Quality Assurance Results Research Articles

Different Aspects of the Elemental Analysis of Honey by Flame Atomic Absorption and Emission Spectrometry: A Review

The elemental composition of honey is correlated with the botanical provenience of nectar, pollen, and honeydew that are collected and ripened by bees. In addition to this, the geographical origin related to the locality of an apiary, the soil composition, and climatic conditions may contribute to the origin of elements in honey. The environmental pollution or other anthropogenic processes and activities also have an effect on the quality and the safety of honey since they may be accompanying sources that lead to its contamination and the presence of various trace elements (Cd, Cr, Cu, Fe, Ni, Pb, and Zn). This review article covers the literature devoted to the analysis of honey carried out by the most popular and commonly utilized flame atomic absorption and emission spectrometry, which was published from 1999 to 2011. Various aspects of such analysis are treated in detail, including ways of the sample preparation, the calibration, and the quality assurance of results. In addition, methods and results related to the fractionation analysis of elements in honey by means of chromatographic and non-chromatographic approaches are described.

SU‐E‐T‐415: Investigation of VMAT Patient Specific Quality Assurance Action Levels

Purpose: To examine the appropriateness of patient specific IMRT quality assurance (QA) action levels for use in VMAT QA. Methods: QA measurements were evaluated for the test geometries provided in AAPM Task Group Report 119. The structure sets were copied onto a cylindrical water‐equivalent phantom. Using the Philips Pinnacle treatment planning system, IMRT and VMAT treatments were planned. The plans were delivered and the resulting dose distributions were measured (1) in 2 planes and at 3–4 points in the cylindrical phantom using radiochromic film and ion chamber, respectively, and (2) using a commercial 2D diode array. Ion chamber and diode array measurements were taken five times each, and film measurements were taken three times. Measured planar doses were analyzed using gamma analysis with criteria of 3%/3mm. Measured point doses were analyzed using percent difference. Differences between IMRT QA and VMAT QA results were tested for significance using a Studentˈs t‐test. Results: The radiochromic film results showed averages of 98.9%±1.0% and 99.1%±0.9% (p=0.47) of measured doses within 3%/3mm of calculated doses for IMRT and VMAT plans, respectively. Ion chamber results showed average differences between measured and calculated point doses of − 0.95%±1.5% and −1.8%±1.8% (p<0.01) for IMRT and VMAT plans, respectively. The diode array results showed averages of 98.7%±0.5% and 98.6%±0.7% (p=0.70) of measured doses within 3%/3mm of calculated doses for IMRT and VMAT plans, respectively. Conclusion: Differences between IMRT QA and VMAT QA results were not statistically significant for planar doses measured with radiochromic film and 2D diode array. The average difference between measured and calculated point doses was smaller in IMRT plans (p<0.01); however, the average point dose differences for both IMRT and VMAT were less than 2%. These results suggest that current action levels used in our clinic for evaluating IMRT QA may be applicable to VMAT QA.This work is supported in part by a sponsored research agreement with Elekta, Inc.

SU-E-T-102: Factors That Affect the Accuracy of IMRT Quality Assurance Measurements and Their Clinical Significance

Purpose: The purpose of this work was to perform error analysis on various processes that directly affect the accuracy of quality assurance (QA) measurements for intensity modulated radiation therapy(IMRT)delivery and to gauge their overall clinical impact for various clinical sites. Methods: In this study, we developed a numerical model based on the propagation of errors to quantify the complexity of treatment plans by the level of the intensity of modulation, and correlated the level of the modulation directly to the agreement of the IMRT QA results. We also provide detailed analysis of the uncertainties from IMRT QA results stratified by treatment site specific plans and fidelity in plan delivery. Results: Using a 5%/2mm criterion, it was found that the level of agreement of IMRT QA measurements was better for pelvic and chest plans than for head and neck, breast and brain plans. Errors tended to first increase with an increase in the number of Multi‐leaf Collimator(MLC) segments from 5 to 20 and then decrease with further increase in the number of segments. It was determined that other factors that impact the accuracy of the measurements include measurement device limitations, machine output variations, and phantom setup errors. Similarly, uncertainties in the beam data modeling and the calculation algorithm, as well as the initial beam commissioning data are main contributing factors to the accuracies of the treatment planning systems. Conclusions: The overall agreement of IMRT QA results is affected by both ‐ the accuracy of the measurement and that of the treatment planning system. We will demonstrate that the IMRT QA analysis criteria currently used in many clinics can be modified and improved to reflect the uncertainties of the process using the error propagation model developed in this study.

