Background
Stereotactic body radiotherapy (SBRT) is characterised by highly hypofractionated schemes. The large doses per fraction in SBRT intensify the need for error detection during delivery. Real-time transit dose verification using electronic portal imaging device (EPID), is the only in-vivo dosimetry methodology able to detect errors during treatment delivery.
Aims
The aim of this work is to present the results of the clinical deployment of a real-time delivery verification system for SBRT.
Methods
The verification system uses a dedicated workstation equipped with a frame-grabber card to acquire a real-time stream of image frames from the Varian aS1200 EPID panel. EPID frames acquired during treatment delivery are compared to predicted control-point interval EPID images. Predicted images are obtained using a physics-based analytical prediction model for a 6XFFF beam, modified from a previously presented dual source fluence model. Real-time analysis of machine parameters is performed.
The verification system is largely automated requiring only a patient selection and beam-order confirmation from the therapist. 19 SBRT patients, including spine, pelvic, prostate, and lung, were included in the study.
Results
Seventy-one fractions were successfully verified. Non-verified fractions were the result of therapist forgetting to set up the system, and technicalities during delivery produced by delivery interruptions and storage issues.
Qualitative retrospective analysis indicated that:
Conclusions
A software platform to analyse real-time delivery at a control-point level was developed, demonstrating sufficient performance to operate in the clinical practice.