Imaging system QA of a medical accelerator, Novalis Tx, for IGRT per TG 142: our 1 year experience

Abstract

American Association of Physicists in Medicine (AAPM) task group (TG) 142 has recently published a report to update recommendations of the AAPM TG 40 report and add new recommendations concerning medical accelerators in the era of image-guided radiation therapy (IGRT). The recommendations of AAPM TG 142 on IGRT are timely. In our institute, we established a comprehensive imaging QA program on a medical accelerator based on AAPM TG 142 and implemented it successfully. In this paper, we share our one-year experience and performance evaluation of an OBI capable linear accelerator, Novalis Tx, per TG 142 guidelines.

Figure 1

The Novalis Tx system equipped with MV EPID and KV OBI.

Figure 2

QA phantoms used to evaluate imaging systems: Las Vegas phantom (left), Leeds phantom (middle), Catphan 504 Phantom (right).

Figure 3

QA phantom used to perform the scaling accuracy test in our institute, in which multiple radiopaque markers are embedded.

Figure 4

Planar images of imaging QA phantoms: the MV image of the Las Vegas phantom (left) and the KV image of the Leeds phantom (right).

Figure 5

The QA of beam quality and imaging dose for KV is performed with the R/F high X‐ray detector placed on the top of blue styrofoam block.

Figure 6

CBCT QA with a Catphan phantom: (a) Hounsfield unit verification; (b) high‐contrast resolution; (c) low‐contrast resolution; (d) Hounsfield unit uniformity and noise.

Figure 7

The QA of imaging dose for CBCT is performed with the CTDI chamber inserted at the center hole of the cylindrical phantom.

Figure 8

Positive in the distance means the measured distance was longer than the expected distance. Positive displacement in the longitudinal and lateral directions means that the center of the KVD, KVS, or MVD was displaced to the inferior and right direction from the isocenter. Results of mechanic QA for KVD, KVS, and MVD.

Figure 9

Results of the 29 measurements of the QA of Imaging & Treatment Coordinate Coincidence over a period of 12 months: MV PV imaging isocenter accuracy (top) and KV OBI imaging isocenter accuracy (bottom). The vector displacement was measured between the center of the digital graticule and the center marker in the image.