient ID, beam ID, photon or electron energy, beam MU, gantry angle, couch angle, cough positions, collimator angle, jaw positions, EDW wedge angle and orientations, MLC positions, number of segments, gantry speed, dose rate, applicator size are all checked. The data transfer and/or delivery errors are flagged in the report for each type of delivery. Conclusion: The end‐to‐end data transfer check using TrueBeam log files provides an efficient, reliable and complete beam parameter plan check process for variety of radiation delivery technique. It is more efficient than human chart checking and improves the robustness and quality of chart checking.