Feasibility of using a transmission ion chamber for QA tests of medical linear accelerators.

PURPOSE: To study the feasibility of using the Integral Quality Monitoring (IQM) system for routine quality assurance (QA) of photon beams. METHODS: The IQM system is a commercially available dose delivery verification tool, which consists of a spatially sensitive large area transmission ion chamber, mounted on the Linac collimator, and a calculation algorithm to predict the signals in response to radiation beams. By comparing the measured and predicted signals the system verifies the accuracy of beam delivery. The ion chamber unit is a battery powered system including a dual-electrometer, temperature and pressure sensors, and inclinometers. The feasibility of using the IQM system for routine QA tests was investigated by measuring constancy values of beam parameters, with specially designed tests fields, and comparing them with those determined by a conventional system. RESULTS: The sensitivity of the beam output constancy measurements by the IQM system was found to agree with those measured by a Farmer type ion chamber placed in water phantoms to within 0.1% for typical daily output variation of ± 0.5% and ± 1%. The beam symmetry was measured with a 4 cm × 4 cm aperture at multiple off-axis distances and was found to have a highly linear relationship with those measured in a water phantom scan for intentionally introduced asymmetry between -3% and +3%. The beam flatness was measured with a two-field ratio method and was found to be linearly correlated with those measured by water phantom scan. The dosimetric equivalent of a picket fence test performed by the IQM system can serve as a constancy check of the multileaf collimator (MLC) bank positioning test. CONCLUSIONS: The IQM system has been investigated for constancy measurements of various beam parameters for photon beams. The results suggest that the system can be used for most of the routine QA tests effectively and efficiently.

AAPM task group report 275.S: Survey strategy and results on plan review and chart check practices in US and Canada.

BACKGROUND: AAPM Task Group (TG) 275 was charged with developing practical, evidence-based recommendations for physics plan and chart review clinical processes for radiation therapy. As part of this charge, and to characterize practices and clinical processes, a survey of the medical physics community was developed and conducted. Detailed analyses and trends based on the survey that exceeded TG report length constraints are presented herein. AIMS: The design, development, and detailed results of the TG- 275 survey as well as statistical analysis and trends are described in detail. This is complementary material to the TG 275 report. METHODS AND MATERIALS: The survey consisted of 100 multiple-choice questions divided into four main sections: 1) Demographics, 2) Initial Plan Check, 3) On-Treatment, and 4) End-of-Treatment Chart Check. The survey was released to all AAPM members who self-reported working in the radiation oncology field, and it was kept open for 7 weeks. Results were summarized using descriptive statistics. To study practice differences, tests of association were performed using data grouped by four demographic questions: 1) Institution Type, 2) Average number of patients treated daily, 3) Radiation Oncology Electronic Medical Record, and 4) Perceived Culture of Safety. RESULTS: The survey captured 1370 non-duplicate entries from the United States and Canada. Differences across practices were grouped and presented based on Process-Based and Check-Specific questions. A risk-based summary was created to show differences amongst the four demographic questions for checks associated with the highest risk failure modes identified by TG-275. CONCLUSION: The TG-275 survey captured a baseline of practices on initial plan, on-treatment, and end-of-treatment checks across a wide variety of clinics and institutions. The results of test of association showed practice heterogeneities as a function of demographic characteristics. Survey data were successfully used to inform TG-275 recommendations.

Medical physics practice guideline 4.b: Development, implementation, use and maintenance of safety checklists.

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education, and professional practice of medical physics. The AAPM has more than 8000 members and is the principal organization of medical physicists in the US. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the US. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized. The following terms are used in the AAPM practice guidelines: Must and must not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline. While must is the term to be used in the guidelines, if an entity that adopts the guideline has shall as the preferred term, the AAPM considers that must and shall have the same meaning. Should and should not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances.

Assessment of dose-volume histogram precision for five clinical systems.

