Abstract
Three‐dimensional measurement arrays are an efficient means of acquiring a distribution of data for patient plan delivery QA. However, the tie between plan integrity and traditional gamma‐based analysis of these data are not clear. This study explores the sensitivity of such analysis by creating errors in Helical Tomotherapy delivery and measuring the passing rates with an ArcCHECK cylindrical diode array. Errors were introduced in each of the couch speed, leaf open time, and gantry starting position in increasing magnitude while the resulting gamma passing rates were tabulated. The error size required to degrade the gamma passing rate to 90% or below was on average a 3% change in couch speed, 5° in gantry synchronization, or a 5 ms in leaf closing speed for a 3%/3 mm Van Dyk gamma analysis. This varied with plan type, with prostate plans exhibiting less sensitivity than head and neck plans and with gamma analysis criteria, but in all cases the error magnitudes were large compared to actual machine tolerances. These findings suggest that the sensitivity of ArcCHECK‐based gamma analysis to single‐mode errors in tomotherapy plans is dependent upon plan and analysis type and at traditional passing thresholds unable to detect small defects in the plan.PACS number: 87.55.Qr
Highlights
As complex treatment planning and delivery modalities are adopted as large components of external-beam radiation therapy programs, patient-specific delivery quality assurance (DQA) is necessarily increasing in frequency and complexity
Three-dimensional diode/chamber arrays are attractive as they can sample a large number and spatial distribution of dose points with easy setup and data acquisition, but their role in the DQA process has not been as extensively characterized as classically used methods, in conjunction with helical TomoTherapy (Accuray, Sunnyvale, CA) delivery
We explored the use of the popular VMAT QA device ArcCHECK (Sun Nuclear, Melbourne, FL) with tomotherapy, and attempted to elucidate the effects of delivery errors on DQA results
Summary
As complex treatment planning and delivery modalities are adopted as large components of external-beam radiation therapy programs, patient-specific delivery quality assurance (DQA) is necessarily increasing in frequency and complexity. The results are typically analyzed with a “gamma” type analysis,(2) whereby each measured dose point is compared to the calculated dose, looking for a similar dose within a search distance of fixed size (3%/3 mm being a typical limit). Passing rates of such analyses are well-documented.[3] A similar concept is typically employed with ArcCHECK, but rather than a flat plane through the center of the phantom, many dose points are sampled in a spiral equidistant from the axis of the cylindrical phantom. While the principles are the same and the process has previously been validated for DQA measurements,(4) the connection between plan versus delivery accuracy and the gamma type analysis is less intuitive, and it is unclear what types and magnitude of errors would be reflected in a drop in gamma passing rate
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
