The purpose of this study was to determine if medical linear accelerators (linac) produced by the same manufacturer exhibit operational consistency within their subsystems and components. Two linacs that were commissioned together and installed at the same facility were monitored. Each machine delivered a daily robust quality assurance (QA) irradiation. Linacs and their components operate consistently, but have different operational parameter levels even when produced by the same manufacturer and commissioned in series. These findings have implications on the feasibility of true clinical beam matching.

Unscheduled accelerator downtime can negatively impact the quality of life of patients during their struggle against cancer. Currently digital data accumulated in the accelerator system is not being exploited in a systematic manner to assist in more efficient deployment of service engineering resources. The purpose of this study is to develop an effective process for detecting unexpected deviations in accelerator system operating parameters and/or performance that predicts component failure or system dysfunction and allows maintenance to be performed prior to the actuation of interlocks.

An essential component in the management of early stage and locally advanced breast cancer is whole breast irradiation (WBI), which is typically delivered in the supine position. However, the supine setup may have the limitation of infra-mammary folds, more inclusion of lung and heart, and lateral displacement of breast. In this work, we present the dosimetric results of a prospective study of prone positioning WBI. Twenty-six patients were treated with prone breast positioning in our clinic since 08/2014. CT simulation was conducted with 2.5mm slice thickness. Patients were positioned on the prone breast board with both arms above the head and hands holding the bar to reduce body rotation. The contralateral breast was tucked away and the head was turned away from the treated breast. The planning target volume (PTV) was contoured by the radiation oncologist. Two opposed tangential fields using 6MV photon beams with the field-in-field technique were applied to obtain target coverage and dose uniformity. Cone beam CT (CBCT) was acquired to ensure the prone setup accuracy. Heterogeneity correction was applied in treatment planning. DVH for PTV, ipsilateral lung, total lung, and heart were calculated. Twenty-six patients were divided into three categories based on the PTV volume: 7 in the small breast group (PTV<800cc), 14 in the medium breast group (PTV=800∼1600cc), and 5 in the large breast group (PTV>1600cc). All plans obtained adequate target coverage, i.e., ≥95% of PTV receiving 95% of the prescribed dose (Rx). The average homogeneity index (HI=Dmax/Rx) was 104.6±2.0%. For the large breast group, due to the relatively large separation between critical structures and the target volume, the ipsilateral lung's V20 ∼ 0, V5 < 2% and the mean dose to the total lung < 1 Gy. For the left-sided breast radiation therapy, the mean dose to the heart was 1.7±0.9 Gy and the heart's V5 was 3.3±5.2%. No infra-mammary skin folding was observed for all prone setups. The prone setup for whole breast irradiation has demonstrated favorable ipsilateral lung and heart dose while achieving better dose uniformity. Patients with large or pendulous breasts in particular benefit from prone positioning with reduced toxicity in the heart and lung and skin folding.Poster Viewing Abstracts 2079; Table 1Dosimetric endpoints of prone breast radiation therapy# of ptBreast PTV volume (cc)HI (%)Total Lung V20 (%)Total Lung V5 (%)Ipsilateral Lung V20 (%)Ipsilateral Lung V5 (%)Dmean Total Lung (Gy)Dmean Heart* (Gy)Heart V5* (%)Small (<800 cc)7555±177103.8±2.40.6±1.01.7±2.51.1±1.72.9±3.90.6±0.51.8±1.22.1±2.5Medium (800-1600 cc)141099±193104.9±1.30.4±1.11.1±2.10.8±2.12.2±3.80.6±0.61.7±0.92.5±2.8Large (>1600 cc)52312±582105.0±3.100.4±0.600.5±0.80.5±0.21.7±0.62.2±2.9Total261186±671104.6±2.00.4±1.01.1±2.00.8±1.82.0±3.50.6±0.51.7±0.93.3±5.2* Heart dose evaluation for left breast only. Open table in a new tab