PURPOSE: To investigate the dependency of dose-volume histogram (DVH) behavior and precision on underlying discretization using shapes and dose distributions with known analytical DVHs for five commercial DVH calculators. METHODS: DVHs and summary metrics were extracted from all five systems using synthetic cone and cylinder objects for which the true volume and DVH curves were known. Trends in the curves and metrics were explored by varying the underlying voxelization of the CT image, structure set, and dose grid as well by varying the geometry of the structure and direction of a linear dose gradient. Using synthetic structures allowed for comparison with ground truth DVH curves to assess their accuracy while an algorithm was additionally developed to assess the precision of each system. The precision was calculated with a novel algorithm that treats any "stair step" behavior in a DVH curve as an uncertainty band and calculates the width, characterized as a percent difference, of the band for various DVH metrics. The underlying voxelization was additionally changed and DVHs were extracted for two clinical examples. The details of how each system calculated DVHs were also investigated and tendencies in the calculated curves, metrics, and precision were related to choices made in the calculation methodology. RESULTS: Calculation methodology differences that had a noticeable impact on the DVH curves and summary metrics include supersampling beyond the input grids and interpretation of the superior and inferior ends of the structures. Among the systems studied, the median precision ranged from 0.902% to 3.22%, and interquartile ranges varied from 1.09% to 3.91%. CONCLUSIONS: Commercial dose-evaluation solutions can calculate different DVH curves, structure volume measures, and dose statistics for the same input data due to differences in their calculation methodologies. This study highlights the importance of understanding and investigating the DVH calculation when considering a new clinical system and when using more than one system for data transfer.

Electronic charting of radiation therapy planning and treatment: Report of Task Group 262.

While most Radiation Oncology clinics have adopted electronic charting in one form or another, no consensus document exists that provides guidelines for safe and effective use of the Radiation Oncology electronic medical records (RO-EMR). Task Group 262 was formed to provide these guidelines as well as to provide recommendations to vendors for improving electronic charting functionality in future. Guidelines are provided in the following areas: Implementation and training for the RO-EMR, acceptance testing and quality assurance (QA) of the RO-EMR, use of the RO-EMR as an information repository, use of the RO-EMR as a workflow manager, electronic charting for brachytherapy and nonstandard treatments, and information technology (IT) considerations associated with the RO-EMR. The report was based on a literature search by the task group, an extensive survey of task group members on their respective RO-EMR practices, an AAPM membership survey on electronic charting, as well as group consensus.

Phantom Verification of AAA and Acuros Dose Calculations for Lung Cancer: Do Tumor Size and Regression Matter?

PURPOSE: This study aimed to evaluate dose calculation accuracy for the Eclipse Analytical Anisotropic Algorithm (AAA) and Acuros XB algorithm for various lung tumor sizes and to investigate dosimetric changes associated with treatment of regressing tumors. METHODS AND MATERIALS: A water phantom with cylindrical cork inserts (lung surrogates) was fabricated. Large (202 cm3), medium (54 cm3), and small (3 cm3) solid water tumors were implanted within cork inserts. A plain cork insert was used to simulate a lung without a tumor. The cork inserts and tumors were cut along the long axis, and Gafchromic film was placed between the sections to measure dose distributions. Three-dimensional conformal plans were created using 6 MV and 10 MV beams, and volumetric modulated arc therapy plans were created using 6 MV beams for each tumor size. Doses were calculated using Eclipse AAA and Acuros XB. The measured and calculated dose distributions were compared for each tumor size and treatment algorithm. To simulate a regressing tumor, the original plans created for the large tumor were separately delivered to the phantom that contained a small, medium, or no tumor. The dosimetric effects were evaluated using gamma passing rates with a 2%/2 mm criterion and dose profile comparisons. RESULTS: Agreement between the measurements and AAA calculations decreased as tumor size decreased, but Acuros XB showed better agreement for all tumor sizes. The largest difference was observed for a 6 MV volumetric modulated arc therapy plan created to treat the smallest tumor. The gamma passing rate was 89.7% but that of Acuros was 99.5%. For the tumor regression evaluation, the gamma passing rates ranged from 53% to 99% for AAA. For Acuros XB, the gamma passing rates were >98% for all scenarios. CONCLUSION: Both AAA and Acuros XB calculated the dose accurately for the largest lung tumor. For the smallest and regressing tumors, Acuros XB more accurately modelled the dose distribution compared with AAA.

