Abstract
This paper reports on the commissioning of an Elekta cone‐beam computed tomography (CT) system at one of the first U.S. sites to install a “regular,” off‐the‐shelf Elekta Synergy (Elekta, Stockholm, Sweden) accelerator system. We present the quality assurance (QA) procedure as a guide for other users. The commissioning had six elements: (1) system safety, (2) geometric accuracy (agreement of megavoltage and kilovoltage beam isocenters), (3) image quality, (4) registration and correction accuracy, (5) dose to patient and dosimetric stability, and (6) QA procedures. The system passed the safety tests, and agreement of the isocenters was found to be within 1 mm. Using a precisely moved skull phantom, the reconstruction and alignment algorithm was found to be accurate within 1 mm and 1 degree in each dimension. Of 12 measurement points spanning a 9×9×15‐cm volume in a Rando phantom (The Phantom Laboratory, Salem, NY), the average agreement in the x, y, and z coordinates was 0.10 mm, −0.12 mm, and 0.22 mm [standard deviations (SDs): 0.21 mm, 0.55 mm, 0.21 mm; largest deviations: 0.6 mm, 1.0 mm, 0.5 mm] respectively. The larger deviation for the y component can be partly attributed to the CT slice thickness of 1 mm in that direction. Dose to the patient depends on the machine settings and patient geometry. To monitor dose consistency, air kerma (output) and half‐value layer (beam quality) are measured for a typical clinical setting. Air kerma was 6.3 cGy (120 kVp, 40 mA, 40 ms per frame, 360‐degree scan, S20 field of view); half value layer was 7.1 mm aluminum (120 kV, 40 mA).We suggest performing items 1, 2, and 3 monthly, and 4 and 5 annually. In addition, we devised a daily QA procedure to verify agreement of the megavoltage and kilovoltage isocenters using a simple phantom containing three small steel balls. The frequency of all checks will be reevaluated based on data collected during about 1 year.PACS number: 87.53.Xd
Highlights
22 Lehmann et al.: Commissioning experience with cone-beam...emission computed tomography for many years,(2) but the use of a Cone-beam computed tomography (CBCT) system utilizing a diagnostic X-ray tube and a flat panel detector for radiation therapy positioning is more recent.[3,4,5,6]With CBCT, a full CT scan of the patient on the treatment couch is obtained immediately before radiation delivery, with the CT scan taken and reconstructed in less than 2 minutes
The linear accelerator upon which the CBCT system is mounted is in full clinical operation, following routine commissioning and calibration according to the reports of the American Association of Physicists in Medicine (AAPM) task groups 45 and 51.(24,25) The Synergy system features MV portal imaging, which was clinically implemented after routine testing and calibration according to AAPM TG 58.(26) the AAPM scientific committee is addressing this issue and an AAPM working group on imaging for treatment verification is active, no report has yet been released addressing CBCT commissioning and quality assurance (QA)
We developed a protocol to commission the CBCT system for clinical use. This protocol offers a series of checks and tests to ensure that the CBCT system is safe both mechanically and dosimetrically for patient use and that it performs as expected in terms of predicted repositioning
Summary
22 Lehmann et al.: Commissioning experience with cone-beam...emission computed tomography for many years,(2) but the use of a CBCT system utilizing a diagnostic X-ray tube and a flat panel detector for radiation therapy positioning is more recent.[3,4,5,6]With CBCT, a full CT scan of the patient on the treatment couch is obtained immediately before radiation delivery, with the CT scan taken and reconstructed in less than 2 minutes. Our institution recently installed an Elekta Synergy (Elekta, Stockholm, Sweden) system that uses a kV tube and flat-panel amorphous silicon imager mounted orthogonally to the treatment head. This system of CBCT for image guidance has undergone significant research and development by four major collaborating centers[5,6,9,11,23] and has recently been commercially released. We developed a protocol to commission the CBCT system for clinical use This protocol offers a series of checks and tests to ensure that the CBCT system is safe both mechanically and dosimetrically for patient use and that it performs as expected in terms of predicted repositioning. Some of the checks were adopted, when appropriate, from the manufacturer’s acceptance procedure; others were developed in-house, including a daily isocenter agreement check with a new phantom
Sign-in/Register to view highlights & summary 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 callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
