Quality assurance in intensity modulated radiotherapy by identifying standards and patterns in treatment preparation: a feasibility study on prostate treatments

Quality assurance (QA) in intensity modulated treatments is a complex and time-consuming process. In spite of intensive quality control procedures some types of errors still can go undetected through the course of a treatment. This study aims to develop an objective QA filter for fast, automatic detection of errors, based on the creation of a global platform monitoring treatment parameters by comparison with existing local standards. Since such a conceptually new type of QA has already proven successful for conventional treatments, we aim to extend it to intensity modulated radiotherapy (IMRT) treatments.

The feasibility of developing such a QA platform was evaluated on 12 prostate treatment plans. Apart from the classical treatment parameters, the optimised fluence distributions were compared and screened for repetitive patterns. This screening was performed by calculating specific parameters, defined to characterise the fluence maps.

Repetitive patterns were found in the beam shapes as well as in the intensity distributions, and useful parameters could be defined to quantify typical field patterns. By statistical analysis of these parameters, mean values and tolerance levels were derived, providing a means to automatically filter out unprobable or erroneous intensity modulated treatment fields during the treatment preparation stage.

It is possible to identify parameters quantifying the characteristic patterns found in fluence distributions of intensity modulated fields of a specific treatment, allowing the development of a platform for automatic pre-treatment quality control.