BACKGROUND AND OBJECTIVEOur group created and routinely reviewed a dedicated prostate intensity-modulated radiation therapy (IMRT) delivery program. Previously, a retrospective review of our experience demonstrated that a larger bladder volume reduced radiation dose to the rectum. We conducted an observational study to confirm this relationship.METHODSMen receiving definitive radiation for prostate cancer were eligible for the study. Eligible patients received 2 computed axial tomography (CT) scans on the day of their planning CT scan: 1 with a full bladder and 1 with an empty bladder. On each CT data set, the prostate, rectum, bladder, penile bulb, and femoral heads were contoured. 2 IMRT plans were completed on each dataset: 1 by a medical dosimetrist and 1 by a medical physicist. The study plans targeted the prostate to 79.2 Gray (Gy) while respecting predefined dose tolerances to the other contoured structures. Rectal doses were compared on empty and full bladder CT data sets.RESULTSFrom June 29, 2010 to December 14, 2011, 17 full bladder data sets and 15 empty bladder data sets were available for analysis. Median change in bladder volume was 63 ml. Full vs empty bladder set-up was associated with a statistically significant reduction in the mean rectal dose of 25.41 Gy vs 27.6 Gy (𝑃 = .031).LIMITATIONSSmall sample size and small variations in bladder volumes.CONCLUSIONSA greater bladder volume resulted in a reduced mean dose to the rectum irrespective of planning method.

Purpose: To determine the effectiveness of SPC analysis for a model predictive maintenance process that uses accelerator generated parameter and performance data contained in trajectory log files. Methods: Each trajectory file is decoded and a total of 131 axes positions are recorded (collimator jaw position, gantry angle, each MLC, etc.). This raw data is processed and either axis positions are extracted at critical points during the delivery or positional change over time is used to determine axis velocity. The focus of our analysis is the accuracy, reproducibility and fidelity of each axis. A reference positional trace of the gantry and each MLC is used as a motion baseline for cross correlation (CC) analysis. A total of 494 parameters (482 MLC related) were analyzed using Individual and Moving Range (I/MR) charts. The chart limits were calculated using a hybrid technique that included the use of the standard 3σ limits and parameter/system specifications. Synthetic errors/changes were introduced to determine the initial effectiveness of I/MR charts in detecting relevant changes in operating parameters. The magnitude of the synthetic errors/changes was based on: TG-142 and published analysis of VMAT delivery accuracy. Results: All errors introduced were detected. Synthetic positional errors of 2mm for collimator jaw and MLC carriage exceeded the chart limits. Gantry speed and each MLC speed are analyzed at two different points in the delivery. Simulated Gantry speed error (0.2 deg/sec) and MLC speed error (0.1 cm/sec) exceeded the speed chart limits. Gantry position error of 0.2 deg was detected by the CC maximum value charts. The MLC position error of 0.1 cm was detected by the CC maximum value location charts for every MLC. Conclusion: SPC I/MR evaluation of trajectory log file parameters may be effective in providing an early warning of performance degradation or component failure for medical accelerator systems.

Purpose:To develop a model to analyze medical accelerator generated parameter and performance data that will provide an early warning of performance degradation and impending component failure.Methods:A robust 6 MV VMAT quality assurance treatment delivery was used to test the constancy of accelerator performance. The generated text log files were decoded and analyzed using statistical process control (SPC) methodology. The text file data is a single snapshot of energy specific and overall systems parameters. A total of 36 system parameters were monitored which include RF generation, electron gun control, energy control, beam uniformity control, DC voltage generation, and cooling systems. The parameters were analyzed using Individual and Moving Range (I/MR) charts. The chart limits were calculated using a hybrid technique that included the use of the standard 3σ limits and the parameter/system specification. Synthetic errors/changes were introduced to determine the initial effectiveness of I/MR charts in detecting relevant changes in operating parameters. The magnitude of the synthetic errors/changes was based on: the value of 1 standard deviation from the mean operating parameter of 483 TB systems, a small fraction (≤ 5%) of the operating range, or a fraction of the minor fault deviation.Results:There were 34 parameters in which synthetic errors were introduced. There were 2 parameters (radial position steering coil, and positive 24V DC) in which the errors did not exceed the limit of the I/MR chart. The I chart limit was exceeded for all of the remaining parameters (94.2%). The MR chart limit was exceeded in 29 of the 32 parameters (85.3%) in which the I chart limit was exceeded.Conclusion:Statistical process control I/MR evaluation of text log file parameters may be effective in providing an early warning of performance degradation or component failure for digital medical accelerator systems.Research is Supported by Varian Medical Systems, Inc.