SU-E-T-74: An Improved Dose Calculation Method for MapCHECK in IMRT Quality Assurance

Purpose: The goal of this work is to improve dose calculation for MapCHECK by creating more accurate dose calculation for intensity modulated radiation therapy(IMRT)quality assurance (QA). Methods: All IMRTtreatment plans and the QA dose calculations were created with ADAC treatment planning system (PINNACLE3, Version 9.0, Phillips, Madison, WI). The MapCHECK diode system (Model 1175, Sun Nuclear, Melbourne, FL) was used to do IMRT QAs. The QA dose calculations were done in the original MapCHECK phantom CTimages. While each diode has a much high density, in between the diodes there is air. Using heterogeneity correction algorithm with standard CT number to electron density conversion table, the calculated dose is lower compared with measured dose (large than 5 percent) in some IMRT cases. To improve dose calculation accuracy, we add an override layer to cover the diode and air part in MapCHECK phantom CTimages, the layer is about 1.6 cm×20cm×20cm size and we set the density equal to 1.0, the new dose calculation is based on the modified CTimages. MapCHECK measured and calculated dose were analyzed with commercially available MapCHECK software (Version 4.1). Comparisons are made based on the relative and absolute dose percent difference (3 percent), Gamma Index and distance to agreement. Results: Using the unmodified MapCHECK CTimages for dose calculations, 124 IMRT QA cases were analyzed. 9 cases have large differences with more than 5 percent compared with measured one. Using the improved methods based on modified density for diodes and air, all the 9 cases passed the QA with less than 3 percent dose difference between the calculated dose and measured one. Conclusions: The improved dose calculation method for MapCHECK is easy to use and can get more accurate IMRT QA results.

3D Analysis of Intensity-Modulated Radiation Therapy Quality Assurance Measurement using a 2D Diode Array

Intensity-modulated radiation therapy (IMRT) quality assurance (QA) is often performed using a 2D device and compares measured and computed fluence maps to determine if a field passes or fails certain dose and position criteria. The effects of a measured deviation to the 3D patient spatial dosimetry and dose volume histogram (DVH) are largely unknown because they cannot be analyzed using commercial 2D array IMRT QA systems. We report an in-house treatment planning system (TPS) PLanUNC based 3D IMRT QA analysis approach that has been used in our institution for the past ten years when 2D fluence map IMRT QA failed. In this approach the measured 2D fluence maps are imported back to PLanUNC and used to re-compute 3D patient dosimetry including DVHs. The 2D fluence map IMRT QA criteria is that the measured dose for 95% of the detectors is within 5% of the planned dose, and that the distance-to-agreement be within 4mm (5%/4mm). 22 IMRT plans that had at least one field fail initial QA using MapCHECK 2 are examined using our 3D QA approach. The DVH analysis shows that 19/22 plans that failed initial QA were within 2% of the planned target and critical structure DVHs. 3/22 IMRT plans were found to have DVH difference greater than 2%. The 3D analysis of 2D IMRT QA result shows that when a fluence map QA fails for a single field, often it is clinically insignificant in terms of patient 3D dosimetry

SU-GG-T-109: Comprehensive RapidArc™ Treatment Planning and Quality Assurance for Head and Neck Cancers

