SU‐E‐T‐155: Evaluation of An in Vivo Device for Daily Patient Treatment Delivery Measurements Using a Varian Linear Accelerator

Purpose: A clinical evaluation of a commercially available dosimetric device for in‐vivo monitoring of IMRT and VMAT treatments. Methods: The Device for Advanced Verification of IMRT Deliveries (DAVID) system (PTW, Freiburg, Germany) is a transparent multi‐wire harp chamber that can slide into the wedge slot of a Varian linear accelerator. Its 40 measurement wires correspond to the positions of the leaf pairs of a Millennium‐80 MLC, with a projected spacing at isocenter of 5 mm. The DAVID was inserted into the beam during deliveries of clinically approved IMRT and VMAT treatments. The ability of the DAVID to detect errors in MLC positions was tested by introducing small errors into the plans. The reproducibility of measurements was tested for several disease sites over a series of deliveries. Results: The reproducibility of IMRT and VMAT plans is good. The maximum deviation of any one leaf among all plans and all deliveries was 3.11% (IMRT) and −2.09% (VMAT). The maximum total deviation among all plans and all deliveries was 3.41% (IMRT) and −1.99% (VMAT). The average total deviation among all plans and all deliveries for IMRT was 1.35% ± 1.06% and for VMAT was 0.40% ± 1.35%. When intentional errors were introduced, the DAVID could consistently detect leaf position errors when the resulting gap differed from the plan by great than or equal to 1 mm. Conclusions: The DAVID system is a useful, reliable tool for daily in‐vivo monitoring of patient treatments. It is capable of detecting errors as small as 1 mm, and requires no additional time or effort by the treatment staff for data collection. The DAVID system can provide assurance that every fraction of an IMRT or VMAT treatment is being executed as planned. This work partially supported by PTW (Freiburg, Germany).