Image-guided radiotherapy quality control: Statistical process control using image similarity metrics.

PURPOSE: The purpose of this study was to demonstrate an objective quality control framework for the image review process. METHODS AND MATERIALS: A total of 927 cone-beam computed tomography (CBCT) registrations were retrospectively analyzed for 33 bilateral head and neck cancer patients who received definitive radiotherapy. Two registration tracking volumes (RTVs) - cervical spine (C-spine) and mandible - were defined, within which a similarity metric was calculated and used as a registration quality tracking metric over the course of treatment. First, sensitivity to large misregistrations was analyzed for normalized cross-correlation (NCC) and mutual information (MI) in the context of statistical analysis. The distribution of metrics was obtained for displacements that varied according to a normal distribution with standard deviation of σ = 2 mm, and the detectability of displacements greater than 5 mm was investigated. Then, similarity metric control charts were created using a statistical process control (SPC) framework to objectively monitor the image registration and review process. Patient-specific control charts were created using NCC values from the first five fractions to set a patient-specific process capability limit. Population control charts were created using the average of the first five NCC values for all patients in the study. For each patient, the similarity metrics were calculated as a function of unidirectional translation, referred to as the effective displacement. Patient-specific action limits corresponding to 5 mm effective displacements were defined. Furthermore, effective displacements of the ten registrations with the lowest similarity metrics were compared with a three dimensional (3DoF) couch displacement required to align the anatomical landmarks. RESULTS: Normalized cross-correlation identified suboptimal registrations more effectively than MI within the framework of SPC. Deviations greater than 5 mm were detected at 2.8σ and 2.1σ from the mean for NCC and MI, respectively. Patient-specific control charts using NCC evaluated daily variation and identified statistically significant deviations. This study also showed that subjective evaluations of the images were not always consistent. Population control charts identified a patient whose tracking metrics were significantly lower than those of other patients. The patient-specific action limits identified registrations that warranted immediate evaluation by an expert. When effective displacements in the anterior-posterior direction were compared to 3DoF couch displacements, the agreement was ±1 mm for seven of 10 patients for both C-spine and mandible RTVs. CONCLUSIONS: Qualitative review alone of IGRT images can result in inconsistent feedback to the IGRT process. Registration tracking using NCC objectively identifies statistically significant deviations. When used in conjunction with the current image review process, this tool can assist in improving the safety and consistency of the IGRT process.

Cadaveric verification of the Eclipse AAA algorithm for spine SBRT treatments with titanium hardware.

PURPOSE: To assess the accuracy of the Eclipse Analytical Anisotropic Algorithm when calculating dose for spine stereotactic body radiation therapy treatments involving surgically implanted titanium hardware. METHODS AND MATERIALS: A human spine was removed from a cadaver, cut sagittally along the midline, and then separated into thoracic and lumbar sections. The thoracic section was implanted with titanium stabilization hardware; the lumbar section was not implanted. Spine sections were secured in a water phantom and simulated for treatment planning using both standard and extended computed tomography (CT) scales. Target volumes were created on both spine sections. Dose calculations were performed using (1) the standard CT scale with relative electron density (RED) override of image artifacts and hardware, (2) the extended CT scale with RED override of image artifacts only, and (3) the standard CT scale with no RED overrides for hardware or artifacts. Plans were delivered with volumetric modulated arc therapy using a 6-MV beam with and without a flattening filter. A total of 3 measurements for each plan were made with Gafchromic film placed between the spine sections and compared with Eclipse dose calculations using gamma analysis with a 2%/2 mm passing criteria. A single measurement in a homogeneous phantom was made for each plan before actual delivery. RESULTS: Gamma passing rates for measurements in the homogeneous phantom were 99.6% or greater. Passing rates for measurements made in the lumbar spine section without hardware were 99.3% or greater; measurements made in the thoracic spine containing titanium were 98.6 to 99.5%. CONCLUSIONS: Eclipse Analytical Anisotropic Algorithm can adequately model the effects of titanium implants for spine stereotactic body radiation therapy treatments using volumetric modulated arc therapy. Calculations with standard or extended CT scales give similarly accurate results.

