Risk assessment of a new acceptance testing procedure for conventional linear accelerators

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Abstract

Purpose:

New techniques and materials have recently been developed to expedite the conventional linac acceptance testing procedure (Med Phys. 2017;22), which use the electronic portal imaging device (EPID) for data collection. This new procedure is designed to be more efficient and robust than the conventional approach. The purpose of this work was to perform a comparative risk assessment of the two acceptance testing procedures (ATPs).

Materials and Methods:

Failure Modes and Effects Analysis was used to assess risks for both ATP approaches. Five domain experts (Medical Physicists) comprised the analysis team. The risk assessment method and ranking scales were adopted from the AAPM TG-100. The number of failure pathways and associated risk priority numbers (RPNs) for the two ATP approaches were compared. RPNs > 100 were considered high-priority failure modes.

Results:

Fewer failure pathways were determined for the new ATP (ATPEPID) compared to the conventional ATP (ATPconv) resulting in a 44% difference (n = 233 vs. n = 534, respectively). There were also 35% fewer RPNs > 100 for the ATPEPID (n = 40) compared to the ATPconv (n = 114). Failure pathways and RPNs > 100 for individual ATP tests were 2.0 and 3.5 times higher, on average, for the ATPconv compared to the ATPEPID, respectively. The EPID pixel sensitivity map was identified as a high risk failure for the ATPEPID.

Conclusions:

Potential errors due to human factors were decreased for the ATPEPID compared to ATPconv so it is possible that a largely automated linac ATP can mitigate many error occurrences. Manufacturers should be careful when designing an EPID-based ATP to address errors in the EPID pixel sensitivity map which can potentially lead to a significant impact on patients’ treatment.

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