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Phys Med. 2015 Jul;31(5):493-500. doi: 10.1016/j.ejmp.2015.05.006. Epub 2015 May 29.

Statistical process control for electron beam monitoring.

Author information

1
Servicio de Radiofísica y Protección Radiológica, Consorcio Hospitalario Provincial de Castellón, Avda. Dr. Clará 19, Castellón de la Plana 12002, Castellón, Spain. Electronic address: lopez_juatar@gva.es.
2
Fundación Hospital Provincial de Castellón, Avda. Dr. Clará 19, Castellón de la Plana 12002, Castellón, Spain.
3
Servicio de Radiofísica y Protección Radiológica, Consorcio Hospitalario Provincial de Castellón, Avda. Dr. Clará 19, Castellón de la Plana 12002, Castellón, Spain.
4
Servicio de Oncología Radioterápica, Consorcio Hospitalario Provincial de Castellón, Avda. Dr. Clará 19, Castellón de la Plana 12002, Castellón, Spain.
5
Servicio de Oncología Radioterápica, Consorcio Hospitalario Provincial de Castellón, Avda. Dr. Clará 19, Castellón de la Plana 12002, Castellón, Spain; Facultad de Medicina, Universidad Cardenal Herrera-CEU, C/ Grecia 31, Castellón de la Plana 12006, Castellón, Spain.

Abstract

PURPOSE:

To assess the electron beam monitoring statistical process control (SPC) in linear accelerator (linac) daily quality control. We present a long-term record of our measurements and evaluate which SPC-led conditions are feasible for maintaining control.

METHODS:

We retrieved our linac beam calibration, symmetry, and flatness daily records for all electron beam energies from January 2008 to December 2013, and retrospectively studied how SPC could have been applied and which of its features could be used in the future. A set of adjustment interventions designed to maintain these parameters under control was also simulated.

RESULTS:

All phase I data was under control. The dose plots were characterized by rising trends followed by steep drops caused by our attempts to re-center the linac beam calibration. Where flatness and symmetry trends were detected they were less-well defined. The process capability ratios ranged from 1.6 to 9.3 at a 2% specification level. Simulated interventions ranged from 2% to 34% of the total number of measurement sessions. We also noted that if prospective SPC had been applied it would have met quality control specifications.

CONCLUSIONS:

SPC can be used to assess the inherent variability of our electron beam monitoring system. It can also indicate whether a process is capable of maintaining electron parameters under control with respect to established specifications by using a daily checking device, but this is not practical unless a method to establish direct feedback from the device to the linac can be devised.

KEYWORDS:

Control charts; Electron beam; Process capability ratio; Statistical process control

PMID:
26032002
DOI:
10.1016/j.ejmp.2015.05.006
[Indexed for MEDLINE]

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