Purpose: To assess the dosimetric quality of a two‐arc RapidArc™ plans for the treatment of head and neck cancers and present corresponding quality assurance (QA) results. Method and Materials: Fifty three patients (male=32,female=21, = 61.9 years (range: 25–87 years) treated for nasopharynx, oropharynx, base of tongue and laryngealcancers were included in this study. Treatment doses ranged from 12Gy to 70.4Gy with many cases requiring irradiation of the cervical nodes as well as the primary site. RapidArc™ plans were generated using Varian Eclipse™ 8.6 and consisted primarily of two 358‐degree arcs delivered counterclockwise and clockwise, respectively with a ±5‐degree couch rotation for one of the arcs. Based on the treatment site and target location, there were instances where a 358‐degree arc and a partial arc with 90‐degree couch rotation were used. QA plans were generated and delivered to a solid‐water phantom with a Mapcheck™ detector array centrally mounted between the solid‐water slabs. Results: The RapidArc™ treatment plans were evaluated based on RTOG conformality index (CI), RTOG homogeneity index (HI), monitor units (MUs) and beam‐on time. The primary targets (PTVs) had mean±SD CI and HI values of 0.93±0.04 and 1.10±0.03, respectively. The average number of MUs was 565 (range: 350 – 2144) and beam‐on times ranged from 3 to 5 min. The average %PASS for the plan QA was 99.3% (range: 97.9% – 100%) using the 3% /3mm plan evaluation criteria in Mapcheck™. Conclusion: This dosimetric analysis indicates that a two‐arc RapidArc™ plan provides highly conformai dose distributions to head and neck treatments. QA results have shown that dose calculation and measurement are in good agreement for these plans. Short beam‐on times and few MUs have reduced the overall treatment time (setup + beam‐on times) by ∼40% per patient making RapidArc™ a more efficient delivery technique than multifield IMRT.

SU‐GG‐J‐42: Development of an EPID‐Based Machine and IMRT QA System

Purpose: Interests in electronic portal imaging devices (EPIDs) for radiation dosimetry increase over the past decade, particularly with recent technique advances in amorphous‐silicon EPID. For a clinical quality assurance (QA) program, EPIDs may provide a useful tool with benefits of reduced cost and added convenience, e.g., shortening setup time. This study is to investigate the clinical application of EPID in routine machine and IMRT QA and develop an EPID‐based QA system. Materials and Methods: EPID images were acquired using Varian aS1000 EPID (integrated mode; 6 MV beam; 600 MU/min dose rate). Signal intensity of EPID images were converted to dose maps using a calibrated linear signal‐dose relationship. An integrated EPID‐based QA system was designed, which include functions for machine QA and IMRT QA. For routine machine QA, recommendations by TG‐40 and TG‐45 reports were used. Specific EPID‐based QA procedures and image analysis algorithms were designed and developed for basic QA tasks, e.g., beam flatness/symmetry test and Winston‐Lutz isocenter test. For IMRT QA, a phantom‐less method was proposed, which used fluence maps reconstructed from EPID‐measured fluence as input to treatment plan system for dose calculation and comparison. Results: EPID‐measured machine QA results were comparable to those measured monthly using films in our institute. For example, EPID‐measured parameters were: flatness = 0.9–1.45%; symmetry = 0.48–1.31%; penumbra = 3.2–4 mm at SSD = 150 cm. Star‐shot images were well reconstructed for isocenter check from EPID images acquired at different gantry or collimator angles. The EPID‐based IMRT QA method was able to verify the treatment plan and capture the reasonable plan‐versus‐QA dose difference. Conclusion: The results show that EPID may be properly used as a tool for clinical QA tasks and the developed EPID‐based QA system may be used for machine and IMRT QA. (Research sponsored by Oncology Data Systems, Inc, Oklahoma City, OK)

SU‐GG‐T‐185: Eliminating Errors in Setup and Positioning for Patient‐Specific IMRT QA

Purpose: In patient‐specific IMRT quality assurance (QA), measured planar dose distributions are usually compared to calculated planar dose distributions. Any discrepancies between the two distributions can be due to: 1. Uncertainties in the linac delivery system. 2. Uncertainties in beam modeling in the treatment planning system. 3. Uncertainties in positioning the QA device/dosimeter. The purpose of this study is to develop and implement a method to eliminate all positioning uncertainties that affect the QA results, including the dosimeter or device positioning and MLC positioning errors, and thereby determine residual errors that are attributed to beam modeling and non‐positioning delivery system uncertainties. Method and Materials: Measured and calculated dose distributions are usually compared using a similarity measure such as gamma test or DTA/dose difference (composite) test based on which a pass percentage is determined. We have developed an efficient algorithm that eliminates the affect of setup and positioning errors on the gamma or composite pass percentages. The algorithm is designed to be optimal and fast so as to operate on high resolution (1 mm) dose distributions for misalignments (typically up to 10 mm). Results: An algorithm to align high resolution dose distributions using translation has been implemented in C++ and executes within a few seconds on a PC. The algorithm has been rigorously tested on randomly generated matrices for known misalignments and it is able to predict the shifts very accurately. Conclusion: We have developed a method that eliminates the impact of setup and positioning uncertainties on pass rates for IMRT QA. Any residual discrepancies between measured and calculated planar dose distributions can then be truly attributed to beam modeling and machine output variations.

