(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: A linac delivered pre-configured can reduce the commissioning procedure. A survey on current practice was issued.
Methods: A survey inquiring on acceptance testing, calibration, beam-model and IMRT/VMAT validation, patient-specific QA and external audits during commissioning was distributed among early adopters of Halcyon linacs.
Results: In total 3 USA-sites, 4 in Europe, 2 in Africa and 3 in Australia+Asia participated. In 50% the acceptance procedure was supplemented with additional test. The factory output calibration deviated on average 1.9% (σ=1.4%), and was adjusted in 83%, for deviations ≥0.6%. A calibration in dmax/100cmSSD was used by 67%. The d=5cm/95cmSSD and d=10cm/90cmSSD both in 17%. IAEA-TRS-398 was used by 58%, AAPM-TG-51 by 25%. All performed pre-configured TPS-model verification including output factors, point dose measurements, profiles and depth-dose data acquisition. MLC-transmission and dosimetric leaf gap were verified by 72% and 82%. 67% used 3D waterphantoms. In 45% the model was verified in heterogeneous conditions. Homogeneous phantom end-to-end tests were performed by all for IMRT/VMAT except for one center only commissioning IMRT. AAPM-TG119 was followed by 25%. Point-dose measurements were performed by 91%, 63% used detector arrays. Only 18% used film dosimetry for delivery validation. For 83% anthropomorphic phantoms were used. With 58% and 67% respectively, Lung and H&N treatment solutions were the most verified. External dosimetry audits for output or IMRT/VMAT delivery were executed in 67%. EPID dosimetry was applied by 91% for patient specific pre-treatment QA during ramp-up, completed with film dosimetry in 18%, detector arrays in 64% and point-dose measurements in 82%. 64% used 3%/3mm for gamma while 36% used tighter parameters, 83% used an agreement threshold of ≥95% for accepting quality.
Conclusion: The survey provides information for new Halcyon users. Extensive beam-model verification is still standard practice today. An evolution in commissioning of pre-configured linacs can be expected in the future.
Funding Support, Disclosures, and Conflict of Interest: T Depuydt is currently PI of an ongoing research project funded by the company Varian. T Depuydt and K Poels have received speaker honoraria from Varian.
Keywords
Not Applicable / None Entered.
Taxonomy
TH- External beam- photons: Development (new technology and techniques)
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