Purpose: Statistical process control (SPC) is a quality control method used to ensure that a process is well controlled and operates with little variation. This study determined whether SPC was a viable technique for evaluating the proper operation of a high-dose-rate (HDR) brachytherapy treatment delivery system.Methods and Materials: A surrogate prostate patient was developed using Vyse ordnance gelatin. A total of 10 metal oxide semiconductor field-effect transistors (MOSFETs) were placed from prostate base to apex. Computed tomography guidance was used to accurately position the first detector in each train at the base. The plan consisted of 12 needles with 129 dwell positions delivering a prescribed peripheral dose of 200 cGy. Sixteen accurate treatment trials were delivered as planned. Subsequently, a number of treatments were delivered with errors introduced, including wrong patient, wrong source calibration, wrong connection sequence, single needle displaced inferiorly 5 mm, and entire implant displaced 2 mm and 4 mm inferiorly. Two process behavior charts (PBC), an individual and a moving range chart, were developed for each dosimeter location.Results: There were 4 false positives resulting from 160 measurements from 16 accurately delivered treatments. For the inaccurately delivered treatments, the PBC indicated that measurements made at the periphery and apex (regions of high-dose gradient) were much more sensitive to treatment delivery errors. All errors introduced were correctly identified by either the individual or the moving range PBC in the apex region. Measurements at the urethra and base were less sensitive to errors.Conclusions: SPC is a viable method for assessing the quality of HDR treatment delivery. Further development is necessary to determine the most effective dose sampling, to ensure reproducible evaluation of treatment delivery accuracy. (c) 2013 Elsevier Inc.

BACKGROUND:This study seeks to increase clinical operational efficiency and accelerator beam consistency by retrospectively investigating the application of statistical process control (SPC) to linear accelerator beam steering parameters to determine the utility of such a methodology in detecting changes prior to equipment failure (interlocks actuated).METHODS:Steering coil currents (SCC) for the transverse and radial planes are set such that a reproducibly useful photon or electron beam is available. SCC are sampled and stored in the control console computer each day during the morning warm-up. The transverse and radial - positioning and angle SCC for photon beam energies were evaluated using average and range (Xbar-R) process control charts (PCC). The weekly average and range values (subgroup n = 5) for each steering coil were used to develop the PCC. SCC from September 2009 (annual calibration) until two weeks following a beam steering failure in June 2010 were evaluated. PCC limits were calculated using the first twenty subgroups. Appropriate action limits were developed using conventional SPC guidelines.RESULTS:PCC high-alarm action limit was set at 6 standard deviations from the mean. A value exceeding this limit would require beam scanning and evaluation by the physicist and engineer. Two low alarms were used to indicate negative trends. Alarms received following establishment of limits (week 20) are indicative of a non-random cause for deviation (Xbar chart) and/or an uncontrolled process (R chart). Transverse angle SCC for 6 MV and 15 MV indicated a high-alarm 90 and 108 days prior to equipment failure respectively. A downward trend in this parameter continued, with high-alarm, until failure. Transverse position and radial angle SCC for 6 and 15 MV indicated low-alarms starting as early as 124 and 116 days prior to failure, respectively.CONCLUSION:Radiotherapy clinical efficiency and accelerator beam consistency may be improved by instituting SPC methods to monitor the beam steering process and detect abnormal changes prior to equipment failure.PACS numbers: 87.55n, 87.55qr, 87.56bd.