SU‐GG‐T‐281: Clinical Experience with an EPID‐Based Quality Assurance System for Linear Accelerators

Purpose: To report our experience with the implementation and clinical use of an electronic portal imaging device (EPID) based tool for the routine quality assurance (QA) of linear accelerator (Linac) radiation field geometry. Methods and Materials: The development of an EPID‐base QA tool, eQA, for routine QA of Linac radiation field geometry has previously been reported. Implementation of eQA began in 2007 for both Elekta and Varian Linacs in our clinic, with deployment completed by mid‐2008. The eQA is currently used to perform all radiation field geometry QA, including radiation field size, light vs. radiation field congruence, jaw symmetry, MLC leaf position, and gantry, collimator and couch isocentre. The eQA is routinely used to accurately set the lasers to the radiation isocentre and perform MLC calibrations. Efforts were made to automate much of the eQA functionality, using information in DICOM header tags to automatically identify the type of test and determine associated parameters in the analysis of results. Email summaries of QA results are sent automatically to appropriate staff. Compared to a manual assessment of film‐based measurements, eQA provides reproducible, non‐subjective analysis of the radiation field, reducing the variability in measurements. This has enabled a tightening of the tolerance for radiation field size measurements. Results: The eQA has successfully replaced film for all radiation field geometry tests in our department, and has improved the efficiency of our QA processes. The non‐subjective, reproducible results obtained with eQA have allowed a reduction of radiation field size tolerance from 2 mm to 1 mm. The eQA provides the unique functionality to map the locations of the gantry, collimator and table centre of rotations onto a common reference frame for determining the isocenter sphere. Conclusions: The EPID based software tool has been successfully implemented, improving the efficiency and overall performance of our QA processes.

SU-GG-I-32: Preliminary Performance Evaluation of CBCT Image Reconstruction from Reduced Projection Data by TV-Minimization

Purpose: Kilovoltage CBCT has become a useful clinical tool which provides in‐room image guidance for radiation therapy. Frequent use of CBCT also raises patient safety concern, because tomographic images are obtained by reconstruction from projection data acquired at hundreds of angular views, which may accumulate to an un‐negligible amount of radiationdose. It is therefore desired to develop a low‐dose CBCTimaging technique that requires smaller amount of projection data while can still yield images sufficing clinical needs. In this work, we have applied a new TV‐minimization algorithm to reconstructCBCTimages from a fraction of the amount of projection data currently used and have evaluated the image quality according to established quality‐assurance procedures.Materials and methods: We have acquired real projection data of a CATPHAN phantom using a clinical on‐board imaging system (Varian Medical Systems, Palo Alto, CA). We then applied the TV‐minimization algorithm to reconstructimages from subsets of the full, 628‐projection data set. The subsets contain from 360 down to 60 projections. We then examined the reconstructed images by calculating a number of metrics, including spatial resolution, contrast linearity, and low‐constrast resolution, and compared the results to the established quality‐assurance (QA) standards. Results: The imagesreconstructed by use of the TV‐minimization algorithm from the reduced data sets appeared to be comparable to the imagesreconstructed from the full data set by the FDK algorithm. In addition, the tested image‐quality metrics can satisfy the QA requirement for imagesreconstructed from as few as 100 projections. Conclusion: The TV‐minimization algorithm can yield CBCTimages from reduced projection data without significant sacrifice of image quality. The imagesreconstructed from about 100 projections may be potentially useful for clinical applications according to QA results.