Medical Physics Practice Guideline 4.a: Development, implementation, use and maintenance of safety checklists.

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education and professional practice of medical physics. The AAPM has more than 8,000 members and is the principal organization of medical physicists in the United States.The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner.Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized.The following terms are used in the AAPM practice guidelines:Must and Must Not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline.Should and Should Not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances.

Separating the dosimetric consequences of changing tumor anatomy from positional uncertainty for conventionally fractionated lung cancer patients.

PURPOSE: To separate the dosimetric consequences of changing tumor volume from positional uncertainty for patients undergoing conventionally fractionated lung radiation therapy (RT) and to quantify which factor has a larger impact on dose to target volumes and organs at risk (OAR). METHODS AND MATERIALS: Clinical treatment plans from 20 patients who had received conventionally fractionated RT were retrospectively altered by replacing tumor and atelectasis with lung equivalent tissue in the treatment planning system calculations. To simulate positional uncertainty, the isocenter was shifted in both the altered and original plans by 2 and 5 mm in 6 directions. Rotational uncertainty was introduced by rotating each computed tomographic image set by ± 3 degrees about a superior-inferior axis extending through patient center. Additionally, after rotation the isocenter was translated back to its original point within the patient to evaluate whether purely translational corrections could minimize dosimetric consequences due to rotations. RESULTS: Dosimetric statistics for each altered plan were compared with the original. Average changes in the planning target volume (PTV) receiving 95% of prescription dose (PTV V95%) resulting from changing tumor anatomy alone were approximately 0.1%. Average changes in PTV V95% resulting from positional uncertainty were greater (0.2%-4.2%) but were largely independent of whether or not the original tumor volume was present. For 3 patients, increases in volumes receiving 110% of the prescription dose were seen but were largely limited to within the PTV. Translational corrections for patient rotations were effective in minimizing differences in target coverage but had less effect on reducing the maximum spinal cord dose. CONCLUSIONS: Anatomic changes alone, such as reductions in tumor volume and atelectasis, had minimal effect on the overall dose distribution. Greater dosimetric consequences were seen with positional uncertainty. With accurate patient localization, replanning during the course of treatment for conventionally fractionated lung cancer patients may not be necessary.

Influence of patient's physiologic factors and immobilization choice with stereotactic body radiotherapy for upper lung tumors.

The purpose of the present study was to compare the impact of pulmonary function, body habitus, and stereotactic body radiation therapy (SBRT) immobilization on setup and reproducibility for upper lung tumor. From 2008 through 2011, our institution's prospective SBRT database was searched for patients with upper lung tumors. Two SBRT immobilization strategies were used: full-length BodyFIX and thermoplastic S-frame. At simulation, free-breathing, four-dimensional computed tomography was performed. For each treatment, patients were set up to isocenter with in-room lasers and skin tattoos. Shifts from initial and subsequent couch positions with cone-beam computed tomography (CBCT) were analyzed. Accounting for setup uncertainties, institutional tolerance of CBCT-based shifts for treatment was 2, 2, and 4 mm in left-right, anterior-posterior, and cranial-caudal directions, respectively; shifts exceeding these limits required reimaging. Each patient's pretreatment pulmonary function test was recorded. A multistep, multivariate linear regression model was performed to elucidate intervariable dependency for three-dimensional calculated couch shift parameters. BodyFIX was applied to 76 tumors and S-frame to 17 tumors. Of these tumors, 41 were non-small cell lung cancer and 15 were metastatic from other sites. Lesions measured < 1 (15%), 1.1 to 2 (50%), 2.1 to 3 (25%), and > 3 (11%) cm. Errors from first shifts of first fractions were significantly less with S-frame than BodyFIX (p < 0.001). No difference in local control (LC) was found between S-frame and BodyFIX (p = 0.35); two-year LC rate was 94%. Multivariate modeling confirmed that the ratio of forced expiratory volume in the first second of expiration to forced vital capacity, body habitus, and the immobilization device significantly impacted couch shift errors. For upper lung tumors, initial setup was more consistent with S-frame than BodyFIX, resulting in fewer CBCT scans. Patients with obese habitus and poor lung function had more SBRT setup uncertainty; however, outcome and probability for LC remained excellent.

Clinical outcomes and dosimetric considerations using stereotactic body radiotherapy for abdominopelvic tumors.

PURPOSE/OBJECTIVES: To present clinical outcomes, early toxicity, and dosimetric constraints for patients undergoing stereotactic body radiation therapy (SBRT) for abdominal or pelvic tumors. MATERIALS AND METHODS: From May 2008 to February 2010, 47 patients with 50 lesions in proximity to hollow viscous organs at risk, including stomach, duodenum, small bowel, and colon, underwent SBRT at Mayo Clinic. Treated sites included liver (21), lymph node (14), adrenal gland (6), intramuscular (4), pancreas (3), and spleen (2). Treatment planning was performed with full body immobilization and 4-dimensional computed tomography (CT)-based planning with daily cone-beam CT or stereoscopic kV imaging for pretreatment image guidance. SBRT was delivered in 1 to 5 consecutive daily fractions in a single week. The most commonly prescribed dose was 50 Gy in 5 fractions (median 45 Gy, range: 20 to 60 Gy). Toxicities were scored by CTCAE v.3. Local failure was defined as per the Response Evaluation Criteria in Solid Tumors. RESULTS: Median follow-up was 12 months (range: 2 to 28 mo). Tumor responses of the 48 target lesions evaluable by Response Evaluation Criteria in Solid Tumor were complete response in 18 lesions (36%), partial response in 12 lesions (24%), stable disease in 12 lesions (24%), and progressive disease in 6 lesions (12%). Kaplan-Meier estimates of local control, overall survival, and freedom from metastasis at 6 and 12 months were 98%, 90%, and 63%, and 87%, 62%, 37%, respectively. Treatment was well-tolerated acutely without reported grade ≥3 toxicity. Five grade 3 late toxicities were reported, and 1 patient died of complications from duodenal perforation 11 months after SBRT. No dose correlation with toxicity could be established. CONCLUSIONS: SBRT is a practical treatment option for patients with abdominopelvic tumors. Relapse typically occurs outside treatment fields, and most patients achieve a favorable response. The dose constraints used in this cohort of patients was associated with acceptable early treatment-related toxicity.

Radiation oncology information systems and clinical practice compatibility: Workflow evaluation and comprehensive assessment.

PURPOSE: To map the level of clinical practice compatibility with a radiation oncology information system (ROIS) through a workflow- and clinical process-based method aimed at optimizing the safety, efficacy, and efficiency of patient care; to improve the understanding of the critical relationship between the clinical practice and ROIS. METHODS AND MATERIALS: Clinic-specific workflow and infrastructure were classified into clinical processes, information management, and technological innovation integration. Clinical information systems-information technology infrastructure and process maps were generated by a team of experts, representing clinical constituents. These maps served as the basis for evaluating connectivity and process flow and to guide the development of a quantitative survey where all clinical tasks and subprocesses were ranked according to importance in patient care and scored by the team of experts for performance. Process maps and survey output were used to measure ROIS compatibility with the practice and to guide practice improvement. RESULTS: Practice-specific process and infrastructure maps were generated. The developed survey was applied and results indicate a range of ROIS compatibility with clinical workflow and infrastructure. Survey results combined with experiential feedback provided specific prioritized guidance to improve both ROIS performance and clinic-specific processes and infrastructure. CONCLUSIONS: This work provides a systematic and customizable tool to understand and evaluate clinical information and workflow and its compatibility with a given ROIS. The analysis provides insight into workflow improvements and information systems and information technology infrastructure limitations. Participating in such a process provides the entire team with a deeper understanding of the critical relationship between the clinical practice and the ROIS.