Integrating the Healthcare Enterprise - Radiation Oncology (IHE-RO) project is an ASTRO sponsored initiative to facilitate information exchange across different treatment planning systems (TPS). IHE-RO promotes accurate and safe radiation treatment delivery by developing a framework for integration and interoperability of information. In this study we evaluate the status of dose import/export and re-planning functionalities of different TPS. Four planning systems (Elekta XiO v4.6, Elekta Monaco v2.03, Varian Eclipse v8.1, BrainLAB iPlan v4.1.2 with Monte Carlo) were considered for a test case in which a patient previously planned and treated with one TPS presents for re-treatment in a clinic that uses a different TPS. CT data for the test case was imported into one of the TPS and PTV/OARs delineated. Three treatment plans were generated using fixed conformal fields, dynamic conformal arcs, and IMRT. The image set, structure set and plans were exported to a different TPS. A repeat CT scan of the patient was also sent to the new TPS for re-planning. Each TPS was evaluated for import/export of RT images, structures, and dose as well as for its ability to effectively re-plan previously irradiated sites. Integrity and ease of data transfer was also studied. All TPS vendors included in this study allowed export of RT images, structures, plan, and dose. Whereas import of CT images and structure sets was possible with all planning systems, only one TPS currently allows RT plan and dose import. This TPS also displayed composite dose/DVH from old and new plans, if they were calculated on the old data set. Composite dose data may be used to manually optimize PTV/OAR doses. A future plan release is expected to allow dose summation from different image sets as well as fully automated dose optimization. Dose import functionality was independent of plan type, but was easier done from within the same planning system than across different TPS. Fixed field doses were easy to optimize on compared to dynamic conformal arc or IMRT plans. All RT structures and planning information (beam angles, field size, MLC) were accurately transferred across TPS. Other vendor TPS projected to incorporate missing import options and dose optimization features in their future planning release. Patients with recurrence in close proximity to previously treated areas pose a difficult planning challenge. This is especially problematic if the patient was originally planned on a different TPS. The IHE-RO initiative is designed to stimulate integration and portability of RT plan information between various TPS. Although efforts are underway, not all vendors have fully complied with this objective. This study may be useful for vendors and clinicians alike in TPS upgrade decision process.

Purpose: This study retrospectively applies statistical process control (SPC) methods to determine its utility in detecting changes in linear accelerator beam steering parameters prior to equipment failure (interlocks actuated) thereby increasing patient safety. Methods: Steering coil currents (SCC) for the transverse and radial planes are set such that a reproducibly useful photon or electron beam is available. SCC are sampled and stored in the control console computer each day during the morning warm‐up. The transverse and radial ‐ positioning and angle SCC for photon beam energies were evaluated using average and range (Xbar‐R) process control charts (PCC). The weekly average and range values (subgroup n=5) for each steering coil were used to develop the PCC. SCC from September‐2009 (annual calibration) until two weeks following a beam steering failure on June 28th were evaluated. PCC limits were calculated using the first twenty subgroups. Appropriate action limits were developed using conventional SPC guidelines. Results: PCC high alarm action limit was set at six standard deviations from the mean. Low alarm indicators were: (1) nine points in a row on either side of the mean, and (2) two out of three points in a row greater than two standard deviations from the mean. Alarms received following establishment of limits (week twenty) are indicative of a special cause for deviation (Xbar chart) and/or an uncontrolled process (R chart). Transverse angle SCC for 15X and 6X indicated a high alarm on March 11th and March 29th respectively. A downward trend in this parameter continued, with high alarm, until failure. Transverse position and radial angle SCC for both energies indicated a high or low alarm starting in February or March. Conclusions: Patient safety may be improved by instituting SPC methods to monitor the beam steering process and detect abnormal changes prior to equipment failure.

