No abstract

To apply failure mode and effect analysis (FMEA) to generate an effective and efficient initial physics plan checklist. Methods: A team of physicists, dosimetrists, and therapists was setup to reconstruct the workflow processes involved in the generation of a treatment plan beginning from simulation. The team then identified possible failure modes in each of the processes. For each failure mode, the severity (S), frequency of occurrence (O), and the probability of detection (D) was assigned a value and the risk priority number (RPN) was calculated. The values assigned were based on TG 100. Prior to assigning a value, the team discussed the values in the scoring system to minimize randomness in scoring. A local database of errors was used to help guide the scoring of frequency. Results: Twenty-seven process steps and 50 possible failure modes were identified starting from simulation to the final approved plan ready for treatment at the machine. Any failure mode that scored an average RPN value of 20 or greater was deemed "eligible" to be placed on the second checklist. In addition, any failure mode with a severity score value of 4 or greater was also considered for inclusion in the checklist. As a by-product of this procedure, safety improvement methods such as automation and standardization of certain processes (e.g., dose constraint checking, check tools), removal of manual transcription of treatment-related information as well as staff education were implemented, although this was not the team's original objective. Prior to the implementation of the new FMEA-based checklist, an in-service for all the second checkers was organized to ensure further standardization of the process. Conclusion: The FMEA proved to be a valuable tool for identifying vulnerabilities in our workflow and processes in generating a treatment plan and subsequently a new, more effective initial plan checklist was created.

Recently, there has been a resurgence of interest in arc-based IMRT, through the use of 'conventional' multileaf collimator (MLC) systems that can treat large tumor volumes in a single, or very few pass(es) of the gantry. Here we present a novel 'burst mode' modulated arc delivery approach, wherein 2000 monitor units per minute (MU min(-1)) high dose rate bursts of dose are facilitated by a flattening-filter-free treatment beam on a Siemens Artiste (Oncology Care Systems, Siemens Medical Solutions, Concord, CA, USA) digital linear accelerator in a non-clinical configuration. Burst mode delivery differs from continuous mode delivery, used by Elekta's VMAT (Elekta Ltd, Crawley, UK) and Varian's RapidArc (Varian Medical Systems, Palo Alto, CA, USA) implementations, in that dose is not delivered while MLC leaves are moving. Instead, dose is delivered in bursts over very short arc angles and only after an MLC segment shape has been completely formed and verified by the controller. The new system was confirmed to be capable of delivering a wide array of clinically relevant treatment plans, without machine fault or other delivery anomalies. Dosimetric accuracy of the modulated arc platform, as well as the Prowess (Prowess Inc., Concord, CA, USA) prototype treatment planning version utilized here, was quantified and confirmed, and delivery times were measured as significantly brief, even with large hypofractionated doses. The burst mode modulated arc approach evaluated here appears to represent a capable, accurate and efficient delivery approach.

Purpose: To present our preliminary experience with the recently released Calypso lung beacons to track lung tumor location during stereotactic body radiation therapy (SBRT). Materials/Methods: Five recent lung SBRT patients had Calypso lung beacons implanted for tumor tracking during treatment. Beacons were placed by a pulmonologist using fluoroscopic navigation within 1 week prior to planning four-dimensional computed tomography (4DCT) acquisition. Patients were immobilized in a full-body double-vacuum bag. For the first three patients, a verification 4DCT was obtained prior to the first fraction with the patient in the treatment position to assess both beacon migration and motion of tumor and beacons relative to planning day. For each treatment fraction, Calypso was used to position the patient. A verification cone-beam CT (CBCT) confirmed the Calypso-defined target position was appropriate. Real-time Calypso tracking information was also acquired and compared to an action level that was used to determine if the tumor migrated outside of the planning target volume. Results: For four patients, the implant procedure was well tolerated, with average CBCT-based shifts being within 0.2 mm of the shifts reported by Calypso at the time of imaging. The other patient had a small pneumothorax due to very peripheral tumor location and experienced beacon migration. However, the patient quickly recovered from the pneumothorax, and after deactivating that beacon, motion tracking was possible throughout his treatment. Conclusions: All patients were successfully treated with SBRT using the newly released Calypso lung beacons, with initial positioning confirmed by this clinic's current clinical standard of CBCT. The system allowed us to validate, with real-time confirmation, that the planned internal target volumes were appropriate to each day's extent of actual tumor motion. An efficient and effective workflow for utilizing the new lung beacons for SBRT treatments was developed.