Quality Assurance in the Prospective Multi-institutional Trial on Definitive Radiotherapy Using High-dose-rate Intracavitary Brachytherapy for Uterine Cervical Cancer: The Individual Case Review

To assess compliance with the radiotherapy protocol of a multi-institutional prospective study (JAROG0401/JROSG04-2), which investigated the efficacy and toxicity of definitive radiotherapy using high-dose-rate intracavitary brachytherapy (HDR-ICBT) for early-stage uterine cervical cancer patients. Individual case reviews (ICRs) were performed on all 60 study participants. Radiotherapy data were submitted to the quality assurance (QA) committee, which performed ICRs on 16 QA items according to previously selected criteria. The items focused on quality of external beam radiotherapy (EBRT), HDR-ICBT and both. Each item was determined to be either acceptable or a deviation. The QA committee performed ICR three times as planned, two during the patient accrual and the final one just after the final patient accrued. The QA results of the first and second reviews were reported back to the investigators after each ICR. In 40 cases (67%), all 16 QA items were classified as acceptable. One deviation was found in 16 cases, two deviations were identified in 3 cases and three deviations were noted in 1 case. The most frequently observed deviation was missing the rules for determining point A (10 cases). The items described by quantitative values, such as prescribed doses, certain time intervals and overall treatment time, were well followed. The proportion of deviations gradually decreased during the ICR process. The present ICR demonstrated the favorable radiotherapy compliance with the JAROG0401/JROSG04-2 protocol. The QA process using ICRs can potentially be used to improve the quality of radiotherapy, including HDR-ICBT in the multi-institutional prospective studies for cervical cancer.

Results of 9 Years of IMRT Quality Assurance in a French Comprehensive Cancer Center

Intensity-modulated radiation therapy (IMRT) presents a challenge in terms of quality assurance (QA) measurements. Even if no gold standard exists to validate QA results, ion chamber (IC) and dosimetric films still play an important role. Since 2001, more than 800 patients have been treated with IMRT for Head and Neck (H&N), prostate, and anal cancer in our cancer. We present here our QA results combining both methods. All patients were treated using a sliding window technique with a 120 multi-leaves collimator (MLC, Varian Linac). IMRT optimization was done using the Helios inverse planning software. Plans were validated before treatment by comparing the computed dose in a composite plan created in a phantom with the absolute and relative measurements in the same phantom. The real gantry angles were used for computation and measurements for the first 30 H&N patients compared to a fixed (0 deg) gantry angle. Absolute isocenter measurements were done in phantoms (square or cylindrical) using IC with a 0,125 cc detection volume connected to dosimeters (Unidos PTW). Relative dose was measured using 2D dosimetric film (Kodak XomatV) the first years and the EDR2 film thereafter. A calibration curve was systematically created in all series of films to obtain more complete data on absolute dose than allowed by the IC. 190 H&N field measurements with the gantry in real treatment position were made. The mean difference between computed and measured dose at isocenter for each field was 0.72% ± 3.2 (± 1 SD). With gantry fixed at 0°, this difference was 1.33% ± 3.2 for 808 H&N fields, 0.07 ± 1.2 for 2319 prostate fields, and 0.37% ± 0.62 for 108 prostate fossa fields. More complex pelvic fields for locally advanced prostate and anal canal cancers resulted in mean differences of 0.49% ± 1.9 for 26 fields and 2.07% ± 2.8 for 109 fields, respectively. The mean difference between computed and measured dose at isocenter for the sum of all fields of each patient was 0.05% ± 0.9 for 383 prostate cases, 1.49% ± 1.9 for 158 H&N cases, 0.37% ± 0.3 for 23 cases of prostatic fossa, 0.80% ± 0.3 for 4 cases of prostate treated with pelvic fields, and 2.31% ± 0.6 for 17 cases of anal canal cancer. Using film dosimetry and absolute dose for the 100 first H&N patients (500 films), the mean of the point crossing a 3% gamma index and 3 mm was 92% ± 6.5. For the 300 first prostate plans, this value was 99% ± 0.8. More than 3500 IMRT beams were verified using IC +/- absolute dosimetric film before treatment delivery. This QA method validates the reliability of the TPS and Linac and could help physicians for implementing IMRT in their center.

