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Title: SU-E-T-571: Newly Emerging Integrated Transmission Detector Systems Provide Online Quality Assurance of External Beam Radiation Therapy

Abstract

Purpose: Two newly emerging transmission detectors positioned upstream from the patient have been evaluated for online quality assurance of external beam radiotherapy. The prototype for the Integral Quality Monitor (IQM), developed by iRT Systems GmbH (Koblenz, Germany) is a large-area ion chamber mounted on the linac accessory tray to monitor photon fluence, energy, beam shape, and gantry position during treatment. The ion chamber utilizes a thickness gradient which records variable response dependent on beam position. The prototype of Delta4 Discover™, developed by ScandiDos (Uppsala, Sweden) is a linac accessory tray mounted 4040 diode array that measures photon fluence during patient treatment. Both systems are employable for patient specific QA prior to treatment delivery. Methods: Our institution evaluated the reproducibility of measurements using various beam types, including VMAT treatment plans with both the IQM ion chamber and the Delta4 Discover diode array. Additionally, the IQM’s effect on photon fluence, dose response, simulated beam error detection, and the accuracy of the integrated barometer, thermometer, and inclinometer were characterized. The evaluated photon beam errors are based on the annual tolerances specified in AAPM TG-142. Results: Repeated VMAT treatments were measured with 0.16% reproducibility by the IQM and 0.55% reproducibility by the Delta4 Discover.more » The IQM attenuated 6, 10, and 15 MV photon beams by 5.43±0.02%, 4.60±0.02%, and 4.21±0.03% respectively. Photon beam profiles were affected <1.5% in the non-penumbra regions. The IQM’s ion chamber’s dose response was linear and the thermometer, barometer, and inclinometer agreed with other calibrated devices. The device detected variations in monitor units delivered (1%), field position (3mm), single MLC leaf positions (13mm), and photon energy. Conclusion: We have characterized two new transmissions detector systems designed to provide in-vivo like measurements upstream from the patient. Both systems demonstrate substantial utility for online treatment verification and QA of photon external beam radiotherapy.« less

Authors:
; ; ; ;  [1]
  1. UC Davis Cancer Center, Sacramento, CA (United States)
Publication Date:
OSTI Identifier:
22496285
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 42; Journal Issue: 6; Other Information: (c) 2015 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; EXTERNAL BEAM RADIATION THERAPY; FEDERAL REPUBLIC OF GERMANY; IN VIVO; IONIZATION CHAMBERS; LINEAR ACCELERATORS; PATIENTS; PHOTON BEAMS; QUALITY ASSURANCE; RADIATION MONITORS; TRANSMISSION; VARIATIONS

