Utilization of image-guided radiation therapy equipment to enhance stereotactic body radiation therapy commissioning

Julian R. Perks, J. Lehmann, S. Narayan, S. Semon, R. Stern, S. Vijayakumar, J. Purdy

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

2 Scopus citations


Purpose: To aid the clinical implementation of a hybrid system of both in house and 'off the shelf' commercial components for stereotactic body radiation therapy (SBRT), utilizing the latest image-guided techniques. Materials and Methods: A new Elekta Synergy accelerator with Beam Modulator (4 mm leaves and maximum field size 21 × 16 cm2) was commissioned in the Pinnacle3® treatment planning system v.8.0d for routine patient care. Additionally, both imaging systems (MV and kV) were fully commissioned for routine portal imaging and cone beam CT. The Pinnacle3® system does not contain an algorithm that recognizes the fiducial markers of the stereotactic body, therefore custom software was written. The clinical implementation was undertaken in the following sequence: (1) volunteers (who received no radiation) were used to familiarize staff with the SBRT fitting and derive a simulation procedure; (2) a phantom was used to check that a point determined from the planning CT could be aligned on the linear accelerator using cone beam CT; (3) an enhanced Winston Lutz test was devised and performed to determine the coincidence of the rotation center points of the imaging equipment and the linear accelerator gantry, and (4) finally an 'end-to-end' test was performed to confirm the overall SBRT system performance. Results: Initial studies yielded a robust simulation procedure which placed limits on the maximum patient size that could be accommodated in the SBRT frame and the diaphragm compression that could be used for tumor immobilization. The maximum shift needed to bring two separate points in the stereotactic space into alignment by the cone beam CT system, determined using the grey value alignment algorithm, were 0.5 and 1.2 mm, respectively. The initial Winston Lutz test based on the room lasers alone found a maximum shift of 1.4 mm. By employing an enhanced alignment technique, standard for the CBCT system, the average difference was reduced to < 0.3 mm. Finally the 'end-to-end' test was successfully performed with a test phantom from an independent testing center. Conclusion: The commissioning of SBRT was greatly enhanced and accelerated by utilizing the MV and kV onboard imaging capabilities of a modern linear accelerator, e.g. EPID and CBCT, respectively. Cone beam CT validated that the isocenter transfer from the planning CT system to the stereotactic coordinate system of the SBRT frame was accurate and the enhanced MV imaging software gave an improvement to a well-established isocenter test (Winston Lutz).

Original languageEnglish
Title of host publicationRadiosurgery
Subtitle of host publication8th International Stereotactic Radiosurgery Society Meeting, San Francisco, June 2007
Number of pages6
StatePublished - 2010

Publication series

ISSN (Print)1024-2651
ISSN (Electronic)1662-3940


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