Seismic Screening of Public Facilities in Oregon’s Western Counties

The objective of this study was to use rapid visual screening (RVS) methods to identify potential seismic hazards for Oregon's public facilities, including schools, hospitals, fire stations, police stations, and emergency response centers. There were 1,075 buildings screened in nine western Oregon counties. This study is part of a larger effort under the 2005 Oregon Senate Bill 2 to assess the seismic needs and upgrade public facilities in Oregon. RVS methodology generally followed the Federal Emergency Management Agency's FEMA 154 Rapid Visual Screening of Buildings for Potential Hazards: A Handbook. This method identifies structural type and building characteristics that may indicate poor performance under the maximum considered earthquake (MCE). Each building is given a final score related to the probability of collapse under the MCE. Screening was conducted by four individuals over three months. Quality assurance (QA) testing on nine buildings examined consistency between screeners. QA results showed final scores varied between screeners depending on building size, structure type, and architectural cladding. FEMA 154 was developed using California buildings. Differences between Oregon and California construction and the use of FEMA 154 in Oregon are discussed in this paper, reviewing the Uniform Building Code (UBC) and Oregon Structural Specialty Code (OSSC) amendments. The study provided two important conclusions. First, the average final score for buildings screened fell below the FEMA 154 cut-off score of 2.0 Second, the OSSC had an exception to the UBC that allowed the construction of unreinforced masonry buildings two stories or less in height. With this context, screening results can help in assigning priorities for further analysis and seismic retrofits.

The extraction of true profiles for TPS commissioning and its impact on IMRT patient-specific QA

The aim of this work is to investigate the clinical impact of detector size effect on patient specific intensity-modulated radiation therapy (IMRT) quality assurance (QA). Two photon beam models, BM6 and BM4, were commissioned using photon beam profiles measured with a 6 mm diameter and a 4 mm diameter ion chambers, respectively. A method was developed to extract the "true" cross beam profiles, free of volume averaging effect, using analytic fitting/deconvolution. The method was validated using beam profiles measured with a small (0.8 mm) diode detector for small (< or = 10 x 10 cm2) field sizes. These profiles were used to commission a third beam model (BM08). Planar dose distributions for eight IMRT plans (total of 53 fields) were calculated using the three beam models and measured with a two-dimensional detector array. Analysis using percent dose difference and distance-to-agreement criteria between the calculation and measurement was done to benchmark the performance of each beam model. The average passing rates between calculation and measurement were 93.8%, 98.9%, and 99.4% for BM6, BM4, and BM08, respectively, when 3%/3 mm criteria were used. A gradual increase in passing rates was noticed with the decrease in the size of the detector used to collect commissioning data. When 2%/2 mm criteria were used, the average passing rates increased significantly from 81.6% (BM6) to 92.6% (BM4) and 96.8% (BM08). These results quantify the enhancement of IMRT dose calculation accuracy with the reduction in detector size used for photon beam profiles measurement. Our study indicates that volume averaging effect can significantly affect the results of IMRT patient specific QA. By removing the detector size effect in beam commissioning, excellent passing rates can be achieved with more stringent criteria such as 2%/2 mm. The use of more stringent criteria for IMRT patient specific QA would likely result in higher chances of detecting any dosimetric errors arising from the treatment planning or delivery system.

WE-D-AUD B-07: Investigation of a 2D Ionization Chamber Array for Quality Assurance of Intensity Modulated Arc Therapy

Purpose: To characterize a new two‐dimensional ionization chamber (IC) array (IBA, Schwarzenbruck, Germany), commercially referred to as the I'mRT MatriXX, and to evaluate its viability for quality assurance (QA) of intensity modulated arc therapy. Method and Materials: IC array characterization tests included determination of the effective plane of measurement, angle dependency, and investigations into the limiting minimum target volume. The response of the IC array as a function of beam angle with respect to its front face was compared among radiochromic film (type EBT, ISP), planning calculations, and beam measurements using the IC array. The limiting minimum target volume is of interest due to the relatively large detector size and inter‐detector spacing. To investigate the effect on small target volumes, treatment planning calculations for spherical targets with diameters ranging from 0.5 to 4 cm were compared to measurements taken on film and the IC array. Lastly, patient‐specific QA results were compared among film, array measurements, and treatment planning calculations for several treatment sites, including head and neck, pancreas, and cranial‐spinal cases. Results: Our results indicate inherent buildup thicknesses of the 0.48 cm and 5.19 cm for the front and rear faces of the IC array. A large angle dependency of the IC array existed as its response deviated from treatment planning calculations in the range of — 6.2% to 7.5%. However, the film response at the identical angles exhibited a similar trend. Comparisons among treatment plans measured with film and the IC array showed similar regions of disagreement. Film tended to show better agreement in regions of high dose gradients. Conclusion: In general, the IC array performed well in the patient QA tests. However, the user should be aware of the effects of dose gradients and angular dependency on the QA results.

