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Session: Gamma Knife QA Update with TG-178 [Return to Session]

Gamma Knife QA Update with TG-178

S Goetsch1*, P Alvarez2*, N Knutson3*, (1) San Diego Medical Physics, Solana Beach, CA, (2) UT MD Anderson Cancer Center - IROC, Houston, TX, (3) Washington University School of Medicine, St Louis, MO


2:00 PM TG-178 Recommendations - S Goetsch, Presenting Author
2:15 PM Implementing TG -178 into a Robust Modern QA Program - P Alvarez, Presenting Author
2:30 PM Gamma Knife QA from TG 21 to TG-178 - N Knutson, Presenting Author
2:45 PM Q&A - N Knutson, Presenting Author

TH-D-TRACK 7-0 (Thursday, 7/29/2021) 2:00 PM - 3:00 PM [Eastern Time (GMT-4)]

Speaker 1:
This talk describes the report prepared by AAPM Task Group 178, beginning in 2008. The completed report will soon be published in Medical Physics. The scope of the investigation is the calibration and quality assurance of the Leksell Gamma Knife, in use worldwide since the original commercial unit was installed in 1987. The report adopts the formalism described by Alfonso et al (2008) for radiation therapy devices non-compliant with the AAPM Task Group 51 dose in water protocol, to extend its use to the Leksell Gamma Knife. Results of Monte Carlo calibration and subsequent verification by the manufacturer in 2010 provided the missing factors for use of 9 commonly used ionization chambers for three different phantoms. The round-robin measurement conducted by TG 178 in 2011 to 2012 are also reviewed. Quality Assurance recommendations for the latest Leksell Gamma Knife Perfexion and Icon will be presented.

Speaker 2:
This talk aims to present the results of the external audits offered by the IROC Houston QA office Gamma Knife. The program provides a verification of the output of unit and an end-to-end test with an anthropomorphic head phantom. Most of the institutions that use the service are NCI clinical trial’s participants. The output verification requires the irradiation of TLD located in an insert that is compatible with the QA phantom used for ion chamber measurements (cassette for the Elekta ABS ball or insert for the solid water phantom). The SRS head phantom is a plastic shell with an insert that includes a centrally located target, TLD located in the target and gafchromic film. The information presented includes the distribution of the results of the dose comparison at the point of measurement as well as demographic information from these irradiations: models of the unit, calibration protocol use for determination of the output and reference medium.

Speaker 3:
This talk aims to give an example of the evolution of a Gamma Knife QA program, in particular in the context of the recent publication of TG-178 and the development of the Gamma Knife Icon. An extremely well developed for Gamma Knife QA program developed for the Gamma Knife Prefexion model. This system was based on Tg-21 calibration in the Elekta ABS ball. Then in November 2017 we received the Gamma Knife Icon. With the publication of TG-178 (released for public comment in 2018) and IAEA TRS 483 in November 2017, was a great catalyst for the revamping of our QA program. We reviewed every section of our qa program, safety, mechanical, calibration, relative dosimetry, imaging, intrafraction motion management, end to end testing, and secondary dose calculation. Most of the changes there are two common trends, 1) the need to address new technology, and 2) the desire to simplify and improve consistency. This talk discusses some lessons learned during this process.

Learning Objectives:
1. Understand the reasoning behind the creation of TG-178 and the recommendations made within the task group.
2. Understand the importance of external dosimetry audits for Gamma Knife and a review of results seen by IROC
3. See a realword example of how to adopt some of the changes mentioned in TG-178



Gamma Knife, Quality Assurance, Absolute Dosimetry


TH- External Beam- Photons: gammaknife

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