Purpose: This study prospectively applies statistical process control (SPC) methods as a predictive maintenance tool in linear acceleratorphoton beam quality. Methods: Steering coil currents (SCC) are sampled and stored daily during morning warm‐up. The transverse and radial ‐ positioning and angle SCC for photon beams were evaluated using average and range (Xbar‐R) process control charts (PCC). The weekly average and range values (subgroup n=5) for each SCC was used to develop the PCC. Control limits were calculated using the first sixteen subgroups. Run charts of the daily SCC values were maintained and updated weekly. PCC high alarm action limit was set at six standard deviations. Six subgroups in a row all increasing or decreasing were a low alarm indicator. A sustained high alarm of 3 subgroups in conjunction with a low alarm was used as our action threshold (i.e. independent verification of beam flatness and symmetry constancy). Results: Data collection commenced September 2010, following beam steering adjustments during annual calibration. Only alarms received following establishment of limits (week sixteen) were considered valid indicators for deviation or an uncontrolled process. A high alarm was first detected on Jan 25 (15 MV — transverse position). Simulated intervention was triggered by 6 MV — radial angle SCC on February 18th. Beam scans taken and compared to those from the annual calibration indicated a change in symmetry in the transverse plane (0.6% ‐ 6 MV and 1.0% ‐ 15 MV) while the flatness remained effectively unchanged (<0.5%). There were no changes noted in the radial plane for either energy. Conclusions: SPC techniques are able to effectively detect variations in beam steering currents. SPC monitoring of beam steering has the capability to ensure AAPM TG‐142 constancy guidelines of +/− 1% are maintained. Further investigation is required to develop consistent intervention guidelines.

The ASTRO sponsored Integrating the Healthcare Enterprise - Radiation Oncology (IHE-RO) works to address issues of interoperability and information sharing between various radiation oncology systems that impact the quality of care in radiation oncology. IHE-RO has recently completed testing of the Advanced RT Objects Integration Profile, which facilitates the re-planning of a patient on a different treatment planning system (TPS). In this study we assess the current clinical process/status of re-planning using five different vendor's TPS available to the co-authors and which participated in the testing of the integration profile. A 3D conformal and IMRT plan developed using TPS vendor A was exported using its export feature. The CT dataset, RT structure set, RT plan and RT dose were all exported. These plans were imported using the import feature of the remaining vendors (B, C, D, and E). We track and report the import process and any errors or data omissions for each planning method. The imported image data and structure set is used to create a 3D conformal and an IMRT plan on each TPS. These plans are then exported and subsequently imported to each vendor TPS. One system, vendor E, export features were not tested in this study. Vendor systems include Varian Eclipse v 8.1, Elekta XIO v 4.5, Elekta Monaco v 2.03, Nucletron Oncentra Masterplan v 3.3, and BrainLab iPlan v 4.1.1. All the export features of the TPS tested allow the user to determine what components of the plan will be included: image dataset, RT structure set, RT plan and/or RT dose. All the TPS import features were automated once the location of the plan data was defined. The result of plan import was the same regardless of the system exporting the plan or the type of plan (3D or IMRT) exported. Each TPS displayed the results of the import using dialog boxes displaying errors and/or the objects imported. All systems successfully imported the image dataset and the RT structure set. Results of the importation of RT plan and dose was mixed. Vendor D does not currently support dose import. Vendor B, C, and E successfully imported beam geometry. Only Vendor E imported the MLC plan of each beam. Vendor B and E imported RT dose with complete dose-volume analytical capability. The Advanced RT Objects integration profile facilitates the TPS import and export of image dataset(s), RT structure set, RT plan, and RT dose. This integration profile has not been fully implemented by the vendors reviewed in this study. Clinics can request the capability included in this integration profile in their next TPS upgrade or new purchase by including its DICOM conformance statement in the purchase order or request for proposal (RFP). http://wiki.ihe.net/index.php?title = Radiation_Oncology