EORTC 22972–26991/MRC BR10 trial: Fractionated stereotactic boost following conventional radiotherapy of high grade gliomas: Clinical and quality-assurance results of the stereotactic boost arm

Background and purpose The EORTC trial No. 22972 investigated the role of an additional fractionated stereotactic boost (fSRT) to conventional radiotherapy for patients with high grade gliomas. A quality-assurance (QA) programme was run in conjunction with the study and was the first within the EORTC addressing the quality of a supposedly highly accurate treatment technique such as stereotactic radiotherapy. A second aim was to investigate a possible relation between the clinical results of the stereotactic boost arm and the results of the QA. Materials and methods The trial was closed in 2001 due to low accrual. In total, 25 patients were randomized: 14 into the experimental arm and 11 into the control arm. Six centres randomized patients, 8 centres had completed the dummy run (DR) for the stereotactic boost part. All participating centres (9) were asked to complete a quality-assurance questionnaire. The DR consisted of treatment planning according to the guidelines of the protocol on 3 different tumour volumes drawn on CT images of a humanized phantom. The SRT technique to be used was evaluated by the questionnaire. Clinical data from patients recruited to the boost arm from 6 participating centres were analysed. Results There was a full compliance to the protocol requirements for 5 centres. Major and minor deviations in conformality were observed for 2 and 3 centres, respectively. Of the 8 centres which completed the DR, one centre did not comply with the requirements of stereotactic radiotherapy concerning accuracy, dosimetry and planning. Median follow-up and median overall survival were 39.2 and 21.4 months, respectively. Acute and late toxicities of the stereotactic boost were low. One radiation necrosis was seen for a patient who has not received the SRT boost. Three reported serious adverse events were all seizures and probably therapy-related. Conclusions Overall compliance was good but not ideal from the point of view of this highly precise radiation technique. Survival in the subgroup of patients with small volume disease was encouraging, but the study does not provide sufficient information about the potential value of fSRT boost in patients with malignant glioma.Toxicity due to an additional stereotactic boost of 20 Gy in 4 fractions was low and may be considered as a safe treatment option for patients with small tumours.

Ärzteunabhängige Kontrolle der Qualitäten in der Medizin

Currently a physician-independent control of health services can only be managed by means of liability case law. Usually, claims are settled years after the service has been provided, based, though, on medical guidelines that have been established by the medical profession itself at the time of the provision of services. An essential factor in medical quality assurance (QA) is the involvement of the relevant physicians, which should be combined with external controls. Regarding quality in medicine, personal qualification will have to be distinguished from institutional quality and quality of healthcare, which should be ensured by internal and external QA. There is increasing pressure to publish QA results in an institution-related manner. However, the publication of results may lead to the unequal treatment of hospitals, as external QA includes only a limited number of indications (possible misjudgement of overall quality), and refers to different patient populations (no comparable treatment results). However, the publication of such outcome data will prevail in the long-term. The future vision of an external QA system comprises: 1. electronically based patient files and, derived thereof, pseudonymised data sets for QA; 2. IQWiG's participation in the definition of evidence-based indicators for quality assessment as well as the application of these indicators; 3. the full publication of results on an Internet platform.

Po‐Thur Eve General‐11: Data for Intensity Modulated Radiotherapy Planning with Pinnacle for a 6MV Siemens Primus Beam