Citation Formats

Hoffman, D, Chung, E, Hess, C, Stern, R, and Benedict, S. SU-E-T-571: Newly Emerging Integrated Transmission Detector Systems Provide Online Quality Assurance of External Beam Radiation Therapy. United States: N. p., 2015. Web. doi:10.1118/1.4924933.
Hoffman, D, Chung, E, Hess, C, Stern, R, & Benedict, S. SU-E-T-571: Newly Emerging Integrated Transmission Detector Systems Provide Online Quality Assurance of External Beam Radiation Therapy. United States. doi:10.1118/1.4924933.
Hoffman, D, Chung, E, Hess, C, Stern, R, and Benedict, S. Mon . "SU-E-T-571: Newly Emerging Integrated Transmission Detector Systems Provide Online Quality Assurance of External Beam Radiation Therapy". United States. doi:10.1118/1.4924933.
@article{osti_22496285,
title = {SU-E-T-571: Newly Emerging Integrated Transmission Detector Systems Provide Online Quality Assurance of External Beam Radiation Therapy},
author = {Hoffman, D and Chung, E and Hess, C and Stern, R and Benedict, S},
abstractNote = {Purpose: Two newly emerging transmission detectors positioned upstream from the patient have been evaluated for online quality assurance of external beam radiotherapy. The prototype for the Integral Quality Monitor (IQM), developed by iRT Systems GmbH (Koblenz, Germany) is a large-area ion chamber mounted on the linac accessory tray to monitor photon fluence, energy, beam shape, and gantry position during treatment. The ion chamber utilizes a thickness gradient which records variable response dependent on beam position. The prototype of Delta4 Discover™, developed by ScandiDos (Uppsala, Sweden) is a linac accessory tray mounted 4040 diode array that measures photon fluence during patient treatment. Both systems are employable for patient specific QA prior to treatment delivery. Methods: Our institution evaluated the reproducibility of measurements using various beam types, including VMAT treatment plans with both the IQM ion chamber and the Delta4 Discover diode array. Additionally, the IQM’s effect on photon fluence, dose response, simulated beam error detection, and the accuracy of the integrated barometer, thermometer, and inclinometer were characterized. The evaluated photon beam errors are based on the annual tolerances specified in AAPM TG-142. Results: Repeated VMAT treatments were measured with 0.16% reproducibility by the IQM and 0.55% reproducibility by the Delta4 Discover. The IQM attenuated 6, 10, and 15 MV photon beams by 5.43±0.02%, 4.60±0.02%, and 4.21±0.03% respectively. Photon beam profiles were affected <1.5% in the non-penumbra regions. The IQM’s ion chamber’s dose response was linear and the thermometer, barometer, and inclinometer agreed with other calibrated devices. The device detected variations in monitor units delivered (1%), field position (3mm), single MLC leaf positions (13mm), and photon energy. Conclusion: We have characterized two new transmissions detector systems designed to provide in-vivo like measurements upstream from the patient. Both systems demonstrate substantial utility for online treatment verification and QA of photon external beam radiotherapy.},
doi = {10.1118/1.4924933},
journal = {Medical Physics},
number = 6,
volume = 42,
place = {United States},
year = {Mon Jun 15 00:00:00 EDT 2015},
month = {Mon Jun 15 00:00:00 EDT 2015}
}
  • Purpose: Monthly quality assurance (QA) is time consuming for external beam radiation therapy, taking as long as 6–8 hours for each machine. It is due to the use and setup of multiple devices for different QA procedures. We have developed a single system with rotational capability for the measurement of both optical light and radiation which significantly reduces the time spent on Monthly QA. Methods: A single system using mirrors, a phosphor screen and a CCD camera is housed on a cylindrical motor so that it can rotate 360 degrees. For monthly QA, the system is placed on the patientmore » couch of the medical accelerator with the plane of the phosphor screen at isocenter for all measurements. For optical QA such as optical distance indicator, room laser and light field, the optical image is collected directly with the camera. For radiation QA such as beam profile, MLC speed, picket-fence test, collimator rotation, table rotation and gantry rotation, a brass build-up plate is attached to the top of the phosphor screen. Two brass plates with islands of different thickness were designed for photon energy and electron energy constancy checks. Flex map, distortion map and uniformity map were developed to calibrate the motor bearing, camera/lens distortion, and the phosphor screen’s measured response across the field. Results: Following the TG142 guidelines for monthly QA with our system, the overall run time is reduced from 6–8 hours to 1.5 hours. Our system’s rotating design allows for quick testing of the gantry radiation isocenter test that is also independent of the sag of the gantry and the EPID. Conclusion: Our system significantly shortens the time needed for monthly QA by unifying the tests with a single system. Future work will be focused on extending the technology to Brachytherapy, IMRT and proton therapy QAs. This work is funded in part by a sponsor research grant from JPLC who owns the Raven technology. John Wong is a co-founder of JPLC.« less
  • Purpose: The purpose of this study is to investigate the sensitivity of the planar quality assurance to MLC errors with different beam complexities in intensity-modulate radiation therapy. Methods: sixteen patients’ planar quality assurance (QA) plans in our institution were enrolled in this study, including 10 dynamic MLC (DMLC) IMRT plans measured by Portal Dosimetry and 6 static MLC (SMLC) IMRT plans measured by Mapcheck. The gamma pass rate was calculated using vender’s software. The field numbers were 74 and 40 for DMLC and SMLC, respectively. A random error was generated and introduced to these fields. The modified gamma pass ratemore » was calculated by comparing the original measured fluence and modified fields’ fluence. A decreasing gamma pass rate was acquired using the original gamma pass rate minus the modified gamma pass rate. Eight complexity scores were calculated in MATLAB based on the fluence and MLC sequence of these fields. The complexity scores include fractal dimension, monitor unit of field, modulation index, fluence map complexity, weighted average of field area, weighted average of field perimeter, and small aperture ratio ( <5cm{sup 2} and <50cm{sup 2}). The Spearman’s rank correlation coefficient was implemented to analyze the correlation between these scores and decreasing gamma rate. Results: The relation between the decreasing gamma pass rate and field complexity was insignificant for most complexity scores. The most significant complexity score was fluence map complexity for SMLC, which have ρ =0.4274 (p-value=0.0063). For DMLC, the most significant complex score was fractal dimension, which have ρ=−0.3068 (p-value=0.0081). Conclusions: According to the primarily Result of this study, the sensitivity gamma pass rate was not strongly relate to the field complexity.« less