Current external beam quality assurance (QA) recommendations of the AAPMs Task Group 142 are limited to "snapshot" reviews of the accelerator manufacturer specifications on a routine periodic basis. This project aims to investigate a methodology, Statistical Process Control (SPC), and a process that can simply, rapidly, and reproducibly test the accuracy of accelerator mechanical and dosimetric parameters according to TG-142 tolerances using external beam treatment delivery. SPC, a methodology that detects exceptional variability in a process, was used to analyze data acquired while delivering simulated clinical treatment to a custom film phantom. Two external beam radiotherapy delivery techniques typical for prostate treatment were used: a 3-D conformal and an IMRT plan. Treatment delivery was performed twice daily for 10 weeks using a single linear accelerator with Gafchromic film placed in both the transverse and coronal planes. Mechanical parameters (table, gantry, collimator position) and dosimetric parameters (beam energy, dose constancy, and uniformity) were evaluated by sampling each individual film's dose distribution. SPC analysis was performed sampling small regions of interest (ROI) whose ideal locations were determined experimentally and validated. SPC statistics were used to develop process behavior charts (PBC) tracking the sample average and range values. TG 142 QA tests results for the accelerator were tracked in tandem with SPC analysis. Known errors were introduced during treatment delivery to validate the process. QA results indicate a maximum dose variation of <1.5% and other parameters within limits. SPC analysis detected changes in film sensitivity, within the film lot, throughout the test period affecting our results. A 2 mm vertical shift in the position of the film phantom was not observed in the PBC due to the level of random error in our system. While the intentional dose increase and non-uniformity error were detected in the average charts for the transverse plane, false-positives were also detected due to the presence of random errors in the process. Analysis of the PBC derived from both 3D conformal and IMRT delivery indicated the presence of random variation that was detrimental to the methodological goal of detecting systematic error in process behavior. SPC can be used to perform quality control of the treatment process. Knowledge gained in our investigation of the proper location of ROI to evaluate critical aspects of linear accelerator operating parameters was significant. Film dosimetry proved to be too susceptible to changes in formulation, manufacturing, and processing during this study. A stable, high-resolution solid-state detector may be more appropriate.

