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Tales of a Busy Linac

A Rangel*, X Wu, Trillium Health Partners/Credit Valley Hospital, Mississauga, ON, CA,


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To study the impact of treatment workload on the aging needs of a radiation therapy Linac and in turn how Linac aging affects its throughput.

Methods: We reviewed historical data of two Varian Linacs, a 2300iX (installed in 2009) and a Truebeam (installed in 2014, HDMLC/6DoF couch). The data included: treatment hours and types, filament time (FT) and beam-on hours (BOhrs), service hours and type, downtime hours and cost of replacing parts. Significant events in the Linac’s life were also noted.

Results: If we focus only on the first 6 years of each Linac, the iX reached 1,314 BOhrs and TB 1,803 BOHrs. The volume of electron/3DCRT treatments ranged from 45 to 89% in iX, whereas in TB an increase from 29 to 77% in the volume of complex treatments of VMATS and SRS/SRT. The iX experienced a drop of 1% in Linac efficiency, BOhrs/FT from 7 to 6%, whereas TB saw 1% increase in efficiency from 7 to 8%. Considering the parts alone, maintaining the iX to deliver simple treatment accumulatively cost ~CAD$110/BOhr over 6 years, whereas TB to deliver complex treatments cost ~CAD$100/BOhr. Downtime for iX and TB was 16.4 and 13hr/quarter on average.

At the end of 11 years of service, the iX accumulated 2,105 BOhrs. The volume of simple treatments increased to 97%. Its efficiency dropped to 5.5%. Part cost per BOhrs accumulate increased to ~CAD$149/BOhrs. Its downtime raised to 19.9hr/quarter on average. But in the last 5 years, we managed to increase the treatment time by 34% compared to the first 6 years on average.

Conclusion: Both growing treatment workload and high complexity treatments accelerated the Linac age affecting service needs and the cost to beam-on. As the Linac ages, the throughput can be maintained by extending its operation hours and reducing treatment complexity.

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