Due to increasing complexity, modern radiotherapy techniques require comprehensive quality assurance (QA) programmes, that to date generally focus on the pre-treatment stage. The purpose of this paper is to provide a method for an individual patient treatment QA evaluation and identification of a “quality gap” for continuous quality improvement.
A statistical process control (SPC) was applied to evaluate treatment delivery using in vivo electronic portal imaging device (EPID) dosimetry. A moving range control chart was constructed to monitor the individual patient treatment performance based on a control limit generated from initial data of 90 intensity-modulated radiotherapy (IMRT) and ten volumetric-modulated arc therapy (VMAT) patient deliveries. A process capability index was used to evaluate the continuing treatment quality based on three quality classes: treatment type-specific, treatment linac-specific, and body site-specific.
The determined control limits were 62.5 and 70.0 per cent of the χ pass-rate for IMRT and VMAT deliveries, respectively. In total, 14 patients were selected for a pilot study the results of which showed that about 1 per cent of all treatments contained errors relating to unexpected anatomical changes between treatment fractions. Both rectum and pelvis cancer treatments demonstrated process capability indices were less than 1, indicating the potential for quality improvement and hence may benefit from further assessment.
The study relied on the application of in vivo EPID dosimetry for patients treated at the specific centre. Sampling patients for generating the control limits were limited to 100 patients. Whilst the quantitative results are specific to the clinical techniques and equipment used, the described method is generally applicable to IMRT and VMAT treatment QA. Whilst more work is required to determine the level of clinical significance, the authors have demonstrated the capability of the method for both treatment specific QA and continuing quality improvement.
The proposed method is a valuable tool for assessing the accuracy of treatment delivery whilst also improving treatment quality and patient safety.
Assessing in vivo EPID dosimetry with SPC can be used to improve the quality of radiation treatment for cancer patients.
The authors gratefully acknowledge funding support from the Radiation Oncology Institute (Grant ROI2013-912), The Hunter Cancer Research Alliance (HCRA), and the Calvary Mater Newcastle Radiation Oncology Research Fund. TF gratefully acknowledges the award of the UNIPRS scholarship from the University of Newcastle, Australia. The authors also thank Henry Woodruff for his assistance in data collection and Mary-Claire Hanlon for editing manuscript.
Fuangrod, T., Greer, P.B., Simpson, J., Zwan, B.J. and Middleton, R.H. (2017), "A method for evaluating treatment quality using
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