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QA of treatment delivery equipment: teletherapy

Introduction

A number of national and international protocols exist to guide the physicist in the quality assurance of teletherapy equipment. QA programmes (quality control tests) for teletherapy machines with recommended test procedures, test frequencies, and tolerance and action levels are generally structured according to daily, weekly, monthly, and annual tests. More recent publications include also tests on parameters related to the use of more advanced teletherapy equipment having dynamic wedges and multi-leaf collimators (MLC).

Important Principles

A QA programme of teletherapy equipment includes checks of the visual monitoring systems, lasers, output and other beam characteristics, and tests of mechanical characteristics of the gantry, collimator and couch. If a measurement result is within the tolerance level, no action is required; if the measurement result exceeds the action level, immediate action is necessary and the equipment must not be clinically used until the problem is corrected; if the measurement falls between tolerance and action levels, this may be considered as currently acceptable. Inspection and repair can be performed later, for example after patient irradiations. If repeated measurements remain consistently between tolerance and action levels, adjustment is required.

Introduction to References

In the IAEA Handbook typical examples of QA programmes are given based on the AAPM TG-40 and IPEM reports. The more recent AAPM Task Group Report 142 is an update of the TG-40 Report. It specifies new tests and tolerances and has been considerably expanded as compared with the original TG-40 Report. The recommended tolerances accommodate differences in the intended use of the machine functionality, e.g. for non-IMRT, IMRT, and stereotactic delivery. More information on quality assurance of teletherapy equipment can be found in J. Van Dyk's Compendium and in the IAEA Handbook.