Background and purpose: Intensity‐modulated radiation therapy (IMRT) with a Siemens Primus linear accelerator and the Pinnacle V7.6c (IMRT V2.0) treatment planning system requires additional measurements and quality assurance (QA). This study presents the small field data for a 6MV beam and results of the additional QA for small monitor unit (MU) fields and the multi‐leaf collimator (MLC).Materials and methods: Beam measurements included relative output factors, MLC transmission and MLC interleaf transmission, percentage depth doses, and dose profiles. Beam modeling in Pinnacle is discussed. QA measurements included MU linearity and stability, MLC leaf position and abutment, and small MU field symmetry and flatness.Results and discussion: For field sizes 2×2cm2 and larger, ROFs for the two linacs were well within 0.6% of one another. MLC transmission and MLC interleaf transmission agreed with published values. The penumbral width was larger for the upper Y jaws compared to the lower MLC collimator by 1.4mm for the 2×2cm2 field. The Pinnacle model parameters that were adjusted to improve the fit to measured data were C2, K and ECD10×10, as well as the source size. MU linearity was adjusted to reduce the linearity error introduced for small MU IMRT segments. MLC leaf abutment test results are consistent with results at other centres with the same MLC.Conclusions: MU stability and MLC leaf position calibration have an important influence over the accuracy of the delivered dose for small MU segments. Field flatness in the inplane direction will also degrade dose accuracy for small MU segments.

SU‐FF‐T‐374: Quality Assurance of the On‐Board Imager and Cone‐Beam Computed Tomography Systems

Purpose: To develop a comprehensive quality assurance (QA) program for the On‐Board Imager (OBI) used for patient positioning verification and to present the results of QA tests over extended periods from multiple institutions. Radiographic and cone‐beam computed tomography (CBCT) mode have been evaluated. Methods and Materials: The QA program consists of three parts; (1) safety and functionality (2) geometry and (3) image quality. Safety checks evaluate the functionality of collision interlocks and audible alarms. Functional QA checks the flow of clinical operation during tube warm‐up. Geometry QA checks geometrical accuracy and variation of the OBI/CBCT and hardware/software. Image quality QA includes measurements to monitor accuracy and stability of the OBI/CBCT imaging system. Results: All test items show stable functionality for safety and functional QA on a daily bases. The precision of arm positioning is very high with variation of 1mm and average accuracy of &lt; 1mm over 8 months. The average accuracy of the isocenter and couch shift is &lt; 1mm with variation of 1mm over 11 months. Arm position was performed when the results were &gt; 2 mm. Results of geometry QA have been stable within tolerances through the test periods. All tests for Image quality tests also show consistent results within tolerances. Conclusion: We have developed a practical yet comprehensive set of QA tests for the OBI system. Data collected for these tests over the extended period show that the OBI system has mechanical reliability and stable image quality. Nevertheless, the tests were useful in detecting performance deficits in the OBI system that needed recalibration. After accumulating enough experience and confidence on stability and accuracy, some institutions have reduced the frequency of QA checks. However, it is important that all tests are performed on a regular basis within a suggested period to establish a guideline.

SU‐FF‐T‐201: Implementation of EPID Based Quality Assurance Procedures for Radiation and Optical Fields

Purpose: Enhanced radiation and light field quality assurance (QA) procedures have been developed and implemented utilizing amorphous silicon electronic portal imaging devices (EPID). This effort was motivated by the fact that film exposure coupled with hand measurements are extremely time consuming and prone to many sources of error. Method and Materials: The EPID based QA procedure uses specially designed acrylic test templates, containing radio‐opaque led bars to register the position of the optical field. Images of these templates were acquired with the EPID on both Varian and Elekta linear accelerators. A MATLab based computer application was used to automatically assess light/radiation field congruence, radiation field sizes and optical field size and positioning. A three‐month pilot study using two Varian accelerators to assess both 6 MV and 18 MV photon energies was performed to validate the EPID QA procedure's efficacy and quantify its efficiency relative to film QA procedures. Results: The pilot study verified that the EPID QA system results are congruent with the hand measurements obtained from a detailed analysis of film QA measurements. Light/radiation congruence measurement performed using an EPID exhibited an absolute mean deviation of 0.37 ± 0.37 mm (1σ), relative to the film measurements. EPID based radiation field size assessments produced an absolute discrepancy of 0.57 ± 0.44mm (1σ), while film measurements yielded an absolute discrepancy of 0.61 ± 0.55mm (1σ), relative to measurements acquired using RIT software. EPID based measurements were found to be more efficiently performed, reducing the set‐up and analysis time by 55% compared to film. Conclusions: The enhanced EPID QA system can effectively replace film in routine quality assurance tasks for radiation and optical fields. This procedure saves Princess Margaret Hospital 4 man‐hours per week, and provides a user‐independent analysis procedure for objectively assessing routine QA results.