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Hazard Analysis of the Halcyon Linac and Treatment Planning System

T Pawlicki*, G Kim, UC San Diego, La Jolla, CA


(Sunday, 7/29/2018) 5:05 PM - 6:00 PM

Room: Davidson Ballroom A

Purpose: The Halcyon (Varian Medical Systems, Palo Alto) was recently introduced as a self-contained linac and planning system that is tightly controlled by the vendor. The purpose of this work is to determine and analyze the hazards introduced by such a device when used in a clinical environment.

Methods: Systems-Theoretic Process Analysis (STPA) was used to analyze the Halcyon as a self-contained device (linac and treatment planning system). STPA does not make any explicit assumptions on the order of how the work is completed (i.e., a process map is not required) which means that the results of the analysis will be generally applicable to clinics beyond that where the analysis was completed. STPA has the following components: 1) create a description of the system being analyzed including organizational aspects, i.e. analysis scope, 2) create standard engineering control loops to describe the workflow in the context of clinical use that includes control actions and corresponding feedback, 3) determine unsafe states of the control actions, and 4) determine causal scenarios that can lead to the unsafe states of the control actions. The last step provides a list of hazardous situations that may lead to safety-related events.

Results: The scope of the analysis was from the installation of the Halcyon through routine patient treatments and included physicians, physicists, dosimetrist and therapists. The analysis was completed by two physicists with input from the other members of the radiation therapy team. There were 23 control loops created with 54 control actions resulting in over 150 hazardous scenarios. Of the control actions, 10 (18.5%) were equipment-specific and 44 (81.5%) were workflow-specific, respectively.

Conclusion: The Halcyon linac and planning system may present opportunities to streamline or eliminate some routine equipment quality assurance activities while requiring an increase focus on other areas of the workflow.


Quality Assurance, Linear Accelerator, Risk


TH- External beam- photons: Quality Assurance - Linear accelerator

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