  • The traditional prescriptive quality assurance (QA) programs that attempt to ensure the safety and reliability of traditional external beam radiation therapy are limited in their applicability to such advanced radiation therapy techniques as three-dimensional conformal radiation therapy, intensity-modulated radiation therapy, inverse treatment planning, stereotactic radiosurgery/radiotherapy, and image-guided radiation therapy. The conventional QA paradigm, illustrated by the American Association of Physicists in Medicine Radiation Therapy Committee Task Group 40 (TG-40) report, consists of developing a consensus menu of tests and device performance specifications from a generic process model that is assumed to apply to all clinical applications of the device. Themore » complexity, variation in practice patterns, and level of automation of high-technology radiotherapy renders this 'one-size-fits-all' prescriptive QA paradigm ineffective or cost prohibitive if the high-probability error pathways of all possible clinical applications of the device are to be covered. The current approaches to developing comprehensive prescriptive QA protocols can be prohibitively time consuming and cost ineffective and may sometimes fail to adequately safeguard patients. It therefore is important to evaluate more formal error mitigation and process analysis methods of industrial engineering to more optimally focus available QA resources on process components that have a significant likelihood of compromising patient safety or treatment outcomes.« less
  • Purpose: To evaluate the angular dependence correction for Matrix Evolution 2D array detector in quality assurance of volumetric modulated arc therapy(VMAT). Methods: Total ten patients comprising of different sites were planned for VMAT and taken for the study. Each plan was exposed on Matrix Evolution 2D array detector with Omnipro IMRT software based on the following three different methods using 6MV photon beams from Elekta Synergy linear accelerator. First method, VMAT plan was delivered on Matrix Evolution detector as it gantry mounted with dedicated holder with build-up of 2.3cm. Second, the VMAT plan was delivered with the static gantry anglemore » on to the table mounted setup. Third, the VMAT plan was delivered with actual gantry angle on Matrix Evolution detector fixed in Multicube phantom with gantry angle sensor and angular dependence correction were applied to quantify the plan quality. For all these methods, the corresponding QA plans were generated in TPS and the dose verification was done for both point and 2D fluence analysis with pass criteria of 3% dose difference and 3mm distance to agreement. Results: The measured point dose variation for the first method was observed as 1.58±0.6% of mean and SD with TPS calculated. For second and third method, the mean and standard deviation(SD) was observed as 1.67±0.7% and 1.85±0.8% respectively. The 2D fluence analysis of measured and TPS calculated has the mean and SD of 97.9±1.1%, 97.88±1.2% and 97.55±1.3% for first, second and third methods respectively. The calculated two-tailed Pvalue for point dose and 2D fluence analysis shows the insignificance with values of 0.9316 and 0.9015 respectively, among the different methods of QA. Conclusion: The qualitative evaluation of angular dependence correction for Matrix Evolution 2D array detector shows its competency in accuracy of quality assurance measurement of composite dose distribution of volumetric modulated arc therapy.« less
  • Purpose: To test the sensitivity of the quality assurance (QA) tools actively used on a clinical MR-IGRT system for potential delivery errors. Methods: Patient-specific QA procedures have been implemented for a commercially available Cobalt-60 MR-IGRT system. The QA tools utilized were a MR-compatible cylindrical diode-array detector (ArcCHECK) with a custom insert which positions an ionization chamber (Exradin A18) in the middle of the device, as well as an in-house treatment delivery verification program. These tools were tested to investigate their sensitivity to delivery errors. For the ArcCHECK and ion chamber, a baseline was established with a static field irradiation tomore » a known dose. Variations of the baseline were investigated which included rotated gantry, altered field size, directional shifts, and different delivery time. In addition, similar variations were tested with the automated delivery verification program that compared the treatment parameters in the machine delivery logs to the ones in the plan. To test the software, a 3-field conformal plan was generated as the baseline. Results: ArcCHECK noted at least a 13% decrease in passing rate from baseline in the following scenarios: gantry rotation of 1 degree from plan, 5mm change in field size, 2mm lateral shift, and delivery time decrease. Ion chamber measurements remained consistent for these variations except for the 5 second decrease in delivery time scenario which resulted in an 8% difference from baseline. The delivery verification software was able to detect and report the simulated errors such as when the gantry was rotated by 0.6 degrees, the beam weighting was changed by a percent, a single multileaf collimator was moved by 1cm, and the dose was changed from 2 to 1.8Gy. Conclusion: The results show that the current tools used for patient specific QA are capable of detecting small errors in RT delivery with presence of magnetic field.« less