Purpose/Objective(s)Examine the feasibility of incorporating a dual energy subtraction technique to enhance and improve target localization for thoracic radiotherapy treatment.Materials/MethodsModern linear accelerators now include kilovoltage on-board imagers (OBI) to aid in target localization. These systems are being used to generate daily cone beam CTs (CBCT) to determine if the target volume is properly positioned for treatment; however, radiation dose and time delays may be a problem over the course of a multiple week treatment. CBCT scans are needed to adequately determine the target lesion location in the thorax because conventional 2D x-ray images have poor soft tissue visualization due to anatomical superposition of soft tissue and complicated bony anatomy (mainly ribs). Additionally, CBCT images are known to have decreased visualization and poor delineation of target volumes due to breathing motion artifact blur caused by long acquisition times.Dual-energy (DE) subtraction imaging is a mathematical technique used to separate an image into tissue-only and bone-only images using two rapidly acquired x-ray images with different energy spectra. DE tissue-only images allow for the removal of overlying bony structure and will provide substantially enhanced visibility of soft tissue anatomy, including lung lesions, for external-beam radiotherapy targeting.For this study, 3 simple objects were placed on the chest of an anthropomorphic phantom to simulate lung nodules and 2 x-ray images (120 and 70 kVp) were acquired using an OBI on a 21ix Clinac. The DE subtraction technique was performed to generate a tissue-only image, which was assessed for improved visibility of the embedded nodules due to the removal of the ribs in the lung region.ResultsThe included Figure shows the high energy, low energy, and tissue-only DE images. The 3 simulated nodules are clearly more visible in the DE subtraction image. Note the excellent subtraction of the entirety of the bony ribs in the chest region.Conclusions Purpose/Objective(s)Examine the feasibility of incorporating a dual energy subtraction technique to enhance and improve target localization for thoracic radiotherapy treatment. Examine the feasibility of incorporating a dual energy subtraction technique to enhance and improve target localization for thoracic radiotherapy treatment. Materials/MethodsModern linear accelerators now include kilovoltage on-board imagers (OBI) to aid in target localization. These systems are being used to generate daily cone beam CTs (CBCT) to determine if the target volume is properly positioned for treatment; however, radiation dose and time delays may be a problem over the course of a multiple week treatment. CBCT scans are needed to adequately determine the target lesion location in the thorax because conventional 2D x-ray images have poor soft tissue visualization due to anatomical superposition of soft tissue and complicated bony anatomy (mainly ribs). Additionally, CBCT images are known to have decreased visualization and poor delineation of target volumes due to breathing motion artifact blur caused by long acquisition times.Dual-energy (DE) subtraction imaging is a mathematical technique used to separate an image into tissue-only and bone-only images using two rapidly acquired x-ray images with different energy spectra. DE tissue-only images allow for the removal of overlying bony structure and will provide substantially enhanced visibility of soft tissue anatomy, including lung lesions, for external-beam radiotherapy targeting.For this study, 3 simple objects were placed on the chest of an anthropomorphic phantom to simulate lung nodules and 2 x-ray images (120 and 70 kVp) were acquired using an OBI on a 21ix Clinac. The DE subtraction technique was performed to generate a tissue-only image, which was assessed for improved visibility of the embedded nodules due to the removal of the ribs in the lung region. Modern linear accelerators now include kilovoltage on-board imagers (OBI) to aid in target localization. These systems are being used to generate daily cone beam CTs (CBCT) to determine if the target volume is properly positioned for treatment; however, radiation dose and time delays may be a problem over the course of a multiple week treatment. CBCT scans are needed to adequately determine the target lesion location in the thorax because conventional 2D x-ray images have poor soft tissue visualization due to anatomical superposition of soft tissue and complicated bony anatomy (mainly ribs). Additionally, CBCT images are known to have decreased visualization and poor delineation of target volumes due to breathing motion artifact blur caused by long acquisition times. Dual-energy (DE) subtraction imaging is a mathematical technique used to separate an image into tissue-only and bone-only images using two rapidly acquired x-ray images with different energy spectra. DE tissue-only images allow for the removal of overlying bony structure and will provide substantially enhanced visibility of soft tissue anatomy, including lung lesions, for external-beam radiotherapy targeting. For this study, 3 simple objects were placed on the chest of an anthropomorphic phantom to simulate lung nodules and 2 x-ray images (120 and 70 kVp) were acquired using an OBI on a 21ix Clinac. The DE subtraction technique was performed to generate a tissue-only image, which was assessed for improved visibility of the embedded nodules due to the removal of the ribs in the lung region. ResultsThe included Figure shows the high energy, low energy, and tissue-only DE images. The 3 simulated nodules are clearly more visible in the DE subtraction image. Note the excellent subtraction of the entirety of the bony ribs in the chest region. The included Figure shows the high energy, low energy, and tissue-only DE images. The 3 simulated nodules are clearly more visible in the DE subtraction image. Note the excellent subtraction of the entirety of the bony ribs in the chest region. Conclusions

The use of image- based 3D treatment planning has significantly increased the complexity of commercially available treatment- planning systems ( TPSs). Medical physicists have traditionally focused their efforts on understanding the calculation algorithm; this is no longer possible. A quality assurance ( QA) program for our 3D treatment- planning system ( ADAC Pinnacle(3)) is presented. The program is consistent with the American Association of Physicists in Medicine Task Group 53 guidelines and balances the cost- versus- benefit equation confronted by the clinical physicist in a community cancer center environment. Fundamental reproducibility tests are presented as required for a community cancer center environment using conventional and 3D treatment planning. A series of nondosimetric tests, including digitizer accuracy, image acquisition and display, and hardcopy output, is presented. Dosimetric tests include verification of monitor units ( MUs), standard isodoses, and clinical cases. The tests are outlined for the Pinnacle(3) TPS but can be generalized to any TPS currently in use. The program tested accuracy and constancy through several hardware and software upgrades to our TPS. This paper gives valuable guidance and insight to other physicists attempting to approach TPS QA at fundamental and practical levels.