PurposeThis is a proof-of-principle study investigating the feasibility of using late gadolinium enhancement magnetic resonance imaging (LGE-MRI) to detect left atrium (LA) radiation damage.Methods and materialsLGE-MRI data were acquired for 7 patients with previous external beam radiation therapy (EBRT) histories. The enhancement in LA scar was delineated and fused to the computed tomography images used in dose calculation for radiation therapy. Dosimetric and normal tissue complication probability analyses were performed to investigate the relationship between LA scar enhancement and radiation doses.ResultsThe average LA scar volume for the subjects was 2.5 cm3 (range, 1.2-4.1 cm3; median, 2.6 cm3). The overall average of the mean dose to the LA scar was 25.9 Gy (range, 5.8-49.2 Gy). Linear relationships were found between the amount of radiation dose (mean dose) (R2 = 0.8514, P = .03) to the LA scar-enhanced volume. The ratio of the cardiac tissue change (LA scar/LA wall) also demonstrated a linear relationship with the level of radiation received by the cardiac tissue (R2 = 0.9787, P < .01). Last, the normal tissue complication probability analysis suggested a dose response function to the LA scar enhancement.ConclusionsWith LGE-MRI and 3-dimensional dose mapping on the treatment planning system, it is possible to define subclinical cardiac damage and distinguish intrinsic cardiac tissue change from radiation induced cardiac tissue damage. Imaging myocardial injury secondary to EBRT using MRI may be a useful modality to follow cardiac toxicity from EBRT and help identify individuals who are more susceptible to EBRT damage. LGE-MRI may provide essential information to identify early screening strategy for affected cancer survivors after EBRT treatment.

Ultrasound (US) image guidance systems used in radiotherapy are typically calibrated for soft tissue applications, thus introducing errors in depth-from-transducer representation when used in media with a different speed of sound propagation (e.g. fat). This error is commonly referred to as the speed artifact. In this study we utilized a standard US phantom to demonstrate the existence of the speed artifact when using a commercial US image guidance system to image through layers of simulated body fat, and we compared the results with calculated/predicted values. A general purpose US phantom (speed of sound (SOS) = 1540 m s(-1)) was imaged on a multi-slice CT scanner at a 0.625 mm slice thickness and 0.5 mm x 0.5 mm axial pixel size. Target-simulating wires inside the phantom were contoured and later transferred to the US guidance system. Layers of various thickness (1-8 cm) of commercially manufactured fat-simulating material (SOS = 1435 m s(-1)) were placed on top of the phantom to study the depth-related alignment error. In order to demonstrate that the speed artifact is not caused by adding additional layers on top of the phantom, we repeated these measurements in an identical setup using commercially manufactured tissue-simulating material (SOS = 1540 m s(-1)) for the top layers. For the fat-simulating material used in this study, we observed the magnitude of the depth-related alignment errors resulting from the speed artifact to be 0.7 mm cm(-1) of fat imaged through. The measured alignment errors caused by the speed artifact agreed with the calculated values within one standard deviation for all of the different thicknesses of fat-simulating material studied here. We demonstrated the depth-related alignment error due to the speed artifact when using US image guidance for radiation treatment alignment and note that the presence of fat causes the target to be aliased to a depth greater than it actually is. For typical US guidance systems in use today, this will lead to delivery of the high dose region at a position slightly posterior to the intended region for a supine patient. When possible, care should be taken to avoid imaging through a thick layer of fat for larger patients in US alignments or, if unavoidable, the spatial inaccuracies introduced by the artifact should be considered by the physician during the formulation of the treatment plan.

The purpose of this study is to design a real-tissue phantom for use in the validation of deformation algorithms. A phantom motion controller that runs sinusoidal and non-regular patient-based breathing pattern, via a piston, was applied to porcine liver tissue. It was regulated to simulate movement ranges similar to recorded implanted liver markers from patients. 4D CT was applied to analyze deformation. The suitability of various markers in the liver and the position reproducibility of markers and of reference points were studied. The similarity of marker motion pattern in the liver phantom and in real patients was evaluated. The viability of the phantom over time and its use with electro-magnetic tracking devices were also assessed. High contrast markers, such as carbon markers, implanted in the porcine liver produced less image artifacts on CT and were well visualized compared to metallic ones. The repositionability of markers was within a measurement accuracy of +/-2 mm. Similar anatomical patient motions were reproducible up to elongations of 3 cm for a time period of at least 90 min. The phantom is compatible with electro-magnetic tracking devices and 4D CT. The phantom motion is reproducible and simulates realistic patient motion and deformation. The ability to carry out voxel-based tracking allows for the evaluation of deformation algorithms in a controlled environment with recorded patient traces. The phantom is compatible with all therapy devices clinically encountered in our department.

Purpose: To compare and contrast two commercial SRS QA phantoms. Methods: Both phantoms were evaluated in terms of their ease of setup as well as the time required to switch inserts for different tests. They were both used to evaluate the coincidence of the radiation and laser isocenters of a linear accelerator. End‐to‐end dosimetric tests were also performed using both ion chambers and films along two planes through the center of the phantoms. Since one phantom allows for multiple ion chamber orientations, a test was also performed to determine the effect of having the chamber oriented along the radiation beam axis’. Results: Changing inserts took 2 minutes on average for one phantom compared to 5 minutes for the other. The laser/radiation isocenter coincidence as determined from each phantom showed a maximum difference of 0.2mm. Ion chamber results were within 0.5% of the expected values when the chamber was perpendicular to the beams but measured a 3% underdose when the chamber was along the beam direction. Gamma (2%,2mm) pass rates of corresponding films were within 1% between phantoms. Conclusion: The results of the corresponding tests run on both phantoms were comparable, showing that the phantoms were equivalent for the subset of SRS QA tests run here. However, the under dose observed when the chamber was parallel to the beam direction suggests